Fox squirrels (Sciurus niger) are a common sight here in Grinnell and much of the midwest. Indeed, fox squirrels seem to have made themselves quite comfortable in what is, ostensibly, an urban landscape here on campus. McCleery et al. 2007 takes a look at a similar situation on Texas A&M University Main Campus, tracking squirrels to examine their use of habitat in an urban environment. As more rural landscapes are urbanized, it is imperative to learn how squirrels, among other city-dwelling animals, interact with the urban environment so these areas may be managed to encourage, or discourage, their presence.
To track the habitat use of fox squirrels, the campus was delineated into four main habitat substrates: pavement, building, grass, and tree canopy. Prior to the study campus squirrels were trapped and fitted with a collar and radio transmitter. These radio-collared squirrels were tracked from September 2003 to August 2005, with the squirrels being located 2-3 times a week at random intervals. When located, their habitat substrate and activity were recorded into the GIS database. With these methods, the researchers were able to analyze habitat use according to both spatial and temporal scales. These scales included point-study area, range-study area, and point-range. Tree selection and squirrel activity were also examined.
Figure 2 (below) shows point-study area selection ratios of urban substrates (calculated by taking observed habitat use divided by expected habitat use for each substrate and season). Similar figures were used to depict the results from the other spatial scales. They found that fox squirrels strongly select for tree canopy regardless of scale and activity level. Conversely, fox squirrels generally avoid pavement but do not exclude it from the core areas of their ranges. It was also observed that fox squirrels used buildings both as a substrate and daytime refuge during the winter and spring. Tree selection analysis indicates that the squirrels generally avoided pines, bald cypress, and arborvitae, but selected for live oaks. During periods of activity squirrels selected for trees with greater canopy area and diameter at breast height.
These findings suggest that squirrels select for substrates similar to those they use in the wild, while adapting to, exploiting, or simply tolerating, features of the urban environment. This adaptability is likely what makes squirrels so successful in many urban areas, such as Grinnell College Campus. Our study takes a broad view of squirrel habitation on campus by comparing present-day nest distribution to that observed by a previous study. Our goal is to see how squirrel nest distribution has changed, if at all, since this study was conducted and investigate potential causes. Specifically, we want to examine if derecho damage sustained by trees on campus has affected squirrel nest distribution.
References
McCleery, R. A., Lopez, R. R., Silvy, N. J., & Kahlick, S. N. (2007).
Habitat use of fox squirrels in an urban environment. The Journal of wildlife management, 71(4),1149-1157.
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In what situations would you foresee trying to encourage squirrels to inhabit an area? Conversely, it seems like discouraging their presence would require removing their habitat: do you think that this might do more harm than good?
ReplyDeleteWhat is meant by "periods of activity"? Is this when they are foraging or playing with others? Did the authors have any explanation for why during the periods of activity the squirrels selected for trees with greater canopy area? Is it because there is simply more space for them to move around in the tree or does it have something to do with avoiding predation?
ReplyDeleteThat sounds like an interesting study! Do you know if they put collars on all the squirrels on their campus? or how many squirrels they put collars on to the total population size?
ReplyDeleteAlso, though we haven't done much analysis yet, have you found a similar preference of live oak trees in Grinnell squirrels?