Photoperiodic regulation of the reproductive axis in male zebra finches, Taeniopygia guttata.

In arid central Australia, breeding of zebra finches (Taeniopygia guttata) tends to take place immediately after the aperiodic rainfall-this being irrespective of the time of year. As a result, zebra finches have traditionally been considered nonphotoperiodic. Despite this, there are some published reports of photoperiodic effects on behavior in zebra finches. Therefore, we transferred singly housed male zebra finches from a photoperiod of 14 h light and 10 h dark per day (14L:10D) to either 20L:4D or 8L:16D. Control birds remained exposed to 14L:10D. Plasma LH, testicular volume, and body mass were assessed at the start of the experiment and at intervals for a period of 56 days. Testicular mass was measured at the end of the 56-day period. Plasma LH increased significantly in the 20L:4D group after 14 days, but decreased again by 56 days, presumably an effect of increased gonadal steroid negative feedback. Plasma LH did not change significantly in the other two groups. Testicular volume increased steadily in the 20L:4D group during the treatment period and it was significantly higher than that of the 8L:16D group at the end of the experiment. After 56 days of treatment, combined testicular mass in the 20L:4D group was much greater than that of the 8L:16D group, but not quite statistically different from the 14L:10D group. There was no statistical difference in testicular mass between the 14L and 8L groups. Body mass did not differ between any of the groups at any time in the experiment. Our results are consistent with zebra finches being photoperiodic to some degree, despite their opportunistic breeding strategy. When considered in conjunction with recent reports of photoperiodic responses in tropical avian species, these data suggest that the ability to respond to changing photoperiod is more common among avian species than previously hypothesized.