The Density and Distribution of Gray Squirrels in a Suburban Environment
Andersen, Kenneth K.
University of Wisconsin-Stevens Point, College of Natural Resources
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The density and distribution of gray squirrels in a suburban environment were studied from October 1980 through November 1981 on Oak Park Estates, Plover, Wisconsin. Environmental variables potentially affecting density and distribution included location of gardens and birdfeeders, amount and type of artificial feed available, season of feeding squirrels, and presence or absence of pets and children. Vegetation of the study area and an adjoining buffer zone is predominately red oak (Quercus rubra) and white pine (Pinus strobus). Black cherry (Prunus serotina) and blackberry (Rubus allegheniensis) dominate the understories. Production of acorns was good in 1980, but the acorn crop in 1981 was poor. Population estimates based on Schnabel’s mark-recapture formula were calculated for 5 trapping periods beginning in January 1981 and ending in November 1981. Estimates were highest for the winter, spring, and summer of 1981 and lowest for the September and November trapping periods 1981. The high winter population may have been a result of squirrel immigration and low emigration off the study area and presence of feed in birdfeeders. Population averages were higher for traps located near gardens (x=7.4) versus traps located large distances from gardens (x=5.7). Males were dominant during all trapping seasons except early summer 1981. Male gray squirrels may be over-represented, because they generally have larger home ranges and are more active year-round than females. Adults outnumbered juveniles during all seasons except winter and early summer 1981. Gray squirrels were well distributed throughout the study area. The majority of captures on an adjoining buffer zone occurred along the southern edge, which may have been a result of close proximity to a major woods and less disturbance by pets and children. Adult and juvenile males were captured most often. Trap success was highest near gardens and bird feeders. Trap success was reduced by disturbance from pets and children, trapping of squirrels by residents, and consumption of bait by songbirds. Home range appears to be larger for suburban gray squirrels than wild squirrels. Adult males had the largest home range followed by adult females, juvenile males, and juvenile females, respectively. Average home range size of all gray squirrels was nearly 6 times that of wild squirrels in Michigan. Influencing factors on a suburban gray squirrel's home range appear to be social rank, presence of birdfeeders and gardens, and pets. A questionnaire survey of area residents was conducted to obtain· data on environmental variables possibly affecting gray squirrel densities and distributions. No statistical relationships were established due to a limited sample size of homes. There appears to be a relationship between locations of gardens and bird-feeders, and movements and concentrations of suburban gray squirrels. The influence of birdfeeders appears to be related to type and quantity of feed made available. Sunflower seeds, provided in large quantities year-round, attract the greatest number of squirrels to feeders. Other factors that may influence suburban gray squirrels are pets, season of feeding at feeders, type of vegetables in gardens, and children. The most corm1on complaint residents of Oak Park Estates have concerning gray squirrels is the eating of, and damage to, garden vegetables. Damage of property was next in occurrence on questionnaires. Approximately 25% of all residents indicated they have had no problems with squirrels. The majority of Oak Park Estate residents indicate that there is about the right number of gray squirrels on their respective properties. Problems encountered in this study included trap disturbance by pets and children, removal of marked squirrels by residents, and a small sample size of homes which prohibited statistical analysis.