Seasonal variation in photogonadal response of the tropical weaver bird

Abstract

A marked seasonal variation in photogonadal response of the tropical weaver bird has been demonstrated by shifting the birds from normal day length to continuous light every month of the year. While the gonadostimulatory effect of the long photoperiod was immediate during progressive, peak, and regressive phases of the reproductive cycle, the response was delayed by 1 to 3 months during the quiescent and regressive phases, respectively. Although a progressive decline in photosensitivity ensues after the gonads have attained a peak, weaver finches, unlike other photoperiodic passerine forms, do not develop a typical photorefractoriness which is described as spontaneous gonadal collapse and absence of redevelopment under continued long photoperiod. This is evident from the following: (1) gonadal activity is sustained indefinitely in extended long days; (2) during the period of gonadal regression birds are still photosensitive; (3) the sexually quiescent gonads of the postreproductive period can eventually be stimulated by long days; (4) the delayed photoresponse at this time cannot be “broken” by a pretreatment with long dark periods.