Photoperiodic control of reproduction in a female migratory bunting (Emberiza bruniceps)

Abstract

AbstractTwo series of experiments were performed with photosensitive female redheaded buntings. In the first series, birds were exposed to various cycles (8L/16D, 12L/12D, 13L/11D, 15L/9D, and 20L/4D) for 35 days. In the second, birds were maintained for a period of 120 days under long day lengths (15L/9D), short day lengths (8L/16D), and normal day lengths (NDL). Periodic laparotomies of birds under these schedules indicated that long days induced ovarian growth followed by regression and refractoriness, short days were ineffective, and that the birds in NDL showed ovarian growth during periods in the summer of increasing day lengths, followed by spontaneous regression. Groups of photorefractory birds in long days were transferred to short days (8L/16D) for different periods in order to terminate the refractoriness before returning them to 15L:9D for another 20 days. The results from both series of experiments suggest that the female redheaded bunting uses photoperiods as a primary environmental source of information in regulating its reproductive responses. The threshold for its gonadal activities is a photoperiod of 12–13 h daily. A period of insensitivity (photorefractoriness) develops in buntings that are photostimulated, requiring about 8 weeks of short days for its termination.