Waterfowl in an inland swamp in New South Wales. 3. Breeding

Abstract

The breeding of nine species of waterfowl was investigated in a permanent swamp in inland New South Wales in a drought period. Some species were under study for 56 months and all nine were investigated concurrently for a period of one year. The sexual cycles of all species were determined by either one or both of two basic factors. First, fixed seasonal events that regulated breeding to the same general period each year, and second, the availability of certain preferred foods. The latter were considered to be particularly important for those species with erratic breeding seasons or breeding seasons of highly variable length. The three species, musk duck, blue-billed duck, and hardhead, that utilize deep-water habitats were shown to breed more regularly each year than the remaining six species that utilize shallow-water habitats, including the littoral zone and the edge of the swamp. Fixed annual factors then may be more influential in initiating the sexual cycle of those three species. Many of the phenomena in the breeding seasons seemed to be related to the nutritional status of the birds, which was determined by changes in the availability of certain foods. Many of the changes in the availability of food were determined by fluctuations in water level. It is concluded that the most important effects of variations in water level are changes in the food supply of adult birds, and these determine the breeding season.