. The Canadian field-naturalist. 1989 Weir and Hanson: Food Habits of Great Horned Owls 13. S. TAIGA Figure 1. Locations of Great Horned Owl food study areas, near Dawson, Yukon Territory (64°N, 139° W) and Bethel, Alaska (61°N, 160° W). Key; B — Bethel, D — Dawson, open circles — study areas, dashed line — outer limits of our definition of northern taiga; much of the area is above treeline. weight, to give approximate adjusted numbers of hares. We treated set T data in the same way, assuming that all hares in that set were adult. The estimated average weights of other mammals were minimum wei
. The Canadian field-naturalist. 1989 Weir and Hanson: Food Habits of Great Horned Owls 13. S. TAIGA Figure 1. Locations of Great Horned Owl food study areas, near Dawson, Yukon Territory (64°N, 139° W) and Bethel, Alaska (61°N, 160° W). Key; B — Bethel, D — Dawson, open circles — study areas, dashed line — outer limits of our definition of northern taiga; much of the area is above treeline. weight, to give approximate adjusted numbers of hares. We treated set T data in the same way, assuming that all hares in that set were adult. The estimated average weights of other mammals were minimum weight plus 40% of weight range, from Whitaker (1980); this was closest to averages for five small mammals in our areas for which there were large samples (Durst 1984; Weir, unpublished). Bird weights were from University of Alaska Museum data (R. E. G. Clarke, personal communication to DW). We made substantial assumptions, and there are other, untestable assumptions in the use of estimated average weights (Jaksic and Marti 1984). We therefore emphasize unadjusted numbers and relatively broad, log2 scale prey weight-classes. Populations of Potential Prey In the Yukon Territory area in 1980, birds were surveyed by spot-mapping, and small mammals by snap-trapping, in plots totalling 100 ha (Weir, unpublished). There were extensive bird and mammal observations for 10 years on the Tuluksak, and birds were surveyed in 1983, by the fixed-width strip census method in plots totalling 130 ha (Petersen et al, in press; Weir, unpub- lished). Small mammals were surveyed by snap- trapping in eight areas in 1980-81 (Durst 1984). Bird and mammal censuses in both areas were mainly in woodland, both on virgin ground and on that mined 20-70 years earlier. They were mostly in the valley floors, where Great Horned Owls nested. The abundance of hares when pellets were collected was indicated broadly by dates of peaks in the 10-year hare population cycle. Results Pellet Contents The numbers
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