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Stress hormones suggest opposite trends of food availability for planktivorous and piscivorous seabirds in 2 years

TitleStress hormones suggest opposite trends of food availability for planktivorous and piscivorous seabirds in 2 years
Publication TypeJournal Article
Year of Publication2008
AuthorsZ. Benowitz-Fredericks, M, Shultz, MT, Kitaysky, AS
JournalDeep-Sea Research II
Volume55
Pagination1868–1876
Abstract

Apex predators can provide valuable information about effects of climate variability on trophodynamicsin the Bering Sea. We used corticosterone (the primary avian stress hormone, ‘‘CORT’’) as a proxy ofchanges in prey availability for planktivorous and piscivorous seabirds. CORT secretion reflects energybalance in breeding individuals and can be used to monitor changes in the marine environment thatalter food availability. We tested whether CORT in planktivorous least auklets (Aethia pusilla) andpiscivorous thick-billed murres (Uria lomvia) on two Pribilof Islands differed spatially or temporally in2003 and 2004. During June–September of each year, we sampled birds breeding on St. Paul andSt. George Islands. We found that seasonal dynamics of CORT varied between years. Although theseasonal dynamics were similar between islands in a year, in 2004 there were inter-island differences inCORT levels for both species. In 2003, CORT in murres was low throughout the season, suggesting thattheir prey availability (primarily forage fishes) was consistently good. In 2004, CORT levels suggestedthat overall food availability was poor for murres and declined as the season progressed. For auklets,inter-annual variability was associated with contrasting intra-seasonal patterns in the availability ofzooplankton prey (primarily Neocalanus spp.). In 2003, high early-season (June) CORT indicated thatauklets were food-limited, but CORT decreased in July, suggesting that the availability of zooplanktonimproved as the season progressed. In 2004, CORT was low early in the season (June), but an abruptincrease late in the season (July) suggests that food became scarce. Our data indicate that environmentaldifferences between 2003 and 2004 affected prey availability for planktivorous and piscivorous alcids inopposite ways. These results suggest that in the shelf regions of the Bering Sea, the populations of apexpredators feeding on zooplankton may be affected by environmental fluctuations differently than thosefeeding on forage fish.

DOI10.1016/j.dsr2.2008.04.007
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