Daily and photoperiod variations of basal and stress-induced corticosterone concentrations in house sparrows (Passer domesticus)

Corticosterone concentrations were measured in captive house sparrows (Pass er domesticus) and found to vary both daily and with different photoperiods . Basal corticosterone was highest during the dark hours of the daily cycle and lowest during the light hours. This trend remained constant when the b irds were held on short-day and long-day light cycles, and while the birds were undergoing a prebasic molt. At all times, corticosterone concentration s significantly increased in response to the stress of handling and restrai nt. Stress-induced corticosterone concentrations, however, only reflected a daily rhythm when the birds were held on short-days. Furthermore, even tho ugh mean basal corticosterone concentrations were equivalent over the short -day, long-day, and molt, total corticosterone output in response to stress was lower in molting birds, especially at night. Therefore, these data ind icate that captive house sparrows modulate corticosterone in daily cycles t hat change in response to photoperiod.