Two principal methods of study were used in this investigation. The
first involved recording the snow depth and support quality
("penetrability") in feet and tenths of feet (Verme 1968). Snow
measurements were taken during the winters of 1966-67, 1967-68, and
1968-69, in which large differences in snow conditions existed. Ten
such measurements were made weekly near Isabella, Minnesota, in an open
aspen (_Populus tremuloides_) stand away from influences that might
have caused drifting or other unusual snow conditions; the measurements
were averaged. Penetrability was determined with Verme's
snow-compaction gauge--a 3-foot piece of 1-1/8-inch (outside diameter)
copper tube filled with lead to total 3 pounds, which gives a weight
per area of 211 gm./cm.^2. To obtain a measurement, the pipe is held
vertically with its lower end just flush with the snow, and then is
released. The depth to which it sinks is considered the penetrability
of the snowpack by a walking deer.
Although the snow conditions measured at Isabella are not
representative of the entire study area, year-to-year comparison in the
Isabella area should also apply generally throughout the region.
The second technique used in this study was observing the movements of
wolves and deer. This was usually done from low-flying aircraft, and
was facilitated by the use of radiotracking, as described by Mech _et
al._ (p. 1). Close inspection of wolf-killed deer was made from the
ground (Mech and Frenzel, p. 35).