Predictive habitat models derived from nest-box occupancy for the endangered Carolina northern flying squirrel in the southern Appalachians

Abstract

In the southern Appalachians, artificial nest-boxes are used to survey for the endangered Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus), a disjunct subspecies associated with high elevation (>1385 m) forests. Using environmental parameters diagnostic of squirrel habitat, we created 35 a priori occupancy models in the program PRESENCE for boxes surveyed in western North Carolina, 1996−2011. Our best approximating model showed CNFS denning associated with sheltered landforms and montane conifers, primarily red spruce Picea rubens. As sheltering decreased, decreasing distance to conifers was important. Area with a high probability (>0.5) of occupancy was distributed over 18 662 ha of habitat, mostly across 10 mountain ranges. Because nest-box surveys underrepresented areas >1750 m and CNFS forage in conifers, we combined areas of high occupancy with conifer GIS coverages to create an additional distribution model of likely habitat. Regionally, above 1385 m, we determined that 31 795 ha could be occupied by CNFS. Known occupied patches ranged from <50 ha in the Long Hope Valley in North Carolina to approximately 20 000 ha in the Great Smoky Mountains National Park along the North Carolina−Tennessee boundary. These findings should allow managers to better define, protect and enhance existing CNFS habitat and provide a basis for future surveys. Owing to model biases, we view this as only a first approximation. Further research combining den selection with foraging habitat use across the full range of elevations, landforms and forest types is needed to increase predictive accuracy of CNFS distribution and sub-population viability.

Winter habitat associations of eastern spotted skunks in Virginia

“…We derived elevation (meters above sea level), slope (degrees), aspect (sine‐transformed) using 30‐m digital elevation models (DEM; U.S. Geological Survey 2000). We calculated a topographic exposure index (TEI), where higher TEI values indicate greater topographic exposure, using the zonal statistics tools in ArcMap, by subtracting the average elevation of a 1.75‐km 2 circular area around each camera (Evans et al , Ford et al ). We buffered each camera location based on average male winter home range estimate for the species (1.75 km 2 ; Lesmeister et al ).…”

Comparison of survey techniques on detection of northern flying squirrels

“…Our study took place in the Blue Ridge subdivision of the southern Appalachian Mountains physiographic province on Roan High Bluff (latitude 36°5.65′N, longitude 82°8.49′W) in the Roan Mountain Highlands, Pisgah National Forest, Mitchell County, North Carolina. We conducted our surveys in pure red spruce–Fraser fir forests above 1,800 m. The study site was considered high‐quality Carolina northern flying squirrel habitat (Ford et al , ), and recent and concurrent capture records of this subspecies were obtained at the site from live‐trapping and telemetry data (C. A. Diggins, unpublished data). The elevation of our study site excluded potential captures of southern flying squirrels, which cease to be sympatric with Carolina northern flying squirrels at the spruce–northern hardwood ecotone at approximately 1,370 m and above.…”

“…The Carolina northern flying squirrel ( G. sabrinus coloratus ), a federally endangered subspecies, is a secretive, nocturnal gliding mammal found in disjunct, high‐elevation “sky islands” of red spruce ( Picea rubens )–Fraser fir ( Abies fraseri ), eastern hemlock ( Tsuga canadensis ), and adjacent northern hardwood forests with a boreomontane conifer component in the southern Appalachian Mountains, USA (USFWS , Payne et al , Weigl et al , Kelly et al , Ford et al ). Similar to northern flying squirrels in boreal forest habitats of Canada and the northern United States, the southern Appalachian subspecies is traditionally surveyed using live‐trapping and artificial‐nest‐box monitoring (Carey et al , Loeb et al , Ford et al ). However, traditional methods are labor‐intensive and result in extremely low capture rates for this subspecies (USFWS , Reynolds et al , Weigl et al , Hughes , Ford et al ).…”

“…Similar to northern flying squirrels in boreal forest habitats of Canada and the northern United States, the southern Appalachian subspecies is traditionally surveyed using live‐trapping and artificial‐nest‐box monitoring (Carey et al , Loeb et al , Ford et al ). However, traditional methods are labor‐intensive and result in extremely low capture rates for this subspecies (USFWS , Reynolds et al , Weigl et al , Hughes , Ford et al ). In multiple areas of North Carolina, Tennessee, and Virginia, USA, efforts to document Carolina northern flying squirrel presence via trapping or nest box monitoring often have been unsuccessful or have taken years of surveys, even if habitat quality and quantity were similar to known occupied areas (Weigl et al ; C. A. Kelly, unpublished data; R. Reynolds, Virginia Department of Game and Inland Fisheries, personal communication).…”

“…Capture rates for these long‐term nest‐box‐monitoring programs are low: 5.8% and 8% of box checks produced captures in North Carolina and Virginia, respectively (Reynolds et al ; C. A. Kelly, unpublished data). Past nest‐box surveys have been focused on lower elevation or easily accessible sites because efforts to survey higher elevation sites or more remote sites were logistically difficult (Ford et al ; C. A. Kelly, unpublished data). In addition to being labor‐intensive during installation and subsequent monitoring, nest boxes typically have lag‐time of several years before utilization by flying squirrels occurs and produce low recapture rates, making population estimates difficult (Ford et al ).…”