Many studies on wildlife populations focused on their natural histories in pristine settings. However, our landscapes are increasingly comprised of urban environments characterized by buildings, high availability of food, water, and energy, and perhaps more importantly more humans. Naturally, we would expect populations in urban environments to display a different set of physiology, habitat selection, and behaviors than their rural counterparts. Thus, it is important to study urban populations systematically. McCleery & Parker (2011) looked at city squirrels. Specifically, they investigated the influence of urban environments on fox squirrel range overlap.

Photo from Grinnell Magazine by Grant Dissette '12

Squirrels are territorial. Studies have shown that squirrels in the traditional rural settings are hierarchical and characterized by extensive overlapping of ranges (Koprowski 1996). McCleery & Parker examined the spatial overlap in squirrel ranges during different seasons. They considered more overlap as hierarchical behaviors and less overlap to be territorial behaviors.

The urban part of the study was conducted on the main campus of Texas A&M University dominated by buildings, pavement, and manicured exotic greases, while the rural part was on a private ranch of the University of undisturbed hardwood forest and meadows with no little to no human activity. Twenty squirrels (10 male, 10 female) from each site were trapped with wire-cage traps and tagged with radio-telemetry collars. Their seasonal ranges were recorded and calculated.

The results show a reduced seasonal range overlap by squirrels on the urban site. The study also found that urban squirrels used fewer nests in winter and in general fewer tree cavities and shelters. McCleery and Parker believe that squirrels adjust their behavior to use spaces based on their environmental conditions. They proposed that range boundaries might be influenced by buildings and the increased habitat unevenness may help delineate territories. They think cavities might be a limited resource on urban sites and maintained for exclusive use, such as pregnant females.

In our campus ecology project, Sharene, Jocelyn, and I will be examining a slightly different aspect of urban squirrel populations – preferred nesting locations. We record the tree species where nests are found, their coordinates, and the position of the nests in the tree. In addition, we will also be comparing our data to a previous data set also collected by Grinnell students and see if the preferences of squirrels have changed over time.

 References

Koprowski, J.L. (1996). Natal philopatry, communal nesting, and kinship in fox squirrels and gray squirrels. J. Mammal.77, 1006–1016.

McCleery, R. A., & Parker, I. D. (2011). Influence of the urban environment on Fox Squirrel Range Overlap. Journal of Zoology, 285(3), 239–246. https://doi.org/10.1111/j.1469-7998.2011.00835.x