Prairie dog responses to vector control and vaccination during an initial Yersinia pestis invasion

We evaluated the invasion of plague bacteria Yersinia pestis into a population of black-tailed prairie dogs (Cynomys ludovicianus; BTPDs) in South Dakota. We aimed to ascertain if Y. pestis invaded slowly or rapidly, and to determine if vector (flea) control or vaccination of BTPDs assisted in increasing survival rates. We sampled BTPDs in 2007 (before Y. pestis documentation), 2008 (year of confirmed invasion), and 2009 (after invasion). We estimated annual BTPD re-encounter rates on three 9-ha plots treated annually with deltamethrin dust for flea control and three 9-ha plots lacking dust. In 2007 and 2008, approximately half the adult BTPDs live-trapped were injected subcutaneously with either an experimental plague vaccine (F1-V fusion protein) or placebo formulation; the remaining individuals were not inoculated. From 2007 to 2009, we sampled 1559 BTPDs on 2542 occasions. During 2007-2008, the prevalence and intensity of fleas on BTPDs were 69-97% lower on the dusted vs. no dust plots. From 2007 to 2008, the annual re-encounter rate of non-inoculated BTPDs was 150% higher on the dusted vs. no dust plots. During the same interval on the dusted plots, the re-encounter rate was 55% higher for vaccinated adult female BTPDs vs. nonvaccinated adult females, but the annual re-encounter rate was 19% lower for vaccinated adult males. By late August 2008, BTPDs were nearly extirpated from the no dust plots. During 2007-2008 and 2008-2009 on the dusted plots, which persisted, the BTPD re-encounter rate was 41% higher for vaccinated vs. non-vaccinated adult females but 35% lower for vaccinated adult males. Yersinia pestis erupted with vigor as it invaded. Flea control enhanced BTPD survival but did not offer full protection. Flea control and F1-V vaccination seemed to have additive, positive effects on adult females. Annual re-encounter rates were reduced for vaccinated adult males; additional experimentation is needed to further evaluate this trend.

Plague mitigation for prairie dog and black-footed ferret conservation: Degree and duration of flea control with 0.005% fipronil grain bait

Sylvatic plague, a primarily flea-borne zoonosis, is a significant threat to prairie dogs (Cynomys spp., PDs) and their specialized predators, endangered black-footed ferrets (Mustela nigripes, BFFs). Host-fed fipronil baits have proven effective in controlling fleas on PDs for the purposes of plague mitigation and BFF conservation. Currently, annual treatments are the norm. We tested the long-term efficacy of fipronil bait treatments with black-tailed PDs (C. ludovicianus, BTPDs) and BFFs in South Dakota, USA. During 2018-2020, we provided BTPDs on 21 sites with grain bait formula, laced with 0.005% fipronil (50 ​mg/kg); 18 non-treated sites functioned as baselines. In 2020-2022, we live-trapped, anesthetized, and combed BTPDs for fleas. Flea control was significant for at least 639-885 days. Flea abundance on the treated sites was < 0.5 fleas/BTPD for ∼750 days. During 2020-2022, we sampled BFFs for fleas on 4 BTPD colonies treated with fipronil grain bait and 8 non-treated colonies. Flea control was significant with BFFs, but flea abundance began to rebound within ∼240 days post-treatment. When feasible, the combination of insecticide treatments, such as fipronil baits, and BFF vaccination against plague provide a "two-pronged" protection approach for these endangered carnivores. If fipronil bait treatments are less effective with predatory BFFs than PDs, as found herein, the "two-pronged" approach might be used to protect BFFs and biennial fipronil bait treatments might be used to protect PDs. If BFF vaccination is not possible, or few BFFs can be vaccinated, annual fipronil bait treatments might be used as a precaution to protect BFFs. Flea densities might be surveyed to determine when/where more frequent treatments seem useful.

Using hair cortisol analysis to understand the biological factors that affect black-footed ferret (Mustela nigripes) stress physiology

The black-footed ferret (Mustela nigripes) was driven to near extinction due to habitat loss and an introduced disease, sylvatic plague (Yersinia pestis). After 35 years of breeding in ex situ facilities, the black-footed ferret has been experiencing infertility with seminal traits declining in males and only about a third of breeding-aged females are whelping. Our goal was to use hair cortisol analysis to determine if the ex situ population was experiencing chronic stress that was affecting reproduction by comparing captive ferrets to wild individuals. Our specific objectives were to (i) compare hair cortisol concentrations (HCCs) between age classes (juveniles versus adults), (ii) compare the HCCs of in situ and across different ex situ facilities and (iii) determine the relationship between HCCs and reproductive success. Overall, wild juveniles had higher HCC than wild adults. Our generalized linear mixed model determined that the parameters that best predict HCC for adults were the interactions among sex, in situ versus ex situ facilities and season. During both seasons, wild females had higher HCCs compared to the ex situ females. During the breeding season, male HCCs across breeding facilities varied and males at the breeding facility with the largest ferret habitats had HCCs similar to wild males. At one breeding facility, HCC was higher in males that sired compared to those that did not sire. In conclusion, ex situ ferrets do not have higher HCC than wild individuals when controlling for season and ex situ habitat size, and ex situ males with higher HCC tended to sire. This suggests that HCC may be metabolically driven and/or that low HCC may be an indication of hypothalamus-pituitary-adrenal axis dysregulation and warrants further investigation both for laboratory validation and biological relevance.

An invasive disease, sylvatic plague, increases fragmentation of black-tailed prairie dog (Cynomys ludovicianus) colonies

Context

A disease can be a source of disturbance, causing population declines or extirpations, altering species interactions, and affecting habitat structure. This is particularly relevant for diseases that affect keystone species or ecosystem engineers, leading to potentially cascading effects on ecosystems.

Objective

We investigated the invasion of a non-native disease, plague, to a keystone species, prairie dogs, and documented the resulting extent of fragmentation and habitat loss in western grasslands. Specifically, we assessed how the arrival of plague in the Conata Basin, South Dakota, United States, affected the size, shape, and aggregation of prairie dog colonies, an animal species known to be highly susceptible to plague.

Methods

Colonies in the prairie dog complex were mapped every 1 to 3 years from 1993 to 2015. Plague was first confirmed in 2008 and we compared prairie dog complex and colony characteristics before and after the arrival of plague.

Results

As expected the colony complex and the patches in colonies became smaller and more fragmented after the arrival of plague; the total area of each colony and the mean area per patch within a colony decreased, the number of patches per colony increased, and mean contiguity of each patch decreased, leading to habitat fragmentation.

Conclusion

We demonstrate how an emerging infectious disease can act as a source of disturbance to natural systems and lead to potentially permanent alteration of habitat characteristics. While perhaps not traditionally thought of as a source of ecosystem disturbances, in recent years emerging infectious diseases have shown to be able to have large effects on ecosystems if they affect keystone species.

Drought-mediated changes in black-tailed prairie dog colonies in the Northern Great Plains

Populations of many mammal species living in grassland ecosystems across North America have been reduced greatly over the past 200 years due to conversion of native prairie to human-related uses. Foremost among these species is the black-tailed prairie dog (Cynomys ludovicianus), populations of which have declined an estimated 98% during that time. In addition to anthropogenic factors including plague, black-tailed prairie dog populations can vary in size in response to grazing by native ungulates, fire, and precipitation. Colonies in the Northern Great Plains have expanded and contracted during dry and wet periods, respectively. Drought reduces vegetation height; tall vegetation is known to limit colony expansion, possibly due to increased predation risk. We used mixed-effects models to analyze data sets of colony areas of black-tailed prairie dogs spanning 16–22 years and 983 total colony counts, from 142 unique colonies at Badlands National Park and Wind Cave National Park, South Dakota, United States, and Scotts Bluff National Monument, Nebraska, United States, to relate areal dynamics of colonies over time to total annual precipitation, drought stress, and plague. We also analyzed the relationship between active-burrow densities and precipitation and drought stress using 7 years of data from 271 colony counts at Badlands National Park. Black-tailed prairie dog colonies expanded in response to drought conditions in all three national parks, with colonies in Wind Cave National Park exhibiting a time-delayed response. In addition, colony area was negatively related to total accumulated precipitation for the preceding 12 months for Scotts Bluff National Monument. Active-burrow density at Badlands National Park decreased in response to drought stress with a time lag of 24–36 months. Plague first was reported at Badlands National Park in 2008 and colony areas decreased dramatically and rapidly during plague epizootic events. Our results support observations that black-tailed prairie dog colonies in the Northern Great Plains expand and contract in response to drought stress and wet weather. Furthermore, our findings provide new insights into the role of climate on a keystone species of conservation importance and demonstrate the value of collecting long-term ecological data.

When generalists behave as specialists: local specialization by American badgers (Taxidea taxus)

Differentiating species according to their relative niche breadth is a common approach in community ecology that can enhance understanding about how species relate to the environment. Although a species might exhibit a generalized ecology across its entire range, on a local scale, individuals might function as specialists. American badgers (Taxidea taxus (Schreber, 1777)) are terrestrial carnivores that have been described most often as generalists. We compared patterns of habitat selection by badgers at three scales to test the hypothesis that badgers would exhibit behaviors more closely aligned with specialists than generalists when inhabiting landscapes with black-tailed prairie dogs (Cynomys ludovicianus (Ord, 1815)). At a course scale, badgers selected for prairie dog colonies across the landscape. At an intermediate scale, we documented significantly greater use of prairie dog colonies within the home ranges of badgers. At fine scales within colonies, badgers used areas that had relatively high densities of prairie dog burrows, where prey was presumably abundant. On multiple scales, badgers exhibited a narrow use of resources in comparison with the resources available. Our study provides additional evidence that badgers behave as specialists when burrowing rodents are highly concentrated and predictable over space and time.

Spatial interactions between sympatric carnivores: asymmetric avoidance of an intraguild predator

Interactions between intraguild species that act as both competitors and predator-prey can be especially complex. We studied patterns of space use by the black-footed ferret (Mustela nigripes), a prairie dog (Cynomys spp.) specialist, and the American badger (Taxidea taxus), a larger generalist carnivore that competes for prairie dogs and is known to kill ferrets. We expected that ferrets would spatially avoid badgers because of the risk of predation, that these patterns of avoidance might differ between sexes and age classes, and that the availability of food and space might influence these relationships. We used location data from 60 ferrets and 15 badgers to model the influence of extrinsic factors (prairie dog density and colony size) and intrinsic factors (sex, age) on patterns of space use by ferrets in relation to space use by different sex and age categories of badgers. We documented asymmetric patterns of avoidance of badgers by ferrets based on the sex of both species. Female ferrets avoided adult female badgers, but not male badgers, and male ferrets exhibited less avoidance than female ferrets. Additionally, avoidance decreased with increasing densities of prairie dogs. We suggest that intersexual differences in space use by badgers create varying distributions of predation risk that are perceived by the smaller carnivore (ferrets) and that females respond more sensitively than males to that risk. This work advances understanding about how competing species coexist and suggests that including information on both intrinsic and extrinsic factors might improve our understanding of behavioral interactions between sympatric species.