During the winters of 1966-67, 1967-68, and 1968-69, the interactions
of wolves (_Canis lupus_) and white-tailed deer (_Odocoileus
virginianus_) were observed in northeastern Minnesota from aircraft.
Snow depth and supporting ability were also measured during these
winters, and the ability of wolves to capture deer was compared for a
period of usual snow conditions versus a period of extreme snow
conditions.
It was found that during February and March 1969, when snow remained
from 2.5 to 3.9 feet deep and failed to support running deer, wolves
were able to capture deer more easily. This was evidenced by kills that
were left partly or completely uneaten, and by a higher rate of
predation by radiotagged wolves and their associates.
Although both wolves and deer floundered in the extremely deep snow,
the relatively lighter weight-load-on-track of wolves evidently gave
them a greater advantage than under the usual snow conditions, when
wolves were observed floundering more than deer. This factor, plus a
decline in the health and vigor of some segments of the deer population
and a tendency for deer to congregate on frozen lakes, where wolves
have an advantage, help explain the increased vulnerability of deer to
wolf predation during the winters of deep snow.