Our study was designed to determine if a large outdoor enclosure is suitable for evaluating the shelter requirements of gray squirrels. We designed and tested an escape-proof enclosure to determine how many squirrels could be maintained without overpopulation, and to determine if reproduction would occur. A 2-acre area in a stand of mixed hardwood about 40 years old with low mast production and few den sites was selected in the West Virginia University Forest, II miles east of Morgantown. The tree canopy was removed from a 30-foot wide strip centered on the fence line, leaving approximately 1.5 acres of canopy inside the enclosure. The squirrel-proof fence was 7.5 feet high with a 3-foot strip of 28-gage sheet metal attached above the 5-foot high base course of I-inch mesh wire. A 3-foot wide I-inch mesh wire was laid on the ground and attached to the bottomofthe fence to prevent animals from going underneath. Materials cost approximately $2,000, and 125 man-days were used to build the fence. We plugged the natural dens and installed 10 den boxes (Barkalow and Soots 1965) 20 to 25 feet up in trees. We did not interfere with leaf nest construction and maintenance. An observation platform was constructed near the enclosure center. Natural foods were supplemented with corn and laboratory rat chow ad lib. Drinking water was supplied. Squirrels were ear-tagged and fur-marked with Nyanzol D dye. (Use of a trade name is for information only, and is not an endorsement by the U. S. Department of Agriculture.) External parasites were controlled by rotenone, and sodium sulfamethazine was added to the drinking water to control coccidiosis. No losses to predation were observed or suspected. Age estimates were made, using the techniques described by Uhlig (1955) and Barrier and Barkalow (1967).
