Demographic characteristics of cottontail rabbit (Sylvilagus floridanus) populations on enclosed areas of natural habitat

Cottontail rabbit populations were studied on three beagle field trial enclosures through the fall and winter, 1972-73. Rabbits were captured in wooden box traps during four, 2-week trapping periods. Captured animals were marked with eartags and tail dyes. Stocking of rabbits occurred on all three study areas and all introduced rabbits were marked to distinguish them from native rabbits.

Sex ratios of both native and stocked rabbits were essentially 50:50 on all study areas. Overlapping of aging criteria in fall and winter cottontails prevented any analysis of cottontail population age structures. The above also prevented analysis of weight trends throughout the fall and winter. However, it was determined that the average weights of stocked and native rabbits were not significantly different.

Flush censuses following each trapping period appeared to be invalid as an index to total population trends. The number of rabbits flushed appeared to be related to the density of cover rather than population density of cottontails. Flush censuses did, however, allow a comparison of the abundance of native and stocked cottontails at each census. The census following the fourth trapping period indicated that stocked cottontails suffered greater mortality than native rabbits.

Organized field trials were attended on the enclosures to gather additional census data. However, these data were not useful because the number of flushers, the area covered and the general intensity of effort lacked standardization from one field trial to the next.

Movements, based on capture locations, exhibited no seasonal trends; average distances traveled by stocked and native cottontails were similar (P = .05). Average distances traveled between capture locations varied from 2.49 grid-units (518 feet) to .50 grid-units (104 feet). An apparent positive relationship between enclosure size and average distance traveled was noted. However, no explanation could be offered for the above phenomenon.

Three vegetative cover types were compared for cottontail utilization. Old field cover was preferred over woodland and pasture vegetation. However, where old field vegetation exhibited a marked loss of cover quality during late winter, an increase in woodland use by cottontails was detected.

Five methods of population estimation were compared and the Eberhardt (1969) method was found to be the most reliable. Population densities varied from .59 to 8.57 rabbits per acre.

Fall and winter mortality rates of 33 to 75 percent were determined from periodic population estimates. Avian predation was the most important mortality factor during the present study. Hawks and owls killed an estimated 58 rabbits on one study area.

Except for a slightly higher mortality rate among stocked cottontails, the present study found no differences in demographic patterns between native and stocked rabbits in enclosed areas of natural habitat.