Prenatal Growth of the Cottontail Rabbit in South Texas

Abstract

This paper reports a study of prenatal growth of cottontail rabbits on the Welder Wildlife Refuge in South Texas. Measurements of known-age cotton- tails showed that the young in utero were smaller than Missouri rabbits of the same ages. However, they were similar in size at birth. A prenatal curve was fitted by hand for crown-rump length; hind foot length and body weight data were also pre- sented. In a study of the population ecology of cottontails on the Welder Wildlife Refuge in South Texas (Bothma and Teer, in press), it was necessary to develop a prenatal growth curve for use in determining conception dates for litters in utero. Since no prenatal growth curves have been developed for cottontails specifically, an attempt was made to do so. The Welder Wildlife Refuge falls within the range of Sylvilagus flor'danus chapmani, but it was apparent that intergrades between S. f. chapmani and S. f. alacer occurred. Hall and Kelson (1959) recog- nize a zone of integradation of chapmani and alacer in South Texas. The Welder Wildlife Refuge lies near this zone. Nonetheless, the char- acters of habitat and coat color are more closely related to chapmani. MATERIALS AND METHODS. A series of 6 covered pens, each 25 ft x 50 ft x 5 ft high, were used. The pens had natural vegetative cover, and were provided with brush and artificial shelters. Commercial rabbit pellets and water were always freely available. A series of males and females were trapped in the field, and the sexes were kept in separate pens for a minimum of 30 days. Since the gestation period of the cottontail rabbit is about 28 days (Lord, 1963), this confinement in-