LOVE, O.P.; VEZINA, F.; WILLIAMS, T.D.; Simon Fraser University; Simon Fraser University; Simon Fraser University: Modulation of corticosterone in birds: effects of breeding stage, season and relationship to nest abandonment.

The mechanistic basis for the interaction between corticosterone (B) and reproduction is still poorly understood. Although previous studies have examined seasonal trends in B secretion, few studies have separated specific effects of reproductive stages from season. In addition, although elevated B levels are known to increase locomotory activity and dispersal and interrupt reproduction, no studies have examined the natural variation in B in relation to nest abandonment. We examined baseline and stress-induced levels of B in wild female European starlings (Sturnus vulgaris) during laying, incubation and chick-rearing, and monitored nest abandonment. Stress-induced levels in chick-rearing birds were significantly lower (28 ng/ml) than incubating (37 ng/ml) and laying birds (48 ng/ml). These trends were independent of season, with laying birds exhibiting high levels throughout the season. Baseline B levels of chick-rearing birds (11 ng/ml) were significantly elevated compared with laying (8 ng/ml) and incubating (6 ng/ml) birds. Abandonment rates were correlated with stress-induced B levels through reproduction, with abandonment decreasing with each successive reproductive stage. Chick-rearing birds may be less sensitive to acute increases in B potentially allowing them to be more resistant to nest abandonment, while also exhibiting elevated baseline levels which may facilitate foraging and feeding of chicks.