COVERDILL, A.J.*; BENTLEY, G.E.; RAMENOFSKY, M.; University of Washington; University of Washington; University of Washington: Circadian control of migratory restlessness in a captive nocturnal migrant

Migration is the biannual movement between breeding and nonbreeding habitats. In captivity, Gambel�s white-crowned sparrows (Zonotrichia leucophrys gambelii) display many of the physiological and behavioral traits observed in free-living birds during migration. Birds in the spring migratory stage held on a photoperiod of 18L:6D (light:dark) display 24 h cycles of activity. They feed and rest during much of the light phase, followed by quiescent behavior just prior to lights off. Migratory restlessness (MR) or intense flight activity is expressed during the dark phase. As this appears to be a daily cycle, we asked whether these behaviors may be the expression of an endogenous circadian rhythm. To test this we exposed birds to constant dim light, which resulted in continuous MR for an average of 36.4 � 5.3 h (N=8), followed by transitions between rest and resumed MR for varying periods of time. Once the photocycle was returned to18L:6D, birds reverted to daily cycles of feed, rest, and quiescence in the light phase and MR in the dark. After 9 days of recovery, birds were exposed to constant bright light. This resulted in repeated daily cycles of quiescence and high levels of activity but not MR. These results imply a circadian influence on this suite of behaviors but also show that particular environmental conditions mask their full expression. For nocturnal migrants dusk may entrain flight onset in concert with optimal conditions while dawn entrains its offset.