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A comparative study of the reproductive behaviour and natural history of three sympatric species of cormorants,… Van Tets, Gerrard Frederick 1959

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A Comparative Study of the Reproductive Behaviour and Natural History of Three Sympatric Species of Cormorants, (Phalacrocorax JurUUj, £. penicillatus,. & £. jpjljfli&uj) at Mandarte Island, B. C. BY Gerrard Frederick van Tets B.A., University of B r i t i s h Columbia, 1956 A thesis submitted in partial fulfilment of the requirements for the degree of Master of Arts in the Department of Zoology. We accept this thesis as conforming to the required standard The University of B r i t i s h Columbia Apr i l , 1959 Abstract. During the four months of summer of 1957 and 1958 the reproductive behaviour and natural history ©f three sympatric species of cormorants, phala^roc.o^a^ auri^qs,. £. pelaqicus. and £. penic^ll^^qs. was studied at Mandarte Island, B.C. The three species were found to select different sites for perching and nesting, and to use different habitats for feeding. A description is given of the external colouration of the various age groups of the three species, based in part on banded birds of known ages. It was found that £. ^ u r i l ^ s and and £. jafilaaiciis are polymorphic prior to breeding and almost monomorphic after the breeding season. No such polymorphism was found in £. fie^cJJJ^tyj. The voices of j?. auri^tus, and g. pelaqicus include several destinct c a l l s , but g. n e t ^ ^ c ^ l a t u ^ has only one c a l l note. On the other hand only £. pen^c^llatijs can flash i t s gular pouch. The various comfort movements and postures were found to be identical to those of other birds. During locomotion specific differences due to anatomy and habitat adaption became apparant. These differences were further emphasized as species specific signals during social contact. The courtship sequence was found to be functionally identical for a l l cormorant species studied, but to d i f f e r specificly at each step in the sequence, where a signal is used. Except for differences due to size and nesting habitat, the method of incubating the eggs and raising the chicks was found to be identical in £. aureus and g. pelag^cus^ It was concluded, that the species specificity of the signals, during courtship and social contact, serves to prevent hybridization, and thus preserves the divergent ecological specialization of the species. This in turn permits a more complete use of the environmental resources. In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t permission f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of Zoology The U n i v e r s i t y of B r i t i s h Columbia, Vancouver Canada. IV Page I n t r o d u c t i o n and L i t e r a t u r e Review..... 1 Methods.... * 7 D e s c r i p t i o n of Mandarte I s l a n d . . 8 Land H a b i t a t S e l e c t i o n 10 Plumage and Molt 13 D e s c r i p t i o n of the D o u b l e - c r e s t e d Cormorant.. 14 D e s c r i p t i o n of the P e l a g i c Cormorant. ....18 D e s c r i p t i o n of the Brandt Cormorant... 21 Value of Plumage f o r F i e l d I d e n t i f i c a t i o n 22 V o i c e ..24 R e s t i n g Postures * .... 26 B a t h i n g and Wing-drying ...28 P reening 29 S t r e t c h i n g Movements »• • 30 E l i m i n a t i o n of Wastes ...31 D e f e c a t i o n . ....31 R e g u r g i t a t i o n . .31 S a l t S e c r e t i o n * .31 Locomotion •« • >32 Walking 32 C l i m b i n g . .32 Swimming 32 D i v i n g • 32 F l y i n g .....33 Soaring 33 v T r a v e l l i n g 34 v Page Taking o f f and A l i g h t i n g on Water . 35 Taking o f f and A l i g h t i n g on Land... 36 Alarm Behaviour 38 G u l l s and Crows vs Cormorants. 3 9 Food and Feeding Behaviour....... 41 F i g h t i n g and Threat Behaviour........ 44 The Hop 46 Wing F l i p p i n g . . . . . . . . . . . . 47 R e c o g n i t i o n D i s p l a y 48 The C o u r t s h i p Sequence 50 Nest B u i l d i n g and Nest Maintenance...... 53 Egg Laying 55 Incubation , 57 Nest R e l i e f . . . 60 Hatching 62 Feeding of Chicks * 63 Watering of Chicks 66 Growth and Development of C h i c k s . . . . . . . . . . 67 Banding and i t s E f f e c t . . . 70 S u r v i v a l , M o r t a l i t y and D i s p e r s a l . 71 C o n c l u s i o n and D i s c u s s i o n . . . . . . . . 75 Summary. « 79 L i t e r a t u r e C i t e d . 81 Table, of I l l u ^ t r a ^ i o n q . F i g . Q 1. North s i d e of Mandarte I s l a n d • » 2. West s i d e of Mandarte I s l a n d 8 3. N e s t i n g - h a b i t a t of Double-crested C o r m o r a n t s " . 1° 4. N e s t i n g - h a b i t a t of Pelagic-Cormorant..* 1 1 5. R o o s t i n g - h a b i t a t of Brandt Cormorant........ ....11 6. Y e a r l i n g Double-crested Cormorant 15 7. A d u l t Double-crested Cormorant. 16 8. Y e a r l i n g P e l a g i c Cormorant... ...19 9. Brandt Cormorant p a n t i n g . .26 10. Brandt Cormorant f o o t i n s p e c t i o n .30 11. F l i g h t of the Double- c r e s t e d Cormorant.. 33 12. F l i g h t of the Brandt Cormorant... .33 13. P e l a g i c Cormorant s i g n a l l i n g b efore take o f f . . . . 36 14. Landing of P e l a g i c Cormorant 37 15. Landing of Double- c r e s t e d Cormorant. 37 16. t h r e a t d i s p l a y of the Do u b l e - c r e s t e d Cormorant..........45 17. A f t e r Hop D i s p l a y 46 18. A f t e r hop d i s p l a y of the Double- c r e s t e d Cormorant ..46 19. W i n g - f l i p p i n g d i s p l a y of the P e l a g i c Cormorant.... .47 20. W i n g - f l i p p i n g d i s p l a y of the Double- c r e s t e d Cormorant...47 21. W i n g - f l i p p i n g . . 47 22. R e c o g n i t i o n D i s p l a y .48 23. R e c o g n i t i o n d i s p l a y of the Dou b l e - c r e s t e d Cormorant 48 24. P e l a g i c Cormorant hopping away from the n e s t ......51 25. Nest r e l i e f of the Double- c r e s t e d Cormorant.... 60 26. Double-crested Cormorant c h i c k begging f o r food ....64 27. Double-crested Cormorant c h i c k being f e d . . . . . . 64 Acknowledgements Thanks are due to a l l those who have given me help and advice during the course of this study. They study was financed by the National Research Council of Canada and the Chapman Memorial Fund of the American Museum of Natural History, and was under the continuous guidance of Dr. I. McTaggart Cowan and Dr. M.D.F.. Udvardy. The fieldwork was made considerably easier by the help and hospitality of Mr. & Mrs. J. Rodd and Mr. & Mrs. R. Matthews of Sidney, B.C. and of Mr. & Mrs. L. Barker of Gooch Island, B.C. Dr. CC. Lindsey identified the fis h samples, and Mr. D.A. McCaughran identified the crayfish. The Canadian Wildlife Service and the Bird Banding Office of the United States Fish & Wildlife Service provided bird bands and birdbanding data. The B.C Nest Records Scheme provided nest record data. Mr. J. Takacs, Mr. D. Kennedy, and Mr. S. Shearman assisted with the f i e l d work. The East Saanich Band of Indians rented us the island for a nominal fee, and cooperated with the f i e l d work. The following persons helped me considerably with advice and information: Dr. J.R. Adams, Mr. R. Arbib, Dr. B. Baggerman, Dr. J.F. Bendell, Dr. G.C Carl, Mr. W.H. Gold, Mr. C.J. Guiguet, Dr. L. von Haartman, Dr. W.S. Hoar, Miss M. Jackson, Dr. A. Kortlandt, Dr. P.A. Larkin, Mr. W. McLaren, Mr. M.T. Myres, Mr. G.C. Odium, Mr. T. Piarse, Miss A.B. Redlich Mr. A. Stiven, Mr. E.D. Wood. 1 A Comparative Study of the Reproductive Behaviour and Natural History of Three Sympatric Species of Cormorants, (P^al„acrpC9r^x £±£±±MM, g. ^ ^ c ^ l j t u j , and g. £^J^iv,.) At Mandarte Island, B.C. Cormorants are a controversial bird. To some people they are a harmful predator on f i s h . To others they are an economic asset. In Japan, China and India lPhalia,q,^ ocii9lra,x ca^fro and g . cap^lla^s, have been trained since prehistoric time to fis h and and hunt for man. This practise has persisted in those regions to this day, and has become a highly skilled art. In Japan i t is also an important tourist attraction. (Gudger 1926, 1929.) The nesting colonies of F^ala.cr^p.rjx, boi|cja.i.ny,,!!!ei,' along the west coast of South America, and of g . flapensis on the west coast of Africa, support a multi million dollar guano industry (Murphy 1936.) In Florida special platforms are built on piles as roosts for g . aurjtus, by guano collectors. (Bent 1922.) 2 In many iso l a t e d coastal parts of the world, where sea-fowling i s practised, cormorant eggs,chicks and even adults are used as food f o r dogs, fur-farm animals and humans. The eggs we were used by early mariners, explorers and s e t t l e r s f o r soap-making. Eskimos employed the primaries f o r arrows and even now i n some parts of the Bering Sea area use the hides f o r making parkas. (Bent 1922, Lewis 1929, Murphy 1936, Williamson 1945, Stresemann 1948.) The feeding habits of cormorants have been a source of much controversy. Many fishermen claim, that because the d i e t of cormorants consists c h i e f l y of f i s h , the shags reduce t h e i r catch. Consequently i n many parts of the world the fishermen have des-troyed and shot up breeding colonies, and have persuaded t h e i r governments to i n s t i t u t e control programs. This has taken the form of bounties on cormorant heads (Steven 1933, Taverner 1915), and the spraying of eggs with o i l and other chemicals (Gross 1951.) The persecution and i n some areas extermination of cor-morants did not show a corresponding increase i n the harvest of f i s h , and i n some areas a decline i n the abundance of commercial and sport f i s h was noted. As a r e s u l t several studies on the food habits of f i s h were i n s t i t u t e d i n various parts of the world. The r e s u l t s of these studies showed, that cormorants feed predomin-antly on bottom dwelling coarse f i s h , which are considered a men-ace to the eggs of food f i s h e s , and that i n open water cormorants feed on dense schools of small f i s h e s . *4 - The conclusion of most authors on the subject i s , that the feeding of cormorants i s not detrimental to the fishing in-* dustry, and that the extermination of cormorants would do more harm than good, (van Dobben 1952, Lewis 1929, Mattingley 1927, McLeod & Bondar 1953, Mendall 1936, Munro 1927, Steven 1933, Taverner 1915.) In Ontario, Manitoba and other parts of the world where f i s h are caught in pound nets, extensive damage by cormor-ants has been reported. (B a i l l i e 1947, Ormand 1947.) This dam-age could have been avoided by not operating the traps during daylight hours. In Holland a small f l a t country, where trees are at a premium, the destruction of trees by nesting colonies of the Common Cormorant, Phalacrosorax fia^o. has become a problem. For not only do arboreal cormorants break of li v e branches for nest material, but their guano i s so strong, that a l l vegeta-tion i t strikes, i s k i l l e d almost immediately (van Dobben 1952, Kortland 1942.) The plumage of cormorants i s not waterproof (Lewis 1929.) This does not permit the cormorants to rests like other waterbirds on the water surface. However the removal of air from the plumage increases the specific gravity of the cormor-ants, and thus aids them during locomotion under water. Cormorants are therefore limited by their aquatic mode of feeding and their t e r r e s t r i a l mode of resting to a shore-line environment. Except for the above limitation their dis-tribution is worldwide (Alexander 1955.) 4 There are about 28 species of cormorant i n the world, amongst which, although they form a homogeneous group, h y b r i d i -zation has never been demonstrated, except for one doubtful i n -stance (Gray 1958). The exact number of cormorant species depends on the c l a s s i f i c a t i o n of the Blue-eyed Shags of the seas surrounding Antarctica, which i s s t i l l i n a state of confusion due to lack of evidence (Behn et a l . 1955, Murphy 1916, Reynolds 1935. ) The cormorants can r e a d i l y be separated into three groups: Cormorants, Shags, and Guanays. The words Cormorant and Shag are used i n the B r i t i s h meaning of those words (Seehohm 1885), and the word Guanay i s the Spanish name f o r PfaflflC^ofiorax, b o u a a n v i l l e i . which i s the main producer of commercial guano i n South America (Murphy 1936.) In the Cormorant group are included phjlflOTcorax carbo. P. auritus. P. c a p i l l a t u s . P. olivaceus. the entire genus Hjlftetjpy. and the f l i g h t l e s s flann^p+.e^up. ^ f r r ^ f i i . They a l l use s t i c k s i n t h e i r nest structure, nest b o t h i n trees and on the ground, and inhabit both inland as w e l l as marine areas. They prefereto f i s h i n shallow bays and estuaries (Taverner 1915, Steven 1933, Lack 1945.) Their chief c h a r a c t e r i s t i c i s that they are able to perch i n trees, and some of them on telephone wires. (Bartholomew 1942, 1943) and rigging of ships (Murphy 1936. ) Shags and Guanays never perch i n trees, and are only found inland as a r e s u l t of storms and fogs (Wigiesworth 1917, McKittrick 1928.) 5 The Shag group includes the long-tailed northern Shags (Seehohm 1885), Phalacrocorax flfftfllffllftAta- £• p e l a a i c u s -and P . u r i l e . and the southern s h o r t - t a i l e d Shags (Murphy 1936), p.tfflc^ f^ frifi arid £. p^m^rd^. The Shags prefer to feed along exposed rocky shorelines (Bent 1922, Murphy 1936, Steven 1933,) and nest underneath rock overhangs on the narrow ledges'and i n the c a v i t i e s of perpendicular c l i f f s (Alexander 1955, Dementjef 1951, Murphy 1936, Selous 1901 Steven 1933.) Their nests, which r a r e l y i f ever include any s t i c k s , and which consist mainly of hay and algae, are cemented to the rocks with the aid of guano. The Guanay group includes the Blue-eyed Shags of the Southern Hemisphere (Murphy 1936), the Brandt Cormorant of the west coast of North America and probably the recently extinct P a l l a s Cormorant, P. p e r s p i c i l l a t u s of the Bering Sea area (Lucas 1896.) The Guanays prefer to nest on wide c l i f f ledges and sheIfs, and on the f l a t tops of small islands and rock needles. Because of t h e i r nesting habits they are the most im-portant producers of recoverable guano. The Guanays are-charac-t e r i z e d by t h e i r habit of usually feeding i n open water i n large fl o c k formations on dense f i s h schools. The courtship and nesting behaviour has been described for one Shag, £. a r i s t o t e l i s by Selous (1901), two Cormorants, £. carbo by P o r t i e l j e (1927) and Kortlandt (1938, 1940, 1953) and J>. ^urfrfof by Lewis (1929) and Mendall (1936), and one Guanay, £. p e n i c i l l a t u s by Townsend (1925) and Williams (1942.) 6 In a l l the above studies only one cormorant species was studied by each author, and as a r e s u l t there have been very few attempts made to correlate i n d e t a i l the courtship of one cormorant to that of another i n a comparative way. Three species of cormorant occur i n the Puget Sound - Georgia S t r a i t region. Two of these the Double-crested Cormorant, JJ. a u r i t u s and the Pelagic Cormorant P,. p e l a a i c u s nest at Mandarte Island, 17 miles north of V i c t o r i a , B.C. The t h i r d , the Brandt Cormorant, P. P l ^ W f l ^ 1 " - though present at Mandarte Island throughout the summer, does not yet nest there. The presence of these three cormorants at Mandarte Island gave me the opportunity to study comparatively t h e i r natu-r a l h i s t o r y and breeding behaviour. The object of t h i s study has been to describe and compare the reproductive behaviour of the three cormorants species, which include a Cormorant, a Shag, and a Guanay, i n order that t h e i r phylogenetic connections and ecological divergencies might be better understood. 7 Methods, The cormorants were studied at Mandarte Island during the summers of 1957 and 1958. Most observations were made from blinds overlooking several cormorant nests* The blinds were constructed out of driftwood. Their locations were such, that they could be entered without flushing the cormorants from t h e i r nests. Other observations were made from the campsite and from a boat i n the waters surrounding Mandarte Island. Individual cormorants were recognized by t h e i r head plumage and i f banded by t h e i r band number. Cormorant chicks were banded during 1955 and 1956 by Mr. E.O. Wood and during 1957 and 1958 by myself at Mandarte Island. Thus known aged banded birds made i t possible to record the plumage of various age-classes. Nest predation by crows and g u l l s made the recording of nest success d i f f i c u l t . During 1957 the nests of 29 Double-crested and 37 Pelagic Cormorants were v i s i t e d one hour aft e r sunset every other night. This proceedure eliminated crow pre-dation, but did not e n t i r e l y stop g u l l predation on Double-crested Cormorant eggs. During these v i s i t s the eggs and chicks were weighed and measured. They were weighed i n a p l a s t i c bag suspended from a spring balance. The eggs were marked with a p e n c i l . Further nest success data was obtained, without f l u s h -ing the cormorants from t h e i r nests, by looking down into the nests from blinds situated above the nests. Mandarte Island i s located i n Haro S t r a i t , 17 miles Worth of V i c t o r i a , B r i t i s h Columbia. I t s l a t i t u d e i s 48° 38* North and i t s longitude i s 123° 17* West. I t has frequently been referred to as Bare Island. (Brooks & Swarth 1925, Munro 1928, Munro & McTaggart Cowan 1947, McTaggart Cowan & Guiguet 1956.) The i s l a n d i s h a l f a mile long and 200 yards wide ( f i g . 1 & 2.) At i t s highest point i t i s 75 feet high. I t i s composed of several sedimentary layers of calcarious sandstone and bands of f o s s i l i f e r o u s conglomerates. I t s long axis runs from southeast to northwest. The rock s t r a t a dip northeast wards. The long southwest shoreline consists of a 50 foot high escarpment, which i s very steep. This escarpment i s used by the cormorants f o r nesting and roosting. The cormorants also frequently perch i n the tops of several dead and l i v i n g Douglas F i r trees, situated i n a two acre woodlot on the northeast side of the i s l a n d . Most of the r e s t of the i s l a n d i s covered by grassy meadows and patches of barren rock, which are separated by g u l l i e s f i l l e d with dense tangles of, stunted Garry Oak, ftuercuf g^rr ya/H« Saskatoon Berry, Amelaqfttor s,pp., Wild Gooseberry, F^b^s, £&&£&£&m> Black berry, Rubus, ,sjffl.« and Wild .Roses, ga8§aJ5JflB. In spring the meadows are covered by Wild Radish, a f t e r page 8 F i g . 1. North s i d e of Mandarte I s l a n d . F i g . 2. West s i d e of Mandarte I s l a n d . ? The i s l a n d also abounds i n a l l the weeds normally found i n waste places. The c l i f f s used by the cormorants are devoid of any vegetation. Only one mammal, the Deer Mouse, Peromvscus M^n^u-,la^m inhabits the i s l a n d . Formerly, the Island was also i n -habited by the introduced European Rabbit, Qryc^lafl^s, c^n^c^l^s,. which died out, probably i n 1955. I t l e f t behind many burrows, which are now u t i l i z e d by Pigeon Guillemot and Tufted P u f f i n . Besides cormorants the following birds also nest on Mandarte Island: Glaucous-winged G u l l , frffllfMJ fllaucescens. 2000 p a i r s , Pigeon Guillemot, Cepphti^ ftolumfoa. 60 p a i r s , Tufted P u f f i n , fo&dj S t t f f j J H f a j 3 p a i r s , Black O v s t e r - c a t c h e r . BftfWI/l1i9lB.Hiq fa^fifo^flij.f. 3 P a i r s » Crow, Corytf§ br^ 9^yr^ 9 h f f ^ > 1 2 p a i r s , Common Red-wina. Aaela^u,^ ft^oenjiftfius. 6 p a i r s , Song Sparrow, Melosoiza melodya. 200 p a i r s , The islan d i s v i s i t e d p e r i o d i c a l l y by i t s owners, the East Saanich Band of Indians, who come to gather g u l l eggs and "sea eggs", the Long-spined Purple Sea Urchin, §&££Qaxi&&£&~ iftrgtjHfi ^ W B W M f • and to spearfish f o r Rock and Ling God. In former days the i s l a n d was t h e i r main gathering place f o r Camas bulbs, which used to be f o r them a source of sugar and starch. The base camp i s situated on the northeast side of the is l a n d . Travel along the i s l a n d was r e s t r i c t e d to the northeast shoreline to avoid disturbing the cormorants, which inhabit the other side. There are four basic types of s o l i d landing places used by cormorants on and around Mandarte Island, namely trees, c l i f f shoulders, c l i f f faces, and various objects near the water. Trees are only used by the Double-crested Cormorants at Mandarte Island. There they go i n to the tops of the Douglas F i r trees to court and perch during damp mornings, and to break o f f green twigs f o r nest material. The Double-crested Cormorants also nest i n trees at Channel and B a l l i n g a l l Island, which are only 12 and 20 miles away from Mandarte Island. The Double-crested Cormorants are r e l a t i v e l y clumsey at landing i n trees and often have to make 3 or 4 attempts, before they f i n a l l y land successfuly i n one. Normally the trees are occupied by g u l l s and crows, which leave h a s t i l y , when the cormorants s t a r t to land. The cor-morants i n turn leave the trees as soon as an eagle or a Great Blue Heron approaches the is l a n d , but t h i s may be due to the g u l l s sounding alarm c a l l s . A l l three species of cormorant, as well as the g u l l s use the c l i f f shoulders. The Glaucous-winged G u l l s are highly t e r -r i t o r i a l and claim almost a l l f l a t open areas including the c l i f f shoulders f o r nesting space. At Mandarte Island, gradually ex-panding colonies of nesting Double-crested Cormorants are r e -placing the g u l l t e r r i t o r i e s just below the crests of some of the c l i f f shoulders. ( F i g . 3.) F i g . 3. N e s t i n g - h a b i t a t of Double-crested Cormorants 11 The large nests of the Double-crested Cormorant are found i n small dense c l u s t e r s , only one cormorant-length apart. The fringe area around these nests i s used as a communal perch-ing area by a l l three species of cormorant. As the colony slowly increases i n size the Double-crested and Brandt Cormorants, which roost and court i n the fringe area, push back the adjacent g u l l t e r r i t o r i e s . This ex-pansion often leads to v i o l e n t f i g h t s between g u l l s and cormor-ants, during which a single g u l l may attack as many as six cormorants at the same time. The Pelagic Cormorants shy away from any f i g h t s and perch on the steep c l i f f faces j u s t below the Double-crested Cormorant nests. At the communal perching areas the status of the Double-crested and the Brandt Cormorants i s almost equal, except that the Brandt Cormorants tend to se l e c t the small f l a t dust covered rock shelves, whereas the Double-crested Cormorants prefer the rougher, more broken parts of the c l i f f shoulders. The narrow ledges on the faces of the 20-60 foot high v e r t i c a l c l i f f s of Mandarte Island are the prefered nesting and roosting s i t e s of the Pelagic Cormorants ( f i g . 4.) On the same faces the Brandt Cormorants use the wider rock shelves and the tops of the rock needles ( f i g . 5.) The Double-crested Cormor-ants avoid the c l i f f faces almost e n t i r e l y . 12 The Pelagic Cormorants prefer to nest and roost under-neath rock overhangs and many of their nests are found inside rock fissures and alcoves. As an exception, in 1958 one lone, but successful, Double-crested Cormorant nest was found on a narrow ledge in the middle of a row of Pelagic Cormorant nests underneath a large rock overhang. Near the water level there are a great number of diverse objects used as temporary perches. They include such objects as rocks, boulders, poles, reefs, floats, buoys, floating logs, etc. A H these objects have in common, that they are close to the water and that they provide firm and unobstructed perches for the cormorants to rest on before and after fishing. A l l three species mix freely on the perches and make equal use of them. These perches are the site for perch right contests and some incipient courtship (Bartholomew 1943, Kortl-landt 1938.) P,iUfla.qe and Cormorants are not sexually dimorphic in the colour and structure of their plumage and unfeathered parts* Double-crested and Pelagic Cormorants are polymorphic in their nuptial and almost monomorphic in their non-nuptial plumage. Brandt Cormorant on the other hand are monomorphic in both their nup-t i a l and non-nuptial plumage. Neither the pre-nuptial nor the post-nuptial molt includes a flightless period, and in practise cormorants are in almost continuous molt throughout the year. An attempt was made to discover constant f i e l d charac-ters, which would aid in the determination of age and species of immature cormorants. This i s a point on which some of the f i e l d guides are quite confusing and to some extent misleading (Alexander 1955, Peterson 1941, Pough 1957.) The plumage descriptions for the Double-crested Cormorant and the Pelagic Cormorant are based on banded birds of known age. Unfortunately there were no banded Brandt Cor-morants at Mandarte Island. 14 The chick j u s t a f t e r hatching i s naked and the eyelids are closed. I t s colour i s pink and only the growth buds of the remiges and r e c t r i c e s give any hint of future feathers. During the next week the skin colour darkens as the chick starts to grow. The throat patch however remains f o r the most part pink. The eyes s t a r t to open on about the fourth day. Black down be-gins to cover the chick from the body upwards and the head i s the l a s t part to be covered by down. The feet become black and remain that way throughout l i f e . Hqtal piipao,?. During the second and t h i r d week the natal down, which i s black, becomes thicker and i s stained grey with guano dust. The down on the head remains sparce. The juvenal plumage i s acquired gradually and reaches completion during the seventh week. The r e c t r i c e s and remiges develop f i r s t , followed by the wing and t a i l coverts, the contour feathers of the upper and lower parts, and f i n a l l y the neck and head feathers. The gular pouch acquires i t s yellow colouration from the lower jaw down-wards. The colour of the juvenal plumage i s as follows: Head feathers - pale brown. Gular patch - yellow with i r r e g u l a r black patches. P o s t - o r b i t a l patch - yellow. P r e - o r b i t a l patch — eithe r black, white or yellow. I r i s - brown. Mouthlining - f l e s h colour. Neck - s i l k y grey brown. Upperparts - brown. Underparts - vermiculated brown and white. Rectrices - black, sometimes with brown t i p s . Remiges - black. Wing converts - slate grey with black edges. This plumage i s acquired during the f i r s t winter and during May i t i s as follows: Head feathers - pale brown to pure black, usually a mottled mixture of various shades of brown and black. Nuptial crests - when present eit h e r black or white or both, always shorter than 10 mm. i n length. u Naked areas of the head - yellow to orange. I r i s - either brown or green. Mouth l i n i n g - f l e s h colour to yellow to pale blue. Neck - pale brown to black, usually a mottled mixture of white, brown and black. Upperparts - eithe r black, or brown, or both. F i g . 6. Y e a r l i n g D o u b l e - c r e s t e d Cormorant. Underparts - white and brown to pure black, usually an irregular quiltlike pattern of white, brown, and black blatches Rectrices - either black or brown* Remiges - either black, or brown, or both* Wing converts - either buff with brown edges or slate grey with black edges. Alula - always brown* During the course of the summer the post-nuptial molt replaces the body coverts, parts, the rectrices and remiges with black feathers. The wing converts are replaced by slate-grey feathers with^black edges. 01) the t a i l the inner most rectrices are re-placed f i r s t , next the outer most and f i n a l l y the remainder. Head feathers - black* Nuptial crests - either black, or white, or both; vary in length and density, proportions of black and white; situated on both sides of the. head above the eyes* Naked areas of the head - yellow to orange* Ir i s - green. Mouthlining - pale irridescent blue. Neck - black with few or no nuptial plumes. Upperparts - black. Underparts - black. Rectrices - black. Remiges - black. a f t e r page 16 Wing converts - slate-grey with black edges. Alula - black. The nuptial crests are lost shortly after egg laying. During the incubation period head and neck become pale brown. The bleaching starts from the head down wards and in July and August extends down to the anterior part of the body. The wing and t a i l feathers are replaced gradually during the course of the summer. Unmated cormorants tend to molt much later than mated ones. 18 The chick at t h i s age i s i d e n t i c a l to that of the Double-crested Cormorant, as described above. From the f i r s t week onwards a purple-grey down st a r t s to cover the chick. As t h i s down thickens a white under down i s developed. The head remains almost naked u n t i l the juvenal plumage develops. The down forms a thick r u f f around the neck, which p e r s i s t s , u n t i l the chick i s ready to leave the nest. The throat patch remains pink. The feet become black and remain that way throughout l i f e . As i n the Double-crested Cormorant the juvenal plumage i s acquired gradually and reaches completion during the seventh week. At 3-4 weeks old the remiges and r e c t r i c e s are well de-veloped. During the 4th and 5th weeks the contour feathers develop. During the 6th week the upper neck and head are covered by a thi n grey down and are s t i l l r e l a t i v e l y naked. A f u l l des-c r i p t i o n of the juvenal plumage i s as follows: Head feathers - grey. Gular patch - pink. I r i s - brown. Neck - grey and black. Upperparts - black, with violet-green iridescence. Underparts - black. Rectrices - black. Remiges - black. Wing coverts - black. This plumage i s acquired during the f i r s t winter and during May i t i s as follows: Head feathers - brown. Crest t u f t s on crown and nape - absent. Naked areas of the head - ei t h e r black or red. I r i s - brown. Mouth l i n i n g -red. Neck - dark brown. Remainder of body feathers - dark brown. During the summer the plumage i s gradually replaced by black feathers i n a sequence s i m i l a r to that described f o r the Double-crested Cormorant. Whilst t h i s i s i n progress the b i r d has a piebald black and brown appearance. This plumage i s acquired during the second winter and in May i t i s as follows: Head feathers - e i t h e r black, or brown, or both. Crest t u f t s on crown and nape - short. Naked areas of the head - eithe r black or red. I r i s - brown. Mouth l i n i n g - red. Neck and remainder of body feathers - either black, or brown, or both. A l u l a - always brown. after page 19 20 The flanks of the rump are pale brown with a few white plumes ou t l i n i n g , where the rump patches w i l l be i n the adult. During the course of the summer most of the plumage i s replaced by black feathers. The black feathers of the nuptial as well as the non-nuptial plumage have a violet-green i r r i d e s c e n t sheen. Head feathers - black. Crest t u f t s on crown and nape - long. Naked areas of the head - red. I r i s - green. Mouth l i n i n g - red. Neck and remainder of body feathers - black. White n u p t i a l plumes are i r r e g u l a r i l y dispersed over the head, neck and upperparts. On both sides of the rump there are dense white patches of short nuptial plumes. During the course of the post-nuptial molt the nuptial plumes of the head and neck are l o s t shortly a f t e r egg la y i n g . During incubation the feathers of the head and neck, and e s p e c i a l l y the cre s t s , turn a coppery bronze colour. The nuptial plumes of the rump patches disappear shortly a f t e r the eggs hatch. Most of the plumage i s gradually replaced by black feathers during the course of the summer. 21 Head feathers - brown. Nuptial crests - absent. Naked areas of the head - v i o l e t - p u r p l e . I r i s - brown. Mouth l i n i n g - b l u i s h pink. Neck - pale brown. Upperparts - brown. Underparts - brown, with buff Y shaped pattern covering sternum and coracoids. Remainder of body feathers - brown. During the course of the summer a l l feathers are r e -placed by dark brown feathers and the Y shaped pattern i s l o s t . Head feathers - black. Nuptial crests - long and white, one p a i r on the cheeks and another p a i r on the rump. Naked areas of the head - eith e r blue or v i o l e t - b l u e , usually hidden. I r i s - blue. Mouth l i n i n g - eith e r blue or v i o l e t - b l u e . Throat feathers - e i t h e r white or buff. Neck and remainder of body feathers - black. During the post-nuptial molt the nuptial crests of the head are l o s t at the end of June and those of the rump at the end of J u l y . The plumage i s replaced by black feathers. When i n t h e i r nuptial plumage the various species* age classes and in d i v i d u a l specimens of cormorants are most diver-gently coloured and feathered. This nuptial polymorphism i s le a s t developed i n the Brandt Cormorant, and tends to disappear during the post-nuptial molt. When observing cormorants i n the f i e l d the throatpatch i s diagnostic. I t i s large and coloured yellow or orange i n the Double-crested Cormorant; normally hidden and coloured v i o l e t or blue i n the Brandt Cormorant; and small and coloured red or black i n the Pelagic Cormorant. In p r o f i l e the head of the Double-crested Cormorant i s large and angular above, the head of the Brandt Cormorant small and sleek and rounded above, and the head of the Pelagic Cor-morant small and angular above, and accentuated by the crests of the adult. The nuptial plumes, which are of a tr a n s i t o r y nature, can only aid i n confirming i d e n t i f i c a t i o n when they are present. The r e l a t i v e darkness of the underparts i s useless and misleading as a f i e l d i d e n t i f i c a t i o n character. The Y shaped pattern on the breast of the Brandt Cormorant i s diagnostic how-ever, The colour pattern of the underparts helps i n d i s t i n g u i -sing juvenile from yearling Double-crested Cormorant and i n dis t i n g u i s i n g between the yearlings of the three species. The wing coverts of the Brandt and the Pelagic Cormor-ants are uniformly coloured, where as the wing coverts of the Common and the Double-crested Cormorant have dark edges and thus are scaly i n appearance. This may be a taxonomic character separating the arboreal Cormorants from the marine Shags and Guanays (Seehohm 1885.) The scaly appearance of the Cormorant's wings may a c r y p t i c pattern resembling leaves of a tree. The colour of the a l u l a i s a useful aging c r i t e r i o n . Vp^cj The Brandt Cormorant is the least vocal of the three cormorants on the west coast of North America (Williams 1942.) It has only one c a l l "Br-r-r Br-r-r", which i t uses in many diverse situations, for which the other two species have de«* stinct c a l l s . The calls of the Double-crested Cormorant are: "Urg urg urg M - just before landing. " T - t - t - t - t - t " - just before take off. MEh-hr eh-hr eh-hrM - during threat. " A r r - r ^ r ^ r - t - t - t - t " - during recognition display. "Ugh^ugh-ugh0 - during wing flipping. "Uhr-uhr-uhr" - just before feeding older chicks. A roar - just after a hop. The calls of the Pelagic Cormorant are: Eeeh eh" - when flying away from the nest. ,,Eh-eh-ehtt - just before landing. "Wr-r-r Wr-r-r" - during threat. "Arr arr arr" - during recognition display by male. "Igh-ugh Igh-ugh" - during recognition display by female. "Ohw" - after landing or completing a hop. The chicks of the Double-crested and Pelagic Cormor-ants chirp for food and hiss in defence. The use and function of the above calls w i l l be des-cribed in detail later together with the movements and displays they are part of. A l l three species have a coughing sound which i s made on land as well as i n the a i r f o r no apparent s o c i a l reason. I t may be either a true cough i n that i t i s used to dislodge an i r r i t a n t from the windpipe, or i t may be an evacuation of g a s t r i c gasses. When at r e s t the cormorants stand with the long axis of the body more v e r t i c a l than h o r i z o n t a l . The long neck i s held i n an S shape and beak i s t i l t e d s l i g h t l y upwards. The cormorants tend to face into a strong wind. The Pelagic Cormorants however on the perpendicular c l i f f faces, must almost always of necessity face into the c l i f f in order to f i n d room f o r t h e i r t a i l s * In the trees the Double-crested Cormorants use t h e i r wings and t a i l s to steady themselves on the swaying branches. On hot s t i l l days and during digestion the cormorants increase t h e i r body surface by holding the bend of the wings away from the body while the wing t i p s remain folded over the t a i l . At the same time the throat and esophagus are increased to t h e i r f u l l e s t extent ( f i g . 9.) and the hyoid arch i s made to vibrate r a p i d l y . This v i b r a t i o n of hyoid arch has been noticed by most observers and some of them were led to believe, that t h i s behaviour i s peculiar to cormorants. However as P o r t i e l j e (1927) points out, and I have observed f o r myself, i t i s a common phenomenon, which occurs i n most b i r d species, though i t i s most r e a d i l y observed i n cormorants. "Panting 1* i s the best word to describe i t , as i t i s analogous i f not homologous to the f a m i l i a r panting of mammals. a f t e r page 26 F i g . 9 . Brandt Cormorant p a n t i n g . During cold weather cormorants tend to reduce t h e i r body surface area as much as possible. One leg i s curled up and often tucked into the ventral feathers. The neck i s folded back and the beak i s put underneath one of the wings. The eyes however usually remain f r e e . In both the above postures the head i s kept r e l a t i v e l y s t i l l and often the cormorants close t h e i r e y e l i d s . This i s the reason, why the cold weather posture has been c a l l e d the sleeping posture by several authors (Heinroth 1955, Kortlandt 1938, Lewis 1929, Mendall 1936.) A l l intergradations between the above two extremes of posture can of course be observed, depending on the temperature of the a i r and the body temperature of the cormorant. Bathing follows most activities of cormorants* It is also used on hot days for cooling and after rain showers for removing mud and g r i t which has been splashed into the feathers. The method of bathing i s the same in most birds but looks more impressive in a large bird such as a cormorant. When bathing the body r o l l s back and forth in a rocking-horse motion, while the wings splash loudly on the water throwing a spray on to the back of the bird. Afterwards the cormorant l i f t s inself v e r t i -cally above the water surface and beats i t s f u l l y extended wings back and forth. This beating of the wings is repeated after the cor-morant lands again on a solid object after having been on the water, but instead of folding the wings back into place at the completion of the movement, they are l e f t hanging out to dry for a variable length of time. This allows for the evaporation of the residual moisture from i t s oily, but not impervious, feathers (Gudger 1929, Heinroth 1955, Lewis 1929.) Preening usually occurs while a cormorant stands up-right, but to a limited extent also when i t is incubating, and i t frequently accompanies wing-drying. Some preening move-ments are usually made at the end of each activity. The preening behaviour i s basically identical in a l l birds. In cormorants a l l feathers within reach of the b i l l are groomed with the aid of the b i l l . Both the b i l l and the back of the head are used in applying the secretion of the o i l gland to the feathers. The feathers of the head and neck are preened d i -rectly (Heinroth 1955, Lorenz 1958) by a rapid scratching movement of the foot. After a period of rest cormorants perform various stereotyped stretching movements, which closely resemble those of other birds. (Heinroth 1955, Kortlandt 1938.) Upvyard^ TOq-stre^h During this movement the folded wings are l i f t e d up-wards and are held parallel to the body while the head and t a i l are depressed. The body i s held in as horizontal a position as the perch of the cormorant w i l l permit. The function of the upwards wing-stretch i s probably to reactivate the pectoral muscles. O n e s i d e d , s t r e t c h In this movement the wing, leg and t a i l feathers of one side only are stretched outwards and backwards. Its function i s probably to activate the limb muscles. Fyfrt JM3<fM9n (Tfrnbergefl During this posture the neck i s bent over sideways and the head i s held with the beak pointing downwards ( f i g . 10.) It probably serves to stretch the neck muscles. Back^ayfls ,fPQlj-S^aJStaq During this movement one leg i s stretched horizontally backwards and the foot i s shaken rapidly. This movement often occurs after head-scratching and was once initiated by another cormorant niblig at the foot of a dozing cormorant above i t . It may either serve to return blood to the foot or to remove ectoparasites. a f t e r page 30 F i g . 10. Brandt Cormorant - Foot i n s p e c t i o n . 31 Cormorants always defecate downhill and no attempt i s made to avoid h i t t i n g birds located lower down the c l i f f . Un-fortunately the guano of c l i f f nesting cormorants i s washed away by r a i n and i s of no commercial value. Cormorants were never observed to defecate i n mid a i r as i s a common practise of g u l l s . When on the water surface cormorants c h a r a c t e r i s t i -c a l l y defecate backwards, a f t e r which they paddle r a p i d l y f o r -wards leaving a white cloud behind them i n the water. P e r i o d i c a l l y the mucous membrane of the stomach i s shed and envelopes a p e l l e t of stones, f i s h bones and c r a y f i s h c u t i c l e s . (Van Dobben 1952, Lewis 1929) This p e l l e t i s sub-sequently ejected through the mouth. At Mandarte Island cormorant p e l l e t s are r a r e l y found because the g u l l s pick them up almost as soon as they are dropped. However four miles away at Greig Island, which i s too bleak even f o r g u l l s to nest on, cormorant p e l l e t s were found to be quite common. Frequently a clear f l u i d can be seen dripping.from a cormorant's beak (Lewis 1929.) In the Double-crested Cormorant t h i s i s sometimes quite profuse and they sometimes f l i c k i t away i n four foot sprays. The function of t h i s drooling i s the removal of s a l t by the s a l t gland. (Schmidt-Nielsen et a l . 1957-1958.) . . „ -m, , . -32 Cormorants w i l l f l y a half mile circle rather than walk 50 feet. Of the three cormorants the Brandt Cormorant i s the most adapt at walking on land. A l l three species waddle with their bodies more vertical than horizontal. Sometimes the wings are used for balance. B B B a B M B B B B H On steep ground the beak i s used as a grapnel. The neck i s stretched upwards and the hook of the upper mandible is lodged,in a crevasse, whereafter the neck muscles pull up the rest of the body, aided by the clawed feet grabbing onto toe holds. This behaviour i s best seen in juveniles but also occurs less frequently in adults. Swimming,. When swimming most of the body is submerged beneath the water surface. The t a i l i s sometimes underneath and at other times above the surface. The neck i s held vertical and beak is usually tipped slightly upwards. An alternating leg-beat i s used for propulsion. Diyincj. •.„•=-.> 5 r • Cormorants only dive from the water surface. A dive is started by l i f t i n g most or a l l of the body out of the water in order to gain the i n i t i a l momentum for going down. The smaller cormorants such as Phalacrocorjuc, j£|jMIS^§» £• pe l a g i c ^ and £. penicillatus, jump out of the water before each dive. The larger £. ^agbj and £. J j J ^ U j on the other hand us-ually glide under the water surface without l i f t i n g the entire body out the water (Bierman 1955.) The propulsion under water i s by using the feet side by side together in a dolphin kick (Lewis 1929, Portielje 1927.) The wings are held somewhat away from the body and are used for steering but not for propulsion. Immediately after emerging from a dive a cormorant stretches i t s neck and looks around warily. It i s when cormorants f l y past that the morphological differences between the three species show up best. The rela-tive postures of head and neck and the differences in wing and t a i l lengths are most striking. The Double-crested Cormorant, which i s the largest of the three, has a long t a i l and short wings, and retracts during fl i g h t the neck upwards ( f i g . 11.) The Brandt Cormorant, which is intermediate in size, has a short t a i l and short wings, and retracts during f l i g h t the neck downwards ( f i g . 12.) The Pelagic Cormorant, which is the smallest, has a short t a i l and short wings, and stretches during f l i g h t the neck straight forwards. Soaring i s relatively rare in cormorants. However when there is a strong SW wind hitting the c l i f f s of Mandarte Island, the Double-crested Cormorants and less frequently the other two species w i l l join the Glaucous-winged Gulls soaring back and forth on the air updrafts. F i g . 11. F l i g h t of the Double-crested Cormorant 34 Also after flying over land the Double-crested Cormorant glide down to just above the water level before con-tinuing i t s f l i g h t movements. Often short glides are made when cormorants are flying in flock formation. Cormorants sometimes travel great distances, includ-ing round trips of upto 100 miles (Behle 1958), in order to feed. During their daily feeding trips and during migration cormorants flying in the same direction tend to join each other and form large flocks and aggregates of flocks consisting often of more than one species (Bartholomew 1943, van Dobben 1952.) These flocks form orderly V shaped formations similar to those of other waterbirds. The flocks break up as haphazardly as they are formed, each cormorant leaving a flock as near to i t s destin-ation as possible. Brandt and Pelagic Cormorants tend to follow shore-lines in their travels and never f l y overland, nor make short-cuts across islands and peninsulas. The Double-crested Cormorants frequently f l y overland and across islands. This is a good f i e l d identification clue. 35 •lato'M. °. f f frnA A l i g h t i n g on Wa^er. Both the take off and the touch down of cormorants occurs into the wind. The take off from water is quite cumber-some and some times f a i l s in rough weather when the water i s too choppy. The feet as well as the wings are used to gain momentum. Usually the wings hit the surface about a dozen times before the cormorant i s clear of the water, and in the a i r . Cormorants touch down on water like ducks, in that they skid on the water surface with their feet, while their wings beat back and forth in order to reduce speed. This i s in contrast to gulls, which hover before alighting on water. Taking of^ and Alighting on land. When not alarmed cormorants normally signal before taking off, and after landing near other cormorants. These signals are as species specific as some morphological character-i s t i c s . Before taking off a cormorant stretches i t s neck and points i t s head in the direction i t wishes to go. The wings are pressed close to the body in preparation for spreading them. The feet remain were they are and often point in a direction opposite to where the cormorant intends to go. This expecially true for Pelagic Cormorants perched against a c l i f f side. As the head and neck are stretched out prior to taking off the following signals were observed: The Double-crested Cormorant inflates i t s head and neck, and makes a " T - t - t - t - t - t 1 1 sound through i t s almost closed b i l l . The Brandt Cormorant deflates i t s head and neck. The Pelagic Cormorant opens i t s mouth wide, and thus displays the red mouth lining. (Fig. 13.) Kortlandt (1938) found the Common Cormorant to signal by depressing the tongue inside the almost closed mouth and by making a "Kro-kro" sound. After flying down from a perch cormorants lose con-siderable altitude. During this descent the Pelagic Cormorant sometimes makes an MEeeh-eh w c a l l note as i t passes closely over the heads of cormorants perched lower down the c l i f f . a f t e r page 36 F i g . 1 3 , P e l a g i c Cormorant s i g n a l l i n g b e f o r e t a k e o f f . 37 Before landing, cormorants depress the tongue and the following calls were heard: "Urg-urg-urg" - Double-crested Cormorant. "Eh-eh-eh" - Pelagic Cormorant. "Br-r-r-r Br-r-r" - Brandt Cormorant. "Kro-Kro" (Kortlandt 1938) - Common Cormorant. just before landing a cormorant f l i e s directly at a point below were i t intends to land. Just before reaching i t , the cormorant sweeps upwards with i t s feet extended. Brandt and Pelagic Cormorants land with their bodies vertical, the neck arched forwards and with the b i l l pointing downwards (fig.14.) Double-crested Cormorants on the other hand land with the body at a 45 degree angle and their necks remain in a retracted S shape ( f i g . 15.) After touching down the head i s slowly raised and the following postures were observed before the cormorants relax. The Double-crested Cormorant gives forth a roar and holds the head horizontally slightly below the arched and in-flated neck. The Brandt Cormorant inflates the head and neck and thus flashes the blue throat patch. The Pelagic Cormorant makes an "Ohw" sound and deflates the head and neck. Kortlandt (1938) found that the Common Cormorant gives forth a roar and inflates the head and neck. In addition the Common Cormorant raises the nape feathers and the feathers covering the coracoids. a f t e r page 37 F i g . 15. Landing of Double-crested Cormorant. Alarm. ,Be^aylgur. At Mandarte Island the cormorants are usually alerted by the alarm calls of the gulls. When alarmed a cormorant brings the wings close in to the body, and stretches the neck upwards as much as possible. The head becomes very mobile and turns from side to side. Alarmed Double-crested Cormorants make collectively sounds, which resemble static on a radio. When the danger comes closer they f l y onto the sea, where they form dense rafts. They do not signal their depar-ture as they normally do when not alarmed. The immature and those cormorants, which are not on nest duty, flush long before those, that are on nest guard. Usual causes for alarm are tourists v i s i t i n g the colony, Indians collecting gull eggs, fishing boats close under the c l i f f s , and last not least ornithologists at work. Even excitment caused by a gull fight or a Great Blue Heron flying over head w i l l alert the cormorants. Blasting at the Malahat Highway 14 miles away was noticed to alert Pelagic Cormorants. Once a Pelegic Cormorant was seen to raise i t s crest tufts when a gull swooped suddenly over i t s head. Once the cause for alarm i s ever the cormorants circ l e in front of the c l i f f s several times before landing, and the f i r s t ones that return often do not signal their arrival, though the later arrivals are very vociferous and elaborate in their signalling. 39 Much has been written about the severe predation on cormorant eggs by gulls and crows (Bent 1922, Finley 1905, Ray 1904, Townsend 1925, Mendall 1936.) No cormorant eggs are lost unless the cormorants have been chased off their nests by man or an eagle. When a nest is l e f t unguarded crows w i l l alight at the nest, peck a dumb-bell-shaped hole in the shell of an egg and use the hole to pick up the egg and f l y away to safety. The gulls on the other hand either swallow an egg whole or hold i t transversely in their beak. In the later case they often smash the egg shortly after-wards in mid ai r . Gulls also w i l l pick up and swallow cormorant chicks which are less than one week old. The Pelagic Cormorant nests, which are situated inside the alcoves and rock crevasses of the vertical c l i f f s are us-ually best protected against gull and crow depredations. The crows only threaten the nests during the day time but the gulls are even able to rob the exposed Double-crested Cormorant nests at night. Cormorants when alarmed, and also when feeding their chicks, w i l l frequently drop f i s h particles around their nests. This habit has led to a considerable amount of scavenging and food parasitism by gulls and crows. Gulls and crows patrol the cormorant nests continually for food, and each part of the c l i f f s at Mandarte Island i s covered by a crow at least once every five minutes. 40 Sometimes a cormorant w i l l regurgitate a fi s h in order to turn i t around inside i t s gullet. When this happens the neck becomes lumpy as the fish i s brought up. If a gull sees this, i t may "buzz11 the cormorant, and several gulls and crows w i l l charge down to feast on the mass of fish the startled cormorant coughs up. Similarily a gull may annoy a cormorant, which has just caught a f i s h , until i t leaves i t s meal behind. Gulls and crows are an asset to a cormorant rookery, in that they keep i t relatively free of rotting f i s h . The crows also help in the removal of f l i e s and maggots. 41 ^ f f ^ n ^ D ^ n ^ ^ t o Befray3,our. The food of cormorants i s entirely aquatic and con-sists chiefly of fi s h and decapods, though amphibians are also occasionally taken (van Dobben 1952, Lewis 1929, Mattingley 1927, McLeod & Bondar 1953, Mendall 1936, Munro 1927, Steven 1933, Taverner 1915.) At the end of July and the beginning of August of 1957 and 1958, while banding Double-crested and Pelagic Cormorants, samples of food regurgitated by nestlings were collected, and included the following species: for the Double-crested Cormorant, the Three-spined Stickleback, Gasferosfeus, aculeal^s. the Saddled Blenny, P^gy j the Bracketed Blenny, P h q l ^ laetus. the Pen-point Bleuny, ApgdirC^thus fJta3gdj4S, the Eel Blenny, Lumjpenus anqu^llaris. the Cabezon, Le^^o^qs, jx j&£uj, and for the Pelagic Cormorant, Blennies, Xiphisteridae, Shrimps, Pandalus sop. A l l the above fishes are non-commercial bottom-dwelling species (Clemens & Wilby 1949.) Only,the shrimps are of some commercial importance. Like many other waterbirds cormorants swim for a while with their eyes under water before feeding. They do not feed at night and rarely at dusk. 42 Odium (1950) records an instance of a Pelagic Cormor-ant attempting to steal a large f i s h from a Brandt Cormorant, which was having d i f f i c u l t i e s with i t . Cormorants also some-times pick up fis h dropped at nesting colonies by Pelicans (Lewis 1929.) Each of the three cormorant species at Mandarte Island has own preferred feeding method and habitat. The Double-crested Cormorant prefers to feed in muddy bays and estuaries. There i t feeds either singly or in large flocks across narrow channels in the out-going tides. Sometimes i t joins feeding flocks of gulls and Brandt Cormorants feeding on schools of fis h in open water. Lewis (1929) records Double-crested Cormorants being attracted to fis h schools by terms. The Brandt Cormorant normally feeds on surfacing f i s h schools in large flocks of a hundred or more birds in open water. It is guided to these schools by Glaucous-winged Gulls hovering over fish* which have been driven to the surface by Common Murres, ffffjia ^alqe. Sometimes a flock of Brandt Cormor-ants feeds in a long line at right angles to a shoreline. When not fishing the Brandt Cormorants s i t on intertidal reefs and wait for the gulls to point out a f i s h school for them. The Pelagic Cormorant usually feeds singly in the intertidal zone of rocky shorelines and also in the surf besides c l i f f s , which drop vertically down into the depths of the sea. 43 When feeding in flock formation a l l cormorant face the same direction and swim and dive parallel to each other in close proximity (Bartholomew 1942.) The front rank dives* while the next rank bathes and keeps the water in continual turmoil, and the rear rank consists of stragglers, which when they lag too far behind take off and land in front of the flock. Near Mandarte Island the flock is usually led by a dozen or more murres, and several Glaucous-winged and Heerman's Gulls hover expectantly overhead. Because of i t s solitary diving behaviour i t was possible to time the Pelagic Cormorant, while i t was fishing in the in-tertidal zone of the north east shoreline of Mandarte Island. Of 65 dives the longest time under water was 70 seconds and the average time under water was 31 seconds. The average time in between dives was 14 seconds. The diving qoutient, which i s the time of the dive divided by the time of the pause between dives was 2.2. The longest diving time recorded for the Double-crested Cormorant is 70 seconds (Munro 1927.) Groebbels (1932) gives the diving quotient for the Common and the Green Cormorant as 2.8. During a single sequence of 17 dives a Pelagic Cormor-ant was seen to come up with a f i s h four times. Many fishes may however have been swallowed under water (Gudger 1929.) Birds fight for two reasons. There are fights for a specific nest or territory, and there are boundary disputes be-tween owners of adjacent nests or t e r r i t o r i e s . In the f i r s t case the antagonists tend to fight to the bitter end where as in the second case the fights tend to become stylized and incon-clusive. Cormorants when fighting for a nest grab each other with their mandibles often locking beaks, and try to force each other off the nest. Sometimes they draw blood during these contests (Kortlandt 1938.) The victor afterwards i s usually quite exhausted and a Pelagic Cormorant was observed to be im-mobile for ten minutes after a prolonged fight. The threat movements and calls made during squabbles between cormorants, which are perched beside each other or have adjacent nests are quite species specific. These movements have in common the following characteristics: The body is held as close to the ground as possible, which results in i t being horizontal when the cormorant i s on either a nest or a horizontal surface, but almost vertical in a Pelagic Cormorant perched on a c l i f f face. The wings are partly spread out and held close to the ground. The head i s oriented towards the opponent. ^5 The movements, though conforming t o a s p e c i e s s p e c i f i c p a t t e r n , are r a p i d and r e t a i n a h i g h degree of spon t a n e i t y and v a r i a b i l i t y . When t h r e a t n i n g the three cormorants a t Mandarte I s l a n d d i f f e r as f o l l o w s : The Do u b l e - c r e s t e d Cormorant s t r e t c h e s out i t s neck and snakes i t s widely-opened mouth a t i t s opponent, w h i l e i t h i s s e s f o r t h an "Eh-hr eh-hr eh-hr"sound ( f i g . 1 6 ) . The Brandt Cormorant throws i t s head r e p e a t e d l y from i t s back towards i t s opponent; w i t h the b i l l c l o s e d and the t h r o a t somewhat i n f l a t e d . When the head i s c l o s e s t to the opponent and j u s t b e f o r e i t i s withdrawn, the head i s shaken, a snapping movement i s made w i t h the b i l l and a> " B r - r - r B r - r - r " sound i s emitted. The P e l a g i c Cormorant moves i t s head up and down and shakes i t a t the same time w i t h the r a i s e d and c l o s e d . At the same time i t u t t e r s a g a r g l i n g , p l a i n t i v e , "Wr-r-r Wr-r-r" sound. A l l t h ree cormorants i n t e r r u p t t h e i r t h r e a t s w i t h n e s t t o u c h i n g movements, which are a l s o made when there I s i no nest p r e s e n t . The: above t h r e a t s are made not o n l y i n t r a -s p e c i f i c a l l y , but a l s o i n t e r - s p e c i f i c a l l y towards crows, g u l l s and other cormorant s p e c i e s . Sometimes the t h r e a t towards a pa s s i n g g u l l , crow or cormorant i n c l u d e s a wing f l a s h , which c o n s i s t s o f the wings being r a p i d l y opened outwards;:. The wing f l a s h i s a t h r e a t movement which i s a l s o used by other b i r d s such as g u l l s and crows. a f t e r page 4 5 F i g . 16. Threat d i s p l a y of the Double - c r e s t e d Cormorant. 46 The floR-The "Hop" is a common bisexual display of cormorants, which was f i r s t described by Selous (1901) for the Green Cor-morant, P^alacro^ora.x a r i ^ o f t e l i g . Since then i t has also been observed in the Common Cormorant by Portielje (1927), in the Brandt Cormorant by Townsend (1925), and in the Double-orested Cormorant by Lewis (1929.) The Hop is a symbolic and reduced f l i g h t . It consists of a hop, which is preceeded by the same display which preceeds f l i g h t and is followed also by the display which follows landing, most elaborately executed (figs. 17 & 18.) Sometimes the displays occur without the intervening hop (Kortlandt 1938, Townsend 1925, Williams 1942.) The displays are as previously described for take off and landing except, that the Brandt and Pelagic Cormorants orient their heads downwards prior to the hop instead of seawards as when about to f l y , and Kortlandt (1938) observed the Common Cormorant vibrating the coracoidal feathers after the hop. Selous (1901) found the posture after a hop in the Green Cormorant to consist of stretching and pointing the head and neck upwards, while the mouth i s held open, thus displaying the yellow mouth lining. The hop is performed throughout the year and in a variety of situations, as for example; perching-site contents (Bartholomew 1943* Kortlandt 1938), courtship, nestrelief, and during the gathering of nest material. a f t e r page h6 PARISTOTELIS A DAP TED FROM S £ L O U S 1901 R?ELAGICUS ADAPTED FROM PHOTO PPENICILLATUS AOAPTEO FROM W I L L I A M S 1942 PAURITUS AOAPTEO FROM PHOTO PCARBO ADAPTED FROM KORTLANOT 1938 FIG. 17. AFTER SPLAY. a f t e r page 46 F i g . 18. A f t e r Hop d i s p l a y of the Double-crested Cormorant Wing-flipping i s a masculine display which has been described for the Common Cormorant by Portielje (1927), for the Double-crested Cormorant by Lewis (1929), and for the Brandt Cormorant by Townsend (1925.) Selous (1901) did not report i t for the Green Cormorant. The movement consists of the tips of the folded wings being moved repeatedly upwards and outwards from the body and back again. During this movement the breast i s held as close to the ground as possible. The movement i s performed only at a nestsite or at a display s i t e . Wing-flipping i s done si l e n t l y by the Pelagic and the Brandt Cormorants, and in these two species consists of a rapid fluttering of the wings in several irregular bursts, while the head i s moved slowly form side to side. On the other hand wing-flipping is performed with a rythmical beat and synchronized sound by the Common and the Double-crested Cormorants (Kortlandt 1938, Lewis 1929, Portielje 1927.) (Figs. 19,20,21.) When wing-flipping the Double-crested Cormorant takes up a very r i g i d posture with the breast lower than i t s abdomen, i t s t a i l pointing upwards and forewards, and i t s b i l l pointing upwards and backwards. The movements of the wings, the pulsat-ions of the cloaca, and the ttUgh-ugh-ughM sound produced are a l l synchronised and occur at a rate of about two beats per second. after page 47 Fig. 20. Wing-flipping display of the Double-crested Cormorant a f t e r page P p E L A G I C U S AOAPTEO FROM PHOTO P P E N I C I L L A T U S A O A P T E O F R O M W I L L I A M S 1 9 4 2 PAURITUS A D A P T E D F R O M P H O T O P C A R B O A O A P T E O F R O M K O R T L A M O T i93e W I N G - F L I P P I N G . 48 Recognition Display. Recognition Display i s a bisexual display which a cormorant performs whenever i t s mate arrives nearby. I t i s only done by a cormorant which i s eith e r standing or s i t t i n g i n the center of eith e r a nest or a display s i t e . I t occurs throughout the year. In each species the recognition display c l o s e l y resembles the threat display, and i s probably derived from i t as a token defence, which as acquired the opposite meaning. I t d i f f e r s from threat display i n that the movements are very slow, s t y l i z e d , elaborate, and r i g i d . The body i s almost always held ; horizontal with the breast lower than the abdomen. The wings are held i n a po s i t i o n which i s normal f o r the temperatures pr e v a i l i n g at the time and not spread downwards as i n threat display. The recognition display ( f i g s . 22 & 23) i s as follows in the various cormorant species: The Double-crested Cormorant stretches i t s neck and slowly waves i t s wide open mouth obliquely upwards and forewards thus showing i t s blue mouth l i n i n g , while i t utters a " A r r - r - r -r - r - t - t - t " c a l l . The Common Cormorant moves i t s head and neck slowly forwards aft e r which i t i s thrown back onto the back with a gargling sound (Kortlandt 1938.) The Brandt Cormorant f i r s t holds the i n f l a t e d head on i t s back, then i t throws i t forwards with a "Br - r - r B r - r - r " sound, afte r which the head i s withdrawn to i t s o r i g i n a l p o s i t i o n . a f t e r page 4-8 PARISIDTELIS A O A P T C O F R O M S E L O U S O O I P p E L A G I C U S Ao A P T E O f R O M P H O T O A PPENICILLATUS A O A P T E O F R O M W I L L I A M S 1 9 3 8 PAURITUS I O A P T E O F R O M P H O T O PCARBO A 0 A P T 6 0 F R O M K O ftT L A N O T 1938 FIG.22. RECOGNITION DISPLAY. after page 48 F i g . 23. Recognition Display of the Double-crested Cormorant. The Green Cormorant puts i t s head, neck and t a i l on i t s back in such a manner that the tip of the b i l l touches the tip of the t a i l , and remains in that posture for a short while (Selous 1901.) The Pelagic Cormorant moves i t s head vertically up and down, during which the male makes an "Arr-arr-arr" sound and the female a rhythmical "Igh-ugh Igh-ugh" sound. Just before copulation the recognition display is somewhat modified by the female, in that those parts of the display which would interfere with copulation are ommitted, and that the display as a whole becomes less elaborate. How-ever even at that time the recognition can be recognized as such though some authors c a l l i t then a precopulation display. The display becomes equally sketchy at the end of the nesting season during nest-relief. The Courtship, Seqqen.ce. The Courtship Sequence of cormorants i s seldom per-formed in i t s entirety except just prior to egg-laying. How-ever parts of i t are performed throughout the year in a dis-jointed manner during pair-formation and maintenace. Courtship evolves gradually from the play of chicks and perching-site contests amongst juveniles. The f i r s t courtship displays are performed just after the juvenal plumage has been acquired at nine weeks of age (Kortlandt 1938.) Banded yearling Double-crested Cormorants were ob-served to form definite pair bonds and to build and guard nests, f e r t i l e eggs are not laid however until the adult nuptial i s acquired. Double-crested and Common Cormorants reach maturity at two years of age, and the Pelagic Cormorant at three years of age. During pair formation prospective mates chase each other around the communal perching areas and on the water. They present gifts of nest material to each other and perform many courtship movements together. They defend perching sites together and perform the hop in unison. They often preen each other and touch each other a l l over. During this they lock b i l l s playfully, make nestbuilding movements with each others t a i l s (Kortlandt 1938), and entwine their necks. The function of the pairing behaviour, which is much more intimate in cormorants than in many other bird groups, is to reduce and eliminate the individual distance (Hediger 1955), and to reach the high degree of trust needed, in order to mate and raise successfully a brood of chicks within the confined space of only the nest and no more. The f u l l courtship sequence described below is the same for a l l cormorant species studied. F i r s t the male hops towards and onto a potential nest site with some nest material which he places underneath himself. Next he assumes a horizontal posture and returns the threats of the cormorants already established nearby. In between threat-display and nest-touching movements, he does the wing-flipping display. iThis wing-flipping ceases as soon as his mate arrives with elaborate landing display and several hops towards the nest. The male now starts the recognition display towards i t s mate, while the female inspects him and his nest s i t e . During this the heads pass each other alternately on opposit sides. Murphy (1916) observed this head-passing in the Blue-eyed Shag, PJk§A§jx3&££a3 S m & i O u j * Next the pair threaten the surrounding cormorants to-gether and often s i t at right angles in the nest with the bases of their necks crossed. Eventually the male gets up and hops away from the nest ( f i g . 24), and hops or f l i e s away in order to get some nest material. Usually he returns to the nest with a circular f l i g h t even i f the nest material has been gathered only a few feet away from the nest. a f t e r page 51 F i g . 24. Pelagic Cormorant hopping away from the nest. The gathering of the nest material i s repeated many times, and each time the male arrives with more nest material, the female does the recognition display, takes the material the male presents to her and incorporates i t into the nest structure. Subsequently in the nesting sequence the nest building roles are reversed whenever the male relieves the female at the nest. Nest building occurs always after nest r e l i e f . The old guard presents nest material several times to the new guard before leaving for the feeding grounds. Nest building takes place in this manner irrespective of which sex i s the new, and which is the old guard. The male normally presents nest material before and after copulation. Copulation i s preceded by the female in the nest making the recognition display in a modified form, during which the male hops onto her back. During the treading the Double-crested Cormorant male holds the female by the neck with his b i l l , the Pelagic Cormor-ant male holds onto the nest rim, and the Brandt Cormorant bites at both the neck of his mate and at the nest rim. During copu-lation both sexes have their wings closed, except that during a storm the male sometimes opens his wings somewhat for balance. There i s no distinctive post copulation display by either the male or the female other than normal preening and nest mainten-ance movements. Neither wing-flipping nor copulations occurs after there are eggs in the nest. Both are resumed however, with increased vigour, i f the eggs are lost. 53 Neg^frHUtiitap, and, mMmms* The nest structure i s continually added to by cormor-ants throughout the nesting season, from the moment a nest-site is adopted by a pair on a 24 hour basis to the time when the chicks are f u l l y fledged and start to leave the nest. The Double-crested Cormorant weaves sticks at a 45 degree angle into the nest structure with the b i l l . The Brandt and Pelagic Cormorants use the same method for working feathers into their stickless nests of hay and algae. The nests of Double-crested Cormorants consist of a mixture containing sticks, slats, green and dead twigs, algae, eelgrass, herbs, hay, bark, feathers, bird carcasses and bones. The base consists mainly of algae and the lining of hay. The nest material i s obtained from the dri f t l i n e s on the sea, from the tops of trees and shrubs, from meadows and fie l d s , and last but not least, i t i s stolen from other nests whenever possible. On the sea the Double-crested Cormorant usually dives in order to disentangle nest material from the d r i f t lines. Although the Brandt Cormorant does not jret breed at Mandarte Island, i t builds nests there which consist chiefly of the dry stalks of the Wild Radish.Jlaphanus rjjghjnjj^guj, and other herbs. 54 The nest of the Pelagic Cormorants consist of large quantities of hay and some moss-like algae which are cemented to the c l i f f with guano. The nest l i n i n g consists of fresh hay and algae. The continual building up of the nest probably serves to improve and maintain nest s a n i t a t i o n . In addition to building up the nest, cormorants keep the nest bowl clean by p e r i o d i c a l l y picking up f i s h scraps out of the nest bowl and throwing them away. These scraps are eagerly salvaged by the g u l l s and crows which wait nearby. Cormorants however reswallow any whole f i s h that they accidentally drop on the nest rim. Nests and nest s i t e s often change owners before they are f i n a l l y adopted by a p a i r of cormorants on a continuous basis. Deserted nests of even a large size are often demolished over-night by cormorants stealing nest material. 55 At Mandarte Island the Pelagic Cormorant lays from May 26 to August 4, and the Double-crested Cormorant from the end of April to the beginning of July. 49 out of 76 Pelagic Cormorant clutches were started during the second week in June, and 21 out of 35 Double-crested Cormorant clutches were started during the third week in May. At Race Rocks Mr. Odium found that the Pelagic Cormor-ants start to lay on May 26 and that 14 out of 27 clutches were started also during the second week in June. The average weight of 215 Double-crested Cormorant eggs was 51 grams, with 95% of the eggs weighing between 45 and 60 grams. The average weight of 143 Pelagic Cormorant eggs was 40 grams, with 95% of the eggs weighing between 35 and 45 grams. During the fourth week in June the modal clutch size for 35 Pelagic Cormorant nests at Mandarte Island, 21 Pelagic Cormorant nests at Race Rocks, and 38 Double-orested Cormorant nests at Mandarte Island was four. This i s the same as has been recorded for cormorants elsewhere. (Bent 1922, Mendall 1936, Murphy 1936, Dementjef 1952.) The maximum clutch size at Mandarte Island was 5 eggs for the Double-crested and 6 eggs for the Pelagic Cormorant. At banding time during the f i r s t week of August at Mandarte Island the average nest content was found to be as follows, for the Double-crested Cormorant, 2.2 eggs for 43 nests 2.7 chicks for 48 nests and for the Pelagic Cormorant, 2.8 eggs for 49 nests 2,4 chicks for 146 nests At 33 Double-crested Cormorant nests where eggs were repeatedly lost due predation and human disturbance relaying attempts were made as follows: no attempt at 4 nests jL t» ft 3 it 2 •" » 6 M 3 " n 5 M 4 II « 5 II 5 •* 2 *' 0 II tl o tt 7 « u i u 8 " " 1 " At 28 Pelagic Cormorant nests relaying was attempted as follows: no attempt at 10 nests 1 « " 13 " 2 tt it 4 tt 3 M n ! it The maximum number of eggs laid in one nest was 11 eggs for the Double-crested Cormorant, and 7 eggs for the Pelagic Cormorant. 57 I n c u b a t i o n . Incubation s t a r t s soon aft e r the f i r s t egg i s l a i d i n a cormorant's nest. Eggs are both l a i d and hatched successively at i n t e r v a l s of one or more days. The ca l c u l a t i o n of the incubation period presented several d i f f i c u l t i e s because of egg predation by g u l l s and crows. Pelagic Cormorant nests were checked at night and thus crow predation was avoided. These nests were inaccessible to g u l l s at night. For Double-crested Cormorants i t was not possible to study marked eggs because even at night the g u l l s removed them before the parents returned to the nests. Instead, the nest contents were counted d a i l y with a telescope from a b l i n d s i t u -ated above the nests, without scaring away the parent b i r d s . For the purpose of ca l c u l a t i n g the incubation period, the order of laying was assumed to be the same as the order of hatching. Any errors a r i s i n g from t h i s asumption cancel out when calculating the average, but tend to reduce the range and the deviation. Using the above methods the following incubation periods were found. For the Pelagic Cormorant the average was 31 days for 49 marked eggs, 70% requiring 30 to 32 days. The range was 27 to 37 days. For the Double-crested Cormorant the average was 28 days f o r 27 eggs, 80% requiring 27 to 29 days. The range was 25 to 29 days. Dementjef (1952) gives the following incubation periods: 28-30 days for the Common Cormorant, 26 days for the Pelagic Cormorant, 3 weeks for the Red-faced Cormorant, 24-32 days for the Green Cormorant. Lewis (1929) estimated and Mendall (1936) found an incubation period of 25-26 days for the Double-crested Cormor-ant. A 20 gram pebble was found in Double-crested Cormorant nests. Another similar pebble was found in a Pelagic Cormorant nest. The pebbles were probably substitute eggs. During cold weather the eggs are kept warm by placing the feet under them, by keeping the nest lining fluffed up and by the parent on nest duty sitting over them and covering them up. During warm weather the parent Cormorant stands in-side the nest near the nest rim and shades the eggs. After nest r e l i e f wet hay and algae are added to the nest lining to help cool the eggs. The b i l l i s used to r o l l the eggs, in the manner characteristic for most birds. In addition the eggs are moved by the feet and by the sternum. During a storm the incubating cormorants face into the wind. After a rain shower they stand up in the nest and flap their wings vigorously back and forth. When they get 5 9 r e s t l e s s they f i d g i t with the median edges of t h e i r closed wings. The incubating cormorant backs up p a r t l y over the nest rim before defecating. Both members of a pair of cormorants take an equal share in guarding the nest, in incubating the eggs, and in feeding the chicks. Nest r e l i e f i s most carefully executed during the incubation period and at that time i t s sequence is as follows: F i r s t the new guard lands near the nest, signalling as previously described. The old guard replies with the recog-nition display. The new guard then hops, waddles or runs onto the nest rim. On arrival at the nest, the heads of the two cormorants pass and rub along side each other repeatedly in opposite directions on alternating sides. Also they mutually threaten the neighbours and touch each other in various places. During this the old guard remains seated and the new guard standing. After the i n i t i a l salutations the old guard preens for a longer or shorter period and may even rest for several hours before changing places with i t s mate. When ready to take over the new guard crouchs down at right angles to the side of the old guard, and prods i t with i t s b i l l . Where upon the old guard stands up and the new guard sidles under the old guard ( f i g . 25), which backs out of the way and hops towards the c l i f f . After the hop the old guard signals before taking off over the top of i t s mate and f l y away. a f t e r page 6 0 F i g . 25. Nest r e l i e f of the D o u b l e - c r e s t e d Cormorant. As soon as the new guard i s alone, i t r o l l s and re-arranges the eggs onto i t s feet, and f l u f f s up the nest lining and the nest rim, before settling down onto the nest. Shortly afterwards the old guard returns several times with miscellaneous nest material, which i t presents to the new guard, before leaving the immediate v i c i n i t y of the colony to feed. During hot weather, when the nest guard only shades the eggs, the old guard often leaves as soon as the new guard lands nearby. The nests are never deserted unless the guard i s either frightened away, or the heat i s so excessive that the guard leaves for one or two minutes to cool off on the sea. This was observed several times during the heat wave in 1958 and then only among Pelagic Cormorants which had eggs. At that time i t was so hot that even the gulls and crows were not very active. Nest r e l i e f occurs at irregular intervals throughout the day. The hatching procedure of cormorants does not d i f f e r much from that of other bird eggs. The chick hacks the egg open with the egg tooth and can be heard chirping inside the egg as soon as the egg starts to open. It takes the chick about a day to free i t s e l f from the egg (Lewis 1929.) At the time of hatching the incubating cormorant sits very closely and is very restless. It can be observed to r o l l and move the eggs very frequently with the sternum. When the chick is f i n a l l y out of the shell the parent reaches under i t s e l f to throw the empty shell out of the nest with i t s b i l l . Some cormorants leave and desert their nests shortly after the incubation period expires i f their eggs f a i l to hatch, while other cormorants remain sitting on i n f e r t i l e eggs, guarding them 24 hours a day for over two and a half months. Cormorant c h i c k s f e e d d i r e c t l y from the mouth and t h r o a t of t h e i r parents on r e g u r g i t a t e d , p a r t l y - d i g e s t e d food p a r t i c l e s . A t no time was a cormorant parent observed to drop food down the t h r o a t of i t s c h i c k s as claimed by Audubon (1835) and Mendall (1936), and p o s t u l a t e d f o r day o l d c h i c k s by Lewis (1929). During i t s f i r s t week of l i f e the newly hatched c h i c k i s c a r e f u l l y incubated and i s n o r m a l l y h e l d on the f o o t of i t s parent. During i t s f i r s t few days i t begs by waving i t s s m a l l b l i n d head between i t s parents wing and the nest rim, w h i l e making at the same time a squeaky begging c a l l . The parent responds by f o l d i n g i t s neck back along i t s s i d e and c a r e f u l l y p l a c i n g the top of i t s open mouth over the head of the c h i c k , while the lower mandible i s brought h o r i z o n t a l l y a l o n g s i d e the head of the c h i c k . The c h i c k takes up a m i l k y f l u i d c o n s i s t i n g of shredded f i s h (van Dobben 1952) from the trough formed by the a n t e r i o r p o r t i o n of the lower mandible and the g u l a r pouch. A f t e r one or two days sma l l f i s h p a r t i c l e s are a l s o p i c k e d up i n a s i m i l a r manner by the c h i c k * O l d e r chick% which are able to r e a c h .their p a r e n t ' s head, beg by p r o d i n g w i t h t h e i r c l o s e d b i l l s at the c o l o u r f u l g u l a r pouch ( f i g . 26), while making a begging c a l l . . While begging f o r food cormorant c h i c k s always depress the tongue i n s i d e t h e i r mouth, thus g i v i n g t h e i r i n i t i a l l y pink t h r o a t patches an angular appearance. 6 4 As soon as the parent opens i t s mouth, one of the chicks shoots i t s mouth inside, where i t may even pick up whole fishes and shrimps ( f i g . 27.) After the wings start to develop they are waved during begging. The parent cormorants make regurgitation movements prior to feeding the chicks, and the Double-crested Cormorants sometimes make in addition an "Urh-Urh" sound. After feeding a chick the parent makes swallowing movements. When the chicks are four or more weeks old, the parents of more than one chick experience considerable diffi c u l t y in singling out one chick in order to feed i t . Often the parent is pushed off the nest rim by hungry chicks. In such circum-stances the parent usually solves the problem by going some distance away from the nest feeding the f i r s t chick that reaches i t . One Pelagic Cormorant, which had been pushed off the nest several times by i t s chicks, went to a nearby vacant nest and stole some hay, which i t dropped amongst the chicks when i t returned to the nest. The chicks dove at the nest material and while they were thus distracted the Pelagic Cormorant fed the f i r s t chick which resumed begging,, after which i t flew away to fetch more food. After the chicks have l e f t the nests they are fed both at the common perching area as well as on the sea. Chicks are normally fed by their own parents, but they w i l l beg from other cormorants and are occassionally fed by parents other than their own, especially when in strange nests. a f t e r page 6 4 F i g . 27. Double-crested Cormorant c h i c k being f e d 65 Chicks w i l l also beg from each other and put t h e i r heads down each others throats, but i t i s doubtful whether they obtain any food i n t h i s manner. During hot dry days the chicks of the Double-crested Cormorant show begging behaviour which differs markedly from begging for food with the b i l l closed. This is begging for water. It is done by waving the wide open b i l l upwards. In response, the old guard after nest r e l i e f , in-stead of going away to fetch nest material, descends to the sea and f i l l s i t s gullet with water with much head shaking. Within one minute of leaving the nest the old guard returns to the nest rim and from there pours water down the throats of each chick in turn. Often i t also pours some down the throat of i t s mate, for the recognition display closely resembles the begging for water display by the chicks. The old guard repeats the fetching of water several times. At one nest where one of a pair had disappeared after the chicks were about three week old, the remaining parent watered the chicks before i t l e f t them in order to find food. There can be no doubt that this i s a definite i n -stance of birds drinking seawater, as the parents were followed with a telescope from the moment they l e f t the nest, to the moment they returned with seawater. The following measurements were made on Pelagic Cormorant chicks: 1 day old 2 days old 5 days old (3 chicks) (4 chicks) (1 chick) mm. mm. mm. Length 100-120 115*130 150 Wing 16-18 16-19 22 B i l l 8-10 9-10 10 Tarsus 12-15 12-15 19 Lewis (1929) gives the dimensions of a just hatched Double-crested Cormorant chick as: Wing 22mm. B i l l 10mm. Tarsus 12mm. The weight gain of the Pelagic Cormorant during the f i r s t three weeks closely resembles that of the Double-crested Cormorant as measured by Mendall (1936). During thatjperiod the Pelagic Cormorant increases from 30-40 grams to 1150 grams, and Double-crested Cormorant from 30-40 grams to 1300 grams. During the f i r s t week the chick*s activities are confined to feeding and sleeping. After the f i r s t week they start to perform the same comfort movements as their parents* and they begin to defecate over the nest rim outside the nest. After the second week they excerise their growing wings. After the third week they make short excursions beyond the nest rim. At the end of the fourth week and the beginning of the f i f t h week the chicks start to make longer excursions from the nests. They pay v i s i t s to chicks in other nests and present nest material to each other and to their parents. Some of the chicks f a i l to find their way home and remain at the communal perching area, where they continue to be fed by their parent. Sometimes the parents present nest material to these lost chicks. This i s gratefully accepted, and has a marked effect on improving the liveliness and postures of these chicks. The lost and wandering chicks however frequently get pecked in their rumps by some yearlings and adults. One Pelagic Cormorant chick, which was banded, was chased down over a 50 foot c l i f f one evening by a two year old of the same species after i t had wandered away from the nest. However i t was back in i t s own nest the next morning. When at rest, cormorant chicks, like most young animal drape themselves in various odd positions and postures over the nest rim, with their necks often extended and hanging downwards. The threat of cormorant chicks consists of swelling up the head and neck with the mouth wide open and the hyoid arch spread out, and shaking the head at the opponent while making a hissing sound. From the third week onwards the chicks are able to swim and dive i f chased into the water. It i s not until the juvenal plumage is almost complete during the sixth and seventh week, that the chicks start to swim and bath by their own choice Flying starts in cormorant juveniles as in other birds with wing flapping excersises. During which the chick faces the wind and holds onto the nest rim with i t s feet. These wing exercises are most common during a fluctuating irregular wind of moderate speed. During the f i f t h and sixth week the chicks start to make short straight flights from one c l i f f shoulder to another, or along the c l i f f s over the sea. Great d i f f i c u l t y is ex-perienced by young cormorants and young gulls in learning how to bank and turn. Often during a turn they loose control and flutter like a scrap of paper down out of the sky and on to the sea. Juveniles which have swum and flown are easily re-cognised by their cleaner and s i l k i e r appearance, for they have been able to wash off the grey guano dust which gives the other younger chicks a dusty chalkbrush-like appearance. 70 Banding and its^ ^ffect,. The great majority of cormorant chicks were banded, when they were in their third or fourth week. At this age they are reluctant to leave the nest. Unavoidably there are many older chicks present at banding time which do leave the nests and stray quite far from them. However after the banding oper-ation i s over these chicks return to the colony and usually to their own nests. Some of them, however, get adopted at other nests and others remain at the communal perching area, where they are fed by their parents. The one week old and younger chicks suffer severe gull predation. The eggs are less severely damaged, because most of them then present are i n f e r t i l e and rotten, and thus discour-age predation. Because of the great a b i l i t y to survive after thier f i r s t three weeks of age, the banding mortality amongst the chicks of the Pelagic and the Double-crested Cormorants is surprisingly low. 71 s^y^y^t MreMWy . a n c i fl^pmaV The following nest success data were calculated from 34 Double-crested Cormorant nests: Average number of eggs laydd per nest 3.7 Loss due to predation G.3 Loss due to fa i l i n g to. hatch 0.9 Number hatched per nest 2.5 Number fledged per nest 2.4 37 Pelagic Cormorant nests, counted at night, gave the following nest success data calculated up to hatching time, after which mortality was abnormally high: Average number of eggs laidd per nest 3.8 Loss due to predation 1.2 Loss due to fa i l i n g to hatch 0.6 Number hatched per nest 1.9 Using 17 Pelagic Cormorant nests, which were inspected from a blind without flushing the adults from the nests, as were the above mentioned Doubled-crested Cormorant nests, -the following nest success data were calculated from hatching time onwards: Number hatched per nest 2.5 Number fledged per nest 2.0 Kortlandt (1942) calculated for the Common Cormorant a fledging rate of 1.1-1.4 per adult female. Of 165 Double-crested Cormorant nestlings banded at Mandarte Island in 1957, 86 were seen back at the island during the summer of 1958 as non^reproductive yearlings. One of these yearlings was seen on June 6, 1958 with a round open wound a half-inch in diameter on the top of i t s head, this wound had entirely healed by July 12, 1958. Of 264 Pelagic Cormorant nestlings banded at Mandarte Island in 1957, 14 were seen back at the island during the summer of 1958 as non-reproductive yearlings. There were probably many more banded Pelagic Cormorants present, but because of their preference for steep c l i f f faces and their habit of returning to the same perch every night i t was more d i f f i c u l t to see them than the Double-crested Cormorants, which frequent the more exposed and visible c l i f f shoulders. Ten out of 13 Double-crested Cormorant returns had been shot and the remainder was found dead, and out of six Pelagic Cormorant returns one was found wounded, one was trapped, one was found sick, and the remainder found dead. Out of the above returns two Double-crested and two Pelagic Cormorants were found about 100-110 miles away, and the remainder less than 50 miles away from Mandarte Island. According to the U.S. Fish & Wildlife Service bird banding records out of six returns for Brandt Cormorants banded in Oregon in 1913, 1939 and 1940, 3 were found in B r i t i s h Columbia 1 in California, 1 in Washington, and 1 in Oregon. One of these birds was shot 16 years after i t was banded. During the summer the numbers of immature and adult Brandt Cormorants roosting at Mandarte Island increased from about 50 in May and June to about a thousand at the end of August. No Brandt Cormorants were seen in Juvenal plumage at Mandarte Island. During this same period the percentage of adults amongst the Brandt Cormorants varied as follows: 2nd quarter of May 5% 3rd ti it n 14% 4th n n ti 0% 1st tt it June 0% 2nd tt it it 0% 3rd ti II ti 0% 4th II ti ti 1TA 1st n ti July 20% 2nd ti ii it 33% 3rd tt tt 56% 4th tt it If 65% 1st it tt Aug. 15% 2nd it II it W% 3rd n ti it 88# 4th tt ti tt 93% From the above data i t can be concluded that in the vic i n i t y of Mandarte Island and surrounding waters the Double-crested and the Pelagic Cormorants are non-migratory year-round residents, whereas the Brandt Cormorant i s resident Throughout the non-breeding season but migrates away during the summer in order to breed on the open coast of Oregon and Washington. Some of the non-breeding Brandt Cormorants however remain behind in Br i t i s h Columbia during the summer. Aprt from shooting, the post fledging hazards include the following: Epizootics (Bent 1922, Dementjef 1951, Murphy 1936), predation by the Hump-backed Whale and the Angler Fish (Lewis 1929), o i l on the sea (Flack 1957), hitting telephone wires in a storm (Peirson 1922), lightning (Sprunt 1941), strangulation by an eel (Patterson 1928), and failure of the food supply due to a change in sea currents (Fagan 1926.) 75 Lack (1945) demonstrated occurance of ecological separation in closely related sympatric species from a compara-tive study of the feeding behaviour and habitat selection of the Green Cormorant, Ph^lagrocgrax, aristotelis and the Common Cormorant, £. garbo in south western England by Steven (1933.) This principle was found to hold true for the three cormorant species at Mandarte Island. They also were found to d i f f e r specifically in their feeding habits and habitat selection. Thus intrageneric competition between species for nesting space and food is minimized. Darwin in the Origin of Species points out, that as a general phenomenon in plants as well as animals, closely related species tend io vary and d i f f e r most in the same morphological characters. This i s true in cormorants, in that they diverge most in the shape and colouration of the naked parts of the head, the colouration of the mouth lining, and the distribution of the nuptial plumes. Lorenz (1943) and Tinbergen (1946) show how such specific variations as the speculum colouration in ducks can serve as an aid in species recognition. Lack (1947) demonstrated the same principle in Darwin1^ Finches, where the b i l l size and shape aid in species recognition. In social and gregarious animals, such as the cormorants, signals are not only needed for species recognition, but also for communication. For any signal to be effective i t must be 76 simple (Tinbergen 1946, Whatmough 1957.) T h i s l i m i t s the number of d i s t i n c t s i g n a l s p o s s i b l e w i t h i n any one category, f o r example the shape of an organ, the c o l o u r of an organ, the posture of an organ, the speed of a movement, the o r i e n t a t i o n of a movement, the v a r i a t i o n of c a l l notes, e t c . As a r e s u l t the t o t a l number of s i g n a l s a v a i l a b l e to any one animal i s l i m i t e d . Because of t h i s l i m i t a t i o n d i s t i n c t s i g n a l s have to serve s e v e r a l d i v e r s e f u n c t i o n s , as sounds and words do w i t h i n a language^ Thus the meaning of a s i g n a l , l i k e t h a t of a word, depends on the context w i t h i n which i t i s used. A l s o as the same word may have d i f f e r e n t meanings i n d i f f e r e n t language, the same s i g n a l may have d i f f e r e n t meanings i n d i f f e r e n t animal s p e c i e s . F o r example a D o u b l e - c r e s t e d Cormorant w i t h i t s head h e l d h i g h and i n f l a t e d s i g n i f i e s t h a t i t i s about t o f l y or hop, whereas a Brandt Cormorant i n a s i m i l a r posture s i g n i f i e s t h a t i t j u s t complete a f l i g h t or hop. A D o u b l e - c r e s t e d Cormorant c h i c k w i t h i t s mouth open and upwards, begs f o r water, where as the a d u l t at the nest i n the same posture acknowledges the a r r i v a l of i t s mate. The same s i g n a l i n t h i s s p e c i e s d i f f e r s from t h r e a t only i n the sound emitted and the speed w i t h which i t i s performed. The f u n c t i o n of s p e c i e s r e c o g n i t i o n i n c l o s e l y r e l a t e d sympatric s p e c i e s i s to m a i n t a i n f l o c k bonds and to prevent h y b r i d i z a t i o n . F o r h y b r i d i z a t i o n would tend to d i s s o l v e the e c o l o g i c a l s e p a r a t i o n and s p e c i a l i z a t i o n and thus r e s u l t i n a l e s s complete use of the enviromental r e s o u r c e s . The h y b r i d s would be at a disadvantage in that they would be limited to zone of overlap in the use made of the enviroment by the two parental species, and unless they could find some new niche they would succumb to the dual competition. Therefore members of a species which either f a i l to recognize their own species, or to signify their identity w i l l tend to be selected against through failure to reproduce effectively. Conversely characters which ease species recognition w i l l be favoured by selection. In the cormorants studied the reproductive sequence and social behaviour was found to be identical in gross structure, but to differ in the signals used at each step in the sequence. Thus during social interactions, such as courtship nestrelief and perching site contests, cormorants have a hop, which is a token f l i g h t , and a Recognition display, which is a modified token threat. The Hop emphasises the species specific signals made before and after f l i g h t , and the Recognition display increases the species specificity of the threat by stylizing i t , and slowing i t down. The details of the signals used in any particular situation are as species specific as any morphological taxonomic character. Each signal serves not only as a message to a mate or an opponent, but also as a mechanism for keeping the species separate, by making them incomprehensible to one another. Therefore use can be made not only of morphological character-i s t i c s , b u t also of movements and signals for species i d e n t i f i -cation. 78 Summary. 1) During the f o u r summer months of 1957 and 1958 the r e p r o d u c t i v e behaviour and n a t u r a l h i s t o r y of the D o u b l e - c r e s t e d Cormorant P h a l a c r o c o r a x a u r i t u s , the P e l a g i c Cormorant P. p e l a g i c u s . and the Brandt Cormorant P. p e n i c i l l a t u s was s t u d i e d a t Mandarte I s l a n d , 17 m i l e s n o r t h o f V i c t o r i a , B.C. 2) The three cormorant s p e c i e s were found to d i f f e r i n t h e i r p e r c h i n g - and n e s t i n g - s i t e p r e f e r e n c e , and i n t h e i r f e e d i n g h a b i t a t s e l e c t i o n . . 3;) A f i e l d d e s c r i p t i o n i s g i v e n of the e x t e r n a l c o l o u r a t i o n of the v a r i o u s age groups, based i n p a r t on banded b i r d s of known ages. I t was found t h a t the Double-crested and the P e l a g i c Cormorants are polymorphic p r i o r t o b r e e d i n g and almost monomorphic a f t e r the breeding season. No sueh polymorphism was found i n the Brandt Cormorant. h$ The v o i c e of the Brandt Cormorant i s l i m i t e d to on l y one c a l l note, where as the other two cormorants have a v a r i e t y of c a l l notes f o r v a r i o u s purposes. Only the Brandt Cormorant can f l a s h w i t h i t s t h r o a t p a tch. A l l three s p e c i e s have a cough, which has no s o c i a l f u n c t i o n . 5) The r e s t i n g posture of cormorants i s m o d i f i e d by the weather and the e x t e r n a l temperature. 6) Cormorants bathe and dry t h e i r wings a f t e r most a c t i v i t i e s and a f t e r r a i n storms. T h e i r p r e e n i n g and body care does not d i f f e r much from t h a t of other b i r d s . 7) The f o l l o w i n g s t r e c h i n g movements occur i n cormorants: upwards wing s t r e t c h , one-sided s t r e t c h , f o o t i n s p e c t i o n , and backwards f o o t shaking. 79 8) During f l i g h t the position of the head differs in the three cormorants, and only the Double-crested Cormorant f l i e s overland in B r i t i s h Columbia. 9) The signals made before and after f l i g h t and before landing di f f e r specifically for each cormorant studied. During alarm these signals are ommitted. 10) Gulls and crows clean up f i s h scraps and f l i e s a-round cormorant nest, and prey on deserted eggs and chicks. The gulls also parasite cormorants for food. 11) Gulls guide by hovering and calling the Brandt Cormorants to the f i s h schools which have been driven to the surface by murres. 12) Fights for nests were found to be bitter and to continue until one of the contestants withdraws, whereas fights between neighbours were found to consist of threats, which differed specifically in each cormorant species studied. 13) Pair formation starts before sexual maturity is reached and the adult plumage is acquired. Double-crested Cormorants do not reproduce before they are two years old and Pelagic Cormorants hot before they are three years old. 14) The courtship of cormorants includes a hop, which is a token f l i g h t , a recognition display which i s a token threat, and a wing-flipping display which is a nest-advertizing display of the male. These signals d i f f e r in each species studied. 15) The Double-crested and the Pelagic Cormorants di f f e r in the materials they use for building their nests* The nest is added to after each nestrelief. 16) Both sexes share alike in the incubation and chick raising duties. Nest success data i s given for both the Double-crested and Pelagic Cormorant. 17) The average incubation period was found to be 31 days for the Pelagic Cormorant and 28 days for the Double-crested Cormorant. Double-crested Cormorants were found to relay more frequently than Pelagic Cormorants i f the eggs were lost repeatedly. 18) Cormorants were not found to differ much in their methods of raising the chicks and in the growth and development of the chicks. 19) Mortality due to banding was found to be low, except amongst recently hatched chicks. 20) The limited number of banding returns show that the Double-crested and Pelagic Cormorants are non-migratory near Mandarte Island, and that the Brandt Cormorant migrates to the open coast of Washington and Oregon to breed. 21) It was concluded, that the species specificity of the signals during courtship and social contact serves to prevent hybridization, and thus preserves the divergent ecological specialization of the species, which permits a more complete use of the enviromental resources. 81 Literature cifced. Alexander, W.B. 1955, Birds of the Ocean, 2nd ed. Putnam, London. Audubon, J.J., 1835, Ornithological Biography, J, Edinburg. Bailie, J.L., 1947, The Double-crested Cormorant nesting in Ontario. Canadi.Field.Nat. ,^:119-126. Bartholomew, G.A., 1942, The fishing activities pf the Double-crested Cormorant on San Francisco Bay. Condor, 4$: 13-21 Bartholomew, G.A., 1943, The daily movements of cormorants on San Francisco Bay. Condor, 45: 3-18 Bartholomew, G.A., 1943, Contests of Double-crested Cormorants for perching sites. Condor, 4^: 186-195 Behle, W.H., 1958, The Bird Life of Great Salt Lake, Univ. of Utah Press, Salt Lake City. Behn, F. et a l . , 1955, The Geographic Distribution of the Blue eyed Shags, Plyajbi,venter and Ph.atriqeps. Auk. 2£i 6-13. Bent, A.C,1922, Life Histories of North American Petrels and Pelicans and their A l l i e s . U.S.Nat. Mus.Bull.121. Bierman, W.H.,1955, Bijzonder waarnemingen. Ardea, 4J£: 309. Brooks,A& H.S.Swarth., 1925, A distributional l i s t of the birds of British Columbia. Pacific Coast Avifauna #17. Cooper Ornithological Club, Berkeley. 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