Demographic Factors Contributing to High Raccoon Densities in Urban Landscapes

Abstract

We simultaneously studied raccoon (Procyon lotor) populations inhabiting urban, suburban, and rural open areas in northeastern Illinois, USA, to examine the effects of urbanization on raccoon demographics. We predicted that raccoon density was higher in urbanized than rural landscapes because of increased survival and reproduction rates and greater site fidelity in urbanized areas. Density estimates for both the urban and suburban sites were greater (P < 0.001) than for the rural site during all seasons. Density estimates for the urban and suburban sites were similar (0.177 ≤ P< 0.603) during 4 of seasons. Percentages of porous females were similar among sites. However, higher proportions of juveniles to adult females captured at the urbanized sites may indicate larger litter sizes. Adult female survival was highest at the urban site during the first 2 years, but dropped due to an unknown disease during the final year. Urban raccoons experienced the fewest mortality sources, whereas rural raccoons experienced the most. Disease was the greatest mortality factor at the urban site, while vehicle-related mortalities dominated at the suburban and rural sites. The high ratio of marked to unmarked raccoons captured may indicate greater site fidelity at urbanized sites. Our data suggest that multiple factors, including increased survival, higher annual recruitment, and increased site fidelity, are jointly responsible for high-density raccoon populations in urbanized areas. Direct management of raccoon numbers in urbanized areas likely will require continuous control measures, because raccoons are capable of quickly repopulating an area after the resident population has been reduced. The most effective control measure may be the reduction of anthropogenic food sources that support raccoons at high densities.