PHOTOPERIOD AND THE REFRACTORY PERIOD OF REPRODUCTION IN AN EQUATORIAL BIRD, QUELEA QUELEA

Abstract

SUMMARY In a number of avian species in which testicular development can be evoked by increased daily photoperiods, it has been found that such development cannot be sustained indefinitely and that there is a period following each breeding cycle during which increased daily photoperiods are ineffective. This is the refractory period. Gametogenesis ceases during this phase and its duration plays a critical role in the timing of the breeding cycles. The duration varies from species to species and in most temperate birds lasts some four months. Some authors claim that the whole of the avian breeding cycle is under photoperiodic control and that the duration of the refractory period is determined by variations in daylength, short days dispersing it and long days prolonging it. When the equatorial weaver finch, Quelea quelea, was placed under a 17‐hour daylength, the internal rhythm of reproduction was accelerated and the birds quickly passed into a premature refractory period. During the refractory phase three weeks of short 8‐hour daylengths followed by a 17‐hour photoperiod had no effect on the duration of the refractory period, and birds displayed a recovery of spermatogenetic function at the same time as those maintained under a continuous 17‐hour photoperiod. In each case the refractory period lasted six weeks. Birds maintained under an equatorial daylength of 12 hours also entered a refractory period and, again, pretreatment during the refractory period with shortened lengths of 11·25 hours had no effect on its duration. Quelea which were maintained under a constant photoperiod of 11·25 hours during their refractory period showed a recrudescence of gametogenesis six weeks later, but under an 8–hour daylength the gonads remained regressed to the end of the experiment. It was concluded that in this equatorial species a semi‐autonomous internal rhythm of reproduction operates and the refractory period is independent of photoperiodic fluctuations. There was no evidence of a premature dissipation of this period by a reduced photoperiod, nor was there a prolongation of refractoriness by long daylengths.