Population dynamics and regulation of the Douglas squirrel (Tamiasciurus douglasii) with supplemental food.

If food is in short supply, then provision of addition food should increase the density of Douglas squirrels. A squirrel population was supplied with extra food during the summers of 1977 and 1978 and winter of 1978-1979 in coastal coniferous forest at Maple Ridge, British Columbia. Food produced a 5-to 10-fold increase in squirrel density compared with control populations. Control densities generally varied from 3 to 10 squirrels per trapping area with the experimental population increasing to 65 animals during the winter feeding. This irruption was produced by immigration, more reproduction in females, and increased survival. After the food was withdrawn, the population declined to a level comparable with the controls. We conclude that Douglas squirrel populations fluctuate in accordance with the abundance of food. Territorial behavior may space individuals within populations of Tamiasciurus douglasii but to density levels determined by the available food supply.

The use of weasels for natural control of mouse and vole populations in a coastal coniferous forest.

If the natural enemy component of biological control is functional in small mammals, then the introduciton of weasels should effectively reduce populations of deer mice and Oregon voles. Seven weasels introduced to an area of forest habitat in coastal British Columbia did not appreciably lower the abundance of mice or voles. However, these natural predators may have contributed to the localized extinction of the vole population on the experimental area. Weasels were generally more abundant in the late summer and early fall and preferred clearcut (logged) successional habitats compared with forested areas. The results of this study are discussed with respect to the futility of poison baiting and related techniques of removing rodent pest populations from forest and agricultural land developments.