Sexual behaviour cycles in the wild rabbit, Oryctolagus cuniculus (L.)

Abstract

I t is generally accepted that the period of oestrus in the rabbit is more or less continuous during periods of favourable environmental and nutritional conditions (Hammond and Marshall 1925; Robson 1949; Bullough 1951; Eckstein and Zuckerman 1956). I t is also known of both the domesticated rabbit (Hammond and Marshall 1925) and the wild rabbit (Brambell 1944) that, given suitable conditions, the doe will accept the buck at any time although with reduced frequency during pregnancy. During the course of a biological study at Thurgoona, N.S.W., of 52 repro-ductively active rabbits (35 females and 17 males) confined in a %acre enclosure, a suggestion of a cycle in sexual behaviour became apparent. Observations were intensified and continued daily for 17 weeks, involving 600 man-hours. They covered a period from the end of the 1957-58 summer, through the autumn flush of green pastures when breeding commenced, and concluded in midwinter. Sexual attractive-ness of the does was demonstrated by the behaviour of the males who followed and circled them persistently, attempted copulation, and frequently smelled and nipped a t their hindquarters. Females became sexually attractive for short periods at intervals of 7 days or multiples thereof. Their attractiveness to the males in their group a t these behavioural peaks appeared to vary greatly. When weak the attraction seemed to be analogous with the "weak oestrus" in sheep observed by Quinlan, Steyn, and Vw (1941). At the conclusion of periods of strong sexual attraction the does actively solicited the bucks and fertile copulations occurred, following which the females rapidly lost their attractiveness. The 7-day behavioural cycle continued during pregnancy and was especially evident at 14 days when many pregnant females apparently mated again. After the gestation period of 30-32 days a fresh 7-day cycle commenced, either during the succeeding pregnancy or after an apparent failure to mate or conceive at the post-partum oestrus; and also following known cases of resorption. The initial stimulus to the males was probably an odour since their excitement always commenced after smelling the ground where the females sat, and also since the attractiveness of a female to the males in her group was greatly diminished on rainy nights. In view of evidence that the female rabbit has a follicular cycle of about 7 days (Shibata 1931 ; Buttner and Wienert 1935) or 7-10 days (Hill and White 1933), and of the demonstration by Hamilton (1951) of a regular peak in the number of cornified cells in the vaginal smear from unmated does occurring at 4-6 day intervals, it seems possible that the cycle observed in the mating behaviour of the rabbits at Thurgoona could be associated with follicular development.