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Song variation and learning in island populations of song sparrows Cassidy, Alice Louise Ethel Victoria 1993

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SONG VARIATION AN]) LEARNING INISLAND POPULATIONS OF SONG SPARROWSByALICE LOUISE ETHEL VICTORIA CASSIDYB.Sc. (Honours), The University of Victoria, 1983M.Sc., McGill University, 1987A THESIS SUBMIT[ED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(Department of Zoology)We accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIADecember 1993© Alice Louise Ethel Victoria Cassidy, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of 6:1,The University of British ColumbiaVancouver, CanadaDate 4(jDE-6 (2/88)iiABSTRACTAnimal vocalizations vary greatly between and within species. Male oscinesacquire song 65’ imitation of others, in much the same way that humans learn language. Iinvestigate song variation and the source and timing of song learning by Song Sparrows(Melospiza melodia) in this thesis. I recorded 33,843 songs of 134 birds from 1988-1991on 12 islands in southwest coastal British Columbia. Birds were colour-banded, usuallyin the nest, and many were followed from their birth place through to territoryestablishment in the following spring. The age and “phenotypic” father of every birdborn on Mandarte Island was known during this 4-year period.Individual Song Sparrows did not change their unique repertoires of 5-13 complexSong Types across a range of ages covering their life span. Complete repertoiresrecorded from this species at any age are the same as those in the first year of life, whensong is learned. Two hundred and six continuously recorded songs or 280 songs frompooled sessions were required to achieve 95% confidence that the complete repertoirewas recorded.Birds averaged 8.2 Song Types over all islands and did not sing smaller repertoiresthan those birds in mainland populations. Higher population density and an increasednumber of neighbours at the time of song learning both resulted in larger repertoires.More singing males provide greater acoustic stimulation at the time of song learning.From whom do wild birds learn their songs, and how do individuals choose amongthe models available? Two opposing hypotheses predict that tutors are most likely eitherfathers or neighbours. Twenty-one birds born on Mandarte Island matched no songs withtheir fathers. However, three birds that dispersed from a small island (0.8 ha) with fewtutors to a very poor song environment with only one tutor retained some songs theyheard from their fathers before dispersal (22-68 days of age) and also learned other songsfrom their neighbours after dispersal (273+ days of age). Birds as young as 124 days ofage uttered note sequences that were destined to be in their adult repertoires. Previousiiistudies had shown this to occur at 241 days in the laboratory and 169 days in the field.Juvenile birds that progress rapidly through the stages of song development may obtainterritories more readily than birds who do so more slowly or at older ages.Using the 1989 cohort of juveniles, I could assign every song learned to a particulartutor. I found that while most focal birds shared no songs with older non-neighbours,some birds matched up to nine Song Types with them. These patterns indicate theexistence of preferred tutors. Particular Song Types were copied precisely, and persistedacross up to four generations and eleven years on Mandarte Island. This thesis showsthat Song Sparrows share more identical songs, and learn song over a longer period thanpreviously determined. Both the timing and the source of song learning depends on thequality of the learning environment, measured by the number of tutors and the amount ofsinging.HVTABLE OF CONTENTSSection PageABSTRACT iiFRONTISPIECE ivLIST OF TABLES ixLIST OF FIGURES xACKNOWLEDGEMENTS xiiDEDICATION xiiiCHAPTER 1. INTRODUCTION 1Background 1Study system 3Thesis organization 4CHAPTER 2. DOCUMENTING COMPLETE SONG REPERTOIRES 7Summary 7INTRODUCTION 8METHODS 11Song recording 11Analysis 121. Definitions 122. Making and classifying sonagrams 17RESULTS 18Total number ofsongs recorded vs. estimated repertoire for all birds 18Pooled recordings 21Effect of repertoire size on recording effort necessary to documentthe complete repertoire 21viSection Pagecontinuous recordings 21Probability ofdocumenting the complete repertoire 26DISCUSSION 29Recommendations 31CHAPTER 3. SONG REPERTOIRES OF SONG SPARROWS REMAINSTABLE ACROSS THE LWE SPAN 32Summary 32INTRODUCTION 33METHODS 35RESULTS 35Birds first recorded at <1 year of age 38DISCUSSION 40CHAPTER 4. EFFECTS OF POPULATION DENSITY ANDIMMIGRATION ON REPERTOIRE SIZE OF ISLANDSONG SPARROWS 46Summnamy 46INTRODUCTION 47METHODS 49RESULTS 52Repertoire size vs. degree of immigration 52Repertoire size vs. population density 53Repertoire size vs. number of neighbours 56DISCUSSION 56viiSection PageCHAPTER 5. SONG LEARNING BY SONG SPARROWS 62Summary 62INTRODUCTION 63METHODS 67Coding Song Types 68Coding and randomizing pairs ofbirds 71Song Type matching 72Song similarity 73Tracking movements of one cohort 73RESULTS 74Description of song 74Comparisons of repertoires between focal birds and potential tutors 74Fathers as potential tutors 75Neighbours as potential tutors 75All older territory owners as potential tutors of 1989 cohort 87Summary 92DISCUSSION 97Fathers as potential tutors 97Neighbours or other birds in the population as potential tutors 100Birds from the same cohort as potential tutors 101Similarity of matching songs 101The genetic adaptation and the social adaptation hypotheses:a continuum of learning 103CHAPTER 6. CONCLUDING DISCUSSION 106LiTERATURE CITED 113Section PageAPPENDIX 1. Song summary and sequence coding 125APPENDIX 2. Song recording history for all Song Sparrows in the study 127APPENDIX 3. Song Types that focal birds matched with potential tutors 131APPENDIX 4. Matching and non-matching letter sequences 134viiiLIST OF TABLESTable Page2-I. Recording efforts in this and in previously published studiesof Song Sparrows 93-I. Song Types recorded across years 365-I. Territories travelled through and birds song-matched by eightfocal birds born on Mandarte Island in 1989 89ixxLIST OF FIGURESFigure Page2-1. Sonagrams showing Version A and Version B of a single Song Type 132-2. Sonagrams showing a single Song Type and its Song Subsets andMinor Variations 152-3. Number of Song Types in the repertoire as a function of the numberof songs recorded 192-4. Number of Song Types in the repertoire as a function of the cumulativenumber of songs recorded for 20 birds with more than 500 songsrecorded from all pooled sessions 222-5. Cumulative number of songs uttered as a function of the duration ofrecordings, for those birds I recorded continuously for at least 2 h 242-6. Percent probability of documenting the complete repertoire as a functionof the number of songs recorded continuously, or the number of songsrecorded from all pooled sessions 273-1. Sonagrams showing Song Types of birds first recorded in the yearof birth 414-1. Location of study islands in southwest coastal British Columbia 504-2. Number of Song Types learned as a function of the density (males/ha)in the year that birds were one year of age 544-3. Number of Song Types learned as a function of the number ofneighbours birds had at one year of age 575-1. Sonagraphic structure of basic Note Types in songs of Mandarte IslandSong Sparrows 695-2. Map of territories on Mandarte Island in 1989 and 1990 765-3. Songs of older tutor, pm.bo matched by focal bird (neighbour), gm.odb 78xiFigure Page5-4. Five Song Types in complete repertoire of older tutor, mdb.br andthree Song Types matched by focal bird (neighbour), mw.ww, as wellas two Song Types not matched 805-5. Songs that dispersing birds matched with their father on their natalisland and those matched with their neighbours on islands to whichthey dispersed 825-6. Map of Dock 1, Dock 2, Dock 3 and Forrest Islands to show thedispersal pattern of three birds 855-7. Songs of older tutor, rwdb.rnr matched by focal bird (neighbour), bo.gm;and one Song Type that was passed through four generations of birds:rwdb.mr, bo.gm, go.mo, and mb.gg, remaining unchanged except forone Note 905-8. Two Song Versions of an older tutor r.om, matched by focal bird(his neighbour) pm.bo; and two songs of older tutor pm.bdb, matched byfocal bird (not his neighbour), orn.gdb 935-9. Frequency histograms showing the source of song-matching byfirst-year birds 95xiiACKNOWLEDGEMENTSI thank the Tseycum and Tsawout Indian bands for allowing me access toMandarte Island, and the Brumbaums for access to Ker Island. Jamie Smith supervisedmy work, beginning with teaching me how to steer the Zodiac towards Mandarte Islandwithout crashing into the rocks, and providing generous financial support and relentlessconstructive criticism that I much appreciated. I also thank my supervisory committeefor their efforts. Lee Gass, Robin Liley, Ted Miller and Janet Werker offered muchvaluable input over the course of my studies. I thank all the people who found nests,banded birds and helped with various other fieldwork, especially Wes Hochachka, JamieSmith, Mary Taitt, Lorne Gould, David Westcott, Marlene Machmer, Chris Rogers andLotus Vermeer, and also Peter Arcese, Gwen Jongejan, Doiph Schluter, Arne Mooers,Dick Repasky, Durrell Kapan, Christine Chesson, Gwen Burton, Kelly Stevens,Guillermo Giannico, John Ireland, Horacio de la Cueva and J0 Walker. I thank TedMiller for lending me recording equipment when mine self-destructed, and Durrell Kapanand Jamie Smith for recording birds in 1991. Alistair Blachford provided muchappreciated assistance with all my computing needs. Conversations with MartinAdamson helped greatly with my song comparisons, and I also thank Tracy Appleton forher help with the amino acid sequencing program. The Natural Sciences and EngineeringResearch Council of Canada funded this research through operating and equipmentgrants to Jamie Smith, and a post-graduate fellowship to myself. I was also providedresearch funding from the Canadian Wildlife Service (University Research Grant), theAmerican Museum of Natural History (Chapman Memorial Grant), the University ofBuffalo (T.C. Schneirla Research Grant), and the Association of Field Ornithologists (E.Alexander Bergstrom Research Grant), and supported by teaching assistant positions inthe Department of Zoology. A travel grant from the Faculty of Graduate Studies helpedme attend an international conference. Many people accompanied me to the islands inwinter storms and helped carry outboard motors and the boat out of harm’s way. I thankthem all. My dear friends Colleen Bryden and Tracey Hooper provided encouragementand support, as did my brother John and his family. My parents provided emotional andfinancial assistance, and worried about me every time I went into the field. I wouldespecially like to thank George Campbell for his vital part in helping me complete mydoctorate, from making the switch from fieldwork on Mandarte to data analysis andwrite-up in Vancouver far more enjoyable, to convincing me of my abilities and beingthere for me when I didn’t quite believe in them. I shall long remember the beauty ofMandarte Island, Guinness at just the right temperature at the Stonehouse Pub, and sailcompetitions with the great blue heron squad. Finally, I would like to thank the localVancouver Song Sparrows, whose vocalizations I heard in the final stages of writingreminded me of why I started this degree in the first place.xiiiDEDICATIONI dedicate this thesis to the tutors who have had the most influence on me, mymother and father, Joy and Bill Cassidy. When I think of all the things I have learnedthrough my experiences and education, those acquired from my parents are always themost useful and important - how to double-clutch, knit a sweater, operate an offset press,ride a bicycle, tie my shoelaces, fix cars, soft boil an egg perfectly, respect other people,raise pets with care and love, and realize that health and happiness are the only thingsthat really matter in life. I am still learning from my parents, who are the wisest people Ihave ever known.1CHAPTER 1INTRODUCTIONBackgroundVocalizations are one of several interesting forms of animal communication.Animals vocalize to help find their food, avoid predators, attract mates and defendterritories (Wilson 1975). Vocal communication is well-developed among suchvertebrates as cetaceans, bats and primates, and is perhaps most strikingly shown in birds(Smith 1977). Two arbitrarily defined forms of avian vocalizations are songs and calls.Songs are generally longer and more variable than calls, and are sung primarily by malesduring the breeding season (Nottebohm l972a). In this thesis, I deal only with songsuttered by males.Songs are learned in almost all songbirds (oscines), as well as in some non-oscines,such as Psittacidae (parrots), Trochilidae (hummingbirds), Tetraonidae and Phasianidae(game birds; Mundinger 1982). Cultural transmission of behaviours, includingvocalizations, may show considerable stability over time and space (Cavalli-Sforza et al.1982). It is not yet well understood why some behaviour types are copied by manyindividuals, while others fall into disuse.While most birds have an innate ability to produce species-typical vocalizations,songs of birds raised in acoustic isolation are slower (e.g. Immelmann 1969, Kroodsma1977a), more variable (Marler et al. 1962), or simpler (e.g. Lemon and Scott 1966), andoften do not elicit territorial responses when heard by conspecifics (e.g. Lanyon 1979).Though Mulligan (1966) described songs of Song Sparrows (Melospiza melodia) that wereraised in acoustic isolation as approximately normal, Kroodsma (1977a) found them to belonger, of lower frequency range, and abnormal in organization.2To learn species-specific songs, most young birds must hear and practise them, andsing abnormally if deafened before starting to sing but after hearing models (Konishi1965). Birds can recall sounds that they heard much earlier in life; Swamp Sparrows(Zonotrichia georgiana) produce song components memorized eight months earlier withno rehearsal (Marler and Peters 1981). The hormones testosterone and possibly oestradiolare involved in the production of crystallized song (Nottebohm 1969, Marler et al. 1988).The 11sensitive” period (Thorpe 1958, Marler and Tamura 1964), during which birdslearn songs, varies interspecifically. Some species learn songs early in life, their songsremaining unchanged thereafter (e.g. Marler and Tamura 1964, Nottebohm 1969). In otherspecies, new songs are acquired throughout life (Laskey 1944, Payne and Payne 1977,Jenkins 1978, Yasukawa et al. 1980, Payne 1981).In many species, it is not known whether young birds learn their songs from: 1)their fathers and/or neighbours before dispersing from the natal territory; 2) owners ofterritories through which juveniles travel after independence; 3) birds migrating throughthe natal areas of juveniles; 4) birds on wintering grounds (in migratory species); or 5)owners of territories next to those established by first year birds. The terms “models” and“tutors” are commonly used in the bird song literature to describe those individuals thatjuveniles most match, and are, therefore, considered to be sources of learning. An activerole on the part of the “tutor” is not implied.Individuals and species vary in the numbers of Song Types learned. Repertoiresize varies across species, from the White-crowned Sparrow (Zonotrichia leucophrys),with one Song Type (Marler and Tarnura 1962), to the Brown Thrasher (Toxostoinaruflim), which sings up to several thousand Song Types (Kroodsma and Parker 1977).Within species, differing degrees of variation occur over large geographic areas, betweenpopulations and within local populations (Thielcke 1969, Baptista and King 1980, Krebsand Kroodsma 1980).3Two opposing hypotheses have been suggested to explain the source of songlearning by birds. The genetic adapatation hypothesis (Marler and Tarnura 1962,Nottebohm 1969) suggests that birds imitate their fathers and their fathers’ neighbours, andsong similarity within local areas restricts movements of birds, who then adapt geneticallyto particular habitats. The social adaptation hypothesis (Payne 1982) suggests anadvantage to birds sounding like their neighbours at the time of territory establishment.Whether either of these two hypotheses apply to specific species depends on: 1)similarity of song between birds within populations, or between populations in thosespecies that disperse; 2) where young birds set up territories in relation to birthplace; and3) when young birds learn song. Knowledge of the timing and source of learning inrelation to dispersal of birds is, therefore, critical in determining the origins, mechanismsand significance of spatial and temporal distributions of similar patterns of song withinspecies. This topic is the subject of this thesis.Study systemMost of the data in this thesis were collected on Mandarte Island, British Columbia,approximately 25 km NNE of Victoria. The Mandarte Island population of Song Sparrowshas been studied intensively (Tompa 1964, Arcese and Smith 1985, 1988, Smith et al.1986, Smith 1988, Arcese 1989, Hochachka et al. 1989, Hochachka 1990, Arcese et al.1992).To study song learning in birds, I wanted a species that exhibited sufficientvariation between individuals so that tutors of young birds could be assigned, and I neededa population whose history and pedigree was known. The Mandarte Island Song Sparrowpopulation was ideal. Since 1975, all Song Sparrows have been colour-banded in the nest,so age and father were known. “Father” in my, and all other studies of song learning that Iknow of, is the phenotypic father. Fathers were identified through behavioural4observations; the male copulated with the female who laid the eggs, defended the territoryin which the nest was located, and helped feed nestlings and fledglings. However, onlyupon genetic analysis would we know, with certainty, that putative fathers were genotypicfathers, as a few extra-pair copulations with neighbours have been observed (Smith andArcese 1989). Regardless of whether the “behavioural” father and the “genetic” father arethe same, however, the male birds with which juveniles have the most interaction beforeindependence are the “behavioural fathers”.It is often difficult to study song similarity between fathers and sons, if birds aremigratory or disperse long distances. I was able to follow birds on Mandarte Island frombirth until death. Only four birds born on Mandarte Island are known to have settledelsewhere (Hochachka et al. 1989), and only three immigrant males have establishedterritories (P. Arcese, J.N.M. Smith, W.M. Hochachka and A.L.E.V. Cassidy, unpublisheddata).Birds on some other nearby islands were colour-banded beginning in 1988,therefore I knew the age and father of birds born on these islands since 1989. As well, Ifollowed dispersal of Song Sparrows in these other island populations, often betweenislands, and compared songs between islands.A winter storm on Mandarte Island in the second year of my study reducedpopulation density and increased juvenile survival and recruitment. Thus, I measured songlearning of an entire cohort of young birds in a year when their travels from independenceto territory establishment could be documented, and I could assign the songs they sang toeach of the small number of potential tutors available in the population.Thesis organizationThis thesis deals with two related topics in the study of bird song: variationbetween individuals, and song learning by juvenile birds. Chapter 2 describes the5techniques I used to record the songs of Song Sparrows and to analyze themsonagraphically. A “sonagram” is a “picture of sound” which graphs sound frequency onthe y-axis and time on the x-axis. A challenge in documenting behaviours exhibited byindividuals is knowing when complete repertoires have been reached, or at least being ableto assign probabilities to the estimates. For the 20 birds from whom I recorded the greatestnumbers of songs, over 500 songs/bird, I examined at what recording efforts these birdsreached their complete repertoires. I then used these values to calculate the probability, atthree confidence levels, of documenting a complete repertoire given any number of songsrecorded. Choosing a 95% confidence level, I assessed, for each of the 134 birds fromwhom I recorded songs, whether or not I documented the complete repertoire. Thisprovided the basis for inclusion of particular birds in data sets for other chapters.Chapter 3 includes many data collected over a four-year period. Two previousstudies (Searcy et al. 1985 and Hiebert et al. 1989) had shown that a small sample (n=7) ofcolour-banded Song Sparrows did not change their song repertoires across years. I addedto this data base, with a total of 26 colour-banded birds. In addition, I had a unique chanceto examine Song Types sung by birds just around the time that their repertoires“crystallized”. Chapter 4 investigates whether repertoire size differs appreciably acrosspopulations, and whether it may be related to either population density or the rate of maleimmigration to populations. While it has been suggested that isolated islands, or locationswith low population densities, should result in birds singing smaller repertoires of SongTypes than birds in other areas, empirical evidence is lacking.The question of when and from whom young birds learn songs in the wild isaddressed in Chapter 5. Though the timing of learning in this species was elegantlydocumented by Marler and Peters (1987) in the laboratory, they closed their paper bybegging the question of what happens in the wild. I compared song repertoires of 24 birdsto their most likely potential tutors: fathers and neighbours. Throughout the thesis, I6followed the rules defined in Chapter 2 for assigning Song Types to individuals. Asdescribed in Chapter 2, Song Sparrows sing the same Song Type over and over again,before switching Types, therefore biologists generally agree on the classification of SongTypes in this species. In Chapter 5, I had a new task of determining Song Type similaritybetween individuals. In this chapter, I describe a technique of coding Note Types withineach Song Type, in order to compare Song Types objectively.Finally, in Chapter 6, I return to the two themes of song variation and songlearning, summarizing my findings relevant to these topics, and noting some areas offuture research suggested by the results of my thesis.7CHAPTER 2DOCUMENTING COMPLETE SONG REPERTOIRESSummary- Accurate description of behavioural categories is a necessary precursor to thestudy of their function and organization and also presents a challenge in sampling design.I explored the relationship between recording effort and repertoire size in Song Sparrows(Melospiza melodia). I recorded and analyzed sonagraphically 33,843 songs from 134males at 13 sites in coastal British Columbia between 1988-1991. All but five birds werecolour-banded. Estimated repertoire size increased with recording effort up to about 200songs, then remained constant to a maximum of 2,533 songs recorded, Previous authorshave suggested two criteria for documenting complete repertoires in this species, recordingbirds for a minimum duration of time, and recording a minimum number of songs. Thesuggestion by some previous authors that 3-hour samples of songs document completerepertoires in this species would have estimated complete repertoires for only 75% of thebirds in my data set. I found that a second published criterion of recording 300 songs perindividual would have estimated complete repertoires for 100% (with continuousrecordings) or 96% (with recordings pooled over all sessions) of the birds in my data set.The number of songs and the duration of continuous recording required to sample all SongTypes varied greatly across individuals, as a result of differences in song rate, bout lengthand repertoire size. To achieve 90, 95 and 99% confidence that the complete songrepertoire was recorded, 161, 206 and 225 continuously recorded songs were required. Fornon-continuous recordings, 278, 280 and 445 songs were necessary.8INTRODUCTIONA behavioural repertoire is a set of mutually exclusive, collectively exhaustivebehavioural acts of an animal or species (Fagen 1978). Ideally, we wish to sample therepertoire such that, at some confidence level, the sample accurately estimates thecomplete repertoire. Fagen and Goldman (1977) and Fagen (1978) discuss statisticaltechniques applied to repertoire estimation of a variety of behaviours, and Kroodsma(1982) points out specific challenges of estimating bird song repertoires. Song Sparrowsare common and widespread in North America and are a good subject to investigatetechniques for estimating repertoires. Since 1924, geographic and other variation in theircomplex songs has been noted in many studies. The function and organization of theirsong repertoires have been studied extensively (e.g. Borror 1965, Stoddard et al. 1988).To date, studies of individual song variation in Song Sparrows have varied in theiruse of some or all of the following: sonagrarns, colour-banded birds, large numbers ofbirds and large recording effort per bird (Table 2-I). Early researchers described songs inwords or unique notations (Nice 1943; Saunders 1924,1951; Wheeler and Nichols 1924).Later workers who used tape-recorders and sonagraphs recorded few songs per bird(Mulligan 1963,1966), and usually did not colour-band individuals (e.g. Borror 1965,Eberhardt and Baptista 1977). Recently, some researchers have recorded many songs fromrelatively few birds (Hiebert et al. 1989, Podos et al. 1992). Previous research indicatesthat Song Sparrows sing unique repertoires of about eight discrete Song Types each. Thereis great variation in published repertoire sizes for this species, however, varying from 1-24Song Types from all sources (e.g. Wheeler and Nichols 1924, Mulligan 1963), with 5-14Song Types most commonly reported in those studies with the largest recording efforts(e.g. Kramer and Lemon 1983, Searcy et al. 1985, Hiebert et al. 1989, Podos et al. 1992).One Song Type is often repeated a variable number of times before switching to anotherSong Type in the repertoire, and further variation exists at the level of Song Type.9Table 2-I. Recording efforts in this and in previously published studies of Song Sparrowsong variation. Mean numbers of songs/bird were calculated from published data,presented in first two columns. Data not available indicated by ?. 1 - Nice recorded“hundreds of songs” from eight well-studied birds, but does not present data; 2 - numbernot presented, but surmised from Figure 4 (Kramer and Lemon 1983); 3 - first line is for1980; second line is for 1981; 4 - McArthur recorded 300 songs from “many males”, but hedoes not present data.Mean# of # of songs/ Colour-songs birds bird marked? Reference? ? no Wheeler and Nichols 19241,000 250 4 some Nice 19431884 685 1.3 no Saunders 19511,500 75 20 some Mulligan 19637,212 120 60 no Borror 19651,800 71 25 some Mulligan 196621 ? no Harris and Lemon 1972511 9 57 no Eberhardt and Baptista 19772,2772 6 380 yes Kramer and Lemon 198322 200+ yes Searcy et a.. 198520 300+ yes Searcyetal. 19857 23 200+ yes McArthur l9867 16 7 yes Hiebert et al. 19896,028 12 502 7 Podosetal. 199233,843 . 134 251 yes this study10Previous studies on Song Sparrow song have strived to ensure that completerepertoires were reached, either by recording a minimum number of songs, or by recordingsong over a minimum duration of time. However, only Hiebert et al. (1989) convincinglydemonstrated that the criterion they chose was successful in documenting completerepertoires. Borror (1965) said that 50 songs per bird was inadequate to determinecomplete repertoires. Mulligan (1966) recommended continuous recordings of three hoursin duration, but did not use this technique himself. In two previous studies (McArthur1986 and Searcy et al. 1985), a minimum of 200 songs per bird was set as a criterion torecord complete repertoires. McArthur (1986) recorded 300 songs from “many” of his 23birds, with only one bird adding a new Song Type in the last 100 songs. Likewise, sinceSearcy et al. (1985) “occasionally” found new Song Types after 200 songs recorded, theyraised their criterion to a minimum of 300 songs per bird. Neither of these studies notedwhether they recorded songs continuously or pooled songs from two or more recordingsessions, nor did Searcy et al. (1985) test the possibility that new Song Types were addedafter 300 songs. Hiebert et al. (1989) recorded songs of 16 individual Song Sparrows forat least three consecutive hours each, with no new Song Types recorded after 1.5 hours perbird. Podos et al. (1992) recorded Song Sparrows continuously for “about three hours onone or two consecutive mornings”; this was equivalent to at least 300 songs per bird fromall but one bird, but it is unclear whether continuous three hour recordings were made oneach of two mornings, or pooled over mornings.I applied each of these criteria to a large data set in order to search for a theme inthe techniques of previous workers that could be used to sample the song repertoires ofSong Sparrows. I ask if all event types are best documented by recording a particularnumber of events or by recording events continuously over a block of time? Thoughcontinuous recordings of at least 1.5 hours per bird seem to be the most successfultechnique, this is not always possible in the field. For this reason, I ask what relationship11exists between duration of recordings and the number of songs uttered. In addition, Iinvestigate whether continuous 1.5 hour recordings are always successful in documentingcomplete repertoires of birds recorded on more than one occasion. I then ask if, once theselevels have been reached, can many additional events be recorded without adding a newtype? While I apply these two criteria specifically to song repertoires of Song Sparrows,they can be generalized to recording other types of behavioural events from other species.METHODSSong recordingI recorded Song Sparrows at 13 sites in southwest coastal British Columbia from 9March 1988 to 9 July 1991. Song Sparrows at these sites defend permanent year-roundterritories (Arcese 1989). One hundred and twenty-nine of the 134 birds recorded wereindividually colour-banded. The five unbanded birds were each recorded at different sites,with most songs recorded in a single session, so I am confident of their identities. Bandsconsisted of one numbered (five digits) metal Canadian Wildlife Service band and threecoloured plastic bands (p=purple, b=blue, db=dark blue, o=orange, g=green, w=white,r=red) placed on the legs in unique combinations. Therefore gm.odb had a green bandover a metal band on the left leg and an orange band over a dark blue band on the right leg.I used a Sony Professional Walkman WM-6DC, a Sennheiser ME-80 preamplifying microphone with a foam wind filter and 90-minute chrome cassette tapes, andrecorded songs of birds in two ways. First, I recorded all songs uttered in timed sessionsfor one to seven consecutive half-hour intervals. Second, I recorded all songs uttered inuntimed intervals of less than a half-hour in duration. Most birds were recorded in each ofthe two ways, and many birds were recorded several times in timed sessions. At seven ofthe sites, individuals were recorded on many occasions within and between years. Pooled12recordings are all songs recorded from each individual. Birds were recorded from 0602 hto 2019 h.Analysis1. Definitions-I used the terms listed below in the description and analysis of songs:Note - the smallest unit on a sonagram; a sound producing a continuous trace on asonagram (Mulligan 1963).Song Type - (Figures 2-1 and 2-2) an utterance of approximately 2.5 seconds in length,made up of a unique sequence of Notes (regardless of the number of repetitions ofeach note), including any Versions, Subsets and Minor Variations. Song Type wascalled “Song Pattern” by Borror (1965) and Harris and Lemon (1972) and “SongTheme” by Eberhardt and Baptista (1977).Bout - consecutive series of songs that may vary in minor ways (Versions, Subsets, MinorVariations) but nevertheless conform to a particular Song Type (Mulligan 1963).The number of songs uttered in Bouts varied from 1-74. There was a cleardifference in the sonagraphic structure of Song Types between Bouts. Song Boutwas called “Song Series” by Nice (1943).Song Version- Song Types in which at least the first half of the Notes are the same, butthe ending differs. Songs ending with Trills (same Note repeated many times)often occurred in two Versions, with a different Trill Note in each Version (Figures2-lA and 2-IB). Nice (1943) used Song Version to describe all variations of SongTypes within Bouts.Song Subset - sequence of Notes forming a Subset of a longer Song Type, usually as aresult of Notes missing at the end of the sequence (Figs. 2-2B and 2-2C).13Figure 2-1. Sonagrams showing Version A and Version B of a single Song Type. Thedifference between the two versions is the repeated Note at the end, indicated by thearrows. Frequency (in kilohertz) is on the y-axis, and time (in seconds) is on the x-axis..JpuooestI t.ot Vt7t15Figure 2-2. Sonagrarns showing a single Song Type, A, and its Song Subsets, B and C,each with Notes missing at the ends of the songs, and Minor Variations, D and E, eachwith different Notes at the ends of songs, indicated by the arrows.16lO•A8->1_I__I:: rr1an1 2 secondsrrr.,Jr17Minor Variation- within a Bout of a particular Song Type, songs with the same overallpattern of Note sequence, but with the addition or deletion of single Notes, usuallyin the middle or end of the song (Figures 2-2D and 2-2E). Many authors havenoted this level of variation for Song Sparrows (e.g. Mulligan 1966, Stoddard et al.1988).I have avoided the terms Syllable, Note Complex and Phrase, initially suggested byMulligan (1963). Each of these is a made of a set of Notes. Since the same Note canappear in different Syllables (repeated sets of Notes) and Note Complexes (unrepeated setsof Notes), I felt it was clearest to describe Song Types simply by their Note sequences.2. Making and Classifying Sonagrams -I digitized and analyzed songs on a Multigon Uniscan II Real-Time Analyzer. Tocatalogue Song Types sung by each bird, I used the following technique. I called the firstsong analyzed for each bird Song Type 1 and printed its sonagram (time-frequency chart)on a Mitsubishi Video Copy Processor. I viewed the next song on the monitor andcompared it to the last. If it was exactly the same, or consisted of a Subset of the alreadyprinted sonagram of Notes, I printed no new sonagram. If the next song was the sameSong Type with additional Notes, I printed another sonagram to replace the other, andcatalogued it with that Song Type. Using this technique, each Song Type was defined asthe longest note sequence. If, however, the next song analyzed was a different sequence ofNotes, I printed a sonagram and called this Song Type 2. Eventually, no new sonagramsneeded to be printed, and each subsequent song matched one of the Song Types catalogued(repertoire). Song Versions were lettered A,B N, within the Song Type. For each bird, Isummarized date, time and duration of recording sessions and the sequence of Song Typesuttered (Appendix 1).18Statistical analyses were conducted using SYSTAT (Wilkinson 1990) on log10normalized data. The dispersion around means given is the standard error.RESULTSFrom 134 birds at 13 sites, I analyzed sonagraphically 33,843 songs (mean 251;s.e. = 29.7 songs/bird, range = 1-2,533 songs/bird; Appendix 2). I determined each bird’srepertoire size from pooled recordings. To test the relationship between recording effortand the estimated repertoire size, I analyzed these data using two previously publishedcriteria for estimating complete repertoires: recording a particular number of songs, andrecording continuously for a particular duration of time.Total number of songs recorded vs. estimated repertoire size for all birdsPodos et al. (1992) concluded that they recorded complete repertoires of SongSparrows upon finding a nonsignificant relationship between recording effort andrepertoire size. Applying this model first to my total sample of 134 birds, I found thatrepertoire size increased significantly with recording effort (r=.793, 133 df, p=O.O). Sixty-three percent of the variation in repertoire size was explained by total number of songsrecorded under this model. A linear model clearly does not best describe the data (Figure2-3); repertoire size increased with recording effort to about 200 songs, after which itremained relatively constant.At what minimum recording effort would the significant relationship betweenrepertoire size and recording effort disappear? If I included only those birds for which aminimum of 72 songs were recorded, 48 birds were eliminated from the analysis. Therewas no significant relationship between recording effort and repertoire size (r=. 199, 85 df,p=.O66) for the remaining birds. If I used this technique alone to determine whether Irecorded complete repertoires, any bird with a minimum of 72 songs recorded would meet19Figure 2-3. Number of Song Types in the repertoire as a function of the number of songsrecorded. The number of songs recorded is shown on a logarithmic scale. N=134 birds;33,843 songs.14.12......U) 0)10••••._...e—.0)8••••••••••••c).—............II 06•0).0.....E4..z..—.....02......0IIIIIIIIIIII1111IIIIIIiiiI101001000Numberofsongsrecorded21the criterion. But did every bird from whom I recorded at least 72 songs sing its completerepertoire?Pooled recordingsI examined whether the 20 birds from which I recorded the most songs (> 500)reached their complete repertoires. After each of these birds reached a particular repertoiresize, I recorded many more songs without observing a new type (mean = 715, range = 298-1989; Figure 2-4). I considered this the complete repertoire. The mean recording effortnecessary to document complete repertoires was 185 songs (median = 184), however, therewas much individual variation about this mean (range = 18-544). While some birds in mysample sang all Song Types in their repertoires within the first 50-100 songs I recorded,others sang hundreds of songs before adding new Types (Figure 2-4). Some of the theseindividual differences may be explained by repertoire size.Effect of repertoire size on recording effort necessa;y to document the complete repertoire.The larger the repertoire, the more songs that were required to sample all SongTypes. This was true whether songs were recorded in continuous intervals (r=.42, t=2.55,p=.O2, 31 df) or pooled across sessions (r=.73, t=4.50, p=0.OO, 18 df).Continuous recordingsI examined whether those birds from whom I recorded continuously for at least 2 hreached their complete repertoires within this time (i.e., added no new Song Types aftersome point). On 44 occasions, I recorded a bird for 2-3.5 h continuously. On 33 of these44 occasions, birds reached their complete repertoires during the continuous recording.Birds sang at a fairly constant rate, averaging approximately 100 songs/h (Figure 2-5).The mean number of songs required to document the complete repertoire was 104(median = 88), again with much individual variation about the mean (range = 25-23 1). To22Figure 2-4. Number of Song Types in the repertoire (y-axis) as a function of thecumulative number of songs recorded (x-axis) for 20 birds with more than 500 songsrecorded, pooled from all sessions. Each panel shows data from two birds, one indicatedby a solid line, and the other by a broken line. The total number of songs recorded fromeach bird is shown on the graphs.10864210864210864210884210884210884210864210864210864210884223568/667100 200 300 400 500100 200 300 400 500522 573953100 200 300 400 500100 200 300 400 500-- 601/174100 200 300 400 500 100 200 300 400 500891815J‘ft78100 200 300 400 500 100 200 300 400 5001247100 200 300 400 500 100 200 300 400 50024Figure 2-5. Cumulative number of songs uttered as a function of duration of recording, forthose birds I recorded continuously for at least 2 h. The filled square indicates the meanand the sample size is shown above each square. Vertical bars indicate standard error.The cumulative percent (mode and mean) of complete repertoire documented by the end ofeach half-hour block is: 0.5 h- 50, 48.9; 1.0 h - 100, 76.1; 1.5 h - 100, 86.6; 2.0 h - 100,90.9; 2.5 h - 100, 94.1; 3.0 h - 100, 94.6; 3.5 h - 100, 98.5.4000) C C,300oI0200T44.E44CT J>144I00—I 1E44C.)123t\) c-flDurationofcontinuousrecording,h26sing that number of songs took from 0.5 h (four of 33 cases) to 3.5 h (one of 33 cases),with 1 h being most common (15 of 33 cases).Birds recorded continuously for at least 2 h on more than one occasion exhibitedgreat variation in the number of songs and the recording time required to reach theircomplete repertoires. For example, pm.bo sang his complete repertoire of eight SongTypes in 231 songs in 1989; in 1990 he did the same in only 109 songs. In 1990, op.gmtook 2 h to reach his complete repertoire of seven Song Types, singing 61 songs. Onanother day that same year, he took 1 h, singing 80 songs, to do the same.Birds recorded continuously for at least 2 h on more than one occasion did not singtheir complete repertoires on each occasion. In 1990, gm.odb sang all six Song Types inhis repertoire in 106 songs during 1 h. On a second day, he sang only five of these SongTypes in 66 songs during 2 h. On a third day, he again sang only five Song Types in 418songs during 3 h, this time missing a different Song Type than on the last occasion.Another bird, pg.mg, omitted different Song Types from his complete repertoire on each ofthree long continuous recording occasions in the same year.Probability ofdocumenting the complete repertoireUsing those 20 birds from whom I recorded the most songs and was confident ofsampling their complete repertoires, I calculated the probability of documenting acomplete repertoire for a given recording effort. Fewer songs were required to attain agiven probability of obtaining complete repertoires with continuous recordings than withpooled recordings (Figure 2-6). Two hundred and six continuously-recorded songs allow95% confidence in documenting a complete repertoire, while 280 songs are necessary ifsongs are pooled from different recording sessions. Using the 95% confidence levels, Idocumented complete repertoires from 45 of the 134 birds in my data set.27Figure 2-6. Percent probability of documenting the complete repertoire as a function ofthe number of songs recorded continuously (indicated by broken line), or all songs pooledfrom different recording sessions (indicated by solid line). The inset shows the number ofsongs required, for each recording technique, to document the complete repertoire at threedifferent percent probability levels.28//I4#1’II//(J/I/I>100.0I0100806040200)/IJIIIIrobability99%95%90%IContinuous225206161Pooled445280278200 400 600Number of songs recorded29DISCUSSIONA full documentation of Song Types in repertoires and careful definitions of theunits of analysis, are both essential for studying variation in vocal repertoires (Kroodsma1982). Because Song Sparrows sing a Bout of one Song Type before switching to adifferent Type, there is general agreement amongst researchers on the definition of a SongType. In other species, some variation in repertoire size has been attributed to differencesin researchers’ definitions of Song Types [e.g. Yellow Warbler (Dendroica petechia);Spector 1991].A good estimate of repertoire size can be obtained after a sufficiently long periodof sampling, which appears to depend on the species concerned (Fagen 1978). For somespecies, all event types in a repertoire are very difficult to reach. For example, not allsongs in the very large repertoires of Marsh Wrens (Cistothorus palustris) are everrecorded, but repertoire size can be estimated from sample recordings (Verner 1975). Iused the approach of recording many hundreds of songs from a subset of 20 birds in mydata set, calculating the points at which complete repertoires were achieved, and usingthese points to decide the probability of achieving complete repertoires for those birds withfewer songs recorded. Hiebert et al. (1989) found that 1.5 hours of continuous recordingper bird was sufficient to document complete repertoires for Song Sparrows, with no newSong Types added by any birds in the next 1.5 hours. In contrast, I found that birdsreached their complete repertoires in only 33 of 44 continuous recording sessions of atleast two hours in duration. The birds in these samples sang approximately 100songs/hour; however, higher song rates, up to 360 songs/hour, are possible, especially byunmated males or males singing while their females incubate eggs (A.L.E.V. Cassidy andJ.N.M Smith, unpublished data). Differences in birds’ song rates between my and Hiebertet al)s (1989) study may account for our different results. This difference illustrates theimportance of recording either a minimum number of songs as a criterion by which to30document complete repertoires, or testing whatever criterion is used with additionalrecordings, as done by Hiebert et al. (1989). It is not always possible in the field to recordbirds when singing at their peak rates, nor is the mated status always known. For thesereasons, I suggest that it is better to record a minimum number of events than to recordover a minimum time.If, as claimed by Nice (1943), Song Sparrows went through their completerepertoires, Bout by Bout, before repeating any Song Types, sampling complete songrepertoires in this species would be quite straightforward. My birds did not utter SongTypes in any such obvious pattern. However, since fewer songs were necessary todocument complete repertoires when I recorded birds continuously than when I pooledrecordings from several occasions, it seems that Song Sparrows do order Song Types atsome level. The rules defining this order, however, must be complex. Kramer et al.(1985) found that the rate at which Song Sparrows switched Song Types was positivelycorrelated with the intensity of agonistic stimulation. Furthermore, birds often “counter-sing” in response to other birds by matching a shared Song Type. This has been observedin a variety of species, including Western Meadowlarks (Sturnella neglecta; Falls 1985);Great Tits (Parus major; Krebs et al. 1981, Falls et al. 1982); Marsh Wrens (Kroodsma1979); and Song Sparrows (Stoddard et al. 1992). Therefore, the frequency or pattern inwhich birds sing particular Song Types in their repertoires may depend on the behavioursof other individuals.The number of unique Bouts, rather than the number of songs recorded could beimportant in determining a sampling design to estimate complete repertoires. This “type-token” analysis is discussed by Fagen (1978), and would be worth applying to SongSparrow song. I also found that the larger the repertoire, the greater the number ofrecorded songs was required to obtain the complete repertoire. It would be useful toexamine other possible reasons, besides agonistic stimulation, for differences in the31number of repetitions of Song Types, or Bout length, between individuals, and whetherthis is related to repertoire size. This information would help us understand how birdscycle through discrete Song Types in their repertoires, and how we may better samplethem.Recom,nendationsMy results indicate the value of recording very large samples of behaviours from asubset of subjects, then using those data to determine the criteria for sampling othersubjects. I recommend that song repertoires of Song Sparrows be sampled using thenumber of songs recorded, not the duration of a recording, as the criterion determiningwhen the complete repertoire has been documented. Using three continuous hours as acriterion, only 75% of birds in my large sample sang their complete repertoires. Bycounting songs recorded, regardless of time, 206 continuously recorded songs should yieldthe complete repertoire with 95% confidence, if other populations of Song Sparrows singsimilarly to those in southwest B.C.. If continuous recording is not possible, pooledrecordings of 280 songs should achieve the same confidence level. If more or lessconfidence is desired in documenting the complete repertoire, the number of songsnecessary, using either continuous or pooled recordings, can be obtained from Figure 2-6,where the numbers of songs required to attain 90, 95 and 99% levels are shown in theinset.32CHAPTER 3SONG REPERTOIRES OF SONG SPARROWS REMAINSTABLE ACROSS THE LIFE SPANSummary- To test whether Song Sparrows (Melospiza melodia) continue to learnvocalizations throughout life, I examined the song repertoires sung by 26 colour-bandedbirds from six populations across 2-4 years. Where recording effort was adequate therewas complete overlap in the Song Types documented across years. This is the first studyto show that repertoire stability in this species is general across a range of ages, from lessthan one year to seven years. Unusually good survival of birds born on Mandarte Island in1989 provided me with a unique opportunity to record juvenile songs of birds that I couldfollow from hatching to adulthood. I found that six birds, recorded between July andDecember of 1989, and again as adults in 1990, each sang 2-6 Song Types recognizable intheir adult repertoires. The ages at which these songs were first recorded varied from 124-173 days of age. This is much earlier than previously found in either the field orlaboratory studies of this species, or in other closely related species, except for White-crowned Sparrows. I suggest that juvenile birds who progress through the stages of songdevelopment at faster rates, have an advantage in obtaining territories than birds who do somore slowly or at older ages.33INTRODUCTIONLearning of detailed song characteristics occurs in early life during a “sensitive”period of, for many species, unknown exact length (Slater 1983). In some bird species,individuals learn song only until about one year of age, after which their songs neverchange (e.g. Dowsett-Lernaire 1979). Other bird species continue to learn throughout life,with repertoire size increasing with age (e.g. Nottebohm and Nottebohm 1978, Yasukawaet al. 1980). Other groups of animals exhibit variation in length of learning period. KillerWhales (Orcinus orca) learn their pod-specific song repertoires, which can persist withlittle change for over 25 years (Ford 1991). However, the long, complex songs ofHumpback Whales (Megaptera novaeangliae), which are similar between individuals inone area and season, change progressively over the years (R.S. Payne 1978, Payne et al.1983). Why this variation should exist in nature is largely unknown.A necessary precursor to the explanation of patterns of song similarity betweenindividuals, however, is knowing until what age song is learned, and how this varies acrossand within species. One way to study timing of learning is to compare the earliestutterances of individuals to those sung later. However, because of the difficulty in hearingand recording juvenile vocalizations in the field (Marler and Peters 1982a), littleinformation of this kind exists for wild birds.The songs of many species, such as White-crowned Sparrows (Marler 1970,Baptista and Morton 1988), Indigo Buntings (Passerina cyanea; Payne 1981), Red-wingedBlackbirds (Agelaius phoeniceus; Marler et al. 1972) and Song Sparrows (Nice 1943,Marler and Peters 1987) begin as formless warbles, also called “subsong”, proceedingthrough several stages of “plastic song” before reaching adult repertoires of “ciystallized”,stereotyped songs (Nice 1943, Marler and Peters 1987). Once this final stage has beenreached, no new learning is thought to occur in those species which do not changerepertoires from year to year (Nice, 1943, Marler and Peters 1987). While there is no34evidence that Song Sparrows change their song repertoire size nor content across years,previous studies have either lacked sonagrarns or samples larger than five birds. Becauseno previous authors have recorded known-age Song Sparrows, it is unknown if repertoirestability across all ages is general in this species. Without using tape-recordings orsonagrarns, Nice (1943) noted that several of her colour-banded Song Sparrows sang thesame Song Types across years. Though Borror (1965) reached the same conclusion, he didnot mark birds in any way, and “identified the same birds across years by their song’.Using colour-bands and sonagrams, both Searcy et al. (1985; n=5) and Hiebert et al. (1989;n=2) showed that neither song repertoire size nor content changed across two years;however, age was not noted in either study. Song Sparrows usually live 1-4 years (Smith1988), but can survive to nine years of age (Nice 1943, Hochachka et al. 1989). This is thefirst study to record song repertoires of known-age Song Sparrows across years.Subsong and plastic song aid in the acquisition of skill necessary to perform newmotor coordinations (Nottebohm 1972b). At what age are sounds first uttered that remainin an individual’s adult repertoire? Laboratory studies have shown Song Sparrows to firstsing notes recognizable in their adult repertoires at 241 days of age (Marler and Peters1987) and closely related Swamp Sparrows to do so at 266-340 days of age (Marler andPeters 1982b). Turning to field studies, Kroodsma (1974) found that juvenile Bewick’sWren (Thiyoinanes bewickii) aged 60-135 days of age sang Song Types destined to be intheir adult repertoires. Marler (1970) found traces of adult note structure in the songs ofWhite-crowned Sparrows recorded at about 90 days of age. Nice (1943) first heardrecognizable notes of Song Sparrows at 169-274 days of age. In this chapter, I comparedSong Types of individuals over time. I examined the repertoires of known-age birds sungacross 2-4 years. The ages of birds recorded ranged from less than one year to seven years.For those birds first recorded when aged less than one year, I determined at what age Noteswere first uttered that could be identified in adult songs sung the following year.35METHODSSong recording and analysis techniques are described in Chapter 2. The data set forthis chapter consists of 26 colour-banded birds recorded in more than one year. Fourteenof these birds inhabited Mandarte Island and were of known age. The other 12 birdsinhabited Little Shell, Dock 1, Dock 2, Reay and Rum Islands; three of these birds were ofknown age. A description and map of the study islands is found in Chapter 4.Intensive searches of Mandarte Island were conducted from July through December1989 to locate Song Sparrows born between May and July 1989. Trails were slowlywalked by myself and my assistants, and sightings of all birds were noted on maps tracedfrom a low-level aerial photograph of Mandarte Island. When individuals birds were heardsinging, special notations were made on the maps. Following is a list of all dates (fromJuly-December 1989) on which I or my assistants searched Mandarte Island for juvenilebirds; dates underlined are those on which I was present, and therefore tape-recorded allvocalizations that I heard: July 1-2-4-5-6-7-8-11-12-13-14-15-17-22-24-25-26-27-28-29-31; August 1-2-3-7-8-9-15-17-18-24-25-28-29-30-31; September 1-9-10-1 1-16-17-18-30;October 4-10-11-27-28-29; November 14-15; December 11-12-13-30-31.RESULTSOf a total of 26 birds, 19 were recorded in each of two years, four in each of threeyears, and three in each of four years (Table 3-I). From 21 of 26 birds, the repertoire fromall recordings was considered complete at the 95% probability level (see Chapter 2). Fromthe other five birds, repertoires of 6 (dbr.pm), 7 (pm.gp), 8 (dbr.gm), 9 (rr.mb) and 11(rb.bm) Song Types were recorded, but not enough songs were recorded to document36Table 3-I. Song Types recorded across years. Birds that were banded as adults ofunknown age are indicated by “?“. Song Type numbers are unique to individual birds. *In 1991, a bird with a metal band on the right leg “replaced” dbr.gm in the same territory.Every Song Type of .m matched those of dbr.gm, who, most likely, lost his colour-bands.Year # songsBird rec’d Age Song Types recorded rec’dMandarte Islandmdb.rdb 1988 6 1 2 3 4 5 13219897 12345678910 1019rr.mb 19884 123456789 24519895 2 4 78 14r.om 1988 3 1 5 6 7 9 2619894 12345678910 302mdb.br 1988 2 1 2 3 4 5 6019893 12345 26419904 12345 491bo.gm 19882 123456789 19619893 2345 789 15419904 1 345 7 59pm.bo 1989 1 1 2 3 4 5 6 7 8 170219902 12345678 83119913 2 5 78 25pm.bdb 1989 1 1 2 3 4 5 78019902 12345 594go.mo 1990 1 1 2 3 4 5 6 7 55919912 5 3gm.odb 1989 <1 1 2 3 4 6 7 8119901 1234567 1166dbdb.mp 1989 <1 3 6 7 2419901 12345678 1150ww.mg 1989 <1 1 2 4 6 2419901 123456 867rb.mg 1989 <1 3 9 1019901 123456789 568om.gdb 1989 <1 1 3 191990 1 1 2 3 4 5 6 7 8 55437Year #songsBird rec’d Age Song Types recorded rec’dom.dbp 1989 <1 3 4 5 6 9319901 123456 371Little Shell Islandodb.mb 1989 1 1 2 3 4 5 6 7 8 44919902 12345678 119wb.bm 1989 ? 1 2 3 4 5 6 7 1871990 1 2 3 4 5 6 7 113Dock 1 Islandpw.rm 1988? 12 61989 23456 141990 1 2 3 4 5 6 7 6471991 1 4567 64pr.om 1989 1 1 2 3 4 5 6 37419902 23456 9319913 3 13rdb.dbm 1988 ? 1 2 3 4 5 6 7 8 641989 2 3 4 5 6 8 9 831990 123456 8 1301991 3 5 11dbr.gm* 1988 ? 1 2 3 91989 1 2 3 4 5 6 7 8 1061990 2 11991 1 2 3 4 5 6 7 8 58Dock 2 Islandrp.rm 1989 ? 1 2 3 4 5 7 851990 123456789 529wdb.gm 1989? 12346789 801990 12346789101112 323Reay Islandrb.bm 1989 ? 1 6 7 8 9 10 11 351990 12345678910 76pm.gp 1989 ? 1 2 3 4 5 6 7 1001990 2 3dbr.pm 1989 ? 1 2 3 6 691990 2 3 4 5 6 31Rum Islandmb.wg 1989 1 1 2 3 4 5 6 7 8 9 43319902 12345678 16838complete repertoires. However, since the average of 11 populations of Song Sparrows was8.2 Song Types (s.e. = 0.25; median = 8.0 Song Types; Chapter 4), these repertoires,likely, represent most of the Song Types that these five birds sang.For each of the 26 birds, there was partial or complete overlap in the Song Typesdocumented across years (Table 3-I). This was true for birds of all ages: six birds firstrecorded at less than one year of age, six birds first recorded at one year of age, five olderbirds, first recorded at 2-6 years of age, and nine birds of unknown age. The reason foronly partial overlap of Song Types in some years was, most likely, inadequate recordingeffort in those years, indicated by the last column in Table 3-I, which gives the number ofsongs recorded each year. Recording efforts in given years of less than 206 continuouslyrecorded songs do not reliably document complete repertoires (Chapter 2). For birdsrecorded across three or four years, those Song Types documented one year but not thenext were often documented two years later (bo.gm, pw.rm and rdb.dbm; Table 3-I).These missing songs were, most likely, sung each year and I simply failed to record them.From six birds, with large recording efforts in two or more years, I documented theircomplete repertoires in each of these years (mdb.br, pm.bo, pm.bdb, odb.mb, wb.bm anddbr.grn; Table 3-I).Birds first recorded at <1 year of ageSong Sparrows fledge at 10-11 days of age (Smith 1988, Arcese 1989), and remainin their parents’ territories until 25-35 days of age (Smith 1988, Arcese 1989). Uponindependence, birds on Mandarte Island disperse through the population, often with otherjuveniles, and begin to sing sporadically and faintly in the fall and winter of their year ofbirth. From six birds, born on Mandarte Island between May and July, 1989, I recordedsongs that were loud enough to analyze sonagraphically both from July to December of391989, and again from January to December of 1990. The dates and ages at which I firstrecorded these juvenile birds were:dbdb.mp 29 Aug. 124 daysom.dbp 28 Oct. 133 daysww.mg 17 Sept. 143 daysgm.odb 17 Sept. 143 daysorn.gdb 28 Oct. 169 daysrb.mg 29 Oct. 173 daysFor four of these birds, the date recorded was the first date they were heard singing. Theother two birds were heard singing earlier- rb.mg sang on 30 Aug., at 113 days of age; andom.gdb sang 30 Sept., at 141 days of age, but neither bird was recorded then. In addition, Irecorded the juvenile songs of two other birds born in 1989; however these recordingswere too faint to analyze - go.mo sang on 29 Aug., at 106 days of age, and dbm.ob sang on28 Oct., at 132 days of age.Because of the difficulty in hearing and recording juveniles, as well as the fact thatMandarte Island was not searched every day for singing birds, the dates given are theoldest ages at which juvenile Song Sparrows first sang. I did not describe the context inwhich these vocalizations were uttered, as juveniles almost always sang faintly, and fromdeep within shrubbery. A few times, however, juveniles were recorded singing while nearan older bird who defended the location as his territory.The first recordings made of juveniles in the fall and winter of 1989 containedsequences of Note Types. The Notes in these songs were often unstable, with the samebasic Note Type (of a particular shape) sung first at one frequency, then again at slightlydifferent frequencies. Some Notes were unlike any sung by adult birds. In spite of thissong variability, however, 2-6 sequences of Note Types per juvenile recorded in the year40of birth were identifiable as Song Types in the adult repertoires of the same individualsrecorded the following year (Table 3-I; Figure 3-1).DISCUSSIONI found, with a sample of 26 Song Sparrows from six island populations, that SongTypes sung in one year were also sung in other years. Though I did not documentcomplete repertoires each year for all birds, the presence of so much Song Type overlapacross years by individuals (Table 3-I) suggested that song repertoires do not change insize nor content in Song Sparrows. For those birds with the largest recording efforts eachyear, I documented the complete repertoire each year. The results are consistent withprevious findings (Nice 1943, Borror 1965, Searcy et al. 1985, Hiebert et al. 1989). SongSparrows are “age-limited’ learners (Marler and Peters 1987), that, along with otherspecies, acquire particular Song Types in early life (Immelmann 1969, Kroodsma 1978,Slater 1983), and retain those Song Types throughout life. A new result of this study isthat repertoire stability in Song Sparrows is general across a range of ages. I found nochange in repertoire size nor content in birds first recorded at ages ranging from less thanone year to seven years of age. This covers the range of ages to which Song Sparrows areknown to survive in the wild, save for birds aged eight and nine years. This information isuseful in that repertoire sizes documented for Song Sparrows, given that enough songs arerecorded to document complete repertoires, are the same as those which birds have sungthrough their lives. Thus, investigations of factors related to the number of Song Typeslearned can be conducted using birds of all ages, not just those recorded as first year birds.At what age do Song Sparrows first utter vocalizations that can be identified asSong Types from their subsequent adult repertoires? In a field study of seven SongSparrows, Nice (1943) first heard Stage II and Stage III vocalizations, “short songs not yetcrystallized into adult form, with much warbling”, at 169-274 days of age, and Stage IV,41Figure 3-1. Sonagrams showing Song Types of three Song Sparrows first recorded in theyear of birth (left column) and again the following year (right column). Frequency (inkilohertz) is shown in the y-axis, and one-second time markers are indicated at the bottomof each column. The identity of the singer, as well as the date and age when first recorded,is indicated above the first Song Type for each bird.10om.dbp12December1989-179daysold10r rit f Tr10ww.mg17September 1989-143daysold10 !1010—1gm.odb18September 1989-144daysold10CL.aIL! i________43“practically adult”, and Stage V. “adult stereotyped songs; the final repertoire” at 256-278days of age. In a laboratory study of nine Song Sparrows, Marler and Peters (1987) firstnoted “plastic song”, equivalent to Nice’s (1943) Stages IT and Ill, at approximately 241days of age, and “crystallized” songs, equivalent to Nice’s (1943) Stage V. atapproximately 291 days of age. The six birds in my field study first sang Stage TI-v songsat 124-173 days of age, from 29 August - 29 October, in the year of birth. When recordedagain the following year, the same basic Song Types were identified (Figure 3-1), andwere strikingly similar to the final adult songs sung by the same individuals.Nice (1943) found that transition stages in the development of Song Sparrow songwere rather indefinite. While birds generally attained each of the five stages that shedefined in rough succession, they did not always progress forward from one stage to thenext (Nice 1943). This is also true of other species, including close relatives of SongSparrows. Marler (1970) placed each of two White-crowned Sparrows, caught in the wildat the same time and when aged 35 days, into a soundproof box. One bird first sang notesrecognizable in his adult song on 21 August and the other on 1 September. IndividualSwamp Sparrows in the laboratory begin singing subsong ranging from 235-300 days ofage, plastic song between 266-340 days of age, and fully crystallized song from 335-395days of age (Marler and Peters 1982b). Kroodsma and Pickert (1984) noted individualvariation in the timing of song learning by Marsh Wrens.At the time I first recorded each of the Song Sparrows in my study, he was alreadylocated on, or next to, the territory he occupied the following spring. Arcese (1989)defined Song Sparrows to be territorial if they sang, perched prominently andunchallenged, and/or consistently evicted other males. The juveniles that I recorded sang,sometimes faintly, perched hidden in shrubbery, and were often chased by older territorialbirds. Kroodsma (1974) noted similar behaviours in juvenile Bewick’s Wrens; however, Ido not know if this was true of the wild Song Sparrows that Nice (1943) studied.44Kroodsma’s (1974) juvenile Bewick’s Wrens sang more adult songs upon playback of theirown juvenile warblings than without this stimulation. Most Bewick’s Wrens establishterritories by 60 days of age, the youngest age at which Kroodsma (1974) noted birdssinging Song Types destined to be in their adult repertoires.It is possible that once territories are actively defended, as in Kroodsma’s (1974)wrens, or occupied, though not fully defended, as in my sparrows, birds progress fasterthrough the stages of song development. This idea explains the difference in timing of firstsinging between Nice’s (1943), Marler and Peter’s (1987) and my Song Sparrows. Mybirds sang Song Types recognizable from their adult repertoires at the youngest ages andMarler and Peters’ (1987) individually isolated birds at the oldest. Song Sparrows insouthwest coastal British Columbia, where my study was conducted, defend year-roundterritories. Nice’s (1943) Ohio population was partially migratory, and Marler and Peter’s(1987) New York birds were migrants, who presumably did not occupy their futureterritones until their first spring.I found that juveniles sang low volume songs, often from hidden perches, when onor near their future territories. Arcese (1987) found that floater Song Sparrows, aged 1-6years, were typically extremely secretive and either flew or remained motionless whenterritory owners were near. However, those floaters who maintained their challenges toowners longer by repeatedly returning to sing on contested territories were more likely tosettle than were floaters that remained inconspicuous (Arcese 1987). Juvenile SongSparrows could follow the same tactic. Juvenile birds must practise songs they hear inorder to sing properly (Konishi 1965). Although chased by older birds, it is perhaps thosebirds who persevere and return who secure territories. Whether birds obtain territories, orhow quickly they do so, may be a result of the speed at which they progress through thestages of song development.45The age at which individuals first utter Notes recognizable from their future adultrepertoires indicates when they incorporate songs into their repertoires, and is thereforevaluable to know when determining source of learning in relation to dispersal. Forexample, orn.dbp, when aged 133 days, sang in close proximity to pm.bdb, from whomom.dbp ultimately copied all six Song Types in his adult repertoire (Chapter 5). In SongSparrows, early-hatched young are generally more successful in establishing territoriesthan are those birds born later (Arcese and Smith 1985, Hochachka 1990). Juveniles bornearlier in the season, or arriving earlier than other birds, in the locations destined to be theirterritories may learn sooner, or may learn more songs as a result of lengthened exposuresto the songs of neighbours. In this view, birds would learn most Song Types in theirrepertoires from neighbours. Other patterns of song similarity between juvenile birds andother birds in the population may exist, depending on the length of time that juveniles areexposed to their tutors, and where they are able to establish territories.46CHAPTER 4EFFECTS OF POPULATION DENSITY AND IMMIGRATIONON REPERTOIRE SIZE OF ISLAND SONG SPARROWSSummary - Individual birds within species vary in the number of Song Types in theirrepertoires. Since male birds learn these songs by imitating others, repertoire size could bean effect of the number of potential tutors available at the time of song learning. Twofactors which might affect the number of potential tutors include: degree of isolation ofislands (measured by rate of male immigration) and male population density between orwithin locations. I investigated variation in song repertoire size in Song Sparrows(Melospiza inelodia), by recording 45 birds at 11 island sites over four years. The meanrepertoire size of 8.2 Song Types (s.e. = 0.25; median = 8.0) on islands was within therange previously published for mainland populations of this species elsewhere. There wereno significant differences in mean repertoire size between birds inhabiting groups ofislands varying in the rate of male immigration. Birds learning song in years of highpopulation density sang larger repertoires than those learning song in years of low density.While birds who had more neighbours at the time of song learning showed a weak trend ofsinging larger repertoires than birds who had fewer neighbours, the relationship was notsignificant. These results suggest that a higher number of singing males in the populationprovides greater acoustic stimulation at the time of song learning.47INTRODUCTIONGeographic isolation can alter both genotypic and phenotypic traits in organisms.The songs of birds on islands are often quite different from those of their mainlandcounterparts, perhaps because the founders of island populations brought with them only avery small part of the total population’s song inventory (Thielcke 1969). Birds on islandsmay have songs of simpler structure (Baptista and Johnson 1982), or with impoverishedpools of song components (Baker and Jenkins 1987) compared to the mainland. Incontrast, it has been argued (see examples in Miller 1982) that song may be more complexin impoverished avifaunas, where species recognition is not a constraint.While differences in many traits, including song, have been suggested betweeninhabitants of island and mainland populations, few studies have compared song in thisway. Repertoire size, a value often used to measure song complexity, could differ betweenisland and mainland populations. Naugler and Smith (1991) found that Fox Sparrow(Passerelia iliaca) repertoire size, and other measures of song complexity, were similarbetween island and mainland populations. Borror (1965) noted some differences in thestructure and complexity of Song Sparrow songs between island and mainland populations,but did not discuss repertoire size per Se. Eberhardt and Baptista (1977) concluded that theSong Sparrows they studied in a small ecological island (a park surrounded by unsuitablehabitat) sang reduced repertoires. They proposed that “the original colonizers brought withthem a small repertoire, and descendants were, therefore, born into a relatively pooracoustical environment as compared to Song Sparrows raised in optimum habitatsupporting large numbers of males singing large repertoires”. Tompa (in Mulligan 1966)noted repertoires of apparently reduced size in the Mandarte Island population of SongSparrows. Tompa (1962, 1964) studied population ecology of these birds, but did notspecifically study song.48Another factor that might affect repertoire size is population density, if a greaternumber of tutor males creates a richer acoustic environment for song learning. The effectof density on repertoire size could be studied either temporally or spatially, although theonly two previously published studies that I know of both conducted spatial comparisons.Harris and Lemon (1972) found that Song Sparrow repertoires were smaller in a locationof low population density compared to those in a location of higher density. Kroodsma(1977b) found a similar effect of density on repertoire size among five populations ofBewick’s Wrens. To my knowledge, no one has examined repertoire size in relation todensity over time at a single location. In this study, I examined the effect of populationdensity on repertoire size both temporally and spatially. Temporal effects of density ofrepertoire size were examined on Mandarte Island, where population density fluctuatesstrongly over time (Arcese et al. 1992). Spatial effects of density on repertoire size wereexamined by comparing repertoire sizes of birds inhabiting seven islands that vary inpopulation density, but each remain stable in density over time.Song Sparrows exhibit a moderate and variable repertoire size (Chapter 2 andreferences therein). Here, I compared song repertoire sizes of Song Sparrows inhabitingislands to those of mainland populations reported in the literature. The groups of islands Istudied differed in their rates of immigration, and therefore possibly in the extent to whichnew Song Types were introduced. I determined whether a difference existed in meanrepertoire size between these groups. Finally, I looked for effects of the number ofpotential tutors on the number of Song Types learned, comparing both population densityand the number of adjacent neighbours birds had at the time of territory establishment, totheir repertoire sizes.49METHODSSong recording and analysis techniques are described in Chapter 2. My sampleconsisted of 45 Song Sparrows recorded at 11 island sites in southwest coastal BritishColumbia from 1988 to 1991 (Figure 4-1). From each of these birds, I recorded aminimum of 206 consecutive, or 280 pooled, songs, thus documenting completerepertoires at the 95% probability level (Chapter 2).I assigned islands into groups with low, medium and high immigration rates.Mandarte Island (6 ha), the low immigration site, is approximately 25 km NNE ofVictoria, and 1.3 km from the nearest island inhabited by Song Sparrows. Research on thiscolour-banded population since 1975 has shown that less than 3% of male juvenilesrecruiting to the breeding population are immigrants (Hochachka et al. 1989). OnMandarte, therefore, no immigrants sang in most years. Seven small islands, Little Shell,Ker, Dock 1, Dock 2, Dock 3, Forrest and Rum composed the medium immigration groupand varied in size from 0.3 - 5.0 ha. Although Forrest Island was almost 20 ha, the bird Irecorded inhabited Data Point, a rocky outcrop (of approximately 0.3 ha) separated fromthe rest of the island by a sand spit. These islands are located 2-7.5 km from MandarteIsland. From 1988 to 1991, 70% of the recruits to these breeding populations werejuvenile immigrants, with the rest born locally on the respective islands. In any one year,however, at most one immigrant sang on each island. A single exception to this was 1991,when two immigrants sang on Dock 3 Island, but were the only males on the island. Threesites located on large islands composed the high immigration group: a) Bazan Bay, 9 kmwest of Mandarte Island, on Vancouver Island; b) Reifel Migratory Bird Sanctuary, onWestham Island, 60 km NNE of Mandarte Island; and c) Alaksen National Wildlife Area,also on Westham Island. While there is less detailed information on the origin of recruitsto these populations from 1988 to 1990, each spring many juveniles joined one of these50Figure 4-1. Location of study islands (shaded) in southwest coastal British Columbia.Inset shows location of Westham Island in relation to the other study islands.Docks•b.1RumGooch40ReayShellKerVancouverIslandForrestc%.SidneyBazanBayMandarte(3152populations (Knapton and Krebs 1974), and very few fledglings were raised locally (C.M.Rogers, M.J. Taitt and J.N.M Smith, unpublished data). These Westham populations werestable and had high immigration rates, so that several to many immigrants sang in a givenyear.Forty-four of the 45 birds were colour-banded. Since I recorded all songs from thesingle unbanded bird in a single session, I am confident of his identity. Population densityis defined as the number of territorial males per hectare. This was determined throughdetailed census visits throughout the year. I compared repertoire sizes of birds to the SongSparrow density of the island when focal birds were one year of age. The repertoires that Irecorded from Song Sparrows aged <1-7 years, were the same as those sung at the time ofterritory establishment at one year of age (Chapter 3).Statistical analyses were conducted using SYSTAT (Wilkinson 1990) on log10normalized data. The dispersion around means given is the standard error.RESULTSRepertoire size vs. degree of immigrationThe degree of male immigration could affect repertoire size if immigrantsintroduced new Song Types to islands. I compared the mean repertoire sizes on islandsthat differed in their degree of isolatation, measured by the degree of male immigration.Forty-five individual repertoires averaged 8.2 Song Types (s.c. = 0.25, median =8.0, range = 5-11). There were no significant differences in mean repertoire size betweenthe low immigration (mean = 8.0, s.e. = 0.31, median = 8.0, N=26), the mediumimmigration (mean = 8.6, s.e. = 0.50, median = 9.0, N=14) and the high immigration islandgroups (mean = 8.2, s.e. = 0.66, median = 8.0, N=5;F(2,42)=0.68 p=0.Sll).53Repertoire size vs. population densityIf first-year birds learn more Song Types in years or locations with more potentialtutors, we would expect to find a significant relationship between repertoire size andpopulation density in the year that focal birds were one year old.I determined population density on seven islands from 1988 to 1991. Densities onLittle Shell, Dock 1, Dock 2, Dock 3, Rum and Ker Islands ranged from 2 males/ha onRum Island (5 ha) to 6.7 males/ha on Dock 3 (0.3 ha). These islands remained very stablein density over time. Birds inhabiting these islands, from which I recorded enough songsto estimate complete repertoires, were one year old in 1989, 1990 or 1991. MandarteIsland fluctuated strongly in density over time (Arcese et al. 1992). Birds from which Irecorded enough songs to estimate complete repertoires (see Chapter 2) were one year oldin 1983, 1986, 1987, 1988, 1989, 1990 or 1991. Population density on Mandarte Islandover this time ranged from 0.7-10.3 males/ha (Arcese et al. 1992).I found that while there was much variation in repertoire size at each density,repertoire size was significantly related to population density (r=.443, p=.Ol 1, 32 df;Figure 4-2). Three birds who were one year old in the year of highest density sang 10, 10and 11 Song Types, while two birds who were one year old in the year of lowest densitysang five and eight Song Types each. There was no obvious pattern between repertoiresize and population density when considering only birds on islands other than MandarteIsland. This could be simply a result of the small sample size (N=7 birds from 6 islands),but warrants further investigation.54Figure 4-2. Number of Song Types learned as a function of the density (males/ha) in theyear that birds were one year of age. Solid circles represent birds on Mandarte Island indifferent years; hollow circles represent birds on other islands. The number of birds (ifgreater than one) having particular repertoire sizes is indicated above points.0 C Cu 0 C., 0) C 0 0 I,— 0 a) .0 z zii 10 9 80..2706 (‘756Repertoire size vs. number of neighboursIf the song repertoires learned by first year birds are directly influenced not by allpotential tutors in populations, but by neighbours as potential tutors, we would expect tofind a significant relationship between repertoire size and the number of neighbours focalbirds had when one year of age. Birds had from 1-5 neighbours (17 out of 37 had three).Approximately equal numbers of birds had one neighbour (6 out of 37), two neighbours (7out of 37) or four neighbours (6 out of 37). Since a single bird had five neighbours, Ipooled birds with four or five neighbours for statistical analyses (but graphed these dataseparately). Pooling did not significantly alter the outcome of the analyses presented here.Birds with one, two or three neighbours inhabited Mandarte Island and the other islandsstudied, however, birds with four or five neighbours inhabited only Mandarte Island.There were no significant differences in the mean number of Song Types learnedby birds with one neighbour (mean = 9.0, s.e. = 0.78, median = 9.0), two neighbours (mean= 7.8, s.e. = 0.70, median = 8.0), three neighbours (mean = 7.7, s.e. = 0.37, median 8.0)or four or more neighbours (mean = 9.3, s.e. = 0.47, median = 9.0; F(433) = 1.472, p =.234; Figure 4-3). While birds having four or more neighbours showed a weak trend ofsinging more Song Types than did birds having three or fewer neighbours, this differencewas slight and was not significant (N=30 birds with three or fewer neighbours: mean = 8.0Song Types; N=7 birds with four or more neighbours: mean = 9.3 Song Types; MannWhitney U = 56, p = .053).DISCUSSIONSong Sparrow repertoires in my study averaged 8.2 Song Types, similar to meanvalues for mainland populations: 8.3 in Maine (Borror 1961), 9.0 in Quebec (Harris and57Figure 4-3. Number of Song Types learned as a function of the number of neighboursbirds had at one year of age. The error bars represent standard error, and sample size isshown next to each point.100 a)I•1C o8017II 0II a,.07E z612345(iiNumberofneighbours59Lemon 1972) and 9.2 in New York (Podos et al. 1992). Mulligan (1963, 1966), however,documented repertoires averaging 16 Song Types in the San Francisco Bay area ofCalifornia. This unusual population deserves further study to detect possible reasons forthe large song repertoires. Two other studies of repertoire size in island Song Sparrowsfound similar mean repertoire sizes to mine: 8.1 on Mandarte Island (Hiebert et al. 1989,who recorded none of the individuals I recorded) and 7.3 in an isolated habitat island inGlendale, California (Eberhardt and Baptista 1977). The latter authors suggested thatrepertoires in their study were “reduced as an artifact of isolation in marginal habitat”,however, I find little difference between the mean repertoire size of the Glendalepopulation and those of other populations, with the exception of Mulligan’s (1963, 1966)San Franciso birds.Thielcke (1969, 1973) suggested that the original settlers to isolated islands couldhave been juveniles, whose songs were not fully crystallized. In this view, later recruits tothe population, who are born on the island, learn abberant or simple songs from thefounders, but empirical evidence of this is lacking. To my knowledge, this is the firststudy to compare repertoire sizes on islands varying in their degrees of isolation, andrecording natal and immigrant birds of known age and origin. I found no differences inmean repertoire sizes between groups of islands varying in their immigration rates, andseparated by up to 60 km. Power (1983) found no evidence to support the generalizationthat geographic isolation per se causes much change in variability in island populations ofbirds.To judge whether the number of immigrants to a population is likely to affect thenumber of Song Types learned, we must know when and from whom wild birds learn theirsongs. Immigrants might bring with them Song Types from other locales, or may learnthose types already existing in the population. I found that juvenile Song Sparrowsimmigrating to islands of the smallest density and number of neighbours possible (only the60immigrant and one other bird) introduced new Song Types (those of their fathers) as wellas copying Song Types of their new neighbours (Chapter 5). It is not known whether adultSong Sparrows, whose songs have crystallized, would modify their songs if moved todifferent locations. Lemon (1975) speculated that dispersing cardinals (Cardinaliscardinalis) may introduce new Song Types into their new locations. Adult saddlebacks(Philesturnus carunculatus rufusater) who change location, modify their songs to the newarea (Jenkins 1978). On my 13 islands, no colour-banded adult (N>200) recruited to a newlocale in five years (1987-1991; A.L.E.V. Cassidy and J.N.M. Smith, unpublished data).Furthermore, several adults that were translocated elsewhere returned to their originalislands, flying distances up to 90 km (Arcese 1989; J.N.M. Smith, unpublished data).The number of Song Types learned by birds was significantly related to density inthe year that birds were one year of age. There was also a slight difference in the numberof songs learned between birds having four or more neighbours and birds having three orfewer neighbours. The increase in repertoire size, of about one song, was in the samedirection as that shown by population density. These findings suggest a positive effect ofthe entire population of potential tutors, and not just neighbours, on the number of SongTypes that birds learn. Beecher et al. (M.D. Beecher, S.E. Campbell and P.K. Stoddard,unpublished data) found that young Song Sparrows copied the songs of three to four tutorswho were always neighbours. Though I found that neighbours acted as tutors to youngSong Sparrows, other birds in the population did as well (Chapter 5). This result supportsthe idea that high densities provide more potential tutors to juveniles, or in some waystimulate birds to learn more Song Types from a subset of all available tutors, than theywould learn from the same subset of tutors at lower densities. Within populations, higherdensity implies more neighbours for most males, but also smaller territories that are“packed-in”, thus, birds can easily hear songs of other males in addition to adjacent61neighbours. This extra stimulation could result in birds learning more of the songs theyhear, copying from a combination of neighbours and other birds in the population.I considered density of males only in my analyses. Song Sparrows are usuallymonogamous, however in some years and locations, territories were held by unmated aswell as polygynous males. The effect of song rate, which is higher in unmated males thanmated males, on repertoire sizes learned by juvenile birds should be considered.Larnbrechts and Dhondt (1990) suggested that first-year Great Tits heard manymore Song Types from territorial neighbours than they actually sang. If the number ofpotential tutors that birds had directly affected the number of Song Types they learned, ajuvenile bird might incorporate several to many different Song Types into its repertoirefrom each of its tutors. Accordingly, repertoire size would increase with each newgeneration of learners. An exception is where juveniles had only one potential tutor in thepopulation from whom to copy songs, such as on very small islands.A possible contraint on the upper limit of repertoire size is the amount of brainspace available - intraspecific differences in repertoire size have been attributed tovariation in the size of forebrain song control nuclei in Canaries (Serinus canarius;Nottebohm 1981) and Marsh Wrens (Canady et al. 1984). Furthermore, Kroodsma andCanady (1985) found this neuroanatomical difference to have a genetic basis. I found noassociation between repertoire sizes of fathers and sons (A.L.E.V. Cassidy, unpublisheddata). It is not known to what extent environmental and social factors affect the repertoiresize an individual might sing based on its brain structure alone.62CHAPTER 5SONG LEARNING BY SONG SPARROWSSumnuiiy - Male oscines acquire songs by imitation of other individuals. A key questionin the study of bird song is: from whom and at what age do wild birds learn their songs?This question is difficult to answer, as it requires documentation of all songs sung bymarked birds and by those of their potential tutors, as well as knowledge of the dispersalfates of birds. I was able to gather this information on Mandarte Island and other nearbyislands in southwest coastal British Columbia. I compared song repertoires of 24 SongSparrows (Melospiza inelodia), colour-banded in the nest, to those of their most likelypotential tutors: fathers and neighbours. Of 21 birds born on Mandarte Island and whoestablished territories, none matched any Song Types sung by their fathers. Three birdsborn on the 0.8-ha Dock 1 Island, with four potential tutors, each matched 1-2 Song Typeswith their father. These birds each dispersed 0.3-1.5 km to other islands inhabited by onlyone potential tutor; the impoverished song environments could have contributed to theirretention of songs heard before independence. Twenty-three of 24 birds each matched 1-9Song Types with one or more birds in the populations in which they established territories.More focal birds matched two or more Song Types with older neighbours than they didwith neighbours of the same cohort, and some birds matched songs with non-neighbours.After a severe winter storm in February 1989 on Mandarte Island that killed most of thepopulation, I had a unique opportunity to measure song learning in the 1989 cohort,recording all songs of all potential tutors, those of an entire cohort of surviving maleyoung, and the routes used by these birds from independence to territory establishment. Iwas able to assign every Song Type of all eight breeding birds in this cohort to one of sixolder adults, and found that first year birds often learn songs from birds other thanneighbours.63INTRODUCTIONBird song shows considerable intraspecific variation at the levels of population,neighbourhood and individual (review in Krebs and Kroodsma 1980 and Mundinger1982). Most songbirds sing repertoires of more than one Song Type (Hartshorne 1973,Dobson and Lemon 1975). The spatial distribution of Song Types within and betweenpopulations is determined partly through song learning (Lemon 1975, Krebs andKroodsma 1980), a form of cultural transmission (Cavalli-Sforza et al. 1982) that parallelshuman speech. I think that the most interesting questions in the study of culturaltransmission of behaviours are: 1) what is the length of time over which behaviours can belearned? and 2) how do individuals choose from the sometimes large variety of modelsavailable to imitate?To date, several bird species have been shown to learn song early in life from theirfathers (e.g. Large Cactus Finches, Geospiza conirostris, Grant 1984; Cactus Finches, G.scandens and Medium Ground Finches, G. fortis, Millington and Price, 1985; Zebra Finch,Taeniopygia guttata, Immelmann 1969, Zann 1990), while other birds learn song at thetime of territory establishment from their neighbours (e.g. Bewick’s Wren, Kroodsma1974; Marsh Wren, Vemer 1975; Saddleback, Jenkins 1978; Indigo Bunting, Payne 1981;Village Indigobird, Vidua chalybeata, Payne and Payne 1977; White-crowned Sparrow,Baptista and Morton 1988; Great Tit, McGregor and Krebs 1989). Why should somespecies learn from fathers, and others from neighbours? Two hypotheses, the geneticadaptation (also called assortative mating) hypothesis (Marler and Tamura 1962,Nottebohm 1969) and the social adaptation hypothesis (Payne 1982) have been suggestedto explain patterns of song similarity between individuals.Marler and Tamura (1962) found homogeneity in the single Song Type sung by 10-20 White-crowned Sparrows within each of three populations, and distinctive differencesbetween populations. Nottebohrn (1969) described five distinct song areas of 523 Rufous-64crowned Sparrows (Zonotrichia capensis) in Argentina, across relatively homogeneouspampas habitat. The findings of these two studies suggested that patterns of songsimilarity enhance local genetic adaptation of individuals to habitat or other environmentalfeatures (Marler and Tamura 1962, Nottebohm 1969). In this view, males would learnsong in their natal areas, from fathers or neighbours, before dispersal, and return there tobreed. Females would choose as mates birds who sounded like their fathers. Boundariesbetween areas of dissimilar song act as barriers to dispersal (Baker and Mewaldt 1978).However, the two species whose patterns of song similarity led to the genetic adaptationhypothesis each sing single Song Types. Therefore, it is impossible to determine, withinan area of similar song, from whom young birds learned their song.Kroodsma (1974) found juvenile Bewick’s Wrens to copy songs of neighbours atthe time of first territory establishment, and not their fathers; he suggested that areas ofsong similarity resulted in an competitive advantage to males or stimulated females. Payne(1981, 1982) showed that first year Indigo Buntings that matched the single-songedrepertoires of neighbours were better at holding territories and attracting mates than werethose males that did not match neighbours. He (Payne 1982) coined the social adaptationhypothesis, that proposes an advantage to males sounding like their neighbours. Youngmales would learn song after dispersal, and copy songs of older males when they areestablishing their first territories. Other researchers have suggested that males improvetheir competitive status in direct aggressive encounters with males by mimicking theirsong (Hinde 1958, Lemon 1968). By song matching, birds may either address their songsto specific neighbours (Kroodsma 1974, Krebs et al. 1981), or provide a graded signal ofmotivation (Krebs et al. 1981).Before testing either the genetic adaptation hypothesis or the social adaptationhypothesis, we must know the degree of similarity in song between birds within65populations, or between populations in those species that disperse, where young birds setup territories in relation to birthplace, and when they learn song.In many tests of the social adaptation hypothesis, the species studied were capableof learning new songs throughout life. Examples are Red-winged Blackbird (Yasukawa etal. 1980), Saddlebacks (Jenkins 1978), Village Indigobirds (Payne and Payne 1977), andIndigo Buntings (Payne 1981). Song variation and timing of learning has been studied infew species that do not change their songs through life, but still show evidence of songsharing between individuals. This type of research has been conducted on the singlesonged White-crowned Sparrow (e.g. Baptista 1985), as well as on two wren species thatsing repertoires (Bewick’s Wren, Kroodsma 1974; Marsh Wren, Verner 1975).Seventy years ago, ornithologists were familiar with the great variation in the songsof the Song Sparrow (Wheeler and Nichols 1924), both between and within individuals(Saunders 1924). Margaret Nice’s (1937, 1943) classic and pioneering work on thisspecies set the stage for much research on song learning and function of song, and PeterMailer and his colleagues (review in Mailer 1982a) have conducted many studies ondevelopment of song in this and other species.Previous field studies of Song Sparrows, however, generally agreed that songs wereof such great variation and complexity as to obscure any similarities between individuals.An exception to this is the work of Philip Stoddard and colleagues (e.g. Stoddard et al.1991), who showed that neighbouring Song Sparrows share portions of their repertoires.Nice (1943) found no obvious similarity in song (by ear) between 21 colour-banded SongSparrows and their fathers, and rare cases of neighbouring birds sharing similar songs. Asmall degree of intrapopulation sharing of similar, but not of exact Song Types, was notedby Mulligan (1963, 1966), Borror (1965), Eberhardt and Baptista (1977), and Kramer et al.(1985). McArthur (1986) found some songs to be similar in cadence, but not necessarily in66sonagraphic features, and Harris and Lemon (1972) found that Song Types were nevershared by individuals.Though Song Sparrows are very common and well-studied North Americanpasserines (e.g. Nice 1937, 1943; references in Podos et al. 1992), it is not known when orfrom whom juveniles learn their songs in the wild. In a laboratory study, Marler andPeters (1987) showed that most learning in Song Sparrows occurred between 22-62 days ofage. Their paradigm involved bringing 2-10 day old birds from the wild and playingvarying sets of tape-recorded songs to them until they were 350 days old. However, thetiming of learning of birds tutored with taped songs is not necessarily the same as that ifbirds were exposed to live tutors (Marler and Peters 1987). Live tutors lengthened thesensitive period in White-Crowned Sparrows past 50 days (Baptista and Petrinovich 1984,1986), the age until which this species learns when tutored with taped songs (Marler 1970).Canaries may learn more from birds with whom they have social contact than from tutortapes (Waser and Marler 1977). Parallels have been drawn between the effects of liveinput and social interaction in both language acquisition by humans and song learning inbirds (Pepperberg and Schinke-Llano 1991).In this chapter, I compared song repertoires of Song Sparrows to those of their mostlikely potential tutors: fathers and neighbours, to determine from whom juveniles learntheir songs in wild populations of birds. I conducted this study primarily on MandarteIsland, where a colour-banded population of Song Sparrows of known phenotypic pedigreeis resident throughout the year. All birds born in this population are colour-banded in thenest, and almost all of those surviving to stab1ish territories do so on the island. Only fourbirds born on Mandarte Island are known to have settled elsewhere (Hochachka et al.1989). Thus, I could compare songs of birds to those of their fathers as well as theirneighbours. In addition, a few colour-banded Song Sparrows inhabiting other, nearbyislands were studied in the same way; these birds often dispersed between islands.67A severe winter storm in the second year of my study provided a uniqueopportunity to measure song learning in the Mandarte Island population. In February1989, an unusually cold spell coincided with the loss of over 90 percent of the population.This resulted in a 1989 adult population of only seven males and four females, the lowestdensity recorded on Mandarte Island in 15 years (Arcese et al. 1992). The rate of juvenilerecruitment is inversely related to the density of adults on this island (Arcese et al. 1992).Therefore, an unusually high number of young born in 1989 gained territories (eight of tenmales and five of six females) in 1990. I tracked the movements of each male in thiscohort from fledging to territory establishment, and compared the Song Types they sang tothose of every older potential tutor in the population.METHODSSong recording and analysis techniques are described in Chapter 2. I compared thesong repertoires of 24 “focal birds” to those of two sets of potential tutors: i) fathers, andii) neighbours at the time of territory establishment. Of the 52 birds, 47 inhabitedMandarte Island; the other five inhabited Dock 1, Dock 3 and Forrest Islands (see Figure4-1). These birds were part of a larger pool of male Song Sparrows inhabiting the islandsthroughout the study. However, I included for analyses only those males who: 1) werecolour-banded in the nest (at 5-7 days of age); 2) obtained territories the following year;and 3) for whom I recorded an adequate number of songs to estimate the completerepertoires of the focal bird, his father, and all of his neighbours at the time of territoryestablishment. Therefore, from each focal bird and from each bird to which it wascompared, I recorded 206 continuously recorded songs, or 280 songs pooled from differentrecording sessions (see Chapter 2). A few birds who met most, but not all of these criteria,were included in the analyses; these birds are flagged in Appendix 3.68Many different techniques can be found in the literature to describe and comparesounds. These include: 1) visual inspection of sonagrams; 2) measurement of certaintime-frequency values, which are then subjected to univariate or multivariate statisticalanalyses; 3) computer-based methods using numerical representation of time-frequencyvalues to compute a similarity index between two sounds; and 4) visual coding of notesequences in sonagrarns, which are then compared manually, or using computer matchingprograms (e.g. Borror 1965, Payne et al. 1988, references in Clark et al. 1987 and Chabot1988). I used the last technique, coding Song Types and concealing the identity of birdsuntil comparisons were completed.I used the same technique described in Chapter 2 for determining Song Types ofindividuals. However, to compare sonagrams of Song Types between individuals, I did thefollowing:coding Song TypesI classified each Note of Mandarte Island Song Sparrow songs as one of 12 basictypes, described in words by its gross shape, and coded with one or more letters (seeFigure 5-1):1) up-slurred whistle - A, B, C, D;2) buzz-E,F,G;3) whistle - H, I, J;4) inverted u - K;5) down-slurred whistle - M, N, 0, P;6) click - R;7) down-slash - X;8) click-slur - V;69Figure 5-1. Sonagraphic structure of basic Note Types in songs of Mandarte Island SongSparrows. The gross shape of each Note Type is drawn in “cartoon” form and the letters Iused to code Note Types are indicated. The frequency range over which Note Typesoccurred is indicated.up—slurred10whistleN Dl >1 U 0 S4 0 $4 lxidown-slurredwhistle ci8buzzC6hockeystick kIclick-invertedslurhockeystickRL NJ(FrICE4 2KL j)4whistleclickdownslashslashIwhistle—dropTime(seconds)719) up-slash - Y;10) inverted hockey stick - Z;11) whistle-drop- L;12) hockey stick-Q;Most of these basic types occurred at a variety of frequencies, from 2-10 kHz, insonagrams. I further sub-divided four common basic types (“up-slurred whistle”, “buzz”,“whistle” and “down-slurred whistle”) by the ranges of frequency in which the pure-toneparts of all “whistles”, and the middle parts of “buzzes” occurred (2-4 kHz, >4-6 kHz, >6-8kHz and >8-10 kHz). In all, I classified each Note as one of 22 Note Types. I assignedeach Note Type only once, regardless of the number of times it was immediately repeatedwithin Song Types. Using this technique, I coded each Song Type as a letter sequence,representing the sonagraphic structure of unique Note Types. For example, the lettersequences of sonagrams in Figure 2-lA is CFPFOHC (the first C is repeated twice and thelast C three times in the sonagram), and in Figure 2- lB is CFPFOHU (C is repeated twiceand U is repeated 16 times in the sonagram). The letter sequence of the sonagram inFigure 2-2A is BDECHFIDKJHOE (B is repeated twice).Coding and randomizing pairs of birdsFor each pair of birds (focal and potential tutor), I converted the identities ofindividuals into sets of line numbers (from 1-455; Appendix 1), each line being a lettersequence. I then randomized the order of sets of line numbers, so that when I comparedthe song repertoire of one bird to that of another, I did not know if I was comparing a focalbird to its father or to one of its neighbours.72Song Type matchingI declared each Song Type in the repertoire of one bird in a pair to match or notmatch each Song Type in the repertoire of the second bird in the pair, based on thesimilarity of the letter sequences. The most common occurrences of pairs of matchingSong Types were:i) exact letter sequences (underlining indicates matching Notes):ICKCIHFHOE ICKCIHFHOEBECENBRXRC BECENBRXRCNZHFICECHR NZHFICECHRii) single Note Types replaced by others:CFBFOHC EEEOHCFJjFCHRC EJECHRCiii) exact letter sequences, with additional or different Notes (usually at the end):HFCHXEIRE HFCHXEICCFPFOHC CFPFOHUBKIHGBOKIHBCF BKIHGBOKIHBCFIRSong Types that did not match had:i) several or many different or additional Notes between the matching Notes:CFPFCHN CFOFCEIRNDEKFHIN CKIUIOECBFKRECBERHRC BERKCECii) matching notes that were not in same sequences:IKCEIjjjD HFRCXFNI kept a list of matching and non-matching sequences (Appendix 4) and double-checkedeach comparison of letter sequences for errors, as well as maintenance of the “rules”73defining a “match”. Visual comparisons of sonagrams agreed with those of lettersequences in determining whether pairs of Song Types matched. I compared songrepertoires of the five birds from other than Mandarte Island by visual inspection ofsonagrams, first concealing the identity of pairs I compared.Song similarityFor each pair of birds compared, I calculated song similarity (Harris and Lemon1972): [(number of songs Bird 1 matched with Bird 2 + number of songs Bird 2 matchedwith Bird 1) / (number of songs in repertoire of Bird 1 + number of songs in repertoire ofBird 2)]. I present song similarities as percentages. This equation, which uses the samenumber twice in the numerator, takes repertoire size into consideration when calculatingsimilarity between pairs of birds. For example, if Bird 1 matched all six of his Song Typeswith Bird 2, who sang eight Song Types, the song similarity is 85.7%. Though Bird 1matched 100% of the songs in his repertoire, a perfect match (100% song similarity) wouldhave required Bird 1 to match all eight Song Types from Bird 2.Tracking movements of one cohortI tracked the movements of all eight males born on Mandarte Island in 1989 whosuccessfully established territories in 1990, from fledging in the summer of 1989 until 31March 1990, the date by which all birds had established territories. Dates and locations ofsightings were noted on maps of the island traced from a low-level aerial photograph. Thissame cohort of birds was also recorded singing juvenile song; further description of thetechniques used to track these birds, as well a list of dates on which the island wascensussed, is found in Chapter 3. On each census, the entire island was methodicallysearched for Song Sparrows; therefore, each juvenile likely had a similar chance of being74sighted. I compared the song repertoires of these eight birds to those of all older territoryholders, by visual inspection of sonagrams.RESULTSDescription of songI recorded and sonagraphically analyzed 21,438 songs from 52 Song Sparrows.Songs of Mandarte Island Song Sparrows almost always began with “up-slurred whistles”or “whistles”, much less commonly with “hockey sticks”, and rarely with other NoteTypes. “Buzzes” were usually separated by other Note Types, and, along with “whistles”and “inverted u”, almost never occurred at the ends of songs. Even given these“syntactical” rules, the combination of 22 Note Types allowed for an extraordinary amountof individual variation in Song Types uttered.Though I do not quantify this here, songs recorded on Dock 1, Dock 3 and ForrestIslands were quite different from those recorded on Mandarte Island. From a sample offive birds from three other islands, songs began with “whistles”, “up-slurred whistles”,“down-slashes” and “inverted u”. “Buzzes” were less common in these songs, which alsocontained several Note Types not found in Mandarte Island songs.Comparisons of repertoires between focal birds and potential tutors.I compared the song repertoires of 110 unique bird pairs. Seventy-three of thesewere focal birds and their most likely potential tutors: father and neighbours (Appendix3). Focal birds had from 1-4 neighbours, three being most common (11 of 24). For eightbirds born on Mandarte Island in 1989, I made 37 additional comparisons: the eight focalbirds and all six older territory owners in the population that I had not already compared(as a father or neighbour).75Fathers as potential tutorsMandarte Island - All 21 focal birds in the analysis were born on Mandarte Island and alsoestablished territories there. One bird, gm.odb, had its own father as one of its neighbours;all other birds moved two or more territories away from their fathers (Figure 5-2). Noneshared any Song Types with his father (Appendix 3; compare songs of gm.odb, Figure 5-3B, with those of his father, mdb.br, Figure 5-4A).Other Islands - Three focal birds born on Dock 1 Island, in two different years, had thesame father and dispersed to other islands. One bird, mg.dbw, matched one Song Type(song similarity 11.1%) with his father (Figure 5-5). The other two birds, mb.bw andgb.gm, of the same cohort, matched one Song Type (10.0%) and two Song Types (20.0%),respectively, with their father (Figure 5-5).Neighbours as potential tutorsMandarte Island - Twenty of 21 focal birds on Mandarte Island matched Song Types withone or more neighbours (Appendix 3). In relation to these focal birds, neighbours were: i)all at least one year older, ii) a combination of older and from the same cohort, or iii) allfrom the same cohort.i) older neighbours (n=7)- Two birds (pm.bo, bo.gm) matched some Song Typeswith one neighbour and none with others. Two birds (mdb.rp, mr.dbw) each matchedsome Song Types with one neighbour and different Song Types with another neighbour.Two birds (bp.mdb, dbp.mdb) each matched some of the same Song Types with each oftwo neighbours, and none with a third neighbour. One bird (pm.bdb) matched no songswith either of his two neighbours.ii) combination of older neighbours and those from the same cohort (n=7) - Fourbirds (dbm.ob, mb.gg, gm.odb, oo.om) matched more songs with their older neighbours(song similarities of 93.3%, 87.5%, 85.7% and 82.4%, respectively) than they did with the76Figure 5-2. Map of territories on Mandarte Island in 1989 and 1990. The solid portion ofisland in 1989 was undefended. Unique shading in territories indicates the places of birthof birds born in 1989 (on the 1989 map) and their locations of territory establishment in1990 (on the 1990 map). Thus, cross-hatching indicates that om.dbp, dbdb.mp, ww.rngand gm.odb were born in mdb.br’s territory. Vertical lines indicate that go.mo was born inr.om’s territory. Dots indicate that om.gdb and dbm.ob were born in bo.gm’s territory.Horizontal lines indicate that rb.mg was born in pm.bdb’s territory.Npm.bdbbo.gmpm.bor.om19891990mdb.rdbdbb.mbmdb.brgo.moom.gdbpm.bdbbo.gmgm.odbpm.borb.mgom.dbpdbdb.mpww.mgmdb.brdbm.ob0100200m78Figure 5-3. Songs of tutor pm.bo, A, and focal bird (neighbour) , gm.odb, B. For this andall following sonagrams, frequency (in kilohertz) is shown in y-axis, and one-second timemarkers are indicated at the bottom of each column.7910 A. older tutor, pm.bo 10 B. focal bird (neighbour), gm.odb8[ 8E6L 6L 1 11112Lr—rrrrI4 r r b 4L r r101 1081_______61______V 6j fffffrrrrrr41-2L 21br- 10IIi’IiiI :E1• • _...L_—2L 21lOr- 10.J • 111111(111112L 2110 108[61- 6[4I- 4L.....b..21 2110 10612j I 2jr r r80Figure 5-4. All five Song Types in complete repertoire of older tutor, mdb.br, A, and threeSong Types matched by focal bird (neighbour), mw.ww, B, shown above the line, as wellas two Song Types not matched by focal bird, shown below the line.brA.oldertutor,mdb.brlOrBfocalbird(neighbour),mw.wwSI-8L42•r1r,LJi JyJ4rr’4Err2L 4‘—II1MiI1II41-‘12L2L—10’-1081-61-fL__rL41- 2L2r 10r81- 6rr11111 IliflU’“4F—4’-I•2L2L10’-10r8j-8L 6L41-4Er_r2L2182Figure 5-5. Songs that dispersing birds matched with their father on their natal island andthose matched with their neighbours on islands to which they dispersed. The top boxshows one Song Type of father, rdb.dbm, on Dock 1 Island (Dl) that was matched by sons,gb.gm and rng.dbw. The middle box shows another Song Type of father, rdb.dbm, thatwas matched by sons, mb.bw and gb.gm. The bottom box shows one Song Type thatmg.dbw matched with an unbanded (unb) neighbour on Forrest Island, where heestablished a territory; and two Song Types that mb.bw matched with gb.gm on Dock 3Island (D3), where he established a territory. (The middle box shows a third Song Typethat these two neighbours, who were also brothers, shared.)83rdb.dbm, father of gb.gm and mg.dbwonDi4\\\2p‘rrr’rrr—P10 gb.gmf__((I((r,•4 “ “ rrr—2-.10 ing.dbw864210 mb.bw81_____6’ (I4[.1’2L—10 gb.gm86r’r2_(1 (— p prdb.dbm, father of mb.bw and gb.gmas,.• A rrrrrr.unb neighbour of mg.dbw on Forrest Island_______ø)I1 ‘410 mg.dbw864f-r2io mb.bw864 \ \ \2mb.bw108642101 gb.gm, neighbour on D3‘—l •!f(r 1)1)) ‘— m( rL\ \ ç a2J1At11P10I_ __1i1ll1ii84same cohort neighbour that they most closely matched (87.5%, 16.7%, 76.9% and 80.0%,respectively). Two birds (mw.ww, mdb.oo) matched different Song Types with the olderneighbour than they did with a same cohort neighbour. One bird (ww.mg) matched noSong Types (0%) with his older neighbour, and five Song Types (71.4%) with his samecohort neighbour.lii) neighbours from the same cohort (n=7) - Birds on either end of Mandarte Islandmatched one Song Type (om.dbp; 18.2%) and seven Song Types (rb.mg; 87.5%) with theirsingle neighbours. One bird (go.mo) matched the same single Song Type with each of twoneighbours and none with a third. One bird (mp.dbdb) matched some of the same SongTypes with each neighbour, and one bird (r.om) matched some of the same Song Types, aswell as some different Song Types, with each neighbour. Two birds (dbdb.mp, om.gdb)matched different Song Types with each neighbour.Other Islands - All three focal birds were born on Dock 1 Island and had the same father,rdb.dbm. One bird, mg.dbw, was born in 1989, and established a territory the followingyear at Data Point on Forrest Island, 1.5 km distant (Figure 5-6). Mg.dbw was last seen onhis natal island at 22 days of age. He moved to Dock 3 Island (0.3 km distant, withinhearing distance and void of other Song Sparrows, Figure 5-6), remaining there from 63-273 days of age. He was discovered on Forrest Island in 1990 when just over one year ofage. Mg.dbw matched one Song Type (song similarity 11.1%) with his single neighbourof unknown age, whose territory was separated from that of mg.dbw by a sand spitapproximately 50 m in length (Figure 5-5).The other two birds, rnb.bw and gb.gm, were born in 1990 and establishedterritories the following year next to each other on Dock 3 Island, becoming the soleinhabitants of that island. Gb.gm was last seen on his natal island at 31 days of age, washeard warbling on Dock 2 Island (0.1 km distant and within hearing distance, Figure 5-6)85Figure 5-6. Map of Dock 1, Dock 2, Dock 3 and Forrest Islands to show the dispersalpatterns of three birds, all born on Dock 1 Island. Mg.dbw moved first to Dock 3, then toData Point on Forrest Island, where he established a territory. Gb.gm and mb.bw bothestablished territories on Dock 3 Island, gb.gm first moving to Dock 2 before arriving onDock 3, and mb.bw disappearing to an unknown location before arriving on Dock 3. Theinset shows the number of adult males available as potential tutors to birds in each locationand year.N 1 0Dock3mb.bw0.51.4mg.dbw2kmForrestDock1Island198919901991Docki444Dock2333Dock3002DataPt.1Dock2-SDataPointGD87at 68 days of age, and was first seen on Dock 3 Island at 74 days of age. Dock 3 Islandwas last visited three days earlier with no sign of gb.gm. Mb.bw was last seen on his natalisland at 62 days of age. During visits to Dock 1, Dock 2 and Dock 3 Islands through thenext eight months, he was not seen, first appearing on Dock 3 Island at 323 days of age.This island was last visited 28 days earlier with no sign of mb.bw. Dock 3 Island has verylow vegetation (<irn), thus, it is relatively unlikely that a banded bird present would bemissed on a census visit. Mb.bw and gb.gm each matched four Song Types of their totalrepertoires of 11 Song Types (36.4%) with each other (Figure 5-5).All older territo;y owners in population as potential tutors of 1989 cohortEight male Song Sparrows born on Mandarte Island in 1989 who establishedterritories in 1990 each had a total of six older birds from whom to learn songs (Figure 5-2). Two other males born in 1989 disappeared after independence and are not consideredfurther here. The older birds who were potential tutors to these eight juveniles were the six1989 territory holders. A seventh territory holder, r.om, was last seen in his territory on 4June 1989, and likely died. Since fledglings were first sighted in the vicinity of histerritory on 12 June 1989, r.orn was a potential tutor only to his son, gm.odb. Upon r.om’sdisappearance, pm.bo expanded his territory to include the entire east end of the island.Two territory owners were each potential tutors for a limited time - dbb.mb was last seen15 November 1989 (and not found on the next census date of 12 December) and mdb.rdbwas last seen 12 December 1989 (and not found on the next census date of 30 December);these birds, most likely, died sometime between the dates of their last sightings and thefirst next date on which we searched for them).I recorded complete song repertoires of each of the six potential tutors; these songrepertoires were quite distinct from each other. Only two birds, mdb.br and mdb.rdb,88shared a single Song Type. Therefore, any Song Types that the 1989 cohort matched witholder birds could be traced directly to their source, with the exception of this one song.All eight young birds moved widely, covering four or more of the six territories onthe island at some time between fledging and territory establishment (Table 5-I). Fourbirds were each seen throughout the population, often within days. I was able to assignevery Song Type in the repertoire of each of the eight birds to a Song Type in therepertoire of one of the six potential tutors. A single exception was one Song Type sungby go.mo that was sung by two older birds, as described above. Six of the eight birdsmatched Song Types exclusively with an older bird in whose territory they had beensighted, though not always the most frequently. Each bird had a unique history ofencounters with potential tutors, location of territory establishment, and song similaritywith subsequent neighbours (Table 5-I; Figure 5-2).oni.dbp - born near the east end of the island, moved, upon independence, to thewest end, where he alternated between the territories of pm.bdb and mdb.rdb. He matchedhis complete repertoire of six Song Types with pm.bdb and acquired a territory at the farwest end of the island, after mdb.rdb disappeared. Several first year birds, go.mo,dbdb.mp, orn.dbp and om.gdb sub-divided this area for territories. Om.dbp’s repertoirewas not very similar (18.2%) to that of his single neighbour go.mo.go.ino - born at the far east end of the island, was seen in the territory of every bird,except that of bo.gm; bo.gm’s territory was in the very middle of the island, and go.momost likely moved through it, as I have never seen these birds fly out over the ocean as analternative to flying over land. Go.mo matched one Song Type with pm.bdb, and sinceom.dbp and om.gdb, two of this neighbours, matched six and seven Song Types,respectively, from prn.bdb, they all shared one Song Type. Go.mo matched one SongType each with pm.bo, bo.gm (Figure 5-7) and dbb.mb and though he matched two Song89Table 5-I. Territories travelled through and birds song-matched by eight focal birds bornon Mandarte Island in 1989 that survived to establish territories in 1990. For each focalbird, the first line indicates the location of birth and territory establishment. The secondline indicates the number of times the bird was seen in each territory between fledging insummer of 1989 and 31 March 1990. The third line indicates the number of Song Typesthat the bird matched with each older territory owner. A square around this numberindicates that the older territory owner was an adjacent neighbour. The locations ofterritory owners on the island are west to east (from left to right and top to bottom; seeFigure 5-2). * - go.mo was born at the far east end of the island; his father was r.om, whoseterritory was taken over by pm.bo, shortly after go.mo was born. Also, one of the two SongTypes that go.mo matched with both mdb.br and mdb.rdb cannot be attributed to eitherolder bird, since they both sang the same Song Type; I have included it for both.Focalbird Older territory ownermdb.rdb pm.bdb dbb.mb bo.gm mdb.br pm.boom.dbp terr born5 6 0 0 0 00 6 0 0 0 0go.mo* terr born-b10 5 3 0 2 22 1 1 1 2 1dbdb.mp terr born18 4 0 0 1 30 0 0 0 0 8om.gdb terr born13 3 0 1 0 00 7 0 0 0 1ww.mg terr born5 12 0 1 0 30 0 0 0 6gm.odb born teff1 0 0 0 1 230 0 0 0 [}dbm.ob born teff0 0 0 4 30 0 0 0 0 7rb.mg born terr0 2 0 1 0 230 0 0 0 0 990Figure 5-7. Songs of older tutor, rwdb.mr matched by focal bird (neighbour), bo.gm; andone Song Type that was passed through four generations of birds: rwdb.mr, bo.gm, go.mo,and mb.gg, remaining unchanged except for one Note.10oldertutor,rwdb.mr10focal bird(neighbour),bo.gm886 411’p__61r2211/11/1/4110•10-If’4•/2.‘I/210-rwdb.mr10-bo.gm886164%.%—4———22.10-go.mo10-mb.gg88 6‘——tVtA—2j2j‘092Types each with mdb.br and mdb.rdb, I cannot attribute the source of matching of one ofthese Song Types, since it was sung by both older birds.dbdb.mp, ww.mg and gin.odb- were brothers born near the east end of the islandwho had fairly similar travels across the island. All three birds matched their completerepertoires of Song Types with pm.bo, who was a neighbour of their father, mdb.br. Onlygm.odb settled nearby, the other two moving further to the west and becoming neighbours.Five Song Types that they matched with each other, they also matched with pm.bo.dbin.ob and oin.gdb- were brothers born in the middle of the island. Dbm.obmoved directly to the east, where he matched his complete repertoire with pm.bo andsettled next to him. Om.gdb moved to the west, matching seven Song Types with pm.bdb(Figure 5-8), but not having him as a neighbour. He matched one Song Type with pm.bo,the only example of song matching in which I never saw the younger bird in the olderbird’s territory.rb.ing - was born near the west end of the island. He moved to the east, matchedSong Types with prn.bo, and settled next to cohort, dbm.ob, his single neighbour. Dbm.oband rb.mg matched seven and nine Song Types, respectively, with pm.bo; and, therefore,match seven Song Types with each other.SummaryWhen considering the source of song-matching by all 24 focal birds (Appendix 3),no simple pattern was apparent. While neighbour-neighbour pairs most often shared nosongs (Figure 5-9; top panel), a subset shared 1-7 Song Types. More focal birds matchedtwo or more Song Types with older neighbours than they did with neighbours from thesame cohort. When given a small pooi of tutors, to which every Song Type of everyjuvenile male in the population could be assigned, such as the opportunity on MandarteIsland with the 1989 cohort, I found that while most focal birds shared no songs with older93Figure 5-8. Songs that focal birds matched with birds who were their neighbours and thosethey matched with birds who were not their neighbours. The top box shows two SongVersions of an older tutor r.om, matched by focal bird (his neighbour) pm.bo. The bottombox shows two songs of an older tutor pm.bdb, matched by focal bird (not his neighbour),om.gdb.oldertutor,r.omSongVersionA10-102.oldertutor,r.omSongVersionB1.10-8focalbird(neighbour),pm.boSongVersionAfocalbird(neighbour),pm.boSongVersionB.8rrL111ms2.10focalbird(non-neighbour),om.gdb8•8’,,\.ilIiiiiiIIIiiiiilil6IIflMiIilIMliIiII64.Ge10r6 4r26 410-oldertutor,pm.bdb8•I82.2r-”r6___4.___10-10•88/___61::L.I__rfIf1. rH4lb‘.Jrrrr______pmfff)b.2.1I2.1I.095Figure 5-9. Frequency histograms showing the sources of song-matching by first-yearbirds. The top panel shows the number of first year birds who matched 0-7 Song Typeswith a neighbour from the same cohort (N=30) or an older neighbour (N=28). The bottompanel shows, for the 1989 cohort on Mandarte Island, the number of first year birds whomatched 0-9 Song Types with a neighbour from the same cohort (N=16), an olderneighbour (N=4), or an older non-neigbour (N=44).96///////////////////////////////J121086420Ca)U-0 1 2 3riEl4 5 8 732642D neighbour of same cohortolder neighbour:J older non-neighbourH0 1 2 3 4 5 6 7 8 9Number of Song Types matched97non-neighbours, some birds matched all songs in their repertoires, up to nine Song Types,with older non-neighbours (Figure 5-9; bottom panel). These patterns indicate theexistence of preferred tutors, with older neighbours matched by some juvenile birds, whileolder non-neighbours acted as tutors to others. As a result of several juvenile birdsmatching songs with the same tutor in given years, a number of juveniles share songs withtheir neighbour from the same cohort.DISCUSSIONI found a contrasting result in the source of learning of juvenile Song Sparrows,that seemed to be dependent on the learning environment. Twenty-one first year SongSparrows that were year-round residents on Mandarte Island matched no Song Types withtheir fathers, and matched 1-9 Song Types with other Song Sparrows in the population.However, three Song Sparrows who dispersed from their natal island to other islandsmatched 1-2 Song Types with their father and 1-4 Song Types with their single neighbourson their new islands. For two of these three birds, the single neighbour was a brother fromthe same cohort; for the other bird, the single neighbour’s territory was located across asand spit that neither bird crossed during my observations, though they could hear oneanother.Fathers as potential tutorsFathers can be ruled out as tutors of wild Song Sparrows on Mandarte Island. Infact, it is possible that birds actively avoided matching Song Types sung by their fathers.One bird, gm.odb, whose father was one of three neighbours, had song similarities of85.7% and 76.9% with two unrelated neighbours, and 0% with his father. Another bird,go.mo, matched one or more different Song Types with every older bird on the islandexcept his father. It was not the characteristics of their songs per Se, that prevented the98fathers? Song Types from being matched, since individuals’ songs that were not matched bysons, were matched by other unrelated first year birds.Though I have not examined whether particular Song Types are more likely to bematched than are others, the songs of pm.bo were matched by many more juveniles born in1989 than were songs of other birds in the population (Table 5-I). It is interesting to notethat pm.bo was unmated in 1989; the higher song rates of unmated males may providegreater exposure and stimulation to juvenile birds learning song. If this were true, SongTypes could be learned most often from unmated birds who may have lower lifetimereproductive success than those birds who breed each year. It has been suggested byothers (e.g. Wiens 1982; Payne et al. 1988) that biological and cultural evolution may belargely independent processes. Payne (1981) found that song rate alone did not determinewhich of two tutors juvenile Indigo Buntings copied in the laboratory. Three birds copiedmore song components from a tutor with whom they had social interaction, but who sanglittle, than they copied from a non-social tutor who sang much more than did the socialtutor. To my knowledge, however, the effect of song rate on source of learning in the wild,where birds are free to choose with whom they interact, has not previously been addressed.Song Sparrows fledge at 10-11 days of age (Smith 1988, Arcese 1989) and remainin their parents’ territories until 25-35 days of age (Smith 1988, Arcese 1989). If SongSparrows learned song exclusively between the ages of 22-62 days, as Marler and Peters(1987) found using laboratory conditions, then birds in the wild could learn only fromfathers, as was erroneously suggested for Song Sparrows by BOhner (1990), neighbours offathers, or the adults whose territories they moved through in the first month ofindependence. I found that this was not the case. It has been shown in other species thattiming of learning in the wild is usually later than that determined using laboratoryconditions. For example, Zebra finches in the laboratory learned between 35-80 days of99age (Immelmann 1969, Eales 1985), but likely learned until an older age in the wild (Zann1990).Although no birds on Mandarte Island learned songs from their fathers, this didoccur elsewhere in the study. It is interesting that three Song Sparrows who dispersedfrom their natal island, Dock 1, matched Song Types with their father. Each of these birdsdispersed from a song environment of four potential tutors to very impoverished songenvironments of only one potential tutor each. Dock 3 Island had been uninhabited byterritorial Song Sparrows for two years (J.N.M. Smith and A.L.E.V. Cassidy, unpublisheddata) and Data Point was a relatively isolated habitat island. Though the small number ofpotential tutors (see inset in Figure 5-6), did not affect the number of Song Types learnedby these birds (9, 11, 11), it could have contributed to their retention of Song Types towhich they were exposed before independence. One of the three birds, who remained onhis natal island for at least one month longer than did the other two, matched two SongTypes with his father, the other two birds each matching one Song Type.Kroodsma (1974) found that BewickTsWrens that he recorded at very young agesretained some song components sung by their fathers; he suggested that further exposure tosongs of other adults masked those acquired during early exposure. Payne (1981) foundthat young Indigo Buntings, upon arrival on breeding grounds, sang songs similar to thoseof birds that were isolated from other bunting song during their first springs and summers.Very quickly, however, these birds switched their songs to match adult territorialneighbours. It would be interesting to know what these birds would have sung had theyarrived in an impoverished area with few singing males. The role that the songenvironment plays in determining whether songs of earlier exposure are masked by thoseheard later is not fully understood, but requires more field observations of individualsdispersing to areas that vary in their numbers of tutors.100Neighbours or other birds in the population as potential tutorsI found that 23 of 24 Song Sparrows matched some or all Song Types with one ormore neighbours. In some cases, juveniles even matched both Song Versions of a singleSong Type sung by an older tutor (Figure 5-7). The phenomenon of individuals soundingmore like their neighbours than more distant birds is very widespread among oscines. In areview by Mundinger (1982), 118 species from 27 families (out of 124 species from 28families surveyed) were found to share some song components in this way. It has beenshown in several studies that birds learn preferentially from those birds with whom theyinteract, especially if those interactions are aggressive (Payne 1981, Payne et al. 1981,review in Pepperberg 1985). Nice (1943) heard young Song Sparrows repeat the songs oftheir adult rivals during territory establishment. She further noted that many of these“imitations” were dropped, and others were adopted into their repertoire in somewhatchanged forms.The patterns of song similarity that I found by comparing song repertoires betweenfocal birds and those of their neighbours were complex. My comparisons of the 1989cohort’s repertoires with those of all older birds in the population show that first year birdsoften learn songs from birds other than neighbours. Chaffinches (Fringilla coelebs), whichsing repertoires of Song Types (Marler 1952), copy songs, often precisely, of older birds inthe area, but are no more likely to share songs with neighbours than with any otherindividuals in the population (Slater and Ince 1982). In this species, no sharp songboundaries exist between different parts of the British Isles (Slater et al. 1984).The degree of song similarity between first year birds and their neighbours dependson the number of older birds holding territories in a given year, as well as the pattern ofsettlement of first year birds. Several first year birds who may interact with the same olderbird, and therefore learn his songs preferentially, cannot all become their tutor’sneighbours. On Mandarte Island in 1990, five first year birds established territories west101of the closest older neighbour, resulting in three of the five birds having only same cohortneighbours. While Mandarte Island consists of linearly arranged habitat (Figure 5-2), mostbirds had three neighbours. At another study site, Westham Island, Song Sparrow habitatoccurs along dikes. Here, birds had from one to three neighbours (A.L.E.V. Cassidy,personal observation, M.J. Taitt, unpublished data). Most Song Sparrow habitat, alonghedgerows and riparian vegetation, is likely similar to that found in my study system.Birds from the same cohort as potential tutorsThough it is possible that some first year birds learned Song Types from birds ofthe same cohort, most of the patterns of song similarity suggest that this was unlikely. Forexample, om.dbp and om.gdb, of the same cohort, each matched six Song Types with anolder bird, pm.bdb. It could be suggested from these results that either the two youngerbirds both learned from pm.bdb, or that only one bird did and the other bird copied fromhim. However, a mutual neighbour of the same cohort, go.mo, matched only one SongType with pm.bdb. This Song Type was also sung by om.dbp and om.gdb. If birdslearned from the same cohort, we would expect all three younger birds to sing the same sixSong Types. It is most likely that each of the younger birds learned directly from pm.bdb,go.mo learning only one of his songs, and the other two each learning six. In a study ofsong development in Indigo Buntings, Payne (1981) isolated groups of young birds fromadult song for their first ten months of life. He found that no components in the songs ofthese birds matched, including those of two brothers from the same nest.Similarity ofmatching songsMatching songs between birds and their tutors on Mandarte Island were, in somecases, almost identical. For example, one Song Type remained unchanged, except for asingle Note, across 11 years, and passed through four different individuals (Figure 5-6).102Payne et al. (1981) documented Indigo Bunting songs that were virtually unchanged over aperiod of up to 15 years. On the other hand, I found that acquired songs often departed insome way from their models. I found, like Marler and Peters (1987), that imitation songsoften added or deleted Notes from their tutor models. Note sequences at the beginnings ofSong Types often matched exactly, with endings recombined, probably from other SongTypes. Mulligan (1963, 1966) and Marler and Peters (1982a) suggest that improvisationcould also be important in the generation of song in this and other species. Why birdsshould copy some songs precisely and modify others is intriguing. Perhaps individuals areincapable of uttering some combinations of Notes, and therefore, insert different Notes. Ifound, for birds that dispersed to islands other than their natal islands, that the songs theymatched with either their father on the natal island, or their neighbours on the new islandswere never exact matches (Figure 5-5). In these instances, impoverished songenvironments could result in more improvisation or rearrangement of notes from songs ofseveral individuals. Lemon (1975) suggested that modified imitation songs were a resultof faulty hearing or noisy conditions, but this seems unlikely on Mandarte Island, wherebirds learned songs amid the very noisy environment of a seabird colony, copying manysongs perfectly. Also, birds have been shown to improvise or invent Notes under theexcellent recording conditions afforded in laboratory studies (review by Marler and Peters1982a).My comparison technique defined two Song Types to match if, for example, singleNote Types were replaced by others. I did not distinguish between completely differentNote Types, such as an “inverted u” replaced by a “whistle”, versus Note Types that wereof the same basic type, such as a “whistle” at >2-4 kHz replaced by a “whistle” at >4-6kHz. It would be very worthwhile, however, to examine cultural mutation of Song Typesat this level of detail. During juvenile subsong, birds of many species utter Note Types ata variety of frequencies (e.g. Marler and Peters 1982a), seemingly going through the103frequency range until a perfect match to the model is made. Under what circumstances isthe final frequency of the imitated Note Type different from that of the model, or adifferent Note Type altogether? Birds often match Note Types at precisely the samefrequencies as those of their tutors, out of a large range of possible frequencies (2-10 kHzfor most species). This suggests that there is some biological reason for the incidence ofboth exact replicate songs and songs that are modified in some way by juvenile birds.The genetic adaptation and the social adaptation hypotheses:a continuum of learning opportunityWhether individual species learn song from their fathers, neighbours, or other birdsin the population, social interaction seems to be an important factor in determining thesource of learning (Pepperberg 1985). Where birds learn from neighbours at the time ofterritory establishment, preferred tutors have been shown to be those with which juvenilesinteract in an aggressive way (e.g. Payne 1981, Payne et al. 1981). I found that wherejuvenile birds learned songs from birds who were not neighbours, these were birds throughwhose territories the juveniles had travelled upon independence. Clayton (1987) foundthat young Zebra Finches, who learn from their fathers, preferred tutors who wereaggressive towards them. Slater and Mann (1990) noted that males increased aggressiveintensity towards their offspring after 35 days, when fathers often re-nest and youngbecome independent.The formulation of the genetic adaptation hypothesis was based on the patterns ofsong similarity found in White-crowned Sparrows (Marler and Tamura (1962) and Rufouscollared Sparrows (Nottebohm 1969). However, Baptista (1985) suggested that patterns ofsong similarity in White-crowned Sparrows fit the social adaptation hypothesis better thanthey do the genetic adaptation hypothesis. His banding and recording study indicated thatareas of song similarity were the result of dispersing fledglings or first year birds settling104for the first time and imitating the songs of local territory holders, rather than the result ofyoung birds learning songs from their fathers and settling adjacent to their natal territories.There is no evidence that juvenile Rufous-collared Sparrows either remain withinboundaries of song similarity or that females prefer certain Song Types (Handford andNottebohm 1976). While they found that banded adults returned to areas where they firstsettled, this is common in many passerines. It remains unknown from whom juvenileRufous-collared Sparrows learn song.The only birds that have been shown in the field to learn song preferentially fromtheir fathers breed in unpredictable environments. Zebra Finches live in semi-arid habitatin Australia. Loose breeding colonies form rapidly in response to unpredictable rainfall(Slater and Mann 1990). The three species of Darwin’s Finches shown to learn song fromfathers (Grant 1984, Millington and Price 1985) also exhibit breeding in response to rain.Perhaps there is a selective advantage for rapid individual recognition in these species.Zann (1990) found that the extended breeding season for Zebra Finches allowed young tomature and breed in the same season. Perhaps this could explain the premium on “fast-learning” of song from fathers, to avoid inbreeding at a time when there are many youngbirds around (Zann 1990). In two Darwin’s Finch species, Geospiza fortis and G.scandens, females mate randomly with respect to their father’s Song Type (Millington andPrice 1985), therefore, song is likely not a kin marker but could serve as a cue for speciesrecognition in these species, which live amongst several congeners (Millington and Price1985, Gibbs 1990). In the third species, G. conirostris, however, no female has beenknown to mate with a male of the same Song Type as her father’s, and Grant (1984)suggests a possible kin recognition system for this species.The results of my studies on timing and source of song learning in Song Sparrowsindicate that birds are capable of singing as adults what they heard from their fathers whenvery young, but in most cases copy Song Types from neighbours or non-neighbours in the105population. A “rule-of-thumb” that Song Sparrows may use in learning songs is: i)memorize songs from father when very young and sing these later in life if songs are notmasked from further exposure to many other birds; ii) upon independence, listen to andpossibly practise songs of older birds in the population, and sing as an adult the songs sungby the birds with which juvenile interacted most; iii) when establishing a first territory,continue to sing the last set of Song Types, which becomes the adult repertoire andremains unchanged through life; this repertoire may or may not match one or moreadjacent neighbours, depending on whether neighbours are at least one year older, or fromsame cohort, and also depending on whether these were the birds with which juvenileinteracted the most.106CHAPTER 6CONCLUDING DISCUSSIONThe most interesting results from my thesis were the following:1. Song Sparrows share more identical Song Types than previously shown by otherresearchers (with the exception of Philip Stoddard and colleagues; Stoddard et al. 1988,1991, 1992). This similarity arose from juveniles imitating older neighbours or other birdsin the population, through whose territories they travelled between independence andterritory establishment. Rarely, juvenile birds imitated their fathers. In each case, thesejuveniles dispersed from a small island with few tutors to a very poor song environmentwith only one tutor.2. The length of the learning period in wild juvenile Song Sparrows is longer thanpreviously determined in a laboratory study. Marler and Peters (1987) showed that mostlearning in Song Sparrows occurred between 22-62 days of age. If this occurred in thewild, then birds would likely learn songs from their fathers, fathers’ neighbours, or birdsthrough whose territories the juveniles travelled only in the first month after independence.I found that birds as young as 22-68 days when last exposed to particular tutors matchedSong Types of those tutors as adults. In each of these cases, the tutor was the juvenilebird’s father. Furthermore, the juvenile dispersed to a location with but a single tutor. Thispoor song environment could have resulted in the juveniles’ retention of songs heard muchearlier in life at almost the exact age that Marler and Peters (1987) found most learning(from taped tutors) in Song Sparrows to occur.I found that birds as young as 124 days of age uttered Song Types that weredestined to be in their adult repertoires. Previous studies had shown the earliestrecognizable Notes sung by Song Sparrows to be 241 days in the laboratory (Marler andPeters 1987) and 169 days in the field (Nice 1943). Birds who progress through the stages107of song development more quickly than others may have an advantage in territoryestablishment.I found that birds as old as at least 273 days of age when first observed at newlocations matched Song Types with neighbours. In all cases, these were birds whodispersed to other populations and copied some songs of those areas, while also retainingin their repertoires songs of their fathers.Much of the seemingly endless variety in vocalizations has been explained by theresults of comparative studies. Early research in animal behaviour, including those ofvocalizations, often asked whether traits were innate or acquired (Lanyon 1960, Lemon1975, Immelmann 1980). This led to laboratory studies in which birds of various specieswere raised in acoustic isolation or provided taped tutors. From these studies, it wasdetermined that most passerines learn songs; this is also true of some species from a fewother groups, such as hurnmingbirds, parrots and gamebirds (Nottebohm 1972a, Marlerand Peters 1982a). All other bird species studied to date acquire their vocalizationsgenetically.The finding that most passerines learned songs led to studies of song developmentboth in the field and in the laboratory, though not neccessarily with the same species. Anew question, posed as recently as the mid- 1980’s was: why do the results of laboratorystudies differ from those obtained in the field? Millington and Price (1985) described theintriguing riddle that while laboratory studies have shown young birds to learn theirfathers’ songs, field studies have shown young birds to copy neighbours. There are twoanswers to this question. First, live birds, with which young birds can interact, have beenshown to lengthen the “sensitive period’t during which birds learn songs (e.g. Baptista andPetrinovich 1984, 1986). Therefore, laboratory studies need to be as “natural” as possiblein order to determine from whom birds really learn. Second, species in the wild vary intheir dispersal patterns in relation to their sensitive periods, therefore, some species copy108fathers while others copy neighbours or other birds in the population. Extreme examplesof sensitive period are vocal mimics, who learn through life and imitate other birds, oftenprecisely, and even imitate non-avian sounds (review in Baylis 1982).Two hypotheses have been proposed to explain the variety that exists in songsimilarity between individuals. The genetic adaptation hypothesis (Marler and Tamura1962, Nottebohm 1969) proposed that birds learn from their fathers, and song serves as agenetic marker. The social adaptation hypothesis (Payne 1982) proposed an advantage tobirds who match songs of their neighbours at the time of territory establishment. For manyspecies of birds, timing of learning has not been studied in the laboratory, and only a fewspecies have been studied both in the laboratory and the field; these include Zebra Finches,Darwin’s Finches, White-crowned Sparrows and now, Song Sparrows. All of these specieshave been shown to learn song at later ages in the wild than found in laboratory studies(e.g. Zann 1990, Chapter 5). While all the finch species (Families Estrildidae andFringillidae) have been shown in the wild to learn from fathers, all other species learn fromother birds. Finch species that learn songs from their fathers breed in response to rain, Itis possible that breeding seasons of unpredictable duration have resulted in selection tolearn quickly from fathers, in order to promote kin or species recognition.My approach to studying song variation and song learning was to record very largesamples of song, at least from some individuals, to see at what point in my sampling Ireached complete repertoires, and apply those criteria to the birds from whom I recordedfewer songs. Others may disagree that “complete” repertoires were obtained. However,after documenting complete repertoires from an intensively recorded subset of birds, Irecorded an average of 715 additional songs per bird without observing a new Song Type.It is possible that very rare Song Types were sung only about every 1000 songs uttered.Formulas estimating repertoire size from samples generally assume that Song Types areuttered randomly (e.g. Good 1953, Wiklenthal 1965), however, this is usually not the case.109It seemed logical to me to calculate the percent probability of documenting completerepertoires based on empirical data obtained from well-recorded birds. Future studies ofsong organization could investigate why birds repeat Song Types variable numbers oftimes before switching, and the relationship between the size of repertoires and how birdscycle through them.All birds that learn song go through a “subsong” stage in song ontogeny (Marlerand Peters 1982a). It is difficult, in the field, to document ages at which this stage isreached, because birds often sing very faintly and from hidden perches. I found that birdsrecorded as young as 124 days of age sang the same Song Types the following year. Thesefindings showed that, regardless of the ages at which I recorded repertoires of birds, theseremained unchanged from those sung as first year birds. This information was valuable, asit allowed me to use data from birds for whom I recorded song repertoires only at olderages. A detailed examination of sonagraphic features of the earliest songs uttered mayshow a pattern of how wild birds practise sounds in relation to what they hear frompotential tutors.Many studies of geographic variation in song come from species in which malessing only one Song Type (e.g. R.B. Payne 1978, Marler and Pickert 1984, review in Krebsand Kroodsma 1980). Kroodsma (1972, 1977b) studied geographic variation in the largerepertoires of Bewick’s Wren. While differences in many traits, including song, have beensuggested between inhabitants of island and mainland populations, empirical evidence islacking. As a result of the founder effect (Thielcke 1969), it has been suggested thatrepertoire size, a measure of song complexity, could be smaller in those birds inhabitingisland populations than in birds inhabiting mainland populations. This is because fewernew Song Types might be introduced to islands than to mainland populations. I found nodifference in mean repertoire size between the islands I studied, and those from publishedrepertoire sizes for mainland Song Sparrow populations. Nor did the rate of male110immigration to these islands affect repertoire size. Either of these factors, as well aspopulation density, reflects the number of potential tutors birds have, if they learn afterarriving at that location. I found a significant effect of population density on the numberof Song Types learned. As well, birds who had four or more neighbours when theylearned song sang more Song Types than did those birds with three or fewer neighbours,although the trend was a weak one. Whether population density or the number ofneighbours birds have is more meaningful to birds learning song depends on the timingand source of song learning, which I found to vary between individuals depending on thelearning environment.I found that twenty-one birds born on Mandarte Island who also establishedterritories there learned no Song Types from their fathers. However, three birds born on asmall island with four potential tutors, and who dispersed to impoverished song learningenvironments, matched some Song Types with their father. This early learning, which alsooccurs in other species, is not masked by other sounds heard later in life in such species asZebra Finches and Darwin’s Finches. Here, fast learning is possibly related to theenvironmental conditions in which these species breed. Early learning in species such asBewick’s Wrens and Indigo Buntings, is masked by songs heard later from neighbours atthe time of territory establishment (Kroodsma 1974, Payne 1981). I found that earlylearning in Song Sparrows was masked by songs heard later by neighbours or other birdsin the population. However, this was not true if juveniles found themselves inimpoverished song environments.Twenty-three of 24 birds matched 1-7 Song Types with one or more neighbours. Isuggest that older neighbours are usually the direct source of learning, and that any songsthat birds match with fellow cohort members are a result of both birds learning from thesame tutor. It has been shown in other species (e.g. Payne 1981) that juveniles from thesame cohort do not learn songs from each other. Although I found that neighbours were111often matched by juvenile birds, some birds did not match Song Types with anyneighbours. There was a complex pattern of song similarities between focal birds and theirneighbours. To sort out this complexity, it would be ideal to be able to assign every SongType of one year’s cohort to its source of learning from all potential tutors in thepopulation. I had the opportunity to do this. I chose one year’s cohort for which I had thegreatest knowledge of movements from fledging to territory establishment. I compared thesong repertoires of these birds to those of all older territory owners. I found that some ofthese birds learned some or all Song Types (up to nine songs) in their repertoires not fromneighbours, but from other birds, through whose territories they had passed. Timing ofsong learning in the wild is clearly flexible, and birds encounter many potential tutors.The patterns of song matching that I found with the 1989 cohort explain why some birdsfrom other cohorts did not match all, or sometimes any, Song Types with neighbours.They likely copied songs from other males, whose songs I did not document, andestablished territories next to males other than their tutors. Since this occurred in 1990when there was much available habitat, it likely occurred in other years of higher densitiesand greater competition for space.While the three birds in my study who dispersed and retained Song Types of theirfather each had only a single neighbour, other birds born on Mandarte Island, who did notmatch their fathers’ Song Types, also had single neighbours. An obvious differencebetween these two situations is the total number of singing males that juveniles heard.Perhaps whether birds copy songs from their fathers depends not on the number ofneighbours from whom they can learn, but how much song from the whole population theyhear. More field observations of birds dispersing from their natal populations to otherpopulations are needed to address whether it is the act of dispersing, or the environment towhich birds disperse, that results in their retention of some of their fathers’ songs.112The idea that birds learn more Song Types as a result of increased stimulation notjust from neighbours, but all birds in the population was also supported by my finding thatbirds learned larger song repertoires in years of higher population density than they did inyears of lower density. A weak trend of birds with four or more neighbours to learn moreSong Types than those birds with three or fewer neighbours could be explained by the factthat higher density results in birds not only having more neighbours, but hearing moremales singing close by.Further research could investigate whether birds matching certain Song Types havea social or reproductive advantage over other birds. Gibbs (1990), for example, found thatDarwin’s finches singing the rarest of two Song Types in the population had greaterreproductive success than those birds singing the more common Song Type. Date ofterritory establishment, territory tenure and lifetime reproductive success are a few of thevariables that could be compared to Song Types learned by Song Sparrows in my studysystem. Are those Song Types copied by one generation of learners more likely to becopied by the next generation than are other Song Types that are still heard? What isspecial about those Song Types that remain unchanged across generations? These resultsmay shed more light on the question of why certain Song Types are copied faithfullyacross several generations, and others are modified or dropped altogether.Finally, the responses of the birds themselves to Song Types of differentindividuals or locations determines the significance of the different patterns of songlearning and geographic variation in song that we see in nature. Birds can discriminatebetween vocalizations of different locations, as well as between individuals (references inStoddard et al. 1991). It would be interesting to test whether birds that dispersed to otherislands could discriminate between their natal and dispersed-to islands, and whether birdscan discriminate between Song Types of a neighbour and matching Song Types of theneighbour’s tutors.113LITERATURE CITEDArcese, P. 1987. Age, intrusion pressure and defence against floaters by territorial malesong sparrows. Anim. 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(plc > (07‘““1-5/ /(.4)i5A 6—g2-iA cçj (.-l-)u.A ir 3Q (0s’s—‘. 100) (.4)’ 7 l37 c7 = — .K. 0O7 (.4) 3 t’o- —o?.o. 70 ‘.-+oco (.4). &_i o:&)3 —2/4 24, ‘Zh (23co C. -(b:l— —3 (-:1—2.t& L ‘‘ 16— 810iq. oY. qo— 6 ‘j ‘4?. 13 ‘c6 — g091I , - °“•T I s7 (!c 33J‘t?, @27 g•—io.O Ic’f2 c%1-):._::_ 5 Jc (CI1— S‘Y7B3o @‘77 31 5?—-l3— IO6 73 cs’oay2 l75 5‘bA, i0’ CJ’L3 —‘O—-- 7 3IO6_aL3(, I (s.i’, C r7,(ti. C’10126343 IERFRBKDKIC344 IKBFGKICH345 IKBFGKIHIEIX346 NZHERC347 IXEYFRHCE348 HFNFPRH349 BEZHCXKD350 BEZRHCHNV351 BEKCRH352 BEKCHNVRB353 BHCER354 BHCECNHXHJ355 CKERHR356 BHERCKXHHR357 BHERCKXHN358 YFFCFXHN359 CEPEXXFHF360 CERH361 BGKRE362 HEB363 BECECEIRB364 BBFJKXHR365 BBE3EKHIR366 BEKRFCR367 BEKRFCH368 OKOHOKJRHIOJRXRF369 CXEHREB370 IEYFCECKXFRH371 JXFIRFCRH372 HFYFXENRER373 BEUFHXECK374 CFKDXFOEA375 CFCCRO376 IFBCIECR377 CKCERFGHOEC378 BHEDEKGBOKXN379 CFPFHR380 BECEHRKH381 IRXENERHRD382 IOEHRK383 IOEKFREG384 HEBXNH385 NZHFQFCEBCRBRE386 BCHNECIR387 DBFIRFGHOKBR388 BFDKHNRI389 BECKXEN390 KCFHN391 CFKCENENE392 ERKFCHI393 BEKHFOHCRIR394 CFGFCEIRO395 BHEARHE127Appendix 2. Song recording history for all Song Sparrows in the study. If year born is inbrackets, the bird was banded as an adult of unknown age in the year indicated. A dashindicates recording durations less than a half hour. Individuals were recorded in all yearsthrough the range given; e.g. 88-9 1 means that the bird was recorded in 1988, 1989, 1990and 1991. Whether the repertoire was considered complete is indicated in the last column.A “Y” indicates that the repertoire was considered complete, at 95% probability level, if>206 songs were recorded continuously, or >280 pooled songs were recorded. A “N”indicates that the repertoire was not considered to be complete using these criteria.Cd0. Cc,$:‘MANDARTErwdb.mr 60228 1980 69 67 3.5 10 88 Nmdb.rdb 58701 1982 1151 649 3.0 10 88-89 Ydbb.mb 60272 1982 943 493 3.0 9 89 Yrm.rb 58760 1982 111 102 1.0 7 88 Nmp.bdb 58710 1982 70 38 - 8 88 Ndbw.mdb 58883 1983 181 176 2.0 8 88 Nmb.gw 59399 1983 163 139 1.0 13 88 Ngb.mdb 58821 1983 36 36 0.5 6 88 Nrr.mb 59264 1984 259 163 2.0 9 88-89 Nrp.mdb 58940 1984 217 176 1.5 6 88 Nbb.mdb 59256 1984 167 82 0.5 11 88 Now.wm 58942 1984 132 51 1.0 8 88 Nop.mg 58957 1984 72 38 0.5 4 88 Ngg.mdb 59263 1984 71 71 1.0 6 88 Nob.om 58961 1984 44 44 1.5 6 88 Nbm.gr 58939 1984 4 4 - 1 88 Now.dbm 58955 1984 4 4 - 1 88 Nbm.oo 02078 1985 354 257 3.0 10 88 Yr.om 59481 1985 328 261 2.5 10 88-89 Yrw.nn 59448 1985 305 69 0.5 11 88 Yg.wm 59490 1985 247 94 0.5 5 88 Np.rm 02016 1985 212 119 1.0 6 88 Nrm.oo 02074 1985 177 69 1.0 9 88 Nwp.mo 02058 1985 146 77 0.5 9 88 Nw.om 59470 1985 113 91 3.0 6 88 Nmo.w 59422 1985 70 38 1.5 5 88 Nmdb.br 02230 1986 815 244 3.0 5 88-90 Ybm.wp 02341 1986 754 173 1.5 8 88 Ybo.wm 02399 1986 584 231 1.5 9 88 Ybo.gm 02204 1986 409 196 3.0 9 88-90 Ydbm.wr 02335 1986 257 152 1.0 8 88 Ndbp.mdb 02359 1986 252 252 3.0 9 88 Ygg.mo 02253 1986 188 154 0.5 8 88 N128$°‘MANDARTE (cont.)dbp.mb 02361 1986 91 47 2.0 6 88 Nbp.mdb 02019 1987 522 250 3.0 8 88 Ymdb.rp 02196 1987 442 433 3.0 7 88 Ymdb.oo 02194 1987 265 215 1.5 7 88 Ymr.dbw 02110 1987 261 155 1.0 8 88 Nmo.odb 02116 1987 57 57 1.0 3 88 Nmr.gr 02164 1987 21 13 0.5 3 88 Nmr.rp 02117 1987 16 9 0.5 3 88 Nmdb.pg 02163 1987 11 11 0.5 2 88 Nmw.gr 02111 1987 1 1 - 1 88 Npm.bo 64904 1988 2558 591 3.0 8 89-91 Ypm.bdb 64976 1988 1374 461 3.0 5 89-90 Ygm.odb 69518 1989 1247 418 3.0 6 89-90 Ydbdb.mp 69519 1989 1174 403 3.0 8 89-90 Ygo.mo 69561 1989 956 562 3.0 7 90-91 Yww.mg 69520 1989 891 487 3.0 6 89-90 Yrb.mg 69536 1989 578 389 3.0 9 89-90 Yom.gdb 69547 1989 573 161 3.0 8 89-90 Yom.dbp 54504 1989 464 293 1.0 6 89-90 Ydbm.ob 54509 1989 231 227 3.0 7 90 Ybr.gm 47195 1989 156 56 1.0 6 91 Nmp.dbdb 47195 1990 372 206 1.0 8 91 Ymb.gg 56943 1990 340 179 1.5 9 91 Ypw.om 47197 1990 317 234 1.5 9 91 Ymw.ww 47109 1990 203 72 1.5 10 91 Now.mo 56904 1990 187 158 1.5 7 91 Noo.om 47102 1990 169 151 3.5 8 91 Npm.pr 54635 1990 159 159 2.0 8 91 Nmg.dbdb 47108 1990 155 100 1.0 6 91 Npm.gb 56907 1990 111 84 1.5 7 91 Ngp.rm 47168 1990 92 92 2.0 6 91 Ngw.mg 54631 1990 81 78 1.0 7 91 Nmg.gg 47177 1990 20 20 1.0 5 91 Nwm.gdb 47146 1990 12 12 0.5 3 91 Nwr.pm 54622 1990 10 5 0.5 4 91 NVANCOUVER ISLAND-Bazan Bayunb- ? 299 299 1.5 8 89 YLITtLE SHELLodb.mb 86235 1988 568 251 1.0 8 89-90 Ypg.mg 69590 1989 433 187 3.5 11 90 Ywb.bm 69503 (1989) 300 98 0.5 7 89-90 Y129KERop.gm 54541 1989 739 232 3.0 7 90 Ypb.wm 54547 (1989) 89 30 - 6 90 Nmdb.bdb 56947 (1990) 7 5 1.0 2 90 NDOCK 1pw.rm 86186 (1988) 731 485 3.0 7 88-91 Ypr.om 86236 1988 480 360 3.0 6 89-91 Yrdb.dbm 59042 (1988) 288 56 3.0 9 88-91 Ydbr.gm 59051 (1988) 173 46 3.0 8 88-91 NDOCK 2rp.rm 59044 (1988) 614 485 3.5 9 89-90 Ywdb.gm 69505 (1989) 403 207 3.5 11 89-90 Ybb.bm 54517 (1989) 183 43 1.0 7 90 Nop.pm 69506 (1989) 130 99 2.0 7 89 NDOCK 3gb.gm 56944 1990 230 230 3.0 11 91 Ymb.bw 47139 1990 220 220 3.0 11 91 YFORRESTmg.dbw 69524 1989 393 384 3.0 9. 90 Yunb - 139 125 1.5 9 90 NREAYrb.bm 59059 (1988) 111 34 1.5 11 89-90 Npm.gp 54502 (1989) 103 55 1.0 7 89-90 Ndbr.pm 59058 (1988) 100 24 1.5 6 89-90 Ngr.dbm 59057 (1988) 16 10 - 2 89 NRUMmb.wg 69742 1988 601 203 2.0 9 89-90 Ypr.gm 86224 (1988) 221 87 1.0 6 89 Ypp.dbm 59071 1988 108 65 - 3 89 Nwr.bm 86221 (1988) 62 62 1.0 7 90 Nunb - 5252 1.5 4 90Ngw.wm 59072 (1988) 47 47 0.5 3 89 N130cP’$‘ —$c$;c;_c$$çiGOOCHunb - 87 70 0.5 8 89 NWESTHAM-Reifelmo.wr 12938 1988 722 701 3.0 10 89 Ydbp.mo 43713 1988 484 474 3.0 6 89 Ymo.gdb 48634 1988 53 30 - 2 89 Nunb - 4848 - 7 89Nwo.mo 43531 (1988) 41 19 - 3 89 Ngp.mo 43701 (1988) 39 15 0.5 5 89 Nmo.oo 43700 (1988) 36 35 - 4 89 Nbb.mo 43565 (1988) 32 32 - 2 89 Nmo.gr 38622 (1988) 16 16 - 1 89 Nop.mo 43663 (1988) 16 16 0.5 4 89 Ndbo.mo 43574 (1988) 15 15 - 3 89 Ngw.mo 43548 (1988) 15 15 - 1 89 Nmo.ww 43739 (1988) 14 14 0.5 2 89 Ndbr.mo 43569 (1988) 9 9 0.5 1 89 Nwr.mr 43643 (1988) 5 5 0.5 2 89 Nwo.mr 43647 (1988) 5 5 0.5 1 89 NWESTHAM -Alaksenoo.mb 43658 (1988) 255 255 1.5 9 88 Yunb - 206 206 1.0 8 88 Ygp.mb 43670 (1988) 119 32 - 9 89 Nbo.mb 43672 (1988) 103 34 - 7 89 Nwg.mb 43787 (1988) 83 35 - 6 89 Nmb.bo 69789 (1989) 82 23 - 6 89 Nmdb.gog 69796 (1989) 81 35 - 6 89 Ndbo.mb 43710 (1988) 60 26 - 3 89 Nmb.grg 69787 (1989) 59 35 - 7 89 Nmb.bdb 69793 (1989) 53 53 - 4 89 Nmb.opr 69784 (1989) 51 23 - 5 89 Nmb.dbb 69453 (1989) 44 23 - 8 89 Nmb.dbg 69542 (1989) 30 30 - 3 89 Nmb.dbgdb 69785 (1989) 27 27 - 5 89 Nrdb.mb 43598 (1988) 27 19 - 3 89 Npr.mb 43725 (1988) 25 25 - 2 89 Ninb.bb 69792 (1989) 13 13 - 2 89 Ngw.mb 43656 (1988) 12 12 - 3 89 Nmdb.grg 69797 (1989) 8 6 - 3 89 Nmb.gpp 69786 (1989) 6 6 - 1 89 N131Appendix 3. Song Types that focal birds matched with potential tutors, father (first line foreach focal bird) and neighbours (subsequent lines). Neighbours that were at least one yearolder than focal birds, and had already established territories are indicated by *• Thosebirds for which incomplete repertoires were documented are indicated by -; see Table 2-1for numbers of songs recorded and repertoire sizes. Song Type numbers are unique to eachfocal bird. Where Song Types of a focal bird matched more than one potential tutor, the“matched songs” of the potential tutors also matched each other.Focal Potential Song Types focal bird % songbird tutor matched to potential tutor similarityMandarte IslandBorn 1990mw.ww om.dbp none 0pm.gb- 1 23 7 9 58.8oo.om 123 6 9 55.6mdb.br* 4 8 10 37.5mb.gg dbm.ob none 0go.mo* 1 345 6 7 8 87.5wm.gdb- 8 16.7mg.gg- none 0oo.om bo.gm none 0pm.bo* 1 345 6 7 8 82.4pm.gb- 1 34 6 7 8 80.0mw.ww 1345 8 55.6mp.dbdb om.gdb none 0gw.mg- 23 5 7 9 66.7mg.dbdb- 2 4 6 9 57.1Born 1989om.dbp mdb.br none 0go.mo 2 18.2go.mQ r.om none 0om.dbp 2 18.2om.gdb 2 13.3dbdb.mp none 0dbdb.mp mdb.br none 0ww.mg 123 6 8 71.4om.gdb 4 12.5go.mo none 0om.gdb bo.gm none 0go.mo 2 13.3dbdb.mp 7 12.5ww.mg none 0132Focal Potential Song Types focal bird % songbird tutor matched to potential tutor similarityww.mg mdb.br none 0dbdb.mp 2 345 6 71.4pm.bdb* none 0om.gdb none 0gm.odb mdb.br none 0pm.bo* 1 2345 6 85.7dbm.ob 1234 6 76.9mdb.br* none 0dbm.ob bo.gm none 0pm.bo* 12345 67 93.3rb.mg 12345 6 7 87.5gm.odb 1 345 6 85.7rb.mg pm.bdb none 0dbm.ob 2 3567 8 9 87.5Born 1988pm.bdb mdb.br none 0mdb.rdb* none 0dbb.mb* none 0pm.bo bm.wp none 0r.om* 6 8 22.2mdb.br* none 0Born 1987mdb.rp bm.wp none 0dbw.mdb* 7 13.3mdb.rdb* 4 11.8(+2 neighbours not recorded)mr.dbw rr.mb none 0mdb.br* 2 7 30.8g.wm* 4 15.4mo.w* none 0w.om* none 0bp.mdb rr.mb none 0rw.rm* 12345 7 63.2gy* 3 5 6 46.2wp.mo* none. 0mdb.oo mdb.br none 0dbm.wr* 26 26.7mr.rp- 1 20.0gb.mdb* none 0133Focal Potential Song Types focal bird % songbird tutor matched to potential tutor similarityBorn 1986dbp.mdb bm.oo none 0bb.mdb* 1 2346 7 70.0mp.bdb* 3 6 23.5rm.rb* none 0(+1 neighbour not recorded)bo.gm ob.om- none 0rwdb.mr* 467 31.6op.mg* none 0dbb.mb* none 0(+1 neighbour not recorded)Born 1985r.om ob.om- none 0rw.rm 1269 38.1wp.mo 2 10.5w.om- none 0(+1 neighbour not recorded)Other IslandsDock 1 IslandBorn 1990mb.bw rdb.dbm 7 10.0gb.gm(Dock3) 2679 36.4gb.gm rdb.dbm 6 10 20.0mb.bw (Dock 3) 4 5 9 10 36.4Born 1989mg.dbw rdb.dbm 5 11.1unb (Forrest) 4 11.1134Appendix 4. This page shows an example of pairs of letter sequences that I determined to“match” and “not match”. The only pairs of letter sequences in the “not match” list arethose which were at all close to being a “match”. Most “not match” pairs were verydifferent from one another..$___________Irrh-J j -- i ,‘—L...‘-. Wirc ft or ——-E f’’-fir ):tAdNF _1j;-C FohJ I ‘‘ 22’ —_______.-.i----‘i_ ‘1W’) &cci-tç 2o3 CFIIFPAIz’1&E 2.3’____-:;cf6cGp,zitH1c f3F’xxKIL;s&r.DFCirt._ _____1a_JJ! Ct, --3C1.JEE.1 IU3 iEi4,cH1ICP.CC4L I7 Ck.1C4&11’-__----.—--.---.--—---__2.’_____I /•2:7 2?-c:___- . -- -— JO f.jAT(5—-----


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