Marc R. Matchett

The effect of rearing methods on survival of reintroduced black-footed ferrets

We estimated minimum survival rates for 282 young-of-year, captive-reared, black-footed ferrets (Mustela nigripes) reintroduced into prairie dog (Cynomys spp.) colonies in Wyoming, Montana, and South Dakota. We used night surveys with spotlights to locate ferrets about 1 month and 9 months postrelease. We modeled minimum survival rates using gender, year, site, and 4 rearing methods. Minimum survival rates were highest (30% for 1 month, 20% for 9 months) for ferrets reared from early ages in outdoor pens with simulated prairie dog habitat; survival was lowest for cage-reared ferrets released without pen experience (11% for 1 month, 2% for 9 months). Rearing method and year influenced 1-month survival in a comparison of 3 levels of pen experience (pen rearing as defined above, transfer of kits from zoos to pen facilities at age 60-90 days, transfer at age >90 days) during releases in 1994-95 in Montana. Higher survival was associated with intensive management of coyotes (Canis latrans) in 1995. Survival was not different (P > 0.05) between sites or sexes, regardless of model. We recommend routine use of outdoor pens for prerelease conditioning of black-footed ferret kits.

Enzootic Plague Reduces Black-Footed Ferret (Mustela nigripes) Survival in Montana

Black-footed ferrets (Mustela nigripes) require extensive prairie dog colonies (Cynomys spp.) to provide habitat and prey. Epizootic plague kills both prairie dogs and ferrets and is a major factor limiting recovery of the highly endangered ferret. In addition to epizootics, we hypothesized that enzootic plague, that is, presence of disease-causing Yersinia pestis without any noticeable prairie dog die off, may also affect ferret survival. We reduced risk of plague on portions of two ferret reintroduction areas by conducting flea control for 3 years. Beginning in 2004, about half of the ferrets residing on dusted and nondusted colonies were vaccinated against plague with an experimental vaccine (F1-V fusion protein). We evaluated 6-month reencounter rates (percentage of animals observed at the end of an interval that were known alive at the beginning of the interval), an index to survival, for ferrets in four treatment groups involving all combinations of vaccination and flea control. For captive-reared ferrets (115 individuals observed across 156 time intervals), reencounter rates were higher for vaccinates (0.44) than for nonvaccinates (0.23, p = 0.044) on colonies without flea control, but vaccination had no detectable effect on colonies with flea control (vaccinates = 0.41, nonvaccinates = 0.42, p = 0.754). Flea control resulted in higher reencounter rates for nonvaccinates (p = 0.026), but not for vaccinates (p = 0.508). The enhancement of survival due to vaccination or flea control supports the hypothesis that enzootic plague reduces ferret survival, even when there was no noticeable decline in prairie dog abundance. The collective effects of vaccination and flea control compel a conclusion that fleas are required for maintenance, and probably transmission, of plague at enzootic levels. Other studies have demonstrated similar effects of flea control on several species of prairie dogs and, when combined with this study, suggest that the effects of enzootic plague are widespread. Finally, we demonstrated that the experimental F1-V fusion protein vaccine provides protection to ferrets in the wild.

Spatiotemporal dynamics of black-tailed prairie dog colonies affected by plague

Black-tailed prairie dogs (Cynomys ludovicianus) are a key component of the disturbance regime in semi-arid grasslands of central North America. Many studies have compared community and ecosystem characteristics on prairie dog colonies to grasslands without prairie dogs, but little is known about landscape-scale patterns of disturbance that prairie dog colony complexes may impose on grasslands over long time periods. We examined spatiotemporal dynamics in two prairie dog colony complexes in southeastern Colorado (Comanche) and northcentral Montana (Phillips County) that have been strongly influenced by plague, and compared them to a complex unaffected by plague in northwestern Nebraska (Oglala). Both plague-affected complexes exhibited substantial spatiotemporal variability in the area occupied during a decade, in contrast to the stability of colonies in the Oglala complex. However, the plague-affected complexes differed in spatial patterns of colony movement. Colonies in the Comanche complex in shortgrass steppe shifted locations over a decade. Only 10% of the area occupied in 1995 was still occupied by prairie dogs in 2006. In 2005 and 2006 respectively, 74 and 83% of the total area of the Comanche complex occurred in locations that were not occupied in 1995, and only 1% of the complex was occupied continuously over a decade. In contrast, prairie dogs in the Phillips County complex in mixed-grass prairie and sagebrush steppe primarily recolonized previously occupied areas after plague-induced colony declines. In Phillips County, 62% of the area occupied in 1993 was also occupied by prairie dogs in 2004, and 12% of the complex was occupied continuously over a decade. Our results indicate that plague accelerates spatiotemporal movement of prairie dog colonies, and have significant implications for landscape-scale effects of prairie dog disturbance on grassland composition and productivity. These findings highlight the need to combine landscape-scale measures of habitat suitability with long-term measures of colony locations to understand the role of plague-affected prairie dogs as a grassland disturbance process.

West Nile virus and sage‐grouse: What more have we learned?

Abstract West Nile virus (WNv) has emerged as a new issue in the conservation of native avifauna in North America. Mortality associated with WNv infection decreased survival of female greater sage-grouse (Centrocercus urophasianus) by 25% across 4 populations in Wyoming and Montana, USA, and Alberta, Canada, in 2003. In 2004 WNv spread to populations in Colorado and California, and female survival in late summer was 10% lower at 4 sites with confirmed WNv mortalities (86% survival) than at 8 sites without (96%). We still have no evidence that sage-grouse show resistance to the virus. The 2004 WNv season was not the catastrophe that many had predicted, and the decrease in prevalence of infection and mortality in sage-grouse, humans, and horses (except in California) has left many wondering if the worst has past. Evidence suggests that risk of infection was low in 2004 because unseasonably cool summer temperatures delayed or reduced mosquito production. Moreover, mortalities occurred 2–3 weeks later in 2004 than in 2003, and the shift to later timing was consistent between years at sites where WNv reduced survival both years. Mosquito surveillance data indicated a sharp decline in prevalence and infection rate of adult C. tarsalis in southeast Alberta, the most northern latitude where WNv reduced survival, in 2003 but not in 2004. A full understanding of the implications of WNv for sage-grouse requires a long-term, coordinated monitoring strategy among researchers and a sensitivity analysis to evaluate the role of WNv in population viability. Epidemiological research examining the prevalence and ecology of the virus among reservoir hosts is crucial.

Home-range size and spatial organization of black-footed ferrets Mustela nigripes in South Dakota, USA

Abstract Effective conservation planning for endangered species depends on an understanding of space use patterns. Black-footed ferrets Mustela nigripes depend on prairie dogs Cynomys sp. as prey and use their burrow systems for shelter. The availability of areas with high densities of active prairie dog burrows is the major factor thought to affect their selection of sites and resources. However, we have little knowledge about how the spatial distribution of active prairie dog burrows might influence the spatial organization and home-range size of ferrets. We monitored the movements of black-footed ferrets on a black-tailed prairie dog C. ludovicianus colony in South Dakota to document ferret space use patterns. Home ranges of female ferrets were 22.9 - 95.6 ha in size (x̄ = 56.3 ha, SE = 19.7, N = 6), while male ferret home ranges were on average more than twice as large as those of females (x̄ = 128.3 ha, SE = 68.5, N = 3). The home-range size of female ferrets was correlated with mean active prairie dog burrow utilization distribution (UD) value within ferret home ranges, where home-range size decreased as active prairie dog burrow UD value increased (r2 = 0.974, P < 0.001, N = 6). Ferret space use overlapped more extensively than previously reported, with up to 43% UD overlap between a ferret and the nearest adjacent ferret of the same sex. Areas of overlap tended to have higher active prairie dog burrow UD values, suggesting that the spatial distribution of active prairie dog burrows influenced both home-range size and the amount of space use overlap between ferrets. These findings emphasize the potential influence of resource distribution on carnivore sociobiology and the importance of considering that distribution in assessing habitat for the reintroduction of specialized species.

Implications of Black-tailed Prairie Dog Spatial Dynamics to Black- footed Ferrets

Abstract The spatial dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies affect the utility of these environments for other wildlife, including the endangered black-footed ferret (Mustela nigripes). We used location data of active and inactive black-tailed prairie dog burrows to investigate colony structure, spatial distribution, and patch dynamics of two colonies at ferret recovery sites. We used kernel-based utilization distributions (UDs) of active and inactive burrows from two time periods (six and 11 years apart) as the basis for our analysis. Overall, the total extent of our prairie dog colonies changed little over time. However, within colonies, areas with high densities of active and inactive prairie dog burrows formed patches and the distribution of these patches changed in size, shape, and connectivity over time. At the Conata Basin site, high-density active burrow patches increased in total area covered while decreasing in connectivity as they shifted towards the perimeter of the colony over time. At the UL Bend site, we observed a similar but less pronounced shift over a longer period of time. At both sites, while at a large scale it appeared that prairie dogs were simply shifting areas of activity towards the perimeter of colonies and abandoning the center of colonies, we observed a dynamic interaction between areas of active and inactive burrows within colonies over time. Areas that previously contained inactive burrows tended to become active, and vice versa, leading us to hypothesize that there are shifts of activity areas within colonies over time as dictated by forage availability. The spatial dynamics we observed have important implications for techniques to estimate the suitability of ferret habitat and for the management of prairie dog colonies. First, fine-scale techniques for measuring prairie dog colonies that account for their patchy spatial distribution are needed to better assess ferret habitat suitability. Second, the shift of high-density areas of active prairie dog burrows, likely associated with changes in vegetation, suggests that through the management of vegetation we might be able to indirectly improve habitat for ferrets. Finally, we found that prairie dog distributions within a colony are a naturally dynamic process and that management strategies should consider the long-term value of both active and inactive areas within colonies.

No Evidence of Persistent Yersina pestis Infection at Prairie Dog Colonies in North-Central Montana

Sylvatic plague is a flea-borne zoonotic disease caused by the bacterium Yersinia pestis, which can cause extensive mortality among prairie dogs (Cynomys) in western North America. It is unclear whether the plague organism persists locally among resistant host species or elsewhere following epizootics. From June to August 2002 and 2003 we collected blood and flea samples from small mammals at prairie dog colonies with a history of plague, at prairie dog colonies with no history of plague, and from off-colony sites where plague history was unknown. Blood was screened for antibody to Y. pestis by means of enzyme-linked immunosorbent assay or passive hemagglutination assay and fleas were screened for Y. pestis DNA by polymerase chain reaction. All material was negative for Y. pestis including 156 blood samples and 553 fleas from colonies with a known history of plague. This and other studies provide evidence that Y. pestis may not persist at prairie dog colonies following an epizootic.

Efficacy of translocations for restoring populations of black-tailed prairie dogs

Abstract We evaluated translocation as a method to promote recovery of black-tailed prairie dogs (Cynomys ludovicianus) after plague-induced population declines in colonies at the Charles M. Russell National Wildlife Refuge, Montana. We translocated prairie dogs in June of 1999 and evaluated the effects of translocation on colony area 1 year and 4 years later. We also assessed effects of release group size and estimated rates of population growth and survival. Initial size of experimental colonies was categorized as inactive (0 ha), small (0.1–2.0 ha), or large (2.0–6.6 ha); numbers of prairie dogs translocated to each colony size class were 0 (control), 60, and 120. Among inactive colonies, the control remained inactive and the colony receiving 60 prairie dogs grew to 1.5 ha by 2000 and after a second release in 2002 was 1.9 ha in 2003. The colony receiving 120 grew to 3.3 ha by 2000 and decreased to 2.6 ha by 2003. Patterns on small and large colonies after 1 year were less dramatic, but in each case the proportional increase in colony area was lowest on the control and highest on the colony receiving 120 prairie dogs. Patterns were more difficult to discern 4 years after translocations. It appears that as large colonies approach historic size, area growth decreases and is slower than on small colonies. Experimental colonies grew 24.6 ha (315%) by 2000 and 72.1 ha (924%) in 4 years compared to non-experimental colonies of similar size that grew 6.5 ha (23%) in 1 year and 26.5 ha (93%) by 2003. Monthly survival rates of prairie dogs during the first 3 months following translocation were higher on large colonies (0.79, 95% CI=0.75–0.82) than on small (0.67, 95% CI=0.62–0.72) or inactive colonies, (0.63, 95% CI=0.57–0.68). Monthly survival rates were relatively high (0.88–1.0) during subsequent intervals and did not vary among initial colony size classes. Recapture rates for all colonies were higher during the fall trapping session (0.83, 95% CI=0.76–0.90) than in the winter (0.59, 95% CI=0.49–0.69). Translocation was effective for restoration of prairie dog populations, particularly on inactive colonies.

Resource Selection by Black-Footed Ferrets in South Dakota and Montana

ABSTRACT: The black-footed ferret (Mustela nigripes), once extinct in the wild, remains one of the most critically endangered mammals in North America despite 18 years of reintroduction attempts. Because black-footed ferrets are specialized predators of prairie dogs (Cynomys sp.), a better understanding of how black-footed ferrets select resources might provide insight into how best to identify and manage reintroduction sites. We monitored ferret resource selection at two reintroduction sites with different densities of prairie dog populations-one that contained a high density of prairie dogs (Conata Basin, South Dakota) and one that was lower (UL Bend, Montana). We evaluated support for hypotheses about ferret resource selection as related to the distribution of active burrows used by black-tailed prairie dogs (Cynomys ludovicianus), interactions between ferrets, and habitat edge effects. We found support for all three factors within both populations; however, they affected ferret resource selection differently at each site. Ferrets at Conata Basin tended to select areas with high prairie dog burrow density, closer to the colony edge, and that overlapped other ferret ranges. In contrast, ferrets at UL Bend tended not to select areas of high active prairie dog burrow density, avoided areas close to edge habitat, and females avoided areas occupied by other ferrets. The differences observed between the two sites might be best explained by prairie dog densities, which were higher at Conata Basin (119.3 active burrows per ha) than at UL Bend (44.4 active burrows per ha). Given the positive growth of ferret populations at Conata Basin, management that increases the density of prairie dogs might enhance ferret success within natural areas. To achieve long-term recovery of ferrets in the wild, conservationists should increasingly work across and outside natural area boundaries to increase prairie dog populations.

Resource Selection Models are Useful in Predicting Fine-Scale Distributions of Black-Footed Ferrets in Prairie Dog Colonies

ABSTRACT. Wildlife-habitat relationships are often conceptualized as resource selection functions (RSFs)—models increasingly used to estimate species distributions and prioritize habitat conservation. We evaluated the predictive capabilities of 2 black-footed ferret (Mustela nigripes) RSFs developed on a 452-ha colony of black-tailed prairie dogs (Cynomys ludovicianus) in the Conata Basin, South Dakota. We used the RSFs to project the relative probability of occurrence of ferrets throughout an adjacent 227-ha colony. We evaluated performance of the RSFs using ferret space use data collected via postbreeding spotlight surveys June–October 2005–2006. In home ranges and core areas, ferrets selected the predicted “very high” and “high” occurrence categories of both RSFs. Count metrics also suggested selection of these categories; for each model in each year, approximately 81% of ferret locations occurred in areas of very high or high predicted occurrence. These results suggest usefulness of the RSFs in estimating the distribution of ferrets throughout a black-tailed prairie dog colony. The RSFs provide a fine-scale habitat assessment for ferrets that can be used to prioritize releases of ferrets and habitat restoration for prairie dogs and ferrets. A method to quickly inventory the distribution of prairie dog burrow openings would greatly facilitate application of the RSFs.