The Timing of Breeding by Zebra Finches in Relation to Rainfall in Central Australia

Abstract

Zebra Finches Taeniopygia guttata are renowned for breeding opportunistically in arid Australia and for their ability to nest immediately in response to rain at any time of year. However, this conclusion has rested on short-term and incidental observations. We monitored breeding of Zebra Finches at Alice Springs, central Australia, over a seven-year period by estimating the month of hatching of free-flying subadults caught at a walk-in trap. Capture-mark-recapture analysis suggested that the monitored population was open and highly mobile and exploited a large home range. Despite gaps in the sampling a multiple regression analysis found a significant statistical relationship between breeding and the incidence of rainfall. When conditions were favourable in a given year Zebra Finches had a very long reproductive period with 10.6 equally good consecutive months for breeding. Breeding was possible in every month of the year but was least in April and greatest n October. Low winter temperatures did not prevent breeding. The heavier the rainfall, the more intense and the longer the breeding episode. Once a breeding episode began, surges of breeding activity corresponded with follow-up rains. We did not observe the immediate response to rainfall described by earlier authors. On the contrary, the statistical analysis revealed that rain had a negative effect on breeding in the month in which it fell, and in the following month. There was a lag between the onset of the first rains and the onset of breeding, ranging from one to two months in summer to two to three months in winter. The statistical analysis revealed that rain four months previously had the most profound positive effect on breeding. Hatching of the first clutches coincided with the first availability of ripening grass seeds. The artificial supply of abundant dry seed, on its own, did not stimulate breeding. The timing of seed set by grasses in central Australia is complex, depending on the species composition, the prevailing temperatures immediately after rain, and the amount and timing of previous falls of rain. We suggest that Zebra Finches track these factors and breed opportunistically as soon as new supplies of seed are available.