Photoperiodic control of ovarian growth in the subtropical house sparrow, Passer domesticus: evidence of an external coincidence system.

Groups of adult female house sparrows (Passer domesticus) were placed under short days (8L/16D) and continuous darkness (DD) after photostimulation by long days (15L/16D) for either 25 or 40 days and another two groups of photostimulated birds were continued on long day (15L/9D) photoperiod. Two groups of photosensitive birds were subjected to 8L/16D or DD and they treated as controls. The rate of ovarian regression was nearly the same under transfer to 8L/16D or DD. Birds placed under long days maintained ovarian growth and this exclude the possibility of refractoriness. However, the photosensitive birds placed under 8L/16D or DD did not show any ovarian growth. The results of these experiments seem to support Bünning - Pittendrigh external coincidence model.