However, during late January, February, and March of 1969 the deer were much more concentrated, mostly in conifer swamps, along southwest-facing slopes, or on lakes. Although groups of two or three animals could be found in scattered inland "pockets" throughout the winter, groups of five or six were not uncommon on lakes during January. The tendency to concentrate continued to increase, and on February 6, as many as 11 deer were observed on one lake; by March 13, group size had increased to as high as 22 deer in the same area. Throughout February and March, heavy concentrations of deer tracks covered most wilderness lakes, further evidencing much greater use of shorelines than had occurred in the two previous winters (fig. 5). No doubt deer tended to concentrate on lakes because travel inland became so difficult. On January 28, two deer were seen plowing through snow up to their necks. Although the snow began settling in February, and the penetrability decreased, by late February running deer still plunged chest-deep and had to hesitate at every bound. These conditions persisted until about March 26, by which time a surface crust strong enough to hold a running deer had formed. [Illustration: _Figure 5.--Under unusually deep snow conditions, deer used lake shores heavily. (Photo courtesy of L. D. Mech.)_] In considering wolf mobility in snow, two types of movement must be recognized: the trot used during general travel, and the bounding used while chasing prey. The trot is an easy gait of about 5 m.p.h. on firm footing (Mech 1970), and can be continued for hours at a time. During periods of deep snow and high penetrability, most wolf travel is on frozen waterways, roads, snowmobile trails, and animal trails, including the wolves' own pathways, which become well packed with frequent use (fig. 6, 7A, B). Such travel was observed during each of the three winters of this study. [Illustration: _Figure 6.--Wolves travel single file in deep snow. (Photo courtesy of L. D. Mech.)_] [Illustration: _Figure 7.--(A) A single wolf must break his own trail through the snow. (Photo courtesy of L. D. Frenzel.) (B) Regular use by a pack keeps trails open. (Photo courtesy of L. D. Mech.)_] The second type of wolf movement affected by snow is the leaping and bounding associated with chasing prey. The shallower angle of the wolf's bound (fig. 8) (compared with that of the deer) often causes the wolf to flounder in snow that presents little hinderance to deer (Mech 1970). Such was the case in January and February 1967 in our study area. During 1967-68 no observations of wolves chasing deer were made by the authors, but reports by other field workers indicated that running conditions were similar to those of 1967. [Illustration: _Figure 8.--Wolves run at a shallow angle, thus hindering them in deep snow. (Photo courtesy of D. H. Pimlott.)_]