Seasonal reproduction in subtropical brahminy myna, Sturnus pagodarum: role of photoperiod.

Experiments were performed to study the extent of the involvement of photoperiod in the timing of seasonal reproduction in brahminy myna (Sturnus pagodarum). The reproductive cycle corresponds to annual variations in day length and there is a marked seasonal variation in the photogonadal response of birds, which is evident when birds are shifted from normal day length to long photoperiods (15L:9D) every month. This is supported by the results from constant long (15L:9D) and short (9L:15D) photoperiodic treatments. Whereas the reproductive cycle was abolished in short photoperiods, a 15L:9D photoperiod induced a single complete gonadal growth-involution cycle after which birds became photorefractory. Further, exposure of birds to 8L:16D during different phases of the reproductive cycle indicated that the effect of short photoperiods on advancement of photosensitivity depended on the reproductive status attained when shifting took place. These laboratory investigations clearly suggest that the annual photocycle affects the timing of the reproductive cycle of brahminy myna.