NESTING SEABIRDS OF THE GULF OF ALASKA 



51 



identical totals but the numbers of birds 

 varied between individual sites. This may be 

 an indication that all of these sites are part of 

 one large composite colony and that, at least 

 in this colony and for this species, the birds 

 shift at will. 



The best record of population flux involving 

 two species has been summarized by Peterson 

 and Fisher (1955). In 1872 and 1873 the 

 murres observed on Walrus Island in the 

 Pribilofs were almost entirely common 

 murres. In 1890 common and thick-billed 

 murres (Uria lomvia) were evenly matched in 

 number. By 1901 the colony was almost exclu- 

 sively dominated by thick-billed murres. In 

 1911 and 1914 the few thick-billed murres 

 present were almost lost among the then 

 dominant common murres. In 1940 thick- 

 billed murres dominated again. When Peter- 

 son and Fisher visited the island in 1953, the 

 situation was again reversed and common 

 murres had almost completely replaced the 

 thick-billed murres. These changes are even 

 more impressive because of the number of 

 birds involved, between 1 and 2 million in 

 1953. There are more tenuous indications that 

 somewhat the same thing may occur between 

 two other congener pairs, the pelagic and red- 

 faced cormorants and the black-legged and 

 red-legged kittiwakes. The causative factor, 

 or factors, is not readily apparent. One possi- 

 bility is long-term climatic fluctuation. 



Dement 'ev and Gladkov (1966) provide an 

 example of abrupt and massive change. Be- 

 fore 1876, the pelagic cormorant abounded on 

 the Commander Islands. During the winter of 

 1876-77, the birds were decimated by an un- 

 known epizootic disease. By spring only a few 

 individuals remained alive. The record shows 

 that by 1882 they were already becoming 

 common again. Red-faced cormorants were 

 apparently not reduced in number because 

 Dement'ev and Gladkov (1966) state that 

 they were common in "the second half of the 

 last century and the beginning of this." Did 

 they flourish only while the pelagic cor- 

 morants were reduced in number? 



Bowles (1908) gives another indication of 

 naturally induced population impact. He 

 noted large numbers of dead seabirds on 

 Washington beaches and the ocean "rather 

 plentifully dotted with sick birds ..." He 

 examined some birds and found "many hun- 



dreds" of tapeworms in every bird. His con- 

 clusion was that their intestines were so 

 solidly packed with tapeworms that starva- 

 tion was "an absolute certainty." 



Some apparent disruptions are long term. 

 In the Gulf of Alaska there is a hiatus in the 

 distributions of a number of small seabirds 

 that are active around their colonies only at 

 night. Repeatedly, the northern Gulf of 

 Alaska shows up as an area of reduced popula- 

 tion, as a boundary between subspecies, or as 

 a limit to a range. This same area has a notice- 

 able lack of total darkness during a substan- 

 tial portion of the breeding season. 



The nocturnal habit no doubt evolved be- 

 cause it was advantageous to concentrate on 

 the breeding grounds only under the cover of 

 darkness, when diurnal predators were at a 

 great disadvantage. Cody (1973) states that 

 Cassin's auklet (Ptychoramphus aleuticus), 

 which is strictly nocturnal around its colonies, 

 avoids these colonies on brightly moonlit 

 nights. He sees this as an apparent response 

 to gull predation. At higher latitudes the 

 small alcids have overcome this disadvantage 

 by swamping predators through their sheer 

 numbers. In the Gulf of Alaska I suspect that 

 few of the small seabirds, except possibly the 

 fork-tailed storm-petrel (Oceanodroma fur- 

 cata), have ever achieved great enough num- 

 bers to offset the impact of extended daylight. 



Past disruptions of seabird populations are 

 both natural and man-induced; however, the 

 documentary record is much too fragmentary 

 to allow us to fully appreciate what has oc- 

 curred or what the long-term effect has been. 

 To give some perspective to the problems as- 

 sociated with assessing change and attempt- 

 ing to understand it, some of the indicators of 

 natural and unnatural change and flux in sea- 

 bird populations are reviewed here. 



The flux in. bird numbers can be related to 

 the time of day, season of the year, and atmos- 

 pheric conditions on a short-term basis. This 

 sort of flux or apparent flux can easily be ex- 

 plained. The underlying cause of some of the 

 longer term flux is not so easily arrived at. 

 Murie (1959), Gabrielson and Lincoln (1959), 

 and Sowl and Bartonek (1974) have noted 

 some of the man-induced changes. These are 

 also explored to some extent in the species ac- 

 counts as they are found to apply. 



I sometimes refer to a colony size class 



