Abstract
Photosensitive Redheaded Buntings (Emberiza bruniceps) were exposed to different artificial photoperiods, and continuous light (LL) and darkness (DD) . The daily photoperiods of 12, 13, 15 and 20 hr per day stimulate the gonadal development and the fattening; the rate of growth is however less in the birds exposed to 12 and 13 hr than those exposed to 15 and 20 hr. In contrast, 6L : 18D, 8L : 16D, 10L : 14D and 11L : 13D light regimes fail to stimulate such activities in 4 weeks. In LL, a gonadal-growth-involution cycle is apparent in a duration of 250 days; DD on the other hand, could not stimulate the hypothalamo-hypophysial axis in a 175-day treatment. The results suggest that light is prerequisite for initiation of physiological processes (such as gonadal growth and fattening) in the Redheaded Buntings, and that this species has a definite photoperiodic threshold at between 11 and 12 hr photoperiod to its reproductive and metabolic activities. Further, a period of insensitivity (photorefractoriness) develops in buntings that are stimulated, similar to many north temperate birds.
