Understanding Squirrel Distribution in an Urban Landscape: What are they nuts for?

 

Squirrels...they’re cute, funny, and sometimes confusing like when they hang out in the South Campus loggia or do other silly things (Image 1). Some might even say they’re Grinnell College’s unofficial mascot. Even though it’s hard to imagine campus without the squirrels, many of us might consider “natural” forests as their true home and find the study of these areas to be most relevant to understanding squirrels and their conservation. As Salsbury et al. (2004) notes, “Effective species management practices in an age of dwindling natural, undisturbed habitats, however, necessitate that populations embedded within urban and agricultural landscapes be examined” (pp.369-370). Salsbury et al. (2004) does just that by studying fox squirrels (Sciurus niger) in Indianapolis, Marion County, Indiana. To their knowledge, they were the first to research squirrel populations living within a “human populated landscape transected by numerous roadways and dominated by residential and nonagricultural commercial properties” (p.370). 

 

Image.1: Mischievous squirrel hanging out in the Grinnell College South Campus loggia

In order to understand how fox squirrels are affected by urbanization and habitat fragmentation, Salsbury et al. (2004) studied six woodlots from 1.1 to 8.3 ha in size and conducted leaf nest and vegetation surveys. For the leaf nest survey, the researchers tried to find all of the leaf nests in each woodlot, and they documented tree species, tree diameter at breast height (dbh), tree height, nest height, nest position, and the presence of vines. When completing the vegetation survey in each woodlot, Salsbury et al. (2004) sampled trees from at least one 100 m transect in the center and at least one 100 m transect that was 5 m from the edge. They noted tree species, tree dbh, the distance between trees and the transects, and the presence of vines. They also estimated the density of shrub and herbaceous cover. Salsbury et al. (2004) found that the squirrels preferred certain tree species but that their preferences differed between woodlots. This suggests that squirrels do not necessarily favor oaks and that other factors beyond tree species are important to them. In addition, larger trees and higher locations in trees tended to house nests. At four out of six of the sites, the squirrels also appeared to prefer trees with vines. Furthermore, Salsbury et al. (2004) found more nests at the disturbed woodlots, which could potentially indicate that squirrels favor areas with dense shrub cover. Together, this research reinforces the idea that squirrels are versatile and that they might even be positively affected by urbanization.  

 

In our campus ecology research project, Hang, Jocelyn, and I will be building upon this research by studying the distribution of squirrel nests around the Grinnell College campus (Image 2). We are recording the tree species that nests are found in and their coordinates as well as the amount and position of nests in trees. We will investigate whether the tree preferences of Grinnell squirrels are also flexible. In addition, we will compare our squirrel nest distribution data to previous student research to see whether the preferences of Grinnell squirrels have potentially changed over time. In particular, we are interested in whether nest distribution has changed more in the sections of campus that experienced greater damage by the 2020 derecho. 

Image.2: Two squirrel nests found in a tree on the Grinnell College campus

Reference 

Salsbury, C. M., Dolan, R. W., & Pentzer, E. B. (2004). The Distribution of Fox Squirrel (Sciurus niger) Leaf Nests within Forest Fragments in Central Indiana. The American Midland Naturalist, 151(2), 369–377. http://www.jstor.org/stable/3566753