A study of the biology of the Wild Rabbt, Oryctolagus cuniculus (L) in confined populations. 3. Reproduction.

Abstract

Evidence is presented for a reproductive cycle in the confined wild rabbits (Oryctolagus cuniculus (L.) ) at Albury. Females become sexually attractive and mate at intervals of 7 days or multiples of 7 days. The cycle appears to continue on into pregnancy, and is not interrupted by resorptions. With increase in density, fecundity decreases. There is an increase in the rate of resorption and an apparent suppression of oestrous behaviour, resulting in a lower number of young born per female. Resorption varies seasonally, with the highest litter loss occuring during winter. There is no apparent relationship between dominance per se and fertility. There is an obvious relationship between age and fertility. Older females have larger and more litters than younger females. There is no apparent direct relationship between dominance and rate of resorption. Resorption decreases with age. Young dominant females resorb at the same high rate as, and produce similarly to, the rest of their age group. Litter size increases from approximately 4.0 at the beginning of the season to about 6.0 at the end. There is no relationship between length of period of gestation and either age or size of litter. The incidence of seasonal breeding in the wild rabbit is explained by postulating an annual cycle in male fertility correlated with the solar cycle, with a single peak in spring, and a bimodal annual cycle in female fertility with a minor peak in the autumn and a major peak in the spring. These cycles are greatly affected by nutritional changes in pastures under varying rainfall and climatic regimes.