Changes in body weight, ovarian growth, and circulating plasma estradiol level in response to programmed photoperiods in blackheaded bunting, Emberiza melanocephala

Abstract

Photosensitive female blackheaded buntings (Emberiza melanocephala) were observed at different photoperiodic schedules of increasing duration to study their effect on body weight, ovarian growth, and circulating plasma estradiol level. Continuous-light (24L:0D) and long-day (15L:9D) photoperiodic regimes showed a significant increase, followed by decrease, in body weight, ovarian growth, and circulating plasma estradiol level. The short photoperiod (8L:16D) showed no effect on body weight, ovarian growth, or circulating plasma estradiol level. During 24L:0D and 15L:9D birds became photorefractory and thus unable to maintain an elevated state of body weight, ovarian growth, or plasma estradiol level. On the other hand, the birds exposed to short photoperiod maintained their photosensitive state throughout the period. The peak attained during 24L:0D and 15L:9D treated groups showed little variation. The present findings indicate that long-day and continuous-light, when given for longer durations, causes photorefractoriness (a state in which birds are unable to respond to light) and thus suggest the involvement of endogenous circadian components in regulating reproduction and associated events during photoperiodic manipulation of light/dark cycles in female blackheaded buntings.