Winter Versus Summer Habitat Selection in a Threatened Ground Squirrel

Abstract

Hibernation is a strategy many species employ to survive periods of thermal stress or resource shortage (e.g., harsh thermal conditions, food limitations) and habitat requirements of hibernating species may differ between summer (the active season) and winter (during hibernation). Accounting for seasonal differences in habitat affinities will help ensure that management actions are more beneficial and land-use policies are more appropriate. The northern Idaho ground squirrel (Urocitellus brunneus) is a federally listed threatened species that is in decline and hibernates for approximately 8 months per year. We collared northern Idaho ground squirrels in Adams County, Idaho from 2013-2017. The majority of northern Idaho ground squirrels we collared selected hibernacula outside of the areas they used during the active season. Furthermore, habitat features of hibernacula locations differed from habitat features of active-season areas. Hibernacula locations had greater canopy closure compared to active-season locations (36.9% and 7.0% canopy closure, respectively) and hibernaculum habitat features (particularly distance to nearest log) influenced overwinter survival. Our results suggest that recovery efforts for northern Idaho ground squirrels should include protection and management for the full range of habitat conditions used throughout summer and winter. More broadly, we emphasize the need to identify and protect habitat during all seasons because habitat requirements can differ substantially during different portions of an animal's annual cycle and effective conservation will require management of year-round habitat needs.

Balancing transferability and complexity of species distribution models for rare species conservation

“…A century of anthropogenic fire suppression has resulted in forest encroachment, which is hypothesized to eliminate habitat and be the primary threat to the species (Burak et al., 2018; Yensen & Sherman, 1997). Northern Idaho ground squirrels use burrows extensively during all seasons and soil properties are thought to play an important role in habitat selection (Goldberg, Conway, Evans Mack, et al., 2020; Yensen, 1991; Yensen et al., 1991). Individuals can hibernate for up to 8 months (Yensen, 1991; Goldberg and Conway, 2021) and south‐facing slopes that receive more solar radiation have a higher probability of presence (Goldberg, Conway, Evans Mack, et al., 2020).…”

“…Northern Idaho ground squirrels use burrows extensively during all seasons and soil properties are thought to play an important role in habitat selection (Goldberg, Conway, Evans Mack, et al., 2020; Yensen, 1991; Yensen et al., 1991). Individuals can hibernate for up to 8 months (Yensen, 1991; Goldberg and Conway, 2021) and south‐facing slopes that receive more solar radiation have a higher probability of presence (Goldberg, Conway, Evans Mack, et al., 2020). South‐facing slopes have more solar radiation that increases the amount of available foraging time during the summer (i.e., the squirrel's active season) by reducing snowpack earlier in the year (USFWS, 2003).…”

“…South‐facing slopes have more solar radiation that increases the amount of available foraging time during the summer (i.e., the squirrel's active season) by reducing snowpack earlier in the year (USFWS, 2003). Conservation efforts to restore northern Idaho ground squirrel habitat, demographic studies at known colonies and surveys to locate new populations are currently being implemented (Allison et al., 2019; Burak et al., 2018; Goldberg, Conway, Evans Mack, et al., 2020; Goldberg, Conway, Tank, et al., 2020; Wagner & Evans Mack, 2020).…”

“…We obtained northern Idaho ground squirrel presence locations (GPS locations) from surveys and live‐trapping conducted from 2001–2018 by Idaho Department of Fish and Game (Wagner & Evans Mack, 2020) and University of Idaho (Allison et al., 2019; Goldberg, 2018). Only active season presence locations were used because suitable hibernacula habitat can be substantially different (Goldberg, Conway, Evans Mack, et al., 2020). When >1 presence point was located within a given 30‐m raster pixel (the spatial resolution of environmental predictor variables), we retained that pixel as a single occurrence to avoid pseudo‐replication.…”

“…We also used statistical regularization to optimize predictive ability under each cross‐validation approach, considered a broad range of values for regularization parameters and assessed the implications of selecting a sub‐optimal regularization parameter (i.e., a sub‐optimal level of model complexity) for predicting habitat suitability of a rare animal. We conducted this analysis with the goal of developing a predictive, spatially transferable SDM to map range‐wide habitat suitability and aid ongoing recovery efforts for northern Idaho ground squirrels ( Urocitellus brunneus ), a small mammal that is federally threatened within the United States and whose current distribution is patchy and irregular within its historical range (Goldberg, Conway, Evans Mack, et al., 2020). Large portions of the northern Idaho ground squirrel range are labelled as unoccupied, but small and previously undiscovered populations are frequently found.…”