Population ecology of black-footed ferrets (Mustela nigripes) in relation to sylvatic plague
Date
2023
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Abstract
Infectious diseases can have significant impacts, both direct and indirect, on the conservation of endangered species. A full understanding of these impacts is hindered by the difficulty of teasing apart disease effects from other factors that led to endangerment, the scarcity of population data from before and after disease detection, and the inherent challenge of studying rare species, which are often difficult to detect. Ideally, a disease and population monitoring strategy will detect outbreaks so effective management and mitigation strategies can be implemented. Disease mitigation strategies, such as vaccination or removal of infected individuals, can be effective but costly to implement and rigorous evaluations of such efforts are rare. Here we present a case study and evaluation of a multi-faceted effort to manage multiple impacts of sylvatic plague (plague hereafter), an invasive disease, in a reintroduced population of endangered black-footed ferrets (Mustela nigripes) and their prey, black-tailed prairie dogs (Cynomys ludovicianus), in Conata Basin/Badlands National Park, South Dakota. Since reintroduction in 1994-1999, this is the largest free-ranging ferret population. Chapter One provides a broad introduction to black-footed ferret natural history, ecology, and conservation efforts. We briefly described the life history of black-footed ferrets, their reliance upon prairie dogs (Cynomys spp.) as prey and habitat engineers, and the conflicts between prairie dogs and agricultural interests that motivated human efforts to eradicate prairie dogs and inadvertently drove ferrets towards extinction. Ensuing captive breeding and reintroduction efforts averted extinction of the species, but plague, caused by Yersinia pestis bacteria, led to high mortality in both black-footed ferrets and prairie dogs, was a second factor in ferret decline, and continues to threaten reintroduced populations. Plague management, through flea vector control and vaccination, is a high priority for the black-footed ferret recovery program, along with maintaining genetic diversity and securing habitat. We concluded that black-footed ferret recovery to date has been partially successful, but challenges remain, and plague represents the largest biological threat. In Chapter Two, we evaluated the efforts to manage plague for black-footed ferrets and prairie dogs at Conata Basin/Badlands National Park. We effectively monitored plague using carnivore serology, prairie dog testing, and visual surveys to detect the invasion of plague and inform our mitigation efforts. Both prairie dog colonies and black-footed ferret populations declined precipitously with the plague epizootic. We applied deltamethrin dust into prairie dog burrows to kill fleas and vaccinated black-footed ferrets against plague during annual monitoring efforts. Our results suggested that dusting was effective in maintaining prairie dog colonies compared to non-dusted colonies and significantly increasing survival of black-footed ferrets. Additionally, our vaccination of black-footed ferrets added incremental gains in ferret survival. These combined efforts of plague surveillance, dusting prairie dog burrows, and vaccinating black-footed ferrets likely prevented extirpation of this population. In Chapter Three, we used stable isotope analysis to understand the effects of plague on the proportion of prairie dogs in black-footed ferret diets. Previous studies on black-footed ferrets found up to one-third of ferret diet is comprised of non-prairie dog rodents. Plague causes high mortality in prairie dogs and other small mammals found on prairie dog colonies, potentially increasing variability in prey available for black-footed ferrets. We sampled black-footed ferrets and two prey items, prairie dogs and deer mice (Peromyscus sonoriensis), before and during a plague epizootic and used stable isotope analysis to estimate the diet proportions in relation to plague and dusting. We found that prior to plague black-footed ferret diets in Conata Basin/Badlands National Park were similar to previous studies, but during a plague epizootic ferrets shifted their diet almost completely to prairie dogs. Dusting prairie dog burrows prior to the invasion of plague had a similar effect in shifting black-footed ferret diets. We concluded that despite observed foraging plasticity, black-footed ferrets can be considered prairie dog colony specialists, and any diet effects following deltamethrin dust treatment are likely less severe than the impacts of plague on unprotected ferret populations.
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Embargo expires: 12/29/2024.
Subject
conservation
endangered species
prairie dog
disease
black-footed ferret
plague