Diurnal rhythms of plasma corticosterone concentrations in racing pigeons (Columba livia domestica) exposed to different light regimens, and the influence of frequent blood sampling.

The effects of two different light regimens and the frequency of blood sampling on the diurnal plasma corticosterone concentrations in racing pigeons (Columba livia domestica) were investigated. The daily light regimens tested were a period of light during the day (DL; lights on 0515-2215) and shifting of the light period by 12 hours (SL; lights on 1715-1015). In the first experiment, the influence of the frequency of blood sampling was investigated by comparing plasma corticosterone concentrations at 28-hr intervals for several days and at 4-hr intervals during one day. Sampling at 4-hr intervals resulted in significantly higher corticosterone concentrations in plasma than sampling at 28-hr intervals. Within both groups, the plasma corticosterone concentrations at the first and last sampling times did not differ significantly. Concentrations of plasma corticosterone were always highest during the dark period, and the corticosterone rhythm in the SL experiment was strictly in phase with the altered light/dark schedule.