Abstract

The New Holland mouse, Pseudomys novaehollandiae, has been reported to have a distinct 5-month breeding season, August to early January, with occasionally an extension to March. Hence it is classified as primarily a seasonal breeder with some of the flexibility of an opportunistic breeder. We present evidence of an extension of the 1991-92 breeding season to at least 10 months, from mid-October or earlier, to late July. In May 62.5% of females were pregnant or lactating whereas 25-44% were pregnant or lactating at different sites in July. Our data from sand-mined dunes extend from Bridge Hill Ridge at the northern end of the Myall Lakes National Park to Tomago near the mouth of the Hunter River. We collate data from studies over the last 20 years, documenting extended breeding in 8 different years, 6 from one region, and at least 4 from another. Twenty years of rainfall data from nearby weather stations in the two regions show extended breeding to be a response to climate, when rainfall between September and March exceeds a threshold value of 750-800mm (approximately 120% of the long-term average), with at least 420-480mm falling during the first three months of the year (approximately 130% of the long-term average). While rainfall appears to be the ultimate factor, we support Kemper''s hypothesis that the proximal factor is most likely to be the abundance or quality of food produced by above-average late summer rainfall.