Extraretinal photoreception during the gonadal photorefractory period in the golden-crowned sparrow

Abstract

Extraretinal photoreception is involved in the perception of light used to measure photoperiodic time during the initiation of gonadal growth in a number of birds. Evidence is presented which demonstrates that extraretinal photoreceptors are also involved in measuring photoperiodic time during the gonadal photorefractory period in the goldencrowned sparrow (Fig. 3). Untreated sparrows were able to terminate the refractory condition while being exposed to long dim days (16DL:8D; DL=0.2 lux). However, birds which had their head feathers clipped to allow more light to penetrate through to the brain were maintained in the refractory state under the same lighting conditions. These results demonstrate that extraretinal photoreception is involved in the maintenance of photorefractoriness in birds.