Kurt T. Smith

Prioritizing winter habitat quality for greater sage‐grouse in a landscape influenced by energy development

Prioritizing habitats that provide the best options for the persistence of sensitive species in human-modified landscapes is a critical concern for conservation. Linking occurrence and fitness parameters across multiple spatial scales provides an approach to address habitat prioritization for species of concern in disturbed habitats. To demonstrate the usefulness of this approach, we generated resource selection and survival risk models as a framework to quantify habitat value for wintering female greater sage-grouse (Centrocercus urophasianus) inhabiting a 6,093-km2 study area in northwest Colorado and south-central Wyoming, USA, being developed for oil and natural gas reserves. Our approach allowed us to evaluate the relative influence of anthropogenic development and environmental attributes characterizing a large landscape on habitat selection and habitat-specific survival in winter for female sage-grouse. When combined, these models provided a spatial representation of habitat quality to inform management and conservation of critical wintering habitats. We used 537 locations from 105 radio-marked female grouse obtained from 18 fixed-wing flights across winters 2007–2008, 2008–2009, and 2009–2010. Wintering sage-grouse selected areas with higher wetness potential (0.75-km2 scale), intermediate (quadratic form) total shrub cover (18.83-km2 scale), higher variability in shrub height (18.83-km2 scale), and less heterogeneity in Wyoming big sagebrush (Artemisia tridentata wyomingensis; 4.71-km2 scale) cover and total shrub cover (18.83-km2 scale). Anthropogenic surface disturbance (0.75-km2 scale) was negatively associated with occurrence. Winter survival for female grouse was positively correlated with heterogeneity in big sagebrush cover at the 0.75-km2 scale, but negatively correlated with heterogeneity in total shrub cover at the 18.83-km2 scale. We did not detect an association between anthropogenic variables and female winter survival. However, displacement of sage-grouse in the energy extraction area may have masked our ability to identify anthropogenic variables potentially influencing survival. Our winter habitat quality map indicated highly effective winter habitat (high occurrence-low survival risk) was limited, only representing 17.1% of our study area. Consequently, displacement from these limited, high-quality winter habitats could have profound consequences to population persistence.

Seasonal habitat selection by elk in north central Utah

Abstract Understanding anthropogenic and environmental factors that influence seasonal habitat selection is critical in establishing conservation objectives for wildlife populations. However, many resource selection studies provide inferences only for single seasons, potentially masking factors essential to populations during other times of the year. Our objective was to model elk (Cervus elaphus) habitat selection for 4 seasons to identify factors influencing selection within and across seasons. Using aerial relocation data, we evaluated seasonal habitat selection for 46 radio-marked, migratory adult female elk in a 6123-km2 landscape in north central Utah, USA, from 1993 to 1997. We evaluated habitat use and availability within estimated seasonal range boundaries by using binary logistic regression to model habitat selection. Habitat use was measured as a response to predictor variables collected from analysis regions around elk locations. Habitat use was compared to habitat availability by measuring those same variables collected from randomly located analysis regions. Our results showed that roads, topography, and vegetation cover influenced elk habitat selection within and across seasons. Roads did not influence elk habitat selection in spring; rather, elk selected areas with aspen (Populus tremuloides) at higher elevations. In summer, elk selected forage-rich habitats, particularly aspen and mountain brush at higher elevations and on cooler aspects. In fall, elk selected sites with steeper slopes at higher elevations in areas with greater cover of aspen and mountain brush than was available in seasonal range boundaries. In winter, elk selected sagebrush (Artemisia spp.)-meadow cover on steeper slopes at lower elevations away from major roads. The full array of seasonal habitat selection patterns we found provides managers with greater options for setting conservation objectives for elk on a year-round basis.

Microhabitat Conditions in Wyoming’s Sage-Grouse Core Areas: Effects on Nest Site Selection and Success

The purpose of our study was to identify microhabitat characteristics of greater sage-grouse (Centrocercus urophasianus) nest site selection and survival to determine the quality of sage-grouse habitat in 5 regions of central and southwest Wyoming associated with Wyoming’s Core Area Policy. Wyoming’s Core Area Policy was enacted in 2008 to reduce human disturbance near the greatest densities of sage-grouse. Our analyses aimed to assess sage-grouse nest selection and success at multiple micro-spatial scales. We obtained microhabitat data from 928 sage-grouse nest locations and 819 random microhabitat locations from 2008–2014. Nest success was estimated from 924 nests with survival data. Sage-grouse selected nests with greater sagebrush cover and height, visual obstruction, and number of small gaps between shrubs (gap size ≥0.5 m and <1.0 m), while selecting for less bare ground and rock. With the exception of more small gaps between shrubs, we did not find any differences in availability of these microhabitat characteristics between locations within and outside of Core Areas. In addition, we found little supporting evidence that sage-grouse were selecting different nest sites in Core Areas relative to areas outside of Core. The Kaplan-Meier nest success estimate for a 27-day incubation period was 42.0% (95% CI: 38.4–45.9%). Risk of nest failure was negatively associated with greater rock and more medium-sized gaps between shrubs (gap size ≥2.0 m and <3.0 m). Within our study areas, Wyoming’s Core Areas did not have differing microhabitat quality compared to outside of Core Areas. The close proximity of our locations within and outside of Core Areas likely explained our lack of finding differences in microhabitat quality among locations within these landscapes. However, the Core Area Policy is most likely to conserve high quality habitat at larger spatial scales, which over decades may have cascading effects on microhabitat quality available between areas within and outside of Core Areas.

Does Wyoming’s Core Area Policy Protect Winter Habitats for Greater Sage-Grouse?

Conservation reserves established to protect important habitat for wildlife species are used world-wide as a wildlife conservation measure. Effective reserves must adequately protect year-round habitats to maintain wildlife populations. Wyoming’s Sage-Grouse Core Area policy was established to protect breeding habitats for greater sage-grouse (Centrocercus urophasianus). Protecting only one important seasonal habitat could result in loss or degradation of other important habitats and potential declines in local populations. The purpose of our study was to identify the timing of winter habitat use, the extent which individuals breeding in Core Areas used winter habitats, and develop resource selection functions to assess effectiveness of Core Areas in conserving sage-grouse winter habitats in portions of 5 Core Areas in central and north-central Wyoming during winters 2011–2015. We found that use of winter habitats occured over a longer period than current Core Area winter timing stipulations and a substantial amount of winter habitat outside of Core Areas was used by individuals that bred in Core Areas, particularly in smaller Core Areas. Resource selection functions for each study area indicated that sage-grouse were selecting habitats in response to landscapes dominated by big sagebrush and flatter topography similar to other research on sage-grouse winter habitat selection. The substantial portion of sage-grouse locations and predicted probability of selection during winter outside small Core Areas illustrate that winter requirements for sage-grouse are not adequately met by existing Core Areas. Consequently, further considerations for identifying and managing important winter sage-grouse habitats under Wyoming’s Core Area Policy are warranted.

Environmental cues used by Greater Sage-Grouse to initiate altitudinal migration

ABSTRACT Migration is a behavioral strategy to access resources that change across a landscape. Animals must ultimately interpret cues to properly time movements that match changing resource quality. Many animals do this by responding primarily to indirect indicators of resource quality such as an internal biological clock or photoperiod. Others are heavily dependent on more direct indicators such as weather or plant phenology. Timing of movement also can be modified by factors specific to individuals. We used time-to-event models for Greater Sage-Grouse (Centrocercus urophasianus) to investigate whether an altitudinal avian migrant was influenced by direct indicators of resource quality when timing migration, and whether timing was influenced by individual characteristics, during the spring (winter to breeding range), summer (breeding to summer range), and fall (summer to winter range) transitional seasons. Greater Sage-Grouse interpreted direct indicators of resource quality, especially temperature, when timing movements between seasonal ranges. Timing was also dependent on individual characteristics including location, reproductive status, and habitat use. After we identified which migration cues were important, we evaluated if migratory and nonmigratory individuals were experiencing similar environmental conditions, which may partly explain why there are different behaviors in a partially migrant population. For the summer and fall transitions, migratory grouse experienced more stimulatory migration cues because of differences in elevation of seasonal ranges. Migratory birds were likely avoiding more rapid plant desiccation in warmer breeding ranges and avoiding higher snow accumulation in colder summer ranges with more precipitation. Altitudinal migrants are likely to use direct indicator cues because they have great utility when migration distances are relatively short. In addition, landscapes with altitudinal migrants have sharp environmental gradients creating conditions conducive for partially migratory behavior in a population.

Nontarget effects on songbirds from habitat manipulation for Greater Sage-Grouse: Implications for the umbrella species concept

ABSTRACT The “umbrella species” concept is a conservation strategy in which creating and managing reserve areas to meet the needs of one species is thought to benefit other species indirectly. Broad-scale habitat protections on behalf of an umbrella species are assumed to benefit co-occurring taxa, but targeted management actions to improve local habitat suitability for the umbrella species may produce unintended effects on other species. Our objective was to quantify the effects of a common habitat treatment (mowing of big sagebrush [Artemisia tridentata]) intended to benefit a high-profile umbrella species (Greater Sage-Grouse [Centrocercus urophasianus]) on 3 sympatric songbird species of concern. We used a before–after control-impact experimental design spanning 3 yr in Wyoming, USA, to quantify the effect of mowing on the abundance, nest-site selection, nestling condition, and nest survival of 2 sagebrush-obligate songbirds (Brewers Sparrow [Spizella breweri] and Sage Thrasher [Oreoscoptes montanus]) and one open-habitat generalist songbird (Vesper Sparrow [Pooecetes gramineus]). Mowing was associated with lower abundance of Brewers Sparrows and Sage Thrashers but higher abundance of Vesper Sparrows. We found no Brewers Sparrows or Sage Thrashers nesting in the mowed footprint posttreatment, which suggests complete loss of nesting habitat for these species. Mowing was associated with higher nestling condition and nest survival for Vesper Sparrows but not for the sagebrush-obligate species. Management prescriptions that remove woody biomass within a mosaic of intact habitat may be tolerated by sagebrush-obligate songbirds but are likely more beneficial for open-habitat generalist species. By definition, umbrella species conservation entails habitat protections at broad spatial scales. We caution that habitat manipulations to benefit Greater Sage-Grouse could negatively affect nontarget species of conservation concern if implemented across large spatial extents.

Reproductive state leads to intraspecific habitat partitioning and survival differences in greater sage-grouse: implications for conservation

Abstract Context. Inter- and intraspecific habitat partitioning is widespread across taxa, yet limited information is available on differences in intraspecific habitat selection by same-sex individuals among differing reproductive states. Understanding habitat selection by conspecifics of different reproductive states may help optimise conservation efforts, particularly for gallinaceous bird species such as greater sage-grouse (Centrocercus urophasianus), which are long-lived but have only moderate reproductive rates. Aims. We predicted that habitat use differed between grouse under different reproductive states and that reproductive investment decreased survival of adults in summer. Methods. We compared habitat characteristics used by brood-rearing and broodless female sage-grouse and evaluated the influence of reproductive investment and habitat use on survival of adult females. Key results. We found that brood-rearing and broodless female sage-grouse partitioned habitat at micro- and macrohabitat scales. Broodless females were more likely to survive the summer. Conclusions. Our findings suggest reproductive state variability in habitat selection by female sage-grouse. Broodless females were roosting and foraging in concealed habitats with intermediate visual obstruction and annual vegetation productivity, but less food forb availability compared with early and late brood-rearing females. In contrast, brood-rearing females likely selected more herbaceous understoreys to predictably maximise foraging opportunities and promote growth of their chicks, which appeared to mitigate the influence of reproductive costs on summer survival, particularly during the late brood-rearing period. Implications. Survival of adult females is critical for population persistence of sage-grouse and other long-lived Galliformes, yet conservation efforts generally focus on habitats used during nesting and brood-rearing. Our results suggest that habitat partitioning is a potential risk-aversion strategy where individuals across different reproductive states likely select habitats to maximise their survival. Conservation efforts should focus on conserving habitats used by both brood-rearing and broodless sage-grouse to ensure population persistence.

Effects of Mowing and Tebuthiuron on the Nutritional Quality of Wyoming Big Sagebrush

ABSTRACT Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) is the most abundant and widely distributed subspecies of big sagebrush and has been treated through chemical application, mechanical treatments, and prescribed burning in efforts thought to improve habitat conditions for species such as greater sage-grouse (Centrocercus urophasianus) and mule deer (Odocoileus hemionus). Although the response of structural attributes of sagebrush communities to treatments is well understood, there is a need to identify how treatments influence the quality of sagebrush as winter food for wildlife. Our purpose was to identify how mowing and tebuthiuron treatments influenced dietary quality of Wyoming big sagebrush in central Wyoming. Two study areas were mowed in January and February 2014, and tebuthiuron was applied in two study areas in May 2014. We constructed 6 exclosures in each of these four study areas (24 total), which encompassed 30 × 30 m areas of treated and untreated sagebrush within each exclosure. Samples of current annual growth were collected from 18 sagebrush plants from treated and 12 plants from control portions of mowing exclosures during November 2013–2015 and tebuthiuron exclosures during November 2014–2015. Samples were analyzed for crude protein and plant secondary metabolites known to influence dietary selection of sagebrush by sagegrouse and other sagebrush-occurring herbivores. Our results suggest mowing and tebuthiuron treatments may slightly increase crude protein concentrations directly after treatments without immediate changes in plant secondary metabolites. Slight increases in dietary quality of sagebrush following treatments coupled with potential trade-offs with loss of biomass associated with treatments corroborates previous research that treating Wyoming big sagebrush may have little benefit for sage-grouse and other sagebrush-dependent wildlife. Future work should evaluate not only how treatments influence sage-grouse habitat use and reproductive success but also how treatments influence other wildlife species in fragile sagebrush ecosystems.

Identification of Columbian Sharp-Tailed Grouse Lek Sites in South Central Wyoming

Abstract. The Columbian Sharp-tailed Grouse (Tympanuchus phasianellus columbianus; hereafter CSTG) occupies approximately 10% of its historic range and is a species of conservation concern in 7 U.S. states and British Columbia. Because little is known about the status of CSTG in Wyoming, we sought to model the relative probability of lek site occurrence within the known distribution of CSTG in the state to identify areas that contained previously undocumented lek sites. The proximity of nesting and brood-rearing habitats to leks advocates their use as a focus of conservation for prairie grouse, including CSTG. We modeled a resource selection function (RSF) to identify areas that were predicted to have a high probability of lek occurrence. In areas identified by the RSF, we searched for leks by conducting ground surveys and surveys from a fixed-wing airplane using aerial infrared (AIR) technology. We identified 6 previously undocumented CSTG leks through ground searches and 4 previously undocumented Greater Sage-Grouse (Centrocercus urophasianus) leks through AIR searches. Newly identified leks represented a 22% increase in the number of known CSTG leks in south central Wyoming. Our method not only improved knowledge of CSTG status in Wyoming, but may also improve identification of unknown lek sites and conservation of lekking habitat and additional reproductive habitats for prairie grouse species in other western states and provinces.