Social behaviour of an experimental colony of wild rabbits, Oryctolagus cuniculus (L.) II. First breeding season

Abstract

Continuing the report on the social behaviour of an experimental colony of the Australian wild rabbit, Oryctolagus cuniculus (L.), developments during the first breeding season are described. Collected data showed the survival value of social status. During the breeding season, which lasted 7 months (June to December 1955), the dominant doe littered at regular monthly intervals, the second ranking doe six times, and the third ranking doe only five times. The survival rate for kittens was highest for those of the dominant ranking doe (56per cent.) and lowest for those of the lowest ranking doe (31 per cent.). This was clearly related to the quality of the breeding sites used; the dominant individual littered within an established burrow whilst the subordinates dropped their litters in isolated breeding stops. The growth rate of the progeny was also highest for those of the dominant doe and lowest for those of the third ranking doe, but seasonal variations influenced the growth of kittens too-animals born during the winter months growing fastest and those during the summer months slowest. Some female progeny of the dominant doe born at the beginning of the season reached maturity at the age of 3 months and bred successfully at the end of the season. Emotional factors played a significant role in sexual activities of both bucks and does. The growing population split spontaneously into separate groups, each with its own dominant pair and its own territory, the boundaries of which were respected by all members of the colony. There were indications of the existence of a family as well as of a group unity. In the colony were adult males who did not join either of the two groups permanently but who were prepared to seize the positions of the dominant bucks whenever the opportunity arose. During the breeding season, 139 kittens were born to three adult and three young does but only 59 survived to maturity. Climatic conditions proved to be the major factor controlling population numbers. During the earlier stages of the breeding season, cold, rainy weather affected mainly the progeny of subordinate individuals but the dry, hot conditions of summer hit all members of the colony irrespective of age or status. Avian predation was the second important factor influencing population numbers. There was no indication of a controlling role by intestinal species of Eimeriu (Coccidia) or any other pathogenic microorganism.