Minnesota Gray and Fox Squirrels

Abstract

Squirrel populations were studied on a 40-acre woodlot in Dodge County, Minnesota, from spring, 1958 to fall, 1960 and to a lesser extent at Camp Ripley in Morrison County in central Minnesota during the winters of 1959-1962. Live-trapping, ear tagging, and releasing for recapture were done on the tract and in nearby woodlots. Litters were tagged in forty den boxes. On the study tract there was one gray squirrel per acre of woods during September and 0.65 per acre during the winter. Only about one pair of fox squirrels was resident. During three years, 22 to 24 young gray squirrels were produced although the age structure of producingfemale populations was different each year. Mating occurred in each month from January to July with half the conceptions occurring from mid-January to early March. Nineteen litters averaged 2.68 young. From all areas of the state the three-year mean of gray squirrel litter counts, embryo/fetus counts and placental site counts was 2.75 per female. In the following two years at Camp Ripley the means of embryo/fetus counts and placental site counts were 3.48 and 3.71. For fox squirrels the combined counts averaged 3.04 in 1958-60 and 3.44 in 1961-62. On the study tract, survival of young gray squirrels to fall was 23% in 1959 and 41% in 1960. In two years, 40% and 48% of all gray squirrels survived from one fall to the next, and 11-12% survived from one fall to the third. Gray squirrels moved through open country between woodlots onehalf mile apart, apparently emigrating. Weights of live-trapped adults varied seasonally. Adult males weighed from 480 to 720 gm and adult females from 476 to 725 gm. Mean weight of 81 of all ages collected from the tract and vicinity was 620 gm in winter. Weight was less in extensive woods of central Minnesota. Mean weight of adult fox squirrels in winter from southern Minnesota was 827 gm while in central Minnesota in one year the mean was 863 gm. Den boxes, though readily used where no natural dens occurred, did not appear to increase survival but actually could have had detrimental effects. Gray squirrels from all regions of the state exhibited variations in ventral surface pelage color. Variations, from all white below to all orange-buff, occurred in the same litter.