The termination of the avian photorefractory period and the subsequent gonadal response

Photorefractory golden-crowned sparrows were held on short days (LD 8:16) for from 3 to 8.5 wk before transfer to photostimulatory long days (LD 16:8). Data on the testicular diameter of the sparrows which terminated the refractory condition and responded to photostimulation were divided into two categories. Gonadal regression occurred sooner in sparrows that were exposed to 3-6.5 wk of short days prior to photostimulation than in sparrows previously held under short days for 7-8.5 wk. The results demonstrate that the duration of the avian gonadal response is dependent on the length of time the birds are held on short days prior to photostimulation.