Seasonal variation in sensitivity of the photoperiodic response system in the subtropical tree sparrow (Passer montanus).

We investigated seasonal variations in response to photoperiods in subtropical tree sparrow (Passer montanus), by examining the effects of long and short days on stimulation of response and termination of refractoriness, respectively. We also assessed whether photoperiodic effects were sex dependent. In one study, wild sparrows were transferred in each month of the year to artificial long days (14L/10D) for 12 weeks. Birds transferred from November to March (female) or April (male) showed gradual increase in gonadal growth and darkening of bill color, while those transferred from April (female) or May (male) to July underwent gradual regression in the above responses. Moult in the wing primaries and body feathers progressed with gonadal regression and the birds transferred from April/May to October exhibited gradual increase and decrease in feathers moult. In another study, 6 weeks of short day (9L/15D) exposure could recover responsivity to long days in refractory birds. Male and female birds responded almost in similar fashion with some variations. Overall, our results show a gradual change over seasons in responsiveness of the endogenous response system to stimulatory effects of long day length. They suggest roles of both long and short day lengths in regulation of seasonal cycles in subtropical tree sparrows. 2012 Wiley Periodicals, Inc