Winter mortality of cottontail rabbits (Sylvilagus jloridanus) was studied within 2 beagle field trial enclosures. Population estimates based on live-trapping indicated a September to February mortality of 45 and 75% on the 2 areas. Predation by hawks and owls was the most important identifiable mortality factor on both enclosures. Flush censuses indicated that imported rabbits suffered a higher rate of mortality than native rabbits. Recommendations for the management of field trial grounds are given.