Seasonal patterns of reproduction in heathland honeyeaters are not responses to changing nectar availability

We monitored nesting attempts of New Holland (Phylidonyris novaehollandiae) and White-cheeked (P. nigra) honeyeaters on two sites throughout 1987 and 1988. Two aspects of the birds' reproduction were correlated with changes in availability of nectar. First, breeding periods of both species were centered on the winter peak of nectar availability. Second, all clutches laid in the first two months of the breeding period failed, and this was the portion of the breeding period when nectar was scarcest. We tested whether these seasonal patterns were caused by changes in availability of food energy by supplying birds on one site with continuous access to sugar-water feeders for 9 months starting in January 1988. Seasonal patterns of nesting effort and nest success were similar for birds on the two sites, and were similar to patterns observed in 1987. We therefore conclude that these patterns were not caused by seasonal changes in availability of food energy. Circumstantial evidence indicated that snake predation may have accounted for most early nest failures. We suggest that predation - rather than scarcity of nectar - may prevent breeding over the warmer months of the year.