BUCK, CLB; O’REILLY, KM; Univ. of Alaska Fairbanks; Univ. of Portland: Brood Size Affects Adrenal Responsiveness of Free-living Kittiwake Chicks

Secretion of corticosterone by black-legged kittiwakes (Rissa tridactyla, BLKI) is linked to nutritional state; and sibling aggression, and brood reduction of BLKI are linked to low forage availability. Therefore, we hypothesized that breeding success of adult BLKI would inversely correlate with levels of plasma corticosterone; and both baseline and adrenal responsiveness of individual BLKI chicks would inversely correlate with both their status in the nest and brood size. During the breeding season, we monitored wild BLKI�s for nest attendance and productivity and sampled both adults and chicks for analysis for analysis of plasma levels of corticosterone. Productivity (chicks fledged/nest attempt) in 2001 was significantly greater than in 2002 and 2003 (0.71, 0.48, 0.25, respectively) and baseline levels of plasma corticosterone of adult kittiwakes were inversely related to productivity. Baseline levels of plasma corticosterone of BLKI chicks (4.41 � 0.70 ng/ml) did not significantly differ among chicks of differing status (singleton, alpha, beta, tertiary) or among chicks occupying nests of different numbers of occupants (1, 2, 3). Adrenal responsiveness of chicks to acute stress varied according to brood size with 3-chick broods exhibiting the most rapid and profound increases in corticosterone followed in rapidity and magnitude by 2-chick and 1-chick broods, respectively. Adrenal responsiveness to acute stress did not vary according to chick status. These data suggest all chicks of multi-chick broods experience more stress than do singletons and the stress load of multi-chick broods increases with number of nest occupants.