Urbanization can significantly alter environments in ways that impact abundance and behavior of urban animals. Fewer natural predators and greater food availability – as well as increased contact with humans – may lead to altered stress responses, increased boldness, and decreased vigilance compared to non-urban populations. The eastern gray squirrel (Sciurus carolinensis) has been very successful in urban environments, demonstrating an ability to habituate to humans and modify its behavior to avoid perceived predation threats, through alterations in flight initiation distance and foraging strategies. In a recent study, my colleagues and I investigated how S. carolinensis differs in relative abundance and flight initiation distance (FID) upon human approach across common urban habitats that vary in human presence and environmental disturbance in the St. Louis metropolitan area. The study specifically addressed: (1) variation in local and landscape-scale habitat, (2) variation in abundance, and (3) variation in FID.
In the fall of 2018, I conducted surveys in 5 urban habitat types (golf courses, neighborhoods, parks, forest, cemeteries) on days of typical land use. For each of the 1.5 hour site surveys, I measured: total squirrel abundance (on the ground or on natural/anthropogenic structure), squirrel behavioral responses (sight distance, FID, escape distance, escape strategy), and habitat differences (distance to the nearest tree, impervious surface cover, number of people within 10 m). We then performed landscape analyses using NLCD land cover, canopy cover, impervious surface, and roads in ArcGIS.
We sampled a total of 17 sites in the St. Louis (MO) metropolitan region (5 neighborhoods, 5 parks, 3 cemeteries, 3 golf courses, and 1 urban forest). We observed 337 squirrels and measured FID for 136 squirrels across the five habitat types. Relative abundance (accounting for sampling effort) varied by habitat type: parks had the greatest abundance, followed by the urban forest, neighborhoods, cemeteries, and golf courses.
Across these land use categories, habitat use and FID differed as well. More squirrels were observed on the ground in parks than in neighborhoods and squirrels in parks had significantly greater FID compared to neighborhoods (i.e., fled at a farther approach distance). The extremely low relative abundances in cemeteries and golf courses was surprising, and so we considered landscape-scale differences between each of the five habitat types to gain insight into these patterns since variation in abundance and FID may also be attributable to differences in human habituation. Individual squirrel responses were correlated with their immediate surrounding habitat, but this response differed in parks and neighborhoods. Across all sites, squirrels had shorter FID (allowed closer approach) in habitat that had greater impervious surface coverage and less residential land use.
Our results suggest that both abundance and behavioral responses to urbanization are heterogeneous within the metropolitan region and may reflect local variation in habituation. Future studies are needed to explore how predictable the effects of these local environmental conditions are in urban areas. Understanding how animals behaviorally respond to urban environments will help explain the ecological consequences of rapid urbanization and has implications for evolutionary responses.
For more information, check out the study by Engel et al. here:
Featured Image: The Eastern gray squirrel (S. carolinensis) is found abundantly in urban environments throughout the St. Louis metropolitan region. Photo by L. Engel.
- Eastern Gray Squirrel Behavior in Urban Environments - April 7, 2020
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