Scale-dependent habitat use in three species of prairie wetland birds

We evaluated the influence of scale on habitat use for three wetland-obligate bird species with divergent life history characteristics and possible scale-dependent criteria for nesting and foraging in South Dakota, USA. A stratified, two-stage cluster sample was used to randomly select survey wetlands within strata defined by region, wetland density, and wetland surface area. We used 18-m (0.1 ha) fixed radius circular-plots to survey birds in 412 semipermanent wetlands during the summers of 1995 and 1996. Variation in habitat use by pied-billed grebes (Podilymbus podiceps) and yellow-headed blackbirds (Xanthocephalus xanthocephalus), two sedentary species that rarely exploit resources outside the vicinity of nest wetlands, was explained solely by within-patch variation. Yellow-headed blackbirds were a cosmopolitan species that commonly nested in small wetlands, whereas pied-billed grebes were an area-sensitive species that used larger wetlands regardless of landscape pattern. Area requirements for black terns (Chlidonias niger), a vagile species that typically forages up to 4 km away from the nest wetland, fluctuated in response to landscape structure. Black tern area requirements were small (6.5 ha) in heterogeneous landscapes compared to those in homogeneous landscapes (15.4–32.6 ha). Low wetland density landscapes composed of small wetlands, where few nesting wetlands occurred and potential food sources were spread over large distances, were not widely used by black terns. Landscape-level measurements related to black tern occurrence extended past relationships between wetlands into the surrounding matrix. Black terns were more likely to occur in landscapes where grasslands had not been tilled for agricultural production. Our findings represent empirical evidence that characteristics of entire landscapes, rather than individual patches, must be quantified to assess habitat suitability for wide-ranging species that use resources over large areas.     

Sensitivity of test strategies used in the Voluntary Johne's Disease Herd Status Program for detection of Mycobacterium paratuberculosis infection in dairy cattle herds

OBJECTIVE: To evaluate sensitivities at the herd level of test strategies used in the Voluntary Johne's Disease Herd Status Program (VJDHSP) and alternative test strategies for detecting dairy cattle herds infected with Mycobacterium paratuberculosis. DESIGN: Nonrandom cross-sectional study. SAMPLE POPULATION: 64 dairy herds from Pennsylvania, Minnesota, Colorado, Ohio, and Wisconsin. Fifty-six herds had at least 1 cow shedding M. paratuberculosis in feces; the other 8 herds were free from paratuberculosis. PROCEDURE: For all adult cows in each herd, serum samples were tested for antibodies to M. paratuberculosis with an ELISA, and fecal samples were submitted for bacterial culture for M. paratuberculosis. Sensitivities at the herd level (probability of detecting infected herd) of various testing strategies were then evaluated. RESULTS: Sensitivity at the herd level of the testing strategy used in level 1 of the VJDHSP (use of the ELISA to test samples from 30 cows followed by confirmatory bacterial culture of feces from cows with positive ELISA result) ranged from 33 to 84% for infected herds, depending on percentage of cows in the herd with positive bacterial culture results. If follow-up bacterial culture was not used to confirm positive ELISA results, sensitivity ranged from 70 to 93%, but probability of identifying uninfected herds as infected was 89%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the testing strategy used in the VJDHSP will fail to identify as infected most dairy herds with a low prevalence of paratuberculosis. A higher percentage of infected herds was detected if follow-up bacterial culture was not used, but this test strategy was associated with a high probability of misclassifying uninfected herds.     

Effects of immunocontraception on a suburban population of white-tailed deer Odocoileus virginianus

Abundant populations of white-tailed deer (Odocoileus virginianus) in North America have altered the structure of some forest communities and caused serious conflicts with farmers, gardeners, and motorists, encouraging the search for novel techniques to control populations of deer and other wildlife. We administered the porcine zona pellucida (PZP) immunocontraceptive vaccine to female white-tailed deer living on the 233-ha campus of the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, USA. Although some tested PZP preparations proved more effective than others, the number of fawns produced per female was significantly lower in treated than untreated females. Following the onset of contraceptive treatments, the population declined by an average of 7.9% per year, and population declines were larger following years when a higher proportion of females was treated. High mortality due largely to deer-vehicle collisions and low population fertility associated with high deer densities facilitated the observed population decline.     

Short-Term Response of Sage-Grouse Nesting to Conifer Removal in the Northern Great Basin

Conifer woodlands expanding into sage-steppe (Artemisia spp.) are a threat to sagebrush obligate species including the imperiled greater sage-grouse (Centrocercus urophasianus). Conifer removal is accelerating rapidly despite a lack of empirical evidence to assess outcomes to grouse. Using a before-after-control-impact design, we evaluated short-term effects of conifer removal on nesting habitat use by monitoring 262 sage-grouse nests in the northern Great Basin during 2010–2014. Tree removal made available for nesting an additional 28% of the treatment landscape by expanding habitat an estimated 9603 ha (3201 ha [± 480 SE] annually). Relative probability of nesting in newly restored sites increased by 22% annually, and females were 43% more likely to nest within 1000 m of treatments. From 2011 (pretreatment) to 2014 (3 yr after treatments began), 29% of the marked population (9.5% [± 1.2 SE] annually) had shifted its nesting activities into mountain big sagebrush habitats that were cleared of encroaching conifer. Grouping treatments likely contributed to beneficial outcomes for grouse as individual removal projects averaged just 87 ha in size but cumulatively covered a fifth of the study area. Collaboratively identifying future priority watersheds and implementing treatments across public and private ownerships is vital to effectively restore the sage-steppe ecosystem for nesting sage-grouse.     

Bird Responses to Removal of Western Juniper in Sagebrush-Steppe

We investigated bird abundance in response to western juniper (Juniperus occidentalis) removal using a short-term chronosequence approach and generated estimates of density and responses to management for the most abundant species. Stands targeted for tree removal were primarily in the middle stages of juniper encroachment (Phase II, 7 851 ha). Trees were removed using hand felling combined with either lop and scatter, single tree burning, or jackpot burning, which were carried out to minimize loss of shrub cover. Brewer’s sparrow (Spizella breweri) density was greater at treated versus untreated portions of the study area. At sites in the third year following tree removal, Brewer’s sparrow density was 23.6 (95% confidence interval [CI]: 19.4–27.8) territories per km² higher than locations that had not yet been treated. This equates to a net increase of 1 212 ? 1 737 nesting pairs within the project area. Green-tailed towhee increased by 4.6 (95% CI: 3.1–6.1) territories per km² for an estimated project-wide increase of 194–381 nesting pairs, and vesper sparrow (Poocetes gramineus) increased by 6.5 (95% CI: 4.6–8.4) territories per km² corresponding to an estimated increase of 460–559 nesting pairs within the project area. Density of gray flycatcher (Empidonax wrighti) was lower in cut areas, and over the entire project area we estimate a net loss of 183–486 nesting pairs as a result of juniper tree removal. This study demonstrates that conifer removal projects designed to retain shrub cover and structure can have benefits to multiple species of ground and shrub nesting birds, including several species of conservation concern.     

Mapping Tree Canopy Cover in Support of Proactive Prairie Grouse Conservation in Western North America

Invasive woody plant expansion is a primary threat driving fragmentation and loss of sagebrush (Artemisia spp.) and prairie habitats across the central and western United States. Expansion of native woody plants, including conifer (primarily Juniperus spp.) and mesquite (Prosopis spp.), over the past century is primarily attributable to wildfire suppression, historic periods of intensive livestock grazing, and changes in climate. To guide successful conservation programs aimed at reducing top-down stressors, we mapped invasive woody plants at regional scales to evaluate landscape level impacts, target restoration actions, and monitor restoration outcomes. Our overarching goal was to produce seamless regional products across sociopolitical boundaries with resolution fine enough to depict the spatial extent and degree of woody plant invasion relevant to greater sage-grouse (Centrocercus urophasianus) and lesser prairie-chicken (Tympanuchus pallidicinctus) conservation efforts. We mapped tree canopy cover at 1-m spatial resolution across an 11-state region (508 265 km²). Greater than 90% of occupied lesser prairie-chicken habitat was largely treeless for conifers (< 1% canopy cover), whereas > 67% was treeless for mesquite. Conifers in the higher canopy cover classes (16 ? 50% and > 50% canopy cover) were scarce (< 2% and 1% canopy cover), as was mesquite (< 5% and 1% canopy cover). Occupied habitat by sage-grouse was more variable but also had a relatively large proportion of treeless areas ($\stackrel{?}{x}$ = 71, SE = 5%). Low to moderate levels of conifer cover (1 ? 20%) were fewer ($\stackrel{?}{x}$ = 23, SE = 5%) as were areas in the highest cover class (> 50%; $\stackrel{?}{x}$ = 6, SE = 2%). Mapping indicated that a high proportion of invading woody plants are at a low to intermediate level. Canopy cover maps for conifer and mesquite resulting from this study provide the first and most geographically complete, high-resolution assessment of woody plant cover as a top-down threat to western sage-steppe and prairie ecosystems.