Sexual cycles of pigeons in arid and semiarid Australia

The gonad cycles of the crested pigeon Ocyphaps lophotes and the common bronzewing Phaps chalcoptera in inland New South Wales, and the plumed pigeon Geophaps plumifera and the red- plumed pigeon G. ferruginea in central and north-western Australia, have been studied. In each species some males were producing abundant sperm and some females had enlarged ovarian follicles in each month of the year. There was a tendency for fewer birds to be at the maximum stage of spermatogenesis in autumn and winter than in other seasons. The size of the testis was not indicative of its spermatogenic state. There were annual cycles of gonad size in each species; the maxima were the spring and summer. The timing of the cycles did not differ in the two plumed pigeons but in both species the maxima were earlier than in the other species. Male common bronze-wings achieved maximum gonad size earlier than did male crested pigeons. In addition to the annual cycle there were significant biannual effects in males. Except for the male and female of the red-plumed pigeon, in which they may have had some biological significance, these biannual effects were probably only included to improve the accuracy of the curve fitting. There were significant effects of rainfall on the gonad cycle of all species except the common bronzewing; these were consistent with the expected effect of rainfall on the birds' food supply and nutrition. It was concluded that, although the gonad cycles were controlled mainly by changes in photo-period, the abundance of food and the effects of rainfall on it were important in modifying the cycle.