REPRODUCTION AND POPULATION CHARACTERISTICS OF WHITE-TAILED JACKRABBITS IN SOUTH DAKOTA

We evaluated the reproductive biology of314 white-tailed jackrabbits (Lepus townsendii) in 44 counties throughout South Dakota from June 2004 to September 2005. We classified jackrabbits as juveniles or adults based on the closure of the proximal epiphysis of the humerus using X-ray analysis. We determined annual reproductive activity through fluctuations in measured weights of reproductive organs for both sexes. The 2005 breeding season started in late February and proceeded until mid-July, approximately 142 days, allowing for females to potentially produce 3.3 litters. We found four distinct breeding periods by the overlap of estimated conception and parturition dates. Mean litter size was 4.6 per female (range 1-8). Prenatal mortality from preimplantation and postimplantation loss was highest (32%) in the first littering period in 2005.