RESUMO
To examine the importance of the inductive light period of a skeleton photoperiod in relation to the endogenous circadian rhythm of photoinducibility mediating photoperiodic induction, P. domesticus were exposed for 28 weeks to a series of skeleton photoperiods, viz. 6L:4D:1L:13D, 6L:6D:1L:11D. 6L:8D:1L:9D and 6L:14D:1L:3D. The inductive effects of 1 hr light pulse at night varied depending on the time of its placement. To compare the inductive effects of complete and its corresponding skeleton photoperiods, birds in the second experiment were subjected for 20 weeks to 12L:12D and 6L:5D:1L:12D given daily or interposed on alternate days with constant darkness (12L:12D/DD and 6L:5D:1L:12D/DD). There was a difference in the rate and magnitude of response between the complete and skeleton photoperiods. It appears that the subtropical house sparrow uses photoperiodic strategy in regulation of its seasonal testicular responses similar to that is reported for its temperate population.