111.5 Saturday, Jan. 7 Gonadal androgen and development of vernal migratory condition in Gambel’s White-crowned Sparrow NEMETH, Zoltan*; RAMENOFSKY, Marilyn; University of California, Davis; University of California, Davis email@example.com
The influence of the gonads on development of vernal migration has been shown to be important as low levels of circulating androgen - testosterone (T) & 5α dihydrotestosterone (DHT) - experienced during the early stages of increasing daylengths are necessary for the development of hyperphagia and premigratory fattening. However, few have addressed effects of wintering levels on the onset of nocturnal migratory restlessness. We eliminated the influence of the gonads by castrating male White-crowned Sparrows before the winter solstice (pre-solstice) and investigated the effects of short-term (16 days) T replacement during winter (post-solstice) on the development of premigratory fattening, muscle hypertrophy, prealternate molt, cloacal protuberance (CP) and nocturnal migratory restlessness in birds held on natural local photoperiod. T replacement increased flight muscle size and fattening directly and post-implant initiated development of nocturnal migratory restlessness. Onset of nocturnal restlessness in these birds coincided with timing of spring departure of the local, free-living White-crowned Sparrow population and preceded the development of migratory activity of control (sham operated) birds by about two weeks. Castrated vehicle controls showed suppressed nocturnal restlessness, lower fat and flight muscle size, as well as reduced CP development. Prealternate molt was slightly delayed in castrated birds relative to sham controls regardless of T replacement treatment. Our study furthers the idea that gonadal androgen is important for development of vernal migration with both immediate and long-term effects on the behavior and physiology of the migration program.