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The inter-relations of the introduced gray squirrel (Sciurus carolinensis) with the ecological conditions in Stanley Park Robinson, Donald Joseph

Abstract

An introduced population of Sciurus carolinensis planted at Stanley Park, Vancouver, B.C. about 1913 has maintained itself successfully for at least 38 years in competition with the indigenous squirrel Sciurus douglasi. This population was studied through a period of 18 months. It was found that the gray squirrel has reached a point of saturation in the mixed deciduous-conifer forest type favored by it. The spring population approximates .7 per acre and the autumn population about 1 per acre. Two litters are born per year to adult squirrels, one to yearlings. These arise from matings in March and April and June and July. The ratio between breeding females and young at weaning age is 1 to 1.6, indicating a very low reproductive success. The gray squirrel is not territorial in its behavior. Females move through an area of 5 to 15 acres with little seasonal variation. In the winter the males have about the same range of movements as the females but during the rest of the year they move in a non random manner over an area of 50 to 55 acres. Polygamy is the rule with several males competing for the receptive female. Dominance among such a group of males is positive, physical and not associated with territory. The most important food plants are the vine maple (Acer circinatum) and the broad-leafed maple (Acer macrophyllum). Food storage takes place in a random fashion within a radius of 50 feet from the source. Subsequent recovery of stored food is by random searching over the storage area. The Douglas squirrel exerts physical dominance over the gray squirrel but has a different habitat preference that reduces competition between the two species. Twenty-six birds nests were watched in the squirrel area and only two were destroyed by them.

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