The reproductive performance of female red foxes, Vulpes vulpes, in central-western New South Wales during and after a drought

The reproductive condition of 295 female red foxes, Vulpes vulpes, collecte d during and shortly after a severe drought in central-western New South Wa les, Australia, was assessed to assist research on the potential use of imm unocontraception. The ovulation and conception rates per vixen for the 222 foxes that ovulated were 4.62 +/- 1.50 and 3.58 +/- 2.18 (mean +/- SD), res pectively. The resorption rate and mean litter size per vixen for the 188 f oxes that were pregnant were 0.47 +/- 0.92 and 3.75 +/- 1.91, respectively. Details of the parameters are provided for each age-class. The proportion of the overall population that was pregnant was 0.847. Conception rates and litter sizes peaked in fifth- and sixth-year vixens, but vixens over 8 yea rs of age produced as many cubs as first-year breeders did. Vixens collecte d during 1996, when rainfall was above average, contained significantly mor e corpora lutea than vixens collected during the drought years 1994 and 199 5. There were no significant differences in other reproductive parameters ( i.e., conception and resorption rates, litter size, and proportion of the p opulation that was pregnant) between the 3 collection years. Mating occurre d within a 3- to 7-week period from mid-June to the end of July and births from early August to late September. From a practical point of view, vixens will need to be targeted with immunocontraceptive baits in autumn.