. The Canadian field-naturalist. 16 The Canadian Field-Naturalist Vol. 94 by calf-cow ratios in winter, did not decline signifi- cantly during 1965-1979 (Table 4, Column 4), the drop in observed X probably indicates a shift from the period of net ingress to one of net egress. Two observations in the later years of the study suggest that egressing individuals were primarily yearlings. Mytton and Keith (unpublished data) re- ported that three radio-collared cows and one bull dispersed permanently from the Rochester Study Area;allwere^ when they left. In 1975-1977, bulls color-collared as
. The Canadian field-naturalist. 16 The Canadian Field-Naturalist Vol. 94 by calf-cow ratios in winter, did not decline signifi- cantly during 1965-1979 (Table 4, Column 4), the drop in observed X probably indicates a shift from the period of net ingress to one of net egress. Two observations in the later years of the study suggest that egressing individuals were primarily yearlings. Mytton and Keith (unpublished data) re- ported that three radio-collared cows and one bull dispersed permanently from the Rochester Study Area;allwere^ when they left. In 1975-1977, bulls color-collared as yearlings were re-observed sig- nificantly less often than adult cows, calves, yearling cows, or adult bulls (Table 6). Adult cows were re- observed more frequently than female calves, or adult and yearling bulls. Three factors could affect sex- and age-specific re-observation rates: (1) differential sur- vival, (2) differential observability, and (3) differential movement. Because Mytton and Keith (unpublished data) found no difference in survival of radio-collared yearlings and adults, or in observability of radio- collared bulls and cows, differential movement was evidently responsible for the very low re-observation rate of yearling bulls. Habitat Use Our index to habitat use was provided by percent /o - Y = + r^= 60 — • • 50 N ^ V • • s^ • • 40 • • • • • • • • • • 30 • • • 20 - 1 1 1 1 MEAN 20 MONTHLY 40 SNOW 60 DEPTH 80 (CM) Figure 8. Relationship between mean monthly snow depth and use of lowlands by Moose at Rochester, Alberta, during helicopter transects. area of different vegetation types within km of Moose locations (Table 7). Mytton and Keith (unpub- lished data) and Hauge and Keith (unpublished data), using radiotelemetry at Rochester and Fort McMur- ray. Alberta, noted greater use of open lowlands by bulls vs. cows in late fall and early winter. We detected no such difference in habitat use, but th
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