POPULATION DYNAMICS IN NORTHERN MARINE BIRDS 



125 



with industrial chemicals, seems to have con- 

 tributed to mass mortality of the same 

 species (called common guillemot in Britain; 

 Holdgate 1971). The seabird victims of this 

 event had metabolized their body fat and as a 

 result, polychlorinated biphenyls (PCB) and 

 other industrial chemicals passed into livers, 

 kidneys, and brains. Again, a storm at the end 

 of a period of stress seems to have been more 

 than the birds could tolerate. 



A further example of a die-off of waterfowl 

 apparently brought on by starvation was 

 given by Barry (1968), who estimated that 

 about 100,000 king eiders (Somateria spec- 

 tabilis) died when they arrived before the ice 

 broke up in the Beaufort Sea in spring 1964. 



Diseases have produced massive die-offs in 

 marine birds. Fowl cholera caused high mor- 

 tality in nesting common eiders (Somateria 

 mollissima) in the Gulf of St. Lawrence in 

 Quebec (Reed and Cousineau 1967) and in 

 Penobscot Bay, Maine, in the early 1960's 

 (H. Mendall, personal communication). 

 Poisoning from a "red tide" (a bloom of the 

 dinoflagellate Gonyaulax tamerensis, caused 

 a die-off of black ducks (Anas rubripes) and 

 herring gulls on the coast of New England in 

 1972. Similarly a die-off of shags (Phalacro- 

 corax aristotelis) on the east coast of England 

 was caused by a "red tide" (Coulson et al. 

 1968). During a period of 1 week 90% of the 

 shag nests on the Fame Islands in North- 

 umberland were deserted and about 80% of 

 the breeding population died. 



Gradual Declines 



When the new volcanic island of Bogoslov 

 emerged in the western Aleutians, Preble and 

 Me A tee (1923) reported that it was colonized 

 by large numbers of pigeon guillemots 

 (Cepphus columba), but in the following 

 decades the guillemots have steadily de- 

 creased (G. J. Divoky, personal communica- 

 tion). As a further example, the nesting popu- 

 lation of Atlantic puffins (Fratercula arctica) 

 in the Atlantic has declined over the past 

 several years, especially those nesting on the 

 Outer Hebrides (Flegg 1972; Harris 1976). 



It is difficult to find seabird species whose 

 nesting grounds have not been affected by 

 humans but whose numbers have been cen- 

 sused. The best illustrations of secular 



changes in relatively constant habitats are 

 probably those available in the British Trust 

 for Ornithology's breeding censuses of song- 

 birds. Songbirds are short-lived and their 

 populations change on relatively short time 

 scales. The northwestern European landscape 

 has remained relatively constant for the last 

 75 years, yet there are observable decade-long 

 trends for example, of willow warblers (Phyl- 

 loscopus trochilus) and dunnock (Prunella 

 modularis). There are detailed data on popula- 

 tion changes in great tits (Parus major) 

 through the work of Kluyver (1951), Lack 

 (1964), and Perrins (1965). 



Effects Reflecting Environmental Change 



Nelson (1966) argued that the increase of 

 gannets in the North Atlantic during this cen- 

 tury has been related to increasing tempera- 

 tures rather than (as usually ascribed) to in- 

 creased food from fish damaged or escaped 

 during commercial fishing. 



Ainley and Lewis (1974) described a particu- 

 larly interesting example of the effects of en- 

 vironmental change on seabird populations. 

 The events begin with the decrease of sea- 

 birds on the Farallon Islands off California as 

 a result of human depredations. Even after 

 fowling was made illegal, the populations of 

 murres, double-crested cormorants (Phalacro- 

 corax auritus), and especially of tufted puffins 

 (Lunda cirrhata) and pigeon guillemots con- 

 tinued to decline as a result of oil pollution. 

 During the last 3 decades the smaller species 

 of seabirds nesting on the Farallons, such as 

 rhinoceros auklets (Cerorhinca monocerata), 

 have increased rapidly and the authors sug- 

 gest that their increase was abetted by an in- 

 crease in the small prey fish, northern an- 

 chovy (Engraulis mordax). One of course ex- 

 pects predators to be affected by changes in 

 the abundance of their prey. During this same 

 period, larger species of seabirds such as 

 double-crested cormorants and tufted puffins 

 have failed to recover their numbers, and the 

 authors speculate that this failure is related 

 to a decrease of the larger prey fish, Pacific 

 sardine (Sardinops caerulea). 



A widely publicized impact of environ- 

 mental fluctuation upon seabird populations 

 is that of the northeast wind, El Nino, off the 

 Peruvian coast. This wind pushes the upwell- 



