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 6 seasons. Percentages of parous 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.

No abstract

The frequency of interactions among individuals is vital to understanding many aspects of a species' behavioral ecology. This also is a fundamental aspect of infectious disease epidemiology. However, the number of times an individual animal comes into contact with another is an extremely difficult parameter to estimate. This paper describes radiocollars (proximity detectors) capable of recording close contacts among radiocollared individuals. We conducted laboratory tests using collars alone (i.e., not fitted on an organism) and field tests of collar performance with collars fitted on 42 free-ranging raccoons (Procyon lotor) within a 20-ha portion of the Ned Brown Forest Preserve in northeastern Illinois, USA. During laboratory tests, we determined variation in detection distance within and among collars, effect of collar orientation on detection distances, and accuracy of recorded duration of proximity and identification of contacted collar. Overall variation in detection distance both within and among collars was relatively low, although we observed intrinsic variation in collar strength. We found little variation in horizontal detection distances with collar orientation, although mean distances for vertical tests were greater than most horizontal means. Recorded contact duration deviated from actual time by 3 seconds for short-duration (10-300 sec), and by 30 seconds for extended-duration (8-14 hr) contacts recorded as a single event. However, there was a tendency for the collars to record extended-duration contacts as multiple events, with the frequency dependent on settings. Identification number of the contacted collar was correctly identified in all cases (n ¼ 1,537). We downloaded 35 of the 42 proximity detectors deployed on free-ranging raccoons. Of these, approximately 57% were functioning properly, 9% exhibited problems apparently correctable in the field, and 34% exhibited problems not correctable in the field. For random pairs of raccoons, daily contact duration and number of contacts (omitting 1-sec contacts) recorded by both detectors did not differ (P ! 0.066). Overall, collars produced accurate information in terms of detection range, duration of contact, and contacted collar identification, and represented a promising improvement over previous methods to assess intraspecific contact rates of secretive, nocturnal, or otherwise unobservable species. Because accurate determination of contact rates requires that a population be saturated with detectors, their use may be most appropriate for species readily trapped. (WILDLIFE SOCIETY BULLETIN 34(5):1333-1344 2006)