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Population and Movement Characteristics of Radio-Collared Striped Skunks in North Dakota During an Epizootic of Rabies

Introduction


The striped skunk (Mephitis mephitis) is the primary species in which rabies is enzootic in midcontinent North America (Charlton et al., 1991). In 1992, skunks accounted for 27% of reported cases of rabies in wild animals in the United States and 20% of all reported cases of rabies in Canada (Krebs et al., 1993). Despite the considerable knowledge about some aspects of rabies (Baer, 1991), only crude estimates of the incidence of rabies in wild animals are available. Infected wild animals are rarely observed; only those submitted to health departments or other diagnostic facilities are included in surveillance reports (Krebs et al., 1993). Charlton et al. (1991) stated that during the clinical period, rabid skunks in captivity may have increased alertness, heightened activity, and aggressive behavior characterized by biting and lack of fear. Little is known, however, about wild animals infected with rabies. Sargeant et al. (1982) demonstrated that interactions and dispersal of striped skunks facilitated transmission of rabies. Murray and Seward (1992) suggested that additional information on rabies in wild animals would be useful in development of control methods.

During both 1991 and 1992, we equipped adult striped skunks with radio-collars in eastcentral North Dakota as part of an evaluation of skunk responses to supplemental feeding. Provision of supplemental food was suggested by Crabtree and Wolfe (1988) as a potential method of reducing depredation by skunks on eggs of ground-nesting birds. We proposed to evaluate movements of skunks in the prairie region in response to supplemental feeding during the waterfowl nesting season. In 1991, we detected rabies in one radio-collared skunk, but others were not tested because they appeared to be healthy. In mid-April 1992, we became aware of a potential epizootic of rabies in our study population. Although the epizootic confounded the food provisioning study, the radio-equipped animals afforded us a unique opportunity to observe a population of wild striped skunks during an epizootic of rabies. Thus, we continued to radio-equip and monitor skunks; we captured new skunks periodically to maintain as large a sample of radio-equipped animals as we could monitor. The purpose of the present report is to provide information on the population of skunks we studied during the rabies epizootic and to contrast observations of animals that contracted rabies with those of animals that remained healthy.

In this report we compare age structure, reproductive rate, and survival rate of populations we studied in 1991 and 1992. For the 1992 population, we compare rates of travel, distances traveled, and home ranges of skunks that died of rabies and healthy skunks. We also describe condition and location of skunks that we found dead or dying, temporal and spatial relations among skunks that died of rabies, evidence of interactions among animals, and skunk responses to feeding sites.


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