Abstract
The annual cycle of reproduction in many birds is regulated by seasonal changes in day length. While a great deal is known about the temperate forms, photoperiodic control of reproduction in tropical and subtropical birds are scanty. Due to the lack of experimental data concerning photoperiodic regulation of reproduction in subtropical and tropical birds, particularly females, we performed the above experiment using subtropical female house sparrow, a resident passerine bird. House sparrow is unique among photoperiodic species in that daily photoperiods of both greater and lesser duration than minimum induces gonadal growth. In the view of contradictory opinion expressed from a number of authors regarding photoperiodic responses of house sparrow, we conducted experiments with photosensitive subtropical female house sparrow in which the birds were exposed to continuous light (LL), continuous dark (DD), short days (8L: 16D), long days (15L: 9D) and natural day length (NDL) . Data from the birds exposed to continuous light and long days shows that ovarian growth was followed by regression and onset of refractoriness; short days and continuous dark failed to make any ovarian response and natural day length capture bird, show gonadal growths only when they received increasing day length of summer. The sparrows exposed under different treatment did not show any significant variation in their body weight responses.
Our results conclude that:
(a) The subtropical house sparrow is photosensitive and light stimulation is a prerequisite to its reproductive activities.
(b) The photoperiodic responses of this bird seems to support the Bunning Hypothesis (external coincidence model) .
