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

Abstract

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 After the food was withdrawn, the population declined to a level comparable with the controls.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.

Mast seeding and mammal breeding: Can a bonanza food supply be anticipated?

“…Squirrels are renowned opportunistic carnivores, missing no chance to acquire animal protein. Each spring and summer when they are breeding they supplement their diet of seeds with a variety of other high-protein foods (Sullivan & Sullivan 1982;Koprowski 1991). They eat insects, carrion, nestling birds, lizards-even young snowshoe hares (Callaban 1993;Petzlaw et al 2006).…”

The biology of arboreal rodents in Douglas-fir forests.

“…It is not clear why these results differ; the results Carey (1989) reported included spring samples from the stands sampled by Buchanan and others (1990). The Douglas' squirrel is not known to routinely switch territories with seasons; however, immigration to areas of high food abundance has been reported (Sullivan and Sullivan 1982). The spring population is that surviving the period of lowest food abundance and is generally the lowest population of the year (Sullivan and Sullivan 1982).…”

“…The Douglas' squirrel is not known to routinely switch territories with seasons; however, immigration to areas of high food abundance has been reported (Sullivan and Sullivan 1982). The spring population is that surviving the period of lowest food abundance and is generally the lowest population of the year (Sullivan and Sullivan 1982). If old growth provides more diverse and abundant food than younger forests, then the spring population should demonstrate differences more markedly than winter populations; but winter populations are composed of adults and juveniles.…”

A Test of Interspecific Effects of Introduced Eastern Grey Squirrels, <em>Sciurus carolinensis</em>, on Douglas's Squirrels, <em>Tamiasciurus douglasii</em>, in Vancouver, British Columbia

“…Densities of Douglas's Squirrels are limited by food availability (Sullivan and Sullivan 1982;Ransome and Sullivan 1997), and old-growth forests provide higherquality habitat for Douglas's Squirrels than younger forests due to greater and more reliable quantities of conifer seed (Buchanan et al 1990). In our study, the densities of Douglas's Squirrels were similar at both sites, suggesting that habitat suitability was similar, and further suggesting that reduced breeding propensity was caused by the presence of Eastern Grey Squirrels, and not simply an artifact of difference in food availability among study areas.…”