In March and April, 1950, seven adult opossums were found dead in the traps. None of these showed any evidence of disease or injury and they were normal in appearance except that they were thin. It was concluded that death had resulted from exposure and starvation in the traps in these animals already in critical condition as a result of winter food scarcity and frequent fasting. Up to this time the procedure had been to check the trap line only on alternate days and no mortality had resulted, even in the coldest part of the winter. The implication is that by spring, opossums are in a condition so critical that they are unable to withstand exposure or fasting and die whenever weather conditions are unusually severe. After these losses in the spring of 1950, trap lines were checked daily. However, in October, 1950, further mortality in traps resulted in the loss of three or more opossums. All three of these were rat-sized young of second litters. These young lacked the abundant supply of fat characteristic of larger opossums in fall, and seemingly were unable to withstand exposure to chilly nights. Such susceptibility to cold might result in heavy mortality in retarded second-litter young when cold weather of autumn is unseasonably early or is unusually severe. Natural enemies of the opossum on the area include the red-tailed hawk, horned owl and coyote. Because of the opossum's nocturnal habits it is rarely exposed to hawk predation. Food habits of the coyote on the area have not yet been investigated. Numerous instances of horned owl predation on opossums have been recorded in the literature. On January 15, 1950, an owl attacked an opossum caught in a live-trap. The trap was found overturned, and a few feet away were entrails and a quantity of opossum hair where the animal was eaten. Low vegetation in the vicinity had many fine down feathers of the owl clinging to it. On December 24, 1950, the carcass of a small adult opossum was found in a pasture near the edge of the woods. The head and tail were intact, but otherwise little more remained than the spinal column, girdles and larger limb bones. White excreta of a large bird beside the carcass indicated predation by a raptor, probably a horned owl. SUMMARY On a natural area, the University of Kansas Natural History Reservation, in Douglas County, northeastern Kansas, the population of opossums was studied, chiefly by live-trapping, in the fall-winter-spring seasons of 1949-50, 1950-51 and 1951-52. The study area provided a varied habitat of elm-oak-hickory woodland, pastureland, and fallow fields. Opossums use all parts of it, but concentrate their activities in the woodland. Opossums being mainly nocturnal were rarely seen in the daytime, except when caught in traps. Reactions to humans varied; some were indifferent, some feigned death, others merely tried to escape, and some defended themselves vigorously, snarling and snapping.