planktivorous deep-feeding birds, the auiclets. were considered 

 separately with respect to water type positions at the surface, 

 the pattern was quite different. 



Aukiets (i.e., least [Aethia pusilla] and crested auklet 

 [A. cristatelUi] abundances combined) were found in the 

 greatest numbers where ASW occurred at depths of at least 

 20 m. At 15 m or shallower, aukiets did not show apparent 

 preference for either ASW or BSW, the same result reported by 

 Day et al. (in prep.). Results of dietary analyses suggest that 

 diet composition of aukiets does not change much from year to 

 year, in terms of the prey species consumed (Bedard, 1969; 

 Springer & Roseneau. 1985; Piatt el al., 1988; Hunt et al.. 

 1990). Zooplankton species are not evenly distributed among 

 water types, so aukiets might be expected to select water types 

 that contained their preferred prey. Again, it is assumed that 

 aukiets have access to each of the water-type habitats considered 

 here. Despite their energetically-costly mode of flight, aukiets 

 have been observed feeding in large aggregations at least 

 1 1 1 km from the nearest colony(Schauer.pcrsonal observation). 

 Most aukiets breeding in the area of this cruise would be able 

 to reach each of these water types within this distance. Based 

 on the results of the zooplankton distribution analysis in this 

 study (see also Springer et al.. 1989). aukiets should occur in 

 greatest abundance in ASW. When water type distribution is 

 examined at 20 m below the surface, aukiets are clearly 

 concentrated in AS W areas. This may be related to concentration 

 of prey at strong property gradients between water types 

 (e.g., halocline, pycnocline). Examination of these data using 

 only surface salinity values obscures this pattern, and no 

 preference between ASW and BSW can be determined. 



Taken as a whole, these results suggest that prey preference 

 dictates foraging habitat selection by seabirds at macroscales. 

 Foraging method is probably more important in explaining 

 mesoscale variations in seabird distribution. 



I am grateful to the US Fish and Wildlife Service and the State 

 Committee for Hydrometeorology. USSR, who made the Third Joint 

 US-USSR Bering & Chukchi Seas Expedition possible. Many thanks 

 also to the captain and crew of the Soviet RA' Akademik Korolev, and 

 to J. Andrew. N. Haubenstock. and B. Bergeron, who collected 

 seabird data and zooplankton samples. C. Chu assisted with computer 

 programming. T.WyllieEcheverria assisted with zooplankton sample 

 processing. T. Whitledge provided access to CTD data. This 

 manuscript benefitted from reviews by C. B. Kepler. C. P. McRoy. 

 E. C. Murphy, and J. A, Miller. This project was supported in part by 

 a grant from the National Science Foundation. USA ( DPP-K4-()52S6). 

 This is contribution number 874 of the Institute of Marine Sciences, 

 University of Alaska, Fairbanks. 



APPENDIX 1 



Species Accounts 



This section summarizes the relative densities of seabirds 

 among water masses at the species level. When possible, 

 information has been provided here regarding locations of 

 nearest known breeding colonies, abundance of North Bering 

 Sea breeding populations, and pertinent foraging habits for 

 each species described. In addition, how each species was 

 reclassified for the analysis of trophic group(s)/water type 

 relationships is noted here. Nineteen seabird species were 



observed in the study area. Some seabird species were observed 

 in such low numbers that statistical analysis of their habitat 

 preferences was not possible. For this reason, these species are 

 not included in the detailed species-specific densities given in 

 Table 2, but their presence in the cruise track area is noted in 

 this section. 



Average densities of all seabird species combined were 

 highest in ASW (49.1 birds/km') (Table 2). Areas influenced 

 by CCW had the next highest total densities (30.2 birds/km=), 

 followed by BSW (8.8 birds/knr). All of the locations of 

 colonies of breeding seabirds referred to below are shown in 

 Fig. 1. 



Northern Fulmar (Fulmaris glacialis) . This surface- 

 feeding seabird was found in average densities in ASW, 

 22 times higher than densities detected in BSW (Table 2). The 

 closest breeding colony of this species is at St. Matthew Island, 

 from which fulmars may tly several hundred kilometers to feed 

 (Sowlsera/., 1978). However, this species is known to forage 

 noctumally, so birds observed by day in the northern Bering 

 Sea could be nonbreeders rather than breeding birds foraging 

 at great distances from their colonies. 



Short-tailed Shearwater {Puffinus tenuirostris) . This 

 species does not breed in the Bering Sea but spends the boreal 

 summer here. This shallow-diving planktivorous species was 

 at least five times more abundant in CCW than in BSW or 

 ASW. Observations were made by J. Andrew during this 

 cruise. 



Fork-tailed Storm-Petrel (Oceanodroma fiircata) . These 

 surface-feeding plankti vores nest mostly in the Aleutian Islands 

 (Sowlser«/., 1978). They are commonly found at sea, north to 

 the latitude of the Pribilof Islands, although there are no reports 

 of nesting there. This species was 28 times more abundant in 

 ASW than in BSW and was absent from CCW. 



Steller's E\dex (Pohsticta stelleri) . Six flying individuals 

 were observed in only one of the transects surveyed, over 

 BSW. Little can be said, therefore, about pelagic habitat 

 preferences of this species. They are noted here because of 

 current interest in the pelagic distribution (largely unknown) of 

 this species. 



Red Phalarope (Phalaropus fulicaria) . This species was 

 seen flying in very low densities (<0. 1 birds/km-) in ASW and 

 BSW. No conclusions can be reached about significant habitat 

 preferences for this species. Results from other studies indicate 

 that mesoscale oceanographic features may be most important 

 in explaining distribution of phalaropes at sea (Brown, 1980). 



Pomarine Jaeger (5/t'/-cY)nvrHf.s7)w?u»7/i».?). Parasitic Jaeger 

 iS. parasiticus), and Long-tailed Jaeger (5. loneicaiidu.'i) . The 

 distribution of these species might be expected to mirror that of 

 fulmars or kittiwakes (Rissa spp. ). which they often parasitize. 

 Observations of jaegers are too limited in this study, however, 

 to draw conclusions about their habitat preferences. Flying 

 jaegers were observed in low numbers in all three water types. 



Herring Gull (Lams anieutatits) and Glaucous Gull 

 (L. Iixperboreiis) . Abundances of the.se two species were too 

 low for determination of habitat preferences 

 (both<0. 1 birds/km-). Only small populations of herring gulls 

 nest in Alaska, with five of the six documented North Bering 

 Sea breeding sites located on St. Lawrence Island. Most of 



395 



