Circadian periodicity and the initiation of gonadal growth in male blackheaded buntings (Emberiza melanocephala)

Abstract

Photosensitive male blackheaded buntings were held under six different light cycles consisting of a 6-hour main photophase coupled with scotophases of various durations (6L/6 (2 n+1) D). Testicular growth was stimulated in buntings by cycle lengths of 12-(6L:6D), 36-(6L:30D) and 60-hours (6L:54D), but not by cycles of 24-(6L:18D), 48-(6L:42D) and 72-hours (6L:66D). These results are consistent with the Bünning hypothesis and indicate that an endogenous rhythm with a period of approximately 24 hours plays a role in the initiation of testicular growth in this bird. © 1981 Springer-Verlag.