What happens in burrows underground when winter snow is on and various carnivores and herbivores are seeking shelter from the cold is a subject that has long intrigued biologists. The fact that such common animals as the woodchuck, weasel, skunk, and cottontail rabbit may often find themselves confronting one another within the narrow confines of a subterranean tunnel suggests that relationships in burrows during the winter may be instrumental in deciding what will survive to spring. Despite a widespread interest in this subject, the labor necessary for the excavation and study of many ground dens in in any one area has seldom been available to the investigator. Consequently, with help furnished by the National Youth Administration, we availed ourselves of the opportunity to make such a study in the winter of 1939-40. This work was a part of the program of the Rose Lake Wildlife Experiment Station in Clinton County, Michigan. The area is owned and operated by the Game Division of the Michigan Department of Conservation for the study of wildlife management on the farm. The experiment station comprises 1181 acres and lies on a glacial moraine. The topography is irregular and the soil pattern is complex, varying f rom welldrained mineral soils, through intermediate types, to poorly-drained organic soils. The dominant forest type is oak and hickory. Woodlots form approximately 12 per cent of the area, marsh and swamp 25 per cent, and crop and pastureland 63 per cent. The interspersion of farmland, woodlots, and drainage areas is shown in figure 1. From the nature of this area it should be favorable to the woodchuck (Marmota monax rufescens Howell), skunk (Mephitis mephitis nigra Peale and Beauvois), Weasel (Mustela frenata noveboracensis Emmons), rabbit (Sylvilagus floridanius mearnsii Allen), and opossum (Didelphis v. virginiana Kerr) which are the most common of the larger burrow-using mammals in the region. Actually, during at least the year previous to this work, the skunk underwent a marked decline, and the cottontail has been "down" in numbers for several years. The spring numbers of the woodchuck were about one per 10 acres on a 100-acre sample trapped in 1940. In this vicinity there may be two or three pairs of weasels to the section. Opossums were frequently seen during the summer and fall of 1939. Foxes had a den on the Rose Lake area in the summer of 1938 and their tracks were seen at intervals during the winter. An occasional badger has also been recorded, although there were no known residents. The objectives of this investigation were: To get a winter inventory of skunks similar to that taken by Allen ('38b) in Kalamazoo County in 1936-37. To get possible observations on the interrelations of animals in ground dens. To obtain statistical data, including measurements, number of nests, openings, depth, etc., on the dens in this locality. To get further records on woodchucks ear-tagged during the summer.