Plasma corticosterone in wild starlings ( Sturnus vulgaris) immediately following capture and in relation to body weight during the annual cycle

Free-living starling ( Sturnus vulgaris) were caught by mist netting. Blood samples were taken from them between 20 sec and 4 min after capture and assayed for corticosterone. Before 1 min corticosterone levels were constant (10.3 nmol litre −1) but after 1 min they increased rapidly (27.0 ± 3.6 nmol litre −1 min −1). Male and female free-living starlings were caught throughout the year with mist nets, and traps placed in nest boxes. Blood samples were taken within 1 min of capture and body weights recorded. Plasma corticosterone varied between 3 and 13 nmol litre −1. In both sexes the level was high during winter and through the breeding season. It fell to low levels during late summer and increased again during autumn. Body weight in both sexes was highest in midwinter and lowest in midsummer but there was no correlation between body weight and plasma corticosterone concentration.