Reproduction and growth of the fox in the Canberra district

Abstract

The reproductive biology of foxes, Vulpes vulpes L., mainly from the Canberra district, was studied during the years 1957 to 1959. Males were infertile from September till March. Females were monoestrous, producing an average litter of 4.25 yearly. Seasonal changes in the weight and morphology of both male and female gonads are explained in relation to the reproductive condition. Resorption of foetuses was rare, and only one case of pseudopregnancy was recorded. Prenatal mortality of about 22 % was made up almost entirely of the pre-placentation loss of ova or blastocysts. Transuterine migration of blastocysts occurred in a number of vixens resulting in an even distribution to each uterine horn. The sex ratio was 53.3 males to 46.7 females in the Canberra district and 54.2 males to 45.8 females outside the district. Neither ratio departed significantly from 50-50. The mean standard measurements of 84 adult male and 60 adult female foxes, together with growth curves of four fox cubs raised in captivity, are given. The weights of 59 cubs shot in the field are presented. Juvenile foxes had reached the same weight as adults by April and were difficult to distinguish from them externally.