. Animal Ecology. Animal ecology. 1 g>gas 2 andcrso 3 ihirasi 4 america na (intro- duced into Ncwfoundland) 5 Souther 1 limit of Wiscon sin glaciation FIG. 23-4 Present distri from distributions a* th winter, on the tips of birch, aspen, cedar, balsam fir, and various other shrubs and small deciduous trees (Shelford and Olson 1935). Small mammals are abundant. In northern Michigan, the populations of two species each of mice, chipmunks, and shrews varied from individuals per hectare () in jack pine to () in black spruce, () in hemlock, () i
. Animal Ecology. Animal ecology. 1 g>gas 2 andcrso 3 ihirasi 4 america na (intro- duced into Ncwfoundland) 5 Souther 1 limit of Wiscon sin glaciation FIG. 23-4 Present distri from distributions a* th winter, on the tips of birch, aspen, cedar, balsam fir, and various other shrubs and small deciduous trees (Shelford and Olson 1935). Small mammals are abundant. In northern Michigan, the populations of two species each of mice, chipmunks, and shrews varied from individuals per hectare () in jack pine to () in black spruce, () in hemlock, () in a white- cedar swamp, and () in white birch (Manville 1949). Perennial animals that remain active over winter have a high tolerance of low temperatures and use food not readily obscured by snow (Snow 1952). The large mammals become browsers in the winter. Wapiti chew bark patches off aspen trees when other forage is difficult to find. Scars thus formed are ideal sites for the development of fungus disease (Packard 1942). Birds feed on seeds extracted from the cones of the coniferous trees, on buds, and on bark insects. When the seed crop fails, large numbers of pine siskins, pine and evening grosbeaks, red crossbills. :a. Post-Pleistocene di (from Peterson 1955). and white-winged crossbills emigrate southward into the United States. Small ground and subterranean animals are well insulated under the snow where temperatures even in the far North may drop only a few degrees below freezing (Pruitt 1957). Some birds, such as the grouse, roost at night in cavities formed in snowbanks. Less than half of the nesting bird population of the western forest biociation migrates for the winter, and then only to lower altitudes on the mountains. In contrast, the birds of the boreal forest are acclima- tized to warm climate, and over 80 per cent migrate hundreds of kilometers to the south. A few mam- mals also migrate, such as the hoary bat in the East and the wapiti and mule d
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
