. The Canadian field-naturalist. 226 The Canadian Field-Naturalist Vol. 89 curate burrow counts were impossible because many burrow entrances were hidden under rocks or in crevices. Table 1—Estimates of lemming burrow densities in three habitats on Truelove Lowland; data are averages of three summers Area sampled (ha) Density (burrows/ha) Raised beaches Polygons Mesic meadows A finer subdivision of the location of bur- rows was attempted in 1970 and 1971. In July 1970 a small (approximately 30 X 50 m), isolated portion of raised beach and the earth mound areas
. The Canadian field-naturalist. 226 The Canadian Field-Naturalist Vol. 89 curate burrow counts were impossible because many burrow entrances were hidden under rocks or in crevices. Table 1—Estimates of lemming burrow densities in three habitats on Truelove Lowland; data are averages of three summers Area sampled (ha) Density (burrows/ha) Raised beaches Polygons Mesic meadows A finer subdivision of the location of bur- rows was attempted in 1970 and 1971. In July 1970 a small (approximately 30 X 50 m), isolated portion of raised beach and the earth mound areas immediately adjacent to it were mapped for lemming burrows (Figure 2). The area examined was bounded by a lake and mesic C. stans meadow, and had a total area of 2300 m-. Clustered burrows individually within about a metre of another burrow were counted as a group; the numbers on Figure 2 indicate the number of burrows within a group. The larg- est concentrations of burrows were in earth mound areas where, for example, a group of 60 burrows lay in an area of about 18m-. Some earth mound areas, however, contained no burrows. Burrows on raised beach proper were strongly associated with frost cracks that served as runways and provided some con- cealment from avian predators. A second beach ridge approximately 625 m long was divided into 25-m- blocks and burrow counts were made in each block (Fig- ure 3). Association of burrows with frost cracks and foreslope transition zone is readily apparent. As elsewhere in the Arctic, micro- topography appears to play an important role in the life of lemmings. In 1971 the proportion of burrows in a number of microhabitats was tallied (Table 2). Frost cracks were clearly heavily used on ridge tops ( Figures 2 and 3); there was a strong association with rocks on backslopes and mesic meadows; and southern exposures were preferred on polygons. Some indication of seasonal shifts in habitat was also obtained in 1971 (Figure 4). Catch- 3 5 3 ^
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