Seasonality of Nesting by Zebra Finches at Armidale, NSW

Abstract

Nests of Zebra Finches were surveyed from 1961 to 1965 at Saumarez Pond near Armidale. About 200 birds used 220 trees for nesting within an area of five square kilometres. Two types of nest (breeding and roosting) varied in number according to the season from eighteen (January 1964) to ninety-eight (October 1961). The number of breeding nests built in a season varied between eighty-one (1963-64) and 154 (1961-62). Nesting success (young fledged from eggs laid) varied little, averaging about forty-four percent (n = 382). No laying occurred in June or July (except once), when temperatures were often below freezing. At least two birds born in spring bred in the autumn of the same breeding season. In contrast to the breeding regime in arid areas, nesting activities of Zebra Finches at Armidale were not directly affected by drought; during the autumn of 1965 the peak of breeding activity was reached in March (19 breeding nests) when no rain had fallen for six weeks and the effect of prolonged drought on the vegetation was apparent. The results may be interpreted in several ways: that low temperatures (but not drought) inhibit breeding or that changes of photoperiods or increased availability of food itself stimulate many individuals to breed in this population. From a review of relevant literature, it is concluded that, if there is a proximate factor for the breeding of Zebra Finches, it must be different in different parts of the range of the species. It is suggested that individual differences exist in response to various proximate factors for reproduction and that the populations in the intermediate climatic zone are more polymorphic with respect to types of response than the populations that occur where the causal relations of environmental factors are predictable, if not periodic, in occurrence.