Barrow area early in the cruise. Jaegers and 

 phalaropes were infrequent and generally seen 

 oiily during the first 2 weeks of the cruise in 

 the study area. Fewer Kittiwakes were seen 

 than had been found by other observers. On 

 the other hand, among the birds we saw most 

 commonly was Ross' Gull, an arctic species 

 that does not breed in the Chukchi Sea at all, 

 and the Ivory Gull that breeds only on Herald 

 Island in the western Chukchi. Many of the 

 loons, Oldsquaw and eider ducks. Glaucous 

 Gulls, and alcids wei'e well offshore in relative 

 abundance, farther from land than one would 

 expect from other published accounts. 



All of these distribution anomalies were the 

 result of various sorts of seasonal movements. 

 Southward fall migration had already taken 

 place or was well advanced in the less tolerant 

 species that feed or breed in the arctic but move 

 to temperate latitudes with the onset of cold 

 weather in the fall. These included the Slender- 

 billed Shearwater, Northern Fulmar, most 

 ducks, geese, phalaropes, jaegers, Sabine's 

 Gull, Arctic Tern, and Grey Whale. East-west 

 dispersal or migration accounted for the pres- 

 ence of Ivory and Ross' Gulls in the Chukchi 

 where they may winter among the open leads 

 in the pack ice. Post-season dispersal of birds 

 that were released from dependence on land for 

 rearing young probably accounts for the 

 pelagic records of a number of species that we 

 recorded, but which were not regularly re- 

 corded far from land during the breeding sum- 

 mer season. These include the Oldsquaw and 

 eiders. Glaucous Gull, murres, guillemots and 

 Horned Puffin. The Parakeet and Crested 

 Auklets were present considerably north of 

 their breeding grounds, the latter species in 

 relative abundance. This post-breeding disper- 

 sal spreads predation pressure on prey species 

 over a much greater range, at a time when food 

 may start to become scarce, than during the 

 breeding season, at the height of plankton and 

 fish abundance. 



ICE AFFINITIES 



Ice was a major factor affecting the distribu- 

 tion and abundance of some species in the study 

 area. Guillemots, for instance, were found al- 

 most exclusively at the edge of the pack ice 

 (figs. 26 and 32). Some of the gulls, likewise, 

 were more abundant near the ice than in open 



water. In order to assess the significance of the 

 affect of ice on the distribution of gulls, 

 watches were divided into two categories ; those 

 with ice and those in open water in which no 

 ice was visible from the ship. The categories 

 were tested statistically by X - (chi square) 

 (table IV). Watches in heavy fog or those in 

 new or grease ice were presumed atypical and 

 were not included in the totals. 



On transects Ivory and Ross' Gulls showed a 

 decided preference for ice areas while the 

 Glaucous Gull showed no significant preference, 

 and the Kittiwake was found primarily in open 

 water. At stations Glaucous, Ivory and Ross' 

 Gulls showed no significant preference, and 

 Kittiwakes avoided ice. The partly contradic- 

 tory results may be the resemblance of a white 

 icebreaker to ice or the natural attraction of 

 gulls to a standing ship. Observations from a 

 moving ship, therefore, probably provide a 

 better indication of a species' ice affinities than 

 those from a standing ship. 



The presence of Ivory and Ross' Gulls in ice 

 areas is not surprising in that both species 

 spend much of the year in the pack ice and are 

 adapted to feeding on organisms found at the 

 surface in ice areas. Furthermore, ice may 

 provide secure roosting and resting sites for 

 these two species (fig. 24). The Ivory Gull was 

 only rarely seen swimming, but it frequently 

 perched on ice cakes (fig. 20). That ice had 

 little affect on the distribution of Glaucous 

 Gulls probably is due to its association with 

 land and its relatively unspecialized feeding 

 habits. The preference of Kittiwakes for open 

 water could not be due to the presence of food, 

 since the Arctic Cod, Boreogadus saida, the 

 only food item found in their stomachs, occurs 

 closer to the surface in ice areas. The Kittiwake 

 was the only gull whose flying ability was not 

 visibly hindered by high winds that we en- 

 countered on many of the open water watches, 

 and there is no evidence that this pelagic 

 species needs land or ice for roosting outside 

 the breeding season. 



FOOD HABITS 



Although a number of species of diverse 

 families of marine birds occurs in the Chukchi 

 Sea in fall, the primary foods of all but the 

 ducks are pelagic crustaceans and small fish, 



125 



