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Gray squirrel density, habitat suitability, and behavior in urban parks


Increased density, increased intraspecific aggression, and a reduced fear of humans have been suggested as the more observable and frequently described characteristics of wildlife species undergoing synurbization, the process of becoming urbanized. The relationship among these variables and how they may be related to environmental variables that change with urbanization is poorly understood. In this paper we explore the relationship between density, intraspecific aggression, and reduced fear of humans in urban populations of gray squirrel. In the summer and fall of 2003 and 2004, we studied a park with a documented high density of gray squirrels, Lafayette Park, Washington, DC, and six urban parks in Baltimore, MD with unknown squirrel densities. We used linear regression (SAS Institute, SAS/STAT user’s guide. SAS Institute, Cary, NC, 2005) to determine if there was a relationship (P < 0.05) between squirrel density and intraspecific aggression, squirrel density and reduced fear of humans (wariness), and squirrel density and habitat suitability. We found a positive association between density and intraspecific aggression (R 2 = 0.81, P < 0.00). A negative relationship between density and wariness (\(R_{{\text{adj}}}^2 = 0.71\), P < 0.00). However, no relationship was evident between habitat suitability and squirrel density (\(R_{{\text{adj}}}^2 = - 0.50\), P = 0.437).

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This project was conducted as part of the Baltimore Ecosystem Study (BES) and supported by the National Science Foundation Long-term Ecological Research program (grant number DEB 0423476). We thank the researchers associated with BES and the USDA Forest Service Northeastern Research Station for the technical support, research staff time, equipment, and in kind services. In addition, we thank the Parks and People Foundation of Baltimore City for their assistance with the geographical and land use data. We also thank the Wildlife Initiative Program at Lincoln University Missouri for providing students to aid in the collection of field data.

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Correspondence to Tommy S. Parker.

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Parker, T.S., Nilon, C.H. Gray squirrel density, habitat suitability, and behavior in urban parks. Urban Ecosyst 11, 243–255 (2008).

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