Ted R. James

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Educational Foundations & Research


A study of the ecology and life history of the whitetailed jack rabbit (Lepus townsendii campanius Hollister, 1915) was conducted in North Dakota between April, 1964 and December, 1965. The objectives of this study included investigations of sex and age characteristics, reproduction, growth and development, movement and habitat utilization, and population structure. Growth and development, reproduction, and population characteristics were determined by autopsy of 836 jack rabbits collected in 21 consecutive months throughout North Dakota. Ear tagging and radio telemetry techniques were utilized to determine movement and home range.

A definite breeding cycle in males was demonstrated by the seasonal fluctuation in testicular and epididvmal weights. Sperm production peaked in March and declined rapidly in late July. The breeding season was observed to be 148 days in length, and was synchronous. Four distinct breeding periods were observed each year. Females produced an average of 3.29 litters, for an average of 14.6 young per season. Pre-implantation loss and resorption were found to account for over 20 per cent of ova shed. The loss of entire litters was estimated to represent an additional seven per cent prenatal loss.

A definite sexual dimorphism was observed, with females being significantly larger than males in every respect except ear length. Three distinct age classes were distinguished on the basis of epiphyseal closure of the humerus. Age Class I individuals became Age Class II at approximately six or seven months, and Age Class II became Age Class III at 13 to 14 months. Developmental and age characteristics were estimated up to 48 months by comparing the dry weight of the lenses with epiphyseal closure, weight, and body measurements.

Investigation of the movements of jack rabbits indicated that adults may move over an area of one section or more. Observations on one juvenile male indicated a home range of 25.6 acres. Jack rabbits apparently move distances of at least four miles into concentration areas during the late fall or winter.

The population contained a significantly greater proportion of females than males, with females being predominant in all age classes. The age structure of the population was observed to be approximately 65 per cent juvenile. The estimated life span and turnover rate for the population were 1.55 and 3.4 years, respectively. Juvenile mortality prior to the severe winter period was estimated to be as high as 75 per cent. A modified life table was devised to indicate the probabilities of animals living long enough to attain a certain lens weight rather than a certain age. The mortality rate was highest for animals in the 222.5 mg lens weight range.