We had scheduled the release for mid-March for several reasons which we felt would maximize chances for success. Deer are concentrated then in the Huron Mountain area and vulnerable to predation. Pregnancy and subsequent whelping of the alpha female might increase her attachment to the new area. Furthermore, the snow is usually deepest then and hinders travel. However, a few days before the release, a freak rainstorm had settled the snow, and cold temperatures had frozen it so hard that animals could walk readily on top, making travel conditions excellent. [Illustration: _Fig. 9.--The anesthetized wolves were placed aboard an aircraft in International Falls, Minnesota (USFWS Photo by Don Reilly)_] [Illustration: _Fig. 10.--The wolves were kept lightly drugged during the flight to Michigan (USFWS Photo by L. David Mech)_] [Illustration: _Fig. 11.--In the Huron Mountain area of Upper Michigan the wolves were taken to another holding pen (Photo by Don Pavloski)_] [Illustration: _Fig. 12.--Biologists checked the signal from each radio-collar before the wolves were released into the holding pen (Photo by Don Pavloski)_] An observation shack 120 feet (36.6 m) from the pen was used to determine the activities and interactions of the four wolves. Weise spent three nights in the shack and also observed the wolves each day of the one-week penned period, for a total of 20 hours of observation (Fig. 14). During preliminary air and ground checks of radio equipment, we discovered that Wolf No. 10 had a defective collar. Thus on March 12, we subdued her with a choker, restrained her with ropes, replaced her collar and released her just after sunset. We then opened the pen, and let the other wolves loose. [Illustration: _Fig. 13.--While in captivity, the wolves were fed primarily on road-killed deer (Photo by Don Pavloski)_] The subsequent locations of the wolves were then checked intermittently through aerial radio-tracking (Mech 1974), with a receiver and antenna from the AVM Instrument Co., Champaign, Illinois, used in a Cessna 172 and a Piper Colt. We made two flights each day for the first 2 days after release, one each day when weather permitted, until April 20, three per week in May, approximately two per week from June through September, and three per week in October and November. A total of 194 hours were flown, 80 per cent by Weise, and the remainder by Hook. Aerial locations were usually recorded to the nearest 40 acres (16 ha.). We also tracked the wolves from the ground whenever interesting or significant activities were observed during flights or were reported by ground observers. Carcasses of prey animals were investigated from the ground after consumption was complete and the wolves had left. Deer eaten by the wolves were considered killed by them if the ground check revealed fresh blood or flesh, or signs of a struggle. Scats were collected along the tracks of the wolves in the snow whenever possible.