Quantifying overlap and fitness consequences of migration strategy with seasonal habitat use and a conservation policy

Abstract

2017. Quantifying overlap and fitness consequences of migration strategy with seasonal habitat use and a conservation policy. Ecosphere 8(11):e01991. 10. 1002/ecs2.1991 Abstract. Our study aimed to delineate seasonal habitats and assess differential fitness related to migration strategy and seasonal habitat use of greater sage-grouse (Centrocercus urophasianus, hereafter "sagegrouse"). In addition, we evaluated benefits gained for sage-grouse through the implementation of the Wyoming Core Area Strategy relative to protection of habitat and differences in nest, brood, and annual female survival. We compared the proportion of seasonal habitats that were within or outside Core Areas as delineated with 75% and 95% kernel density contours (KDE). The proportion of summer and winter habitats (95% KDE) that overlapped Core Areas was 0.69 of summer and 0.50 of winter habitat within a Core Area. We found no differences in nest or brood survival among migration strategies or within and outside Core Areas. However, females that did not migrate out of their respective winter habitat had lower risk of death, which highlighted year-round benefits of winter habitat. Females had lower risk of death during winter with the lowest risk occurring during winter in Core Areas. Higher temperature and lower snow water equivalent during the breeding season and fall were detrimental to female survival, whereas neither had an effect on winter survival. Although Core Areas encompassed a large proportion of winter habitat, our results indicate that Core Areas (as delineated) were not the most direct way to protect winter habitat for sage-grouse. During winter, sage-grouse gathered within habitat conducive to winter survival, indicating that disturbances within these winter habitats may have broad consequences for sage-grouse populations.

Approaches to delineate greater sage‐grouse winter concentration areas

“…The majority of flocks located in non‐Core Areas were adjacent to relatively smaller Core Areas in south‐central and southwest Wyoming (e.g., the 3,754‐km 2 South Rawlins and 1,030‐km 2 Fontenelle Core Areas), which suggests smaller Core Areas are more likely to have mismatches in protection of different seasonal habitats compared to larger Core Areas (e.g., 19,093‐km 2 Greater South Pass Core Area). This was consistent with patterns of sage‐grouse winter habitat use adjacent to small and large Core Areas in other Wyoming studies (Smith et al , Dinkins et al ) and the mismatch of Core Area protections for summer compared to winter seasons (Dinkins et al ). Therefore, in‐depth assessment of seasonal habitat inclusion will be necessary when designating relatively smaller protected areas.…”

“…Sage‐grouse generally have high overwinter survival (Beck et al , Baxter et al , Dinkins et al ), except during severe winters (Moynahan et al , Anthony and Willis ). In addition, Dinkins et al () reported that survival of female sage‐grouse was higher in Core Areas compared to non‐Core Areas during winter. Areas where sage‐grouse WCAs are consistently located in non‐Core Areas during winter may represent shortfalls in current protections, especially when those individuals are connected to smaller Core Areas during other seasons.…”

“…Mountain big sagebrush (A.t. vaseyana) occurred at higher elevations (Knight et al 2014). For a more detailed description of the region, refer to Smith et al (2014Smith et al ( , 2016 and Dinkins et al (2017).…”

“…In addition, we validated the individual-based RSF model by calculating the proportion of locations occurring within each bin from independent sage-grouse locations collected to assess winter sage-grouse habitat use in other studies (Smith et al 2014, Dinkins et al 2017). These studies collected locations of winter use by radio-marked female sage-grouse with aerial telemetry during 2007-2010(Smith et al 2014-2011(Dinkins et al 2017, respectively. For WCA and relative flock size models, we considered models predictive when more large flocks (WCAs) from test data were in the top 2 prediction bins from training data.…”

“…Yet the Core Area Strategy acknowledges that essential seasonal habitats may occur outside of Core Areas; these areas may be necessary to fulfill seasonal habitat requirements of sage‐grouse that breed in Core Areas (USFWS , State of Wyoming ). Sage‐grouse are a partially migratory species with many individuals within populations using spatially distinct breeding and winter habitats (Connelly et al , Dinkins et al , Pratt et al ). During winter, sage‐grouse generally require large expanses of sagebrush above snow in flatter terrain with few anthropogenic features (Doherty et al ; Carpenter et al ; Dzialak et al ; Smith et al , ; Holloran et al ).…”