Christopher P. Kirol

Identifying Greater Sage-Grouse source and sink habitats for conservation planning in an energy development landscape

Conserving a declining species that is facing many threats, including overlap of its habitats with energy extraction activities, depends upon identifying and prioritizing the value of the habitats that remain. In addition, habitat quality is often compromised when source habitats are lost or fragmented due to anthropogenic development. Our objective was to build an ecological model to classify and map habitat quality in terms of source or sink dynamics for Greater Sage-Grouse (Centrocercus urophasianus) in the Atlantic Rim Project Area (ARPA), a developing coalbed natural gas field in south-central Wyoming, USA. We used occurrence and survival modeling to evaluate relationships between environmental and anthropogenic variables at multiple spatial scales and for all female summer life stages, including nesting, brood-rearing, and non-brooding females. For each life stage, we created resource selection functions (RSFs). We weighted the RSFs and combined them to form a female summer occurrence map. We modeled survival also as a function of spatial variables for nest, brood, and adult female summer survival. Our survival-models were mapped as survival probability functions individually and then combined with fixed vital rates in a fitness metric model that, when mapped, predicted habitat productivity (productivity map). Our results demonstrate a suite of environmental and anthropogenic variables at multiple scales that were predictive of occurrence and survival. We created a source-sink map by overlaying our female summer occurrence map and productivity map to predict habitats contributing to population surpluses (source habitats) or deficits (sink habitat) and low-occurrence habitats on the landscape. The source-sink map predicted that of the Sage-Grouse habitat within the ARPA, 30% was primary source, 29% was secondary source, 4% was primary sink, 6% was secondary sink, and 31% was low occurrence. Our results provide evidence that energy development and avoidance of energy infrastructure were probably reducing the amount of source habitat within the ARPA landscape. Our source-sink map provides managers with a means of prioritizing habitats for conservation planning based on source and sink dynamics. The spatial identification of high value (i.e., primary source) as well as suboptimal (i.e., primary sink) habitats allows for informed energy development to minimize effects on local wildlife populations.

Microhabitat Selection for Nesting and Brood-Rearing by the Greater Sage-Grouse in Xeric Big Sagebrush

Abstract. Understanding selection of breeding habitat is critical to conserving and restoring habitats for the Greater Sage-Grouse (Centrocercus urophasianus), particularly in xeric landscapes (≤25 cm annual precipitation). We monitored radio-marked female sage-grouse in south-central Wyoming in 2008 and 2009 to assess microhabitat use during nesting and brood rearing. For each model we grouped variables into three hypothesis sets on the basis of the weight of support from previous research (a priori information). We used binary logistic regression to compare habitat used by grouse to that at random locations and used an information-theoretic approach to identify the best-supported models. Selection of microhabitat for nests was more positively correlated with mountain big sagebrush (Artemisia tridentata vaseyana) than with Wyoming big sagebrush (A. t. wyomingensis) and negatively correlated with cheatgrass. Nesting hens also selected microhabitats with greater litter cover. Microhabitat for brood-rearing had more perennial grass and sagebrush cover than did random locations. Microhabitat variables most supported in the literature, such as forb cover and perennial grass cover, accounted for only 8% and 16% of the pure variation in our models for early and late brood rearing, respectively. Our findings suggest sage-grouse inhabiting xeric sagebrush habitats rely on sagebrush cover and grass structure for nesting as well as brood-rearing and that at the microhabitat scale these structural characteristics may be more important than forb availability. Therefore, in xeric sagebrush, practices designed to increase forb production by markedly reducing sagebrush cover, as a means to increase sage-grouse productivity, may not be justified.

Greater Sage-Grouse (Centrocercus urophasianus) select habitat based on avian predators, landscape composition, and anthropogenic features

ABSTRACT Prey species minimize the risk of predation directly by avoiding predators and indirectly by avoiding risky habitat. Habitat loss and fragmentation have been prevalent in Greater Sage-Grouse (Centrocercus urophasianus; hereafter “sage-grouse”) habitat, which has necessitated a better understanding of mechanisms driving habitat use. Using multinomial logistic regression, we compared landscape attributes and anthropogenic features (indirect mechanisms) and densities of avian predators (direct mechanisms) among 792 sage-grouse locations (340 nests, 331 early brood, and 121 late brood) and 660 random locations in Wyoming, USA, in 2008–2011. Anthropogenic features included oil and gas structures, communication towers, power lines, roads, and rural houses; and landscape attributes included a normalized difference vegetation index (NDVI), topographic ruggedness, the proportion of big sagebrush (Artemisia spp.), and proximity and proportion variables for forested and riparian habitats. Sage-grouse locations were best described with models that included multiple habitat variables and densities of small, medium, and large avian predators. Thus, both indirect and direct mechanisms of predator avoidance were employed by sage-grouse to select habitat and presumably lower their exposure to predation and nest predation. At all reproductive stages, sage-grouse selected flatter locations with a greater proportion of big sagebrush, a higher NDVI, and lower densities of oil and gas structures. Nest locations had a lower density of major roads and were farther away from riparian habitat; early-brood locations had a lower density of power lines and were closer to rural houses; and late-brood locations were closer to riparian habitat. The magnitudes of direct and indirect avoidance by sage-grouse hens were dependent on a sage-grouses reproductive stage. Differential habitat use of female sage-grouse relative to predation risk and food availability was a means for sage-grouse hens to lower their risk of predation and nest predation, while using habitat to meet their energetic requirements and those of their chicks.

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.

The influence of mitigation on sage-grouse habitat selection within an energy development field.

Growing global energy demands ensure the continued growth of energy development. Energy development in wildlife areas can significantly impact wildlife populations. Efforts to mitigate development impacts to wildlife are on-going, but the effectiveness of such efforts is seldom monitored or assessed. Greater sage-grouse (Centrocercus urophasianus) are sensitive to energy development and likely serve as an effective umbrella species for other sagebrush-steppe obligate wildlife. We assessed the response of birds within an energy development area before and after the implementation of mitigation action. Additionally, we quantified changes in habitat distribution and abundance in pre- and post-mitigation landscapes. Sage-grouse avoidance of energy development at large spatial scales is well documented. We limited our research to directly within an energy development field in order to assess the influence of mitigation in close proximity to energy infrastructure. We used nest-location data (n = 488) within an energy development field to develop habitat selection models using logistic regression on data from 4 years of research prior to mitigation and for 4 years following the implementation of extensive mitigation efforts (e.g., decreased activity, buried powerlines). The post-mitigation habitat selection models indicated less avoidance of wells (well density β = 0.18 ± 0.08) than the pre-mitigation models (well density β = -0.09 ± 0.11). However, birds still avoided areas of high well density and nests were not found in areas with greater than 4 wells per km2 and the majority of nests (63%) were located in areas with ≤ 1 well per km2. Several other model coefficients differed between the two time periods and indicated stronger selection for sagebrush (pre-mitigation β = 0.30 ± 0.09; post-mitigation β = 0.82 ± 0.08) and less avoidance of rugged terrain (pre-mitigation β = -0.35 ± 0.12; post-mitigation β = -0.05 ± 0.09). Mitigation efforts implemented may be responsible for the measurable improvement in sage-grouse nesting habitats within the development area. However, we cannot reject alternative hypotheses concerning the influence of population density and intraspecific competition. Additionally, we were unable to assess the actual fitness consequences of mitigation or the source-sink dynamics of the habitats. We compared the pre-mitigation and post-mitigation models predicted as maps with habitats ranked from low to high relative probability of use (equal-area bins: 1 – 5). We found more improvement in habitat rank between the two time periods around mitigated wells compared to non-mitigated wells. Informed mitigation within energy development fields could help improve habitats within the field. We recommend that any mitigation effort include well-informed plans to monitor the effectiveness of the implemented mitigation actions that assess both habitat use and relevant fitness parameters.

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.

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.