UBC Theses and Dissertations
Song variation and learning in island populations of song sparrows Cassidy, Alice Louise Ethel Victoria
Animal vocalizations vary greatly between and within species. Male oscines acquire song by imitation of others, in much the same way that humans learn language. I investigate 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 1988-1991 on 12 islands in southwest coastal British Columbia. Birds were colour-banded, usually in the nest, and many were followed from their birth place through to territory establishment in the following spring. The age and “phenotypic” father of every bird born on Mandarte Island was known during this 4-year period. Individual Song Sparrows did not change their unique repertoires of 5-13 complex Song Types across a range of ages covering their life span. Complete repertoires recorded from this species at any age are the same as those in the first year of life, when song is learned. Two hundred and six continuously recorded songs or 280 songs from pooled sessions were required to achieve 95% confidence that the complete repertoire was recorded. Birds averaged 8.2 Song Types over all islands and did not sing smaller repertoires than those birds in mainland populations. Higher population density and an increased number 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 among the models available? Two opposing hypotheses predict that tutors are most likely either fathers or neighbours. Twenty-one birds born on Mandarte Island matched no songs with their fathers. However, three birds that dispersed from a small island (0.8 ha) with few tutors to a very poor song environment with only one tutor retained some songs they heard from their fathers before dispersal (22-68 days of age) and also learned other songs from their neighbours after dispersal (273+ days of age). Birds as young as 124 days of age uttered note sequences that were destined to be in their adult repertoires. Previous studies 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 obtain territories 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 particular tutor. 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 the existence of preferred tutors. Particular Song Types were copied precisely, and persisted across up to four generations and eleven years on Mandarte Island. This thesis shows that Song Sparrows share more identical songs, and learn song over a longer period than previously determined. Both the timing and the source of song learning depends on the quality of the learning environment, measured by the number of tutors and the amount of singing.