Stanley D. Gehrt

Demographic factors contributing to high raccoon densities in urban landscapes

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.

Resource distribution, female home range dispersion and male spatial interactions: group structure in a solitary carnivore.

We monitored 74 (41 male, 33 female) radiocollared raccoons (Procyon lotor) from February 1990 to July 1992 on the Welder Wildlife Refuge, Texas, to relate male and female space use to each other and to the spatial distribution of water, a critical resource for raccoons. Female home ranges were spatially aggregated early in the study, when standing water occurred in only a few, widely separated patches on the study site, but were randomly distributed during seasons when water was more widely distributed. Adult females generally foraged and rested independently of other adults. Most adult males were arranged in spatial groups whose home ranges overlapped little with those of adjacent groups. These groups were usually composed of three to four individuals; Doncasters (1990, J. theor. Biol., 143, 431-443) test for dynamic interaction and visual observations showed that group members tended to associate positively during resting and foraging activities in all seasons. Among raccoons, as among many other mammals, female spatial patterns are apparently determined primarily by resource distribution, whereas male patterns are influenced by the distribution of females. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

BAT ACTIVITY IN AN URBAN LANDSCAPE: PATTERNS AT THE LANDSCAPE AND MICROHABITAT SCALE

Relatively little attention has been devoted to the urban ecology of bats (Chiroptera) despite their ecological importance. Although previous studies have indicated that urbanization has a negative effect on the abundance of bats and bat activity, this relationship may differ among regions. We monitored bat activity during 1997–1999 in 15–20 natural areas distributed across a 3500-km2 area spanning the Chicago metropolitan area in northeastern Illinois. Our objectives were to elucidate relationships between landscape and microhabitat characteristics and bat activity. Bat activity was correlated with visual estimates of abundance. Among adjacent land-use classes, industrial/commercial use was positively related to bat activity in 1997 and 1999, and the predominant rural land use, agriculture, was negatively associated with bat activity in 1998. Proportion of woodland habitat within study areas was positively related to bat activity in every year. There was a positive relationship between agricultural land ...

Spatial and Temporal Variation in the Diet of Coyotes in the Chicago Metropolitan Area

ABSTRACT Coyotes (Canis latrans) are an opportunistic predator that have adapted to many human-modified environments. Conflicts between coyotes and humans are an increasing concern for managers in urban areas. We examined the spatial and temporal utilization and availability of natural and human-associated food for coyotes in the Chicago metropolitan area, Illinois, USA. We collected 1429 coyote scats from May 2000 to December 2002, and conducted prey surveys in 2002, in 4 sites that varied in their degree of urban development. Dominant food items included small rodents, white-tailed deer (Odocoileus virginianus), fruit, eastern cottontail (Sylvilagus floridanus) and birds. Their availability and occurrence in scats varied among sites and seasons. The occurrence of human-associated food items, which was only found in significant amounts in the most developed site, varied seasonally (2–25%). Because coyotes in less-developed areas had lower dietary diversity, these coyotes may have to venture into developed areas when there is a decline in the abundance of major prey species for that specific area.

SPECIES-SPECIFIC PATTERNS OF BAT ACTIVITY IN AN URBAN LANDSCAPE

Urbanization is currently considered to have a negative effect on biodiversity, including the abundance and diversity of bat (Chiroptera) communities. However, relatively little attention has been devoted to the urban ecology of bats despite their ubiquity and ecological importance. We conducted a study during 1997–1999 to acoustically monitor species-specific distributions and activity patterns for bats in a highly urbanized landscape. Of 11 896 passes recorded during the study that satisfied our criterion for species classification, 8672 (73%) were identified to species. We identified calls from five species (Eptesicus fuscus, Lasionycteris noctivagans, Lasiurus borealis, Lasiurus cinereus, Pipistrellus subflavus) and the Myotis group. Few landscape variables were significantly related to E. fuscus activity; however, L. borealis and L. noctivagans activity had positive relationships with adjacent industrial/commercial land use and an urban index. We determined mean occurrence at monitoring sites for all...

Sexual Differences in Home Ranges of Raccoons

We monitored movements of 30 (11 male, 19 female) adult raccoons ( Procyon lotor ) from February 1990 to July 1992 on the Welder Wildlife Refuge, Texas, to identify differences in seasonal sizes of home range between males and females. Sizes of home range of males varied little ( P > 0.05) among seasons, and males had larger ( P < 0.05) home ranges than females in all seasons. There was considerable variation in size of home range among individual females; however, median sizes of home range for females did not change among seasons. Size of home ranges of males were larger ( P < 0.05) than would be expected based on the relationship between body mass and size of home range in mammals and suggested that movements of males were not dictated solely by energetic requirements. Social behavior appears to play an important role in the size of home range of male raccoons.

Duration of Familial Bonds and Dispersal Patterns for Raccoons in South Texas

Families of raccoons ( Procyon lotor ) were monitored during 1990–1992 on the Welder Wildlife Refuge in south Texas to determine duration of familial bonds and patterns of natal dispersal and philopatry. Analysis of the pre-dispersal movements of 11 family units indicated family bonds often were maintained until juveniles’ first mating season. Twelve of 13 radiocollared males dispersed or died before their second mating season, including eight that were known to be born on the study area, but all radiocollared females ( n = 14) remained within natal areas. Related females maintained extensive spatial overlap, and some continued to den and travel together as adults.

LAND-USE EFFECTS ON PREVALENCE OF RACCOON ROUNDWORM (BAYLISASCARIS PROCYONIS)

The raccoon (Procyon lotor) is the definitive host of Baylisascaris procyonis, a large intestinal roundworm that is zoonotic and can result in fatal or severe central nervous system disease in young children. Prevalence of infection among raccoon populations often is high, and in the midwestern United States, B. procyonis has been reported in 68–82% of raccoons. Raccoon populations have increased in response to changes in human land use, and often reach higher densities in urban and suburban landscapes than rural landscapes. However, shifts in foraging behavior among urban raccoons could impact the transmission of B. procyonis if small vertebrate intermediate hosts are not a significant part of the raccoon diet. The objective of this study was to compare prevalence of B. procyonis infection between urban and rural raccoon populations on a regional scale. Necropsy was done on 204 raccoons collected from September through February during 2000–2005 from seven states across the Midwest (regional sample). Baylisascaris procyonis was found in 54% of examined raccoons. Prevalence differed between land-use types (χ2=11.56, df=1, P=0.0007), and was higher among animals collected from rural locations (65%) than those collected in urban locations (41%). Intensity of infection also differed (F=5.52, df=1, P=0.02), with rural raccoons having greater worm burdens (x¯=29.63±36.42) than urban raccoons (x¯=13.85±18.47). Despite high densities of raccoons in urban landscapes, fewer urban raccoons were infected with B. procyonis, suggesting decreased dependence on intermediate hosts as a food source. This possible explanation was supported by a similar trend in prevalence among subsamples of raccoons collected from three Chicago-area populations (local samples) with differing levels of urbanization, population densities, and foraging behavior that had been intensively monitored during 1995–2002. Decreased transmission of B. procyonis in urban landscapes may be due to decreased predation of intermediate hosts, and contact of juvenile raccoons with B. procyonis eggs may be an important factor in maintaining infections within such populations.

Behavioural aspects of the raccoon mating system : determinants of consortship success

We monitored raccoons Procyon lotor, in southern Texas during the 1990-1992 mating seasons to describe mating behaviour and identify factors affecting consortship success. During most of this study, raccoons were spatially aggregated, with female home ranges congregated around permanent water sources and larger home ranges of male groups encompassing each female group. Consortship success varied among males and ranged from zero to six females per male within a mating season. Individual females consorted with one to four different males during an oestrous period; however, most (62%) females consorted with only one male during their oestrus. Dominance through overt conflict appeared to influence male consortship success. During two mating seasons, one male from each group consorted with females on more days than all other males combined. Body weight of males was positively correlated with number of consortship days. As synchrony of oestrus increased, variance in number of consortship days among males decreased, and access to oestrous females increased for subordinate males. Wounding among males increased during the mating season, and was more frequent for males than for females. The mating system, as determined by consortship behaviour, appeared to shift between polygyny and promiscuity, and possibly varied annually as a result of the timing of oestrous cycles. Copyright 1999 The Association for the Study of Animal Behaviour.

Survivorship of a nonharvested raccoon population in South Texas

To fully understand the effects of harvest and other anthropogenic factors on raccoon (Procyon lotor) populations, information is needed on survival of raccoons that are protected from these types of mortality. We monitored raccoons in South Texas during 1990-93 to determine age- and sex-specific survivorship of a raccoon population protected from legal harvest. Juvenile survivorship was low (S = 0.65) during the nestling stage but increased as young matured and began traveling with mothers. Nestling survival was related to natal den type. Monthly survival distributions differed (P 0.05) between adult males and females. Our annual survival estimates for males and females (S = 0.84) were higher than those reported for a harvested population in Iowa. Our comparison of survival estimates from Iowa and Texas suggests harvest may be additive for raccoons or, if harvest is compensatory, raccoons in Iowa may have lower survival than raccoons in Texas, regardless of harvest.