GAMBLE, J. BROOK; O’REILLY, KATHLEEN M.; BUCK, C. LOREN; University of Alaska Fairbanks; University of Portland; University of Alaska Fairbanks: Effects of Reproductive Stage on Adrenal Responsiveness of Glaucous-winged Gulls

The reproductive period for seabirds is both energetically expensive and potentially stressful. Parents have the dual challenge of maintaining their own body condition while meeting the energetic needs of their growing chicks. Nest sites are often times many kilometers from available food sources. We hypothesized that 1) body condition of glaucous-winged gulls (Larus glaucescens) during the incubation and chick rearing periods in Chiniak Bay, Alaska would be compromised as compared to pre-breeding condition and that 2) plasma levels of corticosterone would increase throughout the reproductive season. We developed an index of body condition and determined that adult body condition significantly degraded as the breeding season progressed (P = <<0.001). We collected either baseline (<<3 minutes after capture) or stress series (<<3, 10, 30, 50 minutes following capture) samples of blood from free-living adult birds caught during pre-breeding, breeding and post-breeding stages. Samples were assayed for levels of corticosterone. Baseline levels did not vary significantly among seasons (P = 0.343) and averaged 2.0 ±� 0.25. However, peak levels attained during the stress series were significantly higher (P <<0.001) during incubation (33.309 ±� 2.35 SE, n= 13) than during chick rearing (26.39 ±� 3.906, n=11). Relatively low and stable baseline concentrations of corticosterone throughout the pre-breeding and breeding season suggest that reproductive birds were not highly energetically stressed at the time of capture and that parent birds modulate adrenal responsiveness and thus peak circulating plasma corticosterone levels with breeding stage.