Ground Biology of Ground Squirrels (Urocitellus spp.) as Prey of Golden Eagles (Aquila chrysaetos) in the Western

Belding’s ground (Urocitellus beldingi) in northern . Photo Credit,deLight Sky Urocitellus Ground Squirrels Biology of Ground Squirrels (Urocitellus spp.) as Prey of Golden Eagles (Aquila chrysaetos) in the Western United States

U.S. Fish and Wildlife Service Regions 1, 2, 6, and 8 Western Team

Front Matter Date: January 31, 2018

Disclaimer The reports in this series have been prepared by the U.S. Fish and Wildlife Service (Service) Western Golden Eagle Team (WGET) for the purpose of proactively addressing energy-related conservation needs of golden eagles in Regions 1, 2, 6, and 8. The team was composed of Service personnel, sometimes assisted by contractors or outside cooperators. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Suggested Citation Bedrosian, G., D.L. Hansen, and R. Spaul. 2018. Biology of Ground Squirrels (Urocitellus spp.) as Prey of Golden Eagles (Aquila chrysaetos) in the Western United States. Unpublished report prepared by the Western Golden Eagle Team, U.S. Fish and Wildlife Service, Regions 1, 2, 6, and 8. Available online at: https://ecos.fws.gov/ServCat/Reference/Profile/97773

Acknowledgements This report was authored by Geoffrey Bedrosian, Dan L. Hansen, and Robert Spaul. The authors are grateful to the following reviewers (in alphabetical order): Colleen Lenihan, Katie Powell, Rebecca Smith, Beatrice Van Horne, Hillary White, and Brian Woodbridge. Eric Yensen provided feedback on a previous version of this report.

Urocitellus ground squirrels—i Overview

Holarctic ground squirrels ( Urocitellus, hereafter “ground squirrels”) are members of the squirrel family of (Sciuridae), which generally live on or in the ground. Ground squirrels are typically grayish or brownish, with the dorsal hair darker than the ventral, a light-colored eye ring, cylindrical bodies, large eyes, and chisel-shaped incisors. Their forelimbs have sharp claws for digging and their longer hind limbs allow for rapid movement. Ground squirrels are smaller-bodied than prairie dogs (Cynomys spp.), (Marmota spp.), and rock squirrels ( spp.).

This report reviews the role of ground squirrels as prey for golden eagles (Aquila chrysaetos), as well as relevant aspects of their natural history, ecology, and management. We discuss seven of ground squirrels that occur within the range of the golden eagle in the conterminous western United States (U.S.) and which have been documented as golden eagle prey: Belding’s (U. beldingi), Columbian (U. columbianus), Merriam’s (U. canus), Piute (U. mollis), Richardson’s (U. richardsonii), Uinta (U. armatus), and Wyoming (U. elegans) ground squirrels. This account does not address other genera (e.g., Otospermophilus spp., see account).

Most ground squirrel species are found at relatively low proportions in breeding season diets of golden eagles, compared to hares and rabbits. However, these ground squirrel species may play an important role in buffering golden eagle food resources in years with low hare and rabbit availability. In contrast, Belding’s ground squirrels can be found at very high densities in irrigated alfalfa (Medicago sativa) fields in northern California where they are the dominant prey species used by nesting golden eagles. It is likely that the abundance of Belding’s ground squirrels influences the high density, occupancy rates and reproductive performance of nesting golden eagles observed in that area. The degree to which golden eagles feed on ground squirrels is likely influenced by the availability of ground squirrel populations, as well as the availability of preferred prey species (hares and rabbits).

Ground squirrels occupy a variety of -steppe, grassland, and montane in the northwestern U.S. Ground squirrels are diurnal and considered semi-fossorial; they spend their nights and take refuge in burrows, but forage above ground. During the active season, ranging from February–March through May–September, burrows provide ground squirrels with cover from severe weather and extreme temperatures, protection from predators, and shelter for rearing young. Ground squirrel diets consist of a variety of grasses and forbs, as well as flowers and seeds, when available. Additional food items include insects, berries, and occasionally carrion of conspecifics.

Contemporary ground squirrel populations typically occur in relatively small local populations within geographically restricted ranges, except where they are exceptionally abundant. Population size and density can fluctuate annually depending on availability of suitable and food. Other influences on ground squirrel abundance include parasites, disease, weather, predators, control programs, and habitat modification. Across the western U.S., anthropogenic habitat modification is thought to be responsible for creating discontinuous populations of many ground squirrel species. Many western shrub-steppe

Urocitellus Ground Squirrels—ii ground squirrel populations have experienced extensive declines across their historical ranges yet most have low national conservation rankings. Regions where habitat alteration is most pervasive and negatively influencing ground squirrels include the Great Basin ecosystem and the Columbia Plateaus of and Oregon.

The U.S. Fish and Wildlife Service recognizes prey densities as potential limiting factors for golden eagles. Furthermore, poorly managed livestock grazing, invasive vegetation, wildfire-caused habitat conversion, and climate change can cause the loss of foraging habitat. Conversion of native grasslands to agriculture has limited suitable habitat for western shrub-steppe species of ground squirrels while providing other species, such as the Belding’s ground squirrel, with new food sources. Conversion of native shrub-steppe to agriculture may have a particularly negative impact on ground squirrels when it occurs on the arable, deep soil communities most favored by ground squirrels. Agricultural areas in shrub-steppe ecosystems may be able to support greater numbers of ground squirrels through management practices that maintain or increase natural cover, thereby enhancing the spatial and functional heterogeneity of the landscape.

Many areas of the West are now locked in a grass/fire cycle with the potential to negatively impact golden eagle prey habitat. Following major wildfires, loss of shrub cover, and subsequent reductions in populations of hares and rabbits, golden eagles may shift their diet to eating more ground squirrels. However, conversion of shrublands to exotic annual grasses can cause wider annual fluctuations in ground squirrel numbers, lower population densities, and lower body masses compared with shrub and native grass habitats. Invasive annual grasses, intense wildfire, and continued habitat conversion are likely to further isolate and restrict ground squirrel populations. Thus, conservation of ground squirrel populations will largely depend on preservation of occupied habitat, particularly for the sagebrush-steppe species that exist as a series of small, isolated populations.

Population control of ground squirrels on agricultural fields is a source of lead contamination to golden eagles that feed on shot carcasses and may also be a source of anticoagulant rodenticide (AR) poisoning. Lead toxicosis and AR poisoning can directly result in mortality, and can also increase the risk to golden eagles of accidental trauma and the likelihood of a fatal collision with vehicles or structures. Lead exposure to golden eagles from shot ground squirrels could be reduced by collecting and disposing of carcasses or by using non-lead ammunition. Secondary exposure of golden eagles to ARs could likewise be reduced by removing poisoned ground squirrel carcasses and generally avoiding the use of poisons that pose a risk to non-target wildlife.

Urocitellus Ground Squirrels—iii Table of Contents Front Matter ...... i Disclaimer ...... i Suggested Citation ...... i Acknowledgements ...... i Executive Summary ...... Error! Bookmark not defined. Table of Contents ...... 1 Importance to Golden Eagles ...... 2 Occurrence in Golden Eagle Diets...... 2 Ground Squirrels in Breeding Season Diets of Golden Eagles ...... 2 Individual Ground Squirrel Species in Breeding Season Diets of Golden Eagles ...... 3 Ground Squirrels in Nonbreeding Season Diets of Golden Eagles...... 4 Influence on Golden Eagles ...... 4 Prey Species Information ...... 5 Physical Description ...... 5 Ecological Roles ...... 6 Distribution ...... 6 Habitat Associations ...... 7 Diet…… ...... 8 Population Fluctuations and Densities ...... 10 Influences on Abundance ...... 11 Parasites and Diseases ...... 11 Weather ...... 11 Predators ...... 11 Control Programs...... 12 Habitat Modification and Loss ...... 13 Population Status ...... 13 Management Considerations ...... 14 Agricultural Conversion ...... 14 Fire and Invasive Grasses ...... 15 Lead and Anticoagulant Rodenticide Exposure...... 16 Information Gaps ...... 17 References ...... 19 Appendix 1: Body sizes of ground squirrels in the western United States...... 28 Appendix 2: Conservation Status of Ground Squirrels in the western United States. 29

Urocitellus Ground Squirrels—1 Importance to Golden Eagles

Occurrence in Golden Eagle Diets

Ground Squirrels in Breeding Season Diets of Golden Eagles

In a review of published, contemporary, and previously unpublished data on diets of golden eagles at 45 study locations in the conterminous western United States (U.S.), Holarctic ground squirrels (Urocitellus spp.; hereafter, "ground squirrels") were among the top three breeding season prey taxa for golden eagles in six (13%) of the reviewed studies based on the percentage of identified prey individuals (Bedrosian et al. 2017; Figure 1; note that some study locations overlapped). Five of those studies were located in shrub-steppe ecosystems in Wyoming (Schmalzried 1976; Millsap 1978; MacLaren et al. 1988) and Idaho (Marzluff et al. 1997; K. Steenhof and M. Kochert, unpubl. data) and the sixth was located in an agricultural setting within an otherwise ecologically similar shrub-steppe area of California near the Oregon border (B. Woodbridge, unpubl. data). Ground squirrels occurred at lower frequencies in nine other study areas in multiple regions of the conterminous western U.S. (Hickman 1968; McGahan 1968; Reynolds 1969; Arnell 1971; Marr and Knight 1983; Keller 2015; Watson and Davies 2015; see Individual Ground Squirrel Species in Breeding Season Diets of Golden Eagles)

Figure 1: Locations of studies in which ground squirrels were in the top three breeding season prey taxa for golden eagles based on percentage of identified prey individuals (based on Bedrosian et al. 2017).

Ground Squirrels—2 Golden eagles may use ground squirrels as a breeding season food source more frequently than reported. In comparison to direct observation of prey deliveries using cameras, identification of prey remains at (the most commonly used method for assessing diets; Bedrosian et al. 2017) underestimated predation on ground squirrels (Lockhart 1976; Heath and Kochert 2016). Analysis of prey remains may be biased toward larger prey whose heavier bones may persist longer in nests (Marti et al. 2007), and it is possible that adults and larger eaglets could consume a ground squirrel in its entirety leaving few identifiable remains.

Individual Ground Squirrel Species in Breeding Season Diets of Golden Eagles

The highest known proportion of ground squirrels in golden eagle diets in the conterminous western U.S. was recorded in the Butte Valley of northern California (37.3%; B. Woodbridge, unpubl. data). Belding’s ground squirrels (U. beldingi) occurred at high densities in alfalfa (Medicago sativa) fields in that area (Whisson et al. 1999) and were the most frequent prey in golden eagle diets (Bedrosian et al. 2017).

Columbian ground squirrels (U. columbianus) made up a small proportion of golden eagle diets in the Columbia Plateau (0.6–1.2%; Marr and Knight 1983; Watson and Davies 2015). The absence of Townsend’s ground squirrels (U. townsendii) and Washington ground squirrels (U. washingtoni) in the diets of golden eagles was consistent with depressed populations of both species because of loss of shrub-steppe habitat to agriculture (Watson and Davies 2015).

Merriam’s ground squirrels (U. canus, formerly considered Townsend’s ground squirrel townsendii; Hoffman et al. 1993; Helgen et al. 2009) were identified at low frequencies in golden eagle diets in the Northern Basin and Range of Oregon (2.4%; Hickman 1968).

Early research in the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA) of southwest Idaho identified low levels of Piute ground squirrels (U. mollis, formerly considered Townsend’s ground squirrel; Hoffman et al. 1993; Helgen et al. 2009) as golden eagle prey (1.0%; Hickman 1968). Data from NCA during the 1970s and 1980s was similar to other cold desert grasslands; Piute ground squirrels appeared to be tertiary prey items of golden eagles (10.6%), behind hares and rabbits (K. Steenhof and M. Kochert, unpubl. data). Golden eagles increased their use of ground squirrels in years of lower numbers of hares and rabbits (Steenhof and Kochert 1988). Golden eagles had a strong preference for black-tailed jackrabbits (Lepus californicus) but selected Piute ground squirrels over all other non-jackrabbit prey (Steenhof et al. 1997). A later study in this area observed Piute ground squirrels as 10 of 18 (56%) of direct prey captures (Marzluff et al. 1997). In contrast, a long-term study in the Central Basin and Range of Utah found that Piute ground squirrels were a rare component of the breeding season diet of golden eagles (0.4%; Keller 2015).

Richardson’s ground squirrels (U. richardsonii) were identified as golden eagle prey in the Northwestern Great Plains of southern Montana (4.5–10.5%; McGahan 1968; Reynolds 1969). A diet study in the same area during 2015 did not find Richardson’s ground squirrel

Ground Squirrels—3 remains, but also had a relatively small sample size (R. Crandall and C. Preston, unpubl. data).

Golden eagles fed on Uinta ground squirrels (U. armatus) in the Wasatch Mountains in Utah at low frequencies (3.4–5.9%; Arnell 1971; Keller 2015). In nearby desert habitats in the Great Basin, ground squirrels were a smaller proportion of the diet of golden eagles, while hares and rabbits were more common (Arnell 1971; Keller 2015). This suggests that golden eagles may utilize ground squirrels more in montane than desert environments due to the greater abundance of hares and rabbits in desert grasslands.

Wyoming ground squirrels (U. elegans) were found at moderately high frequencies in prey remains at golden eagle nests in the Wyoming Basin (12.1–20.3%; Schmalzried 1976; Millsap 1978; MacLaren et al. 1988). Wyoming ground squirrels were the most abundant prey in the area based on line-transect counts, despite their relatively low frequency in prey remains at golden eagle nests (Schmalzried 1976). This could be because of low detection of ground squirrel remains at nests, differences among detection rates for other prey species, or a result of golden eagles preferentially selecting hares and rabbits.

Ground Squirrels in Nonbreeding Season Diets of Golden Eagles

Few studies have investigated golden eagle diets during the nonbreeding season, defined here as the period of time when adults were not feeding young at nests (Woodgerd 1952; Arnold 1954; Edwards 1969; Hayden 1984; Marzluff et al. 1997). Two of these studies identified ground squirrels as prey of golden eagles. In southwestern Idaho, Piute ground squirrels were recorded as prey during seven of 29 (24%) observed prey captures (Marzluff et al. 1997). In the Northwestern Great Plains of Montana, ground squirrel remains (reported as Citellus, most likely a Richardson’s ground squirrel) were identified in 1 of 51 stomachs (2%) from Golden Eagles killed during a bounty in March 1948 (Woodgerd 1952).

Ground squirrels are obligate hibernators with the timing and length of varying with winter weather, spring snow cover, latitude, and elevation (Yensen and Sherman 2003), all of which may affect their seasonal availability as prey for golden eagles. Ground squirrel species hibernate underground during winter months and some estivate (i.e., become dormant) during summer months in hot and dry environments with dates of emergence ranging from January–May and immergence from May–September (Yensen and Sherman 2003). As a result of hibernation and estivation, at a given site most ground squirrels are generally only active, and consequently available as a food source, for 4–5 months out of any given year.

Influence on Golden Eagles

The majority of ground squirrel species exist in relatively small, isolated populations within geographically restricted ranges, including: Columbian, Merriam’s, Piute, Richardson’s, Uinta, and Wyoming ground squirrels. These species were found at relatively low frequencies in the breeding season diets of golden eagles (0.6–20.3%) and occurred as secondary or tertiary food sources behind hares and rabbits (Bedrosian et al. 2017). However, these ground squirrel species may play an important role in buffering golden

Ground Squirrels—4 eagle food resources in years with low rabbit and hare availability (e.g., Steenhof et al. 1988).

In contrast, Belding’s ground squirrels occurred at very high densities in irrigated alfalfa fields in northern California (Whisson et al. 1999) and were the dominant prey species used by nesting golden eagles in that area (Bedrosian et al. 2017). It is likely that the abundance of Belding’s ground squirrels in this area influenced the high density, occupancy rates and reproductive performance of nesting golden eagles observed in this area (B. Woodbridge unpubl. data). In general, however, the relationship between ground squirrels and golden eagle productivity has not been quantified. The abundance of larger prey, such as black- tailed jackrabbits (Steenhof et al. 1997) and cottontails (Sylvilagus spp.; Preston et al. 2017), was strongly positively related to reproductive parameters of golden eagles (see jackrabbit_account and cottontails_account).

Western shrub-steppe and grassland ecosystems are among the highest quality habitats for golden eagles during all stages of their annual cycle (Dunk et al. in prep.). These same habitats are important for ground squirrels (Yensen and Sherman 2003) and the availability of prey may influence continental-scale distribution of golden eagles (Schweiger et al. 2015). Thus, conservation of shrub-steppe and grassland habitats for ground squirrels and other prey communities could be valuable components of golden eagle conservation planning at landscape-scales.

Prey Species Information Physical Description

Ground squirrels are typically grayish or brownish, with the dorsal fur darker than the ventral, cylindrical bodies, short legs, a light-colored eye ring, and large eyes (Yensen and Sherman 2003). Their forelimbs have sharp claws for digging and their longer hind limbs allow for rapid movement. Average body lengths and masses range from 11–16 inches (in) (27–41 centimeters [cm]) and 11.5–28.6 ounces (oz) (325–812 grams [g]) ; Appendix 1).

Ground squirrels can be distinguished from prairie dogs (Cynomys spp.) and marmots (Marmota spp.) by a smaller body size, smaller cranium, and distinctive color patterning of their fur (Howell 1938). Holarctic ground squirrels are smaller-bodied than California ground squirrels (Otospermophilus beecheyi) and rock squirrels (O. variagatus), and have proportionally smaller ears (i.e., pinnae) and tails (Howell 1938). Holarctic ground squirrels are physically similar to Old World ground squirrels (Spermophilus spp.) and were previously classified in that genus; however, Holarctic ground squirrels are primarily found in and can be distinguished from Old World ground squirrels by cranial measurements and genetic analyses (Helgen et al. 2009).

Some researchers have recognized two species-groups within the Holarctic ground squirrels that represent distinct lineages. The “big-eared ground squirrels” (or “columbianus species- group”) includes Belding’s, Columbian, Richardson’s, Uinta, and Wyoming ground squirrels (Davis 1939). These species have proportionally longer bodies, feet, and tails, compared to the “small-eared ground squirrels” (or “townsendii species-group”), which includes

Ground Squirrels—5 Merriam’s and Piute ground squirrels. Although these species-group distinctions are not recognized as subgenera, the relative differences in body size can be used to distinguish among sympatric species in some areas (e.g. Belding’s vs. Merriam’s ground squirrels; Howell 1938; Davis 1939; Hall 1981).

Ecological Roles

Ground squirrels are often considered keystone species because they facilitate productivity through burrowing (Vander Haegen et al. 2001). Burrowing loosens, aerates, moves, and mixes soils while encouraging water infiltration and water holding capacity (Yensen and Sherman 2003). Burrowing activities of Piute and Wyoming ground squirrels in southeastern Idaho significantly increased the total amount of water entering the soil and its penetration depth into the soil (Laundré 1993). High densities of Piute ground squirrel burrows enhanced the productivity of big sagebrush (Artemisia tridentata) and western wheatgrass (Elymus smithii) communities in the Snake River Plain by enhancing water capture from spring runoff (Laundré 1998). Furthermore, burrowing increases habitat heterogeneity by promoting areas of nutrient-rich soil for seed growth, root growth, water infiltration, and altering chemical properties of the soil such as ion exchange capacity, organic matter content, and inorganic nutrient levels (Whitford and Kay 1999). The additional water infiltration that results from burrowing may also enhance decomposition of organic matter, plant survival, and seed germination rates (Laundré 1993).

Ground squirrels shape community structure in other ways as well. Ground squirrel burrows provide access to important below-ground microhabitats for terrestrial fauna that do not dig their own burrows (e.g., cottontails), that gain shelter from above-ground environmental conditions (Lenihan 2007). Ground squirrels can also be considered keystone species because they provide a substantial food source for mammalian, avian, and reptilian predators (Yensen et al. 1992; Vander Haegen et al. 2001). Social groups of ground squirrels (i.e. colonies) create habitat patches of concentrated prey for predators, and decreased populations of colonial burrowing were linked to declines in predator populations in multiple grassland ecosystems (Davidson et al. 2012).

Distribution

Ground squirrels overlap with most of the golden eagle's western range (Figure 2). Various species are found from Alaska, south to west-central , and as far east as Ohio (Howell 1938; Hall 1981; Yensen and Sherman 2003). Occupied habitats within the western U.S. range from rocky areas, evergreen forests and small meadows, intermontane grasslands and large meadows, tall grass prairie, short grass prairie, sagebrush-steppe, and deserts (Yensen and Sherman 2003).

Many species of ground squirrels exist as small, isolated populations, primarily because of habitat loss and fragmentation, and thus their distributions are poorly represented by range maps at larger scales (Yensen and Sherman 2003; Figure 2). Belding’s ground squirrels in northern California and parts of Oregon are an exception to this generalized

Ground Squirrels—6 pattern of small fragmented populations because of their dense concentrations near alfalfa (Marsh 1994; Whisson 1999).

Figure 2: Distributional models of habitats suitable for occupation by ground squirrels (USGS-GAP 2013).

Habitat Associations

Ground squirrels occupy a variety of shrub-steppe, grassland, and montane meadow habitats in the northwestern U.S. where soil conditions are suitable for digging and the construction of subterranean burrows (Helgen et al. 2009). Ground squirrels are diurnal and considered semi-fossorial; they spend their nights and take refuge in burrows, but forage above ground (Yensen and Sherman 2003). During the active season, burrows provide ground squirrels with cover from severe weather and extreme temperatures, protection from aerial and terrestrial predators, and shelter for rearing young (Yensen and Sherman 2003).

Belding’s ground squirrels occupy diverse habitats, including alpine dwarf-shrub, alpine and subalpine meadows, perennial and annual grasslands, sagebrush, agricultural fields, and pastures (McKeever 1966; Turner 1972a, b; Costain 1978; Sherman and Morton 1979; Holekamp 1984). Distribution of Belding’s ground squirrels in the Sierra seems to be restricted to areas with lush bottomland vegetation (Loehr and Risser 1977; Turner 1972a). Belding’s ground squirrels also preferred areas with friable soils for burrowing and nesting (Jenkins and Eshelman 1984).

Columbian ground squirrels in northeastern Oregon, occupied the edges of more mesic forest meadows adjacent to a population of Belding’s ground squirrels that occupied a more xeric sagebrush habitat (Turner 1972b).

Ground Squirrels—7

Merriam’s ground squirrels typically occur in semidesert landscapes, grasslands and pasture, although they also occur in big sagebrush, juniper (Juniperus spp.), shadscale (Atriplex confertifolia) and (Sarcobatus spp.) habitats, and some fallow and lightly-used agricultural lands (Kaufman 2004; Wilson and Cole 2009).

High densities of Piute ground squirrels occurred in winterfat-Sandberg bluegrass () communities, while moderate densities occurred in big sagebrush-dominated communities, and lower concentrations occurred in shadscale and/or exotic plant dominated landscapes (Yensen et al. 1992). In years with normal precipitation patterns, Piute ground squirrels occurred at higher densities in habitat dominated by Sandberg bluegrass, a native bunch grass, than in habitat dominated by native (Van Horne et al. 1997). However, during a drought year, the grass dried out and survival was higher in shrub habitat. Steenhof et al. (2006) reported higher densities within shrub-dominated habitats than grass-dominated areas, and an overall negative relationship between density and the proportion of exotic annual cheatgrass () in the habitat.

Richardson’s ground squirrels typically inhabit short-grass prairie, rolling hills, fields, and croplands (Michener and Koeppl 1985).

Uinta ground squirrels are generally associated with mountain meadows, but are also found in sage-steppe communities with native and exotic grasses and shrubs as well as on agricultural lands (Eshelman and Sonnemann 2000). In western Wyoming, Uinta ground squirrels frequently foraged in shrub communities of rabbitbrush (Chrysothamnus spp.) and sagebrush (Parmenter and MacMahon 1983) and used shrubs extensively for shade (Morse 1978 cited in Eshelman and Sonnemann 2000).

Wyoming ground squirrels generally prefer open sagebrush, grasslands, and subalpine meadows (Zegers 1984) and are considered tolerant of high elevations (>5,500 feet [1700 meters]; Andelt and Hopper 2016). However, Nadler et al. (1971) suggested that competition with Uinta ground squirrels limited the distribution of Wyoming ground squirrels at higher elevations of the Rocky Mountains near Bozeman, Montana. Distribution models developed by the Wyoming Natural Diversity Database suggested that they were associated with middle elevations, moderate sagebrush cover, and predictors describing a warm and stable climate (Keinath et al. 2010). Wyoming grounds squirrels were most abundant in areas with moderately low sagebrush cover (10–12%; Johnson et al. 1996).

Diet

Ground squirrel diets consist of a variety of grasses and forbs, as well as flowers and seeds, when available (Yensen and Sherman 2003). Additional food items include insects, berries, occasionally carrion of conspecifics, and very rarely bird eggs, and baby mice. Prior to hibernation, ground squirrels select foods high in fat content (e.g., seeds); therefore, the availability of high-quality food sources for ground squirrels may be a critical factor to over- wintering survival rates and population levels the following spring (Yensen and Sherman 2003).

Ground Squirrels—8

Belding’s ground squirrels are considered generalized herbivores that forage on , stems, and seeds of grasses as well as alfalfa crops, arthropods, other vertebrates, carrion, and conspecifics (Jenkins and Eshelman 1984). Experimental feeding suggests that Belding’s ground squirrels prefer with high protein and water content, such as mountain dandelion (Agoseris glauca) and Donner Lake lupine ( sellulus; Eshemlan 1982 cited in Jenkins and Eshelman 1984).

Columbian ground squirrels eat a variety of flowers, seeds, bulbs, and fruits as well as matter and conspecifics (Elliot and Flinders 1991). On mountain meadows in Idaho, adults ate clover (Trifolium spp.), yarrow (Achillea mellefolium), and alpine timothy (Phleum alpinum) and juveniles ate aspen fleabane (Erigeron speciousus) and clover during July and August (Elliot and Flinders 1985 cited in Elliot and Flinders 1991). In a nearby study area, adults and juveniles on mountain slopes ate arrowleaf balsamroot (Balsamorhiza saggittata), bluebunch wheatgrass (Elymus spicatus), and silky lupine (Lupinus sericeus) during summer.

Merriam’s ground squirrels generally eat green plants, roots and bulbs, seeds and grains, and insects (Cole and Wilson 2009). Plants in their diet included the flower heads of sunflowers (Helianthus spp.), alfilaria (Erodium spp.), and various legumes, as well as crops such as alfalfa, clover, grasses, grains, and other forage crops (Bailey 1936 in Cole and Wilson 2009).

Piute ground squirrels primarily eat green vegetation and seeds, such as grasses and forbs, as well as shrub parts and animal matter (Rickart 1987). In southwest Idaho, Piute ground squirrel body masses were higher in shrub than in grass habitats, and lowest in areas where native bluegrasses (Poa spp.) were replaced by cheatgrass (Steenhof et al. 2006), suggesting that food resources were more limited in cheatgrass habitats.

Richardson’s ground squirrels primarily eat leaves, flowers, and seeds, as well as insects and the carrion of conspecifics (Michener and Koeppl 1985). In overgrazed pastures in , Richardson’s ground squirrels fed on forage grasses and legumes (e.g., smooth brome Bromus inermis, crested wheatgrass cristatum, red clover Trifolium pratense, white clover T. repens, and white sweet clover Melilotus alba) as well as native plants (blue grama Bouteloua gracilis, amaranth Amaranthus spp., and milkvetch Astragalus spp.; Quanstrom 1968 cited in Michener and Koeppl 1985)].

Uinta ground squirrels were found to vary the types of green vegetation in their diet through the active season in northern Utah (Walker 1968 cited in Eshelman and Sonnemann 2000). Grass leaves made up 90% of the diet shortly after emergence but decreased to only 10% after three months above ground. The proportion of forb leaves increased through the active season, and the amount of grass seeds and forb seeds varied inversely through time. Through the entire active season, 10% of the diet consisted of sagebrush leaves, roots, earthworms (Oligochaeta), soil, and discarded human food.

Wyoming ground squirrels primarily eat forbs and grasses, as well as carrion including conspecifics (Zegers 1984). Seasonal variation in diet may be related to changes in food availability rather than dietary selection (House 1964 cited in Zegers 1984).

Ground Squirrels—9 Population Fluctuations and Densities

Ground squirrel population size and density can fluctuate annually depending on availability of suitable habitat and food (Yensen and Sherman 2003). Population fluctuations may be influenced by winter weather and availability of hibernation burrows, infectious diseases, predator abundance, or annual variations in food availability (Carl 1971; Murie 1992; Dobson 1995). Maximum densities are greatly influenced by juvenile squirrels (Van Horne et al. 1997) and mortality among ground squirrels in their first year can range from 54–97% (Yensen and Sherman 2003). One important factor in first year survival is that heavier females wean litters earlier in the active season, allowing the young more time to gain weight prior to hibernation. In a study of Belding’s grounds squirrels in the Sierra Nevada, overwinter mortality was estimated at 66–70% of juveniles and 36–39% of adults (Sherman and Morton 1984).

Populations of Belding’s ground squirrels in the Snake River Plain were observed with densities ranging from 4.9–120 squirrels per acre (ac) (12–296/hectare [ha]; Whisson et al. 1999). However, densities were reported at only 0.49 per ac (1.2/ha) in alpine meadows (Holekamp 1983).

Studies of Merriam’s ground squirrel population dynamics were not available, but densities were reported as “typical” for ground squirrels at fewer than 20 adults per ac (49/ha; Cole and Wilson 2009). Also similar to other ground squirrel species, population densities can vary depending on food and habitat availability, and seasonally increase after juveniles have weaned (Yensen and Sherman 2003).

Mean densities of Piute ground squirrels were 30 per ac (73/ha) on previously burned sites and 6.1 per ac (15/ha) on shrub sites in the Snake River Plain (Van Horne et al. 1997). A later study in the same area estimated overall squirrel density at 7.04 per ac (2.85/ha), with higher numbers in shrub habitats (11.5 per ac [4.64/ha]) than grass habitats (2.64 per ac [1.07/ha]; Steenhof et al. 2006). Nydegger and Smith (1986) found a strong positive correlation between numbers of Piute ground squirrel burrow entrances and 5-year average population densities. In contrast, Van Horne et al. (1997) detected little relation between densities of burrow entrances and annual densities of squirrels. The authors cautioned that using density of burrow entrances as an indicator of population densities could be misleading and that incremental declines might not be detected.

Densities of adult Richardson’s ground squirrels on sites greater than 25 ac (10 ha) ranged from 0.57–2.1 per ac (1.4–5.2/ha) but smaller study sites less than 5 ac (2 ha) had average densities of 4.9–11 per ac (12–27/ha; Michener and Koeppl 1985).

Uinta ground squirrel population density in an area of mixed trees, shrubs, and grasses in northern Utah ranged from 8.1–12 per ac (20–29/ha) during a five-year period (Slade and Balph 1974).

Wyoming ground squirrel densities in short grass meadows ranged from 0.08 per ac (0.2/ha) in early spring after high over-winter mortality to 0.49 per ac (1.2/ha) in June when young have emerged (Clark 1970). In montane meadows, density was 19 per ac (48/ha) when both juveniles and adults were present.

Ground Squirrels—10

Influences on Abundance

Parasites and Diseases

Ground squirrels host a large variety of parasites including fleas carrying sylvatic plague (Yersinia pestis). Plague caused severe population declines in Townsend’s ground squirrels in Washington (Svihla 1939) and Piute ground squirrels in Utah (Hansen 1956); however, populations of Piute ground squirrels did not decline in Idaho despite the prevalence of plague in the area (Messick et al. 1983). Plague was confirmed in Piute ground squirrels in rural areas of southern and southwestern Idaho in 2015 and 2016 (IDHW 2017). Larger, more continuously distributed populations of ground squirrels harbor a higher number of ectoparasites, such as fleas, ticks, and lice (Yensen and Sherman 2003). Parasitic flies and fly larvae infestations can be lethal (Yensen and Sherman 2003).

Weather

Weather can affect ground squirrel hibernation phenology, reproduction, and survival. Emergence of Piute ground squirrel adult females in the Snake River Plain of southwest Idaho was delayed in response to prolonged snow cover and cold temperatures, and adult immergence advanced in response to drought (Van Horne et al. 1997). A study of Columbian ground squirrels in the Rocky Mountains of southwest Alberta found that populations at higher elevations had smaller litters, females reproduced less frequently and matured later, survival of adults and juveniles was greater, and adults weighed less in the spring (Dobson and Murie 1987). The authors hypothesized that this was because of resource limitation in different environments influencing either genetic differences between populations or phenotypic plasticity. It is likely that other ground squirrel species similarly exhibit variation in their life history characteristics at different elevations and in response to seasonal variation in weather events.

Predators

Ground squirrels are most vulnerable to predation at the end of the active (non- hibernating) season when their running speed declines because of pre-hibernation fat deposition (Yensen and Sherman 2003). Known predators include badgers (Taxidea taxis), long-tailed weasels (Mustela frenata), (Canis latrans), red foxes (Vulpes vulpes), gray foxes (Urocyon cinereoargenteus), prairie falcons (Falco mexicanus), Cooper’s hawks (Accipiter cooperii), northern goshawks (A. gentilis), red-tailed hawks (Buteo jamaicensis), Swainson’s hawks (B. swainsoni), northern harriers (Circus cyaneus), golden eagles, common ravens (Corvus corax), snakes (Pituophis spp.), and rattlesnakes (Crotalus spp.; Yensen and Sherman 2003). In some species of ground squirrels, infanticide by nonlactating females and yearling males can be a significant cause of mortality (Yensen and Sherman 2003).

Ground Squirrels—11 Control Programs

Ground squirrels can be considered a nuisance to farmers and ranchers because they can consume or spoil crops, reduce the ability to control irrigation because of burrowing activities, and compete directly with livestock for forage (Yensen and Sherman 2003). Agricultural products that are susceptible to ground squirrel damage include fruit, seeds, nuts, cereal, and rangeland forage (Marsh 1998). Ground squirrels are regarded as agricultural pests when they exist in high densities adjacent to susceptible crops and range forage (Marsh 1994). Furthermore, burrowing activities can disturb irrigation, weaken manmade structures, and potentially cause injury to people and livestock when burrow entrances are in recreational or agricultural areas.

Lethal control of ground squirrels is so widespread that it is difficult to quantify. Ground squirrels are often perceived as pests despite their roles as keystone species (Delibes- Mateos et al. 2011). As a result, most ground squirrel management in the western U.S. has focused on reducing or eliminating populations associated with agriculture (e.g., Marsh 1994; Knight and Parks 2014; Andelt and Hoopper 2016). Agricultural areas of high commercial value are most likely to engage in population control measures (Delibes-Mateos et al. 2011).

The western U.S. has a long history of using poisons to control ground squirrel populations. Strychnine, a potent nonselective poison, was widely used during the first half of the 20th century (Marsh 1994). This was followed by the use of compound 1080 in the 1950s–1970s, which also impacted non-target wildlife species. Zinc phosphide and “first generation” anticoagulant rodenticide baits (ARs), such as warfarin, chlorophacinone, and diphacinone, were widely used because they were considered cost effective and may remain in use in some areas despite evidence of genetic resistance (Rattner et al. 2014). “Second generation” ARs, such as brodifacoum, bromadiolone, difenacoum, and difethialone, are increasingly being used because they are more acutely toxic at lower doses and thus require only a single bait ingestion to be lethal to ground squirrels. Ground squirrels exposed to ARs can exhibit behavioral changes, such as foraging in the open more frequently and decreased ability to escape from predators, which may make them easier prey for golden eagles and increase risk of secondary poisoning to scavengers (Herring et al. 2017).

Other less cost effective lethal control measures include natural and domestic predators, shooting, and trapping (Knight and Parks 2014; Andelt and Hopper 2016). Of these, shooting appears to be the most common and in some areas occurs as recreational shooting, or “plinking.” In its most extreme form, there are outfitter companies specializing in “sage rat” (Belding’s ground squirrel) shooting in the western Great Basin of northern California and southeastern Oregon (Yuskavitch 2017). In these organized hunts, shooters were reported to have killed 500–1,000 ground squirrels per day using .17 caliber rifles, after which carcasses were left in the field for scavengers. Shot carcasses are a potential source of secondary lead exposure to scavenging golden eagles (Herring et al. 2016).

Control methods that do not require directly killing ground squirrels include: planting tall growing grasses, periodic flooding or irrigation of soils, tilling, and planting shrubs and trees as windbreaks (Yensen and Sherman 2003). Regardless of the method, efforts to control ground squirrels as pests should take into account potential negative effects on

Ground Squirrels—12 golden eagles (Herring et al. 2017) and other non-target species, especially threatened or endangered species (Marsh 1994).

Habitat Modification and Loss

Habitat conversion is considered the largest factor influencing the conservation of North American rodents, and includes agricultural development, urban expansion, grazing, fire suppression, logging of old-growth forest, and recreational activities (Yensen et al. 1998). Historically, overgrazing of shrub-steppe habitats in the late 19th century across the western U.S. facilitated the invasion of exotic grasses and forbs, which in turn provide fuel for increased fire frequency (Yensen et al. 1992). When shrubs are lost to fire, it may alter the microclimate, reduce protective cover and food, and ultimately cause a decrease in ground squirrel populations (Yensen and Sherman 2003).

Across the western U.S., anthropogenic habitat modification is thought to be responsible for creating discontinuous populations of many ground squirrel species (Yensen and Sherman 2003). Regions where habitat alteration is most pervasive and negatively influencing ground squirrels include the Columbia Plateaus of Washington and Oregon (Yensen et al. 1998) and Great Basin ecosystem (Yensen et al. 1992, Steenhof et al. 2006).

Population Status

All seven ground squirrel species discussed here were classified as nationally “Secure” in 1996 by NatureServe (2015) and as “Least Concern” in 2008 by the IUCN (2014). At the state level, many species’ statuses are less certain and some are regulated by state wildlife agencies as nongame species (Appendix 2).

Three ground squirrel species not detailed in this account are considered to be of conservation concern, and it is likely that they were absent or rare in the diets of golden eagles due to low abundance at broad spatial scales. The northern Idaho ground squirrel (U. brunneus) is listed as threatened under the Endangered Species Act (ESA) and the Washington ground squirrel is currently a candidate species for consideration for listing under the ESA (USFWS 2016a). The Southern Idaho ground squirrel (U. endemicus) was also a candidate species until 2015, when it was determined not warranted for listing because the population had stabilized (USFWS 2015). Both the Washington ground squirrel and Townsend’s ground squirrel are state candidate species in Washington (WDFW 2016). Population declines were noted for Washington and Townsend’s ground squirrels because of agricultural conversion and degradation of rangeland habitats (Yensen and Sherman 2003).

Despite their generally low conservation rankings, many western shrub-steppe ground squirrel populations have experienced extensive declines across their historical ranges (Yensen and Sherman 2003). Factors influencing their abundance and distribution across portions of their ranges include “(1) conversion of grassland habitats to cultivation or urban use; (2) deterioration of rangeland and forest meadows due to invasion of exotic annual plants, often resulting from [livestock] overgrazing; (3) shrinking of meadows due to plant succession or conifer encroachment, the result of 100 years of fire suppression; and (4) decades of persecution through poisoning, trapping, and shooting” (Yensen and Sherman

Ground Squirrels—13 2003:224). Habitat has been lost as livestock grazing, cultivation, planned fire, and wildfire have decreased native vegetation such as big sagebrush and perennial grasses (Betts 1990; Yensen et al. 1992). Furthermore, isolated populations of ground squirrels may be vulnerable to extinction by stochastic processes, such as severe weather (Yensen and Sherman 2003).

In cases where different species of ground squirrels coexist, the smaller species can be restricted to less productive and more xeric microhabitats (Yensen and Sherman 2003). For example, the larger, more aggressive Columbian ground squirrel appeared to be replacing smaller cohabitating ground squirrels, including the Idaho ground squirrel (U. brunneus) in Idaho, Belding’s ground squirrel in northeastern Oregon, and Richardson’s ground squirrel in Montana (Yensen and Sherman 2003).

Management Considerations

The U.S. Fish and Wildlife Service (2016:91; hereafter, "Service") stated that "potentially key factors for golden eagles are prey densities and the availability of nest sites near suitable prey populations." Ground squirrels are among the most prevalent prey in golden eagle diets across much of the western U.S. They provide an important breeding season food source when found at high densities and in years when hares and rabbits are scarce (see Importance to Golden Eagles). In areas where shooting and poisoning are used to control ground squirrel populations, golden eagles are at risk of secondary poisoning from shot and poisoned carcasses. Thus, maintaining ground squirrel habitat and reducing exposure to contaminants associated with lethal control activities could be useful conservation measures for golden eagles. Enhancing prey availability may be used to mitigate take of golden eagles, though standards for doing so have yet to be developed (USFWS 2013; Allison et al. 2017).

The Service noted that loss of foraging habitat for golden eagles can be caused by poorly managed livestock grazing, invasive vegetation, wildfire-caused habitat conversion, and climate change (USFWS 2016b). These are also management issues for ground squirrels (this section; also see Influences on Abundance and Population Status). Ground squirrels and golden eagles have broad geographic ranges and varied habitat associations and diets, so management plans to address these threats should be tailored to specific regions and ecosystems. Ecoregional conservation strategies for golden eagles and their prey are available at conservation_strategies_link.

Agricultural Conversion

Conversion of native grasslands to agriculture has reduced the availability of suitable habitat for western shrub-steppe species of ground squirrels (Yensen and Sherman 2003) while providing other species, such as Belding’s ground squirrel, with new and more persistent food sources (Marsh 1998). Population densities of adult Belding’s ground squirrels can become very high (>800/acre; >300/ha) near rich food sources such as pastures and alfalfa fields (Saur 1984). Flood irrigation and frequent tillage can limit ground squirrels on agricultural land, but is unlikely to eliminate them because ground squirrels

Ground Squirrels—14 often live at the margins of agricultural lands in which they feed (Marsh 1994). Ground squirrels can invade new alfalfa fields at very high rates and exclusion fencing might be necessary to prevent recolonization of treated fields (Whisson et al. 1999).

Agricultural conversion, particularly in rangelands, may have a negative impact on ground squirrel populations because of the loss of burrow systems that are essential refuge and energetically costly to construct (B. Van Horne, pers. comm.). Furthermore, subsequent lethal control measures and flooding of burrows with irrigation water could have even greater negative effects that agricultural conversion alone (E. Yensen, pers. comm.). In Wyoming, agricultural conversion of native shrub-steppe has occurred on the most arable, deep soil communities, resulting in a disproportionate loss of the habitats on which ground squirrels depend (Johnson et al. 1996). The was found at its lowest densities with 2% big sagebrush cover and its highest densities between 12 and 15% (Johnson et al. 1996). This suggests that sagebrush is an important habitat component, most likely due to providing cover, rather than as a food source.

Agricultural areas in sage-steppe ecosystems may be able to increase biodiversity through management practices that maintain or increase natural cover, thereby enhancing the spatial and functional heterogeneity of the landscape (Fahrig et al. 2011). Accomplishing this goal does not necessarily call for re-creating historical conditions, but rather, incorporating a mosaic of high-quality natural habitats within agricultural regions. In addition, dispersal corridors between suitable areas are needed to allow ground squirrels to recolonize sites where they have been extirpated (Yensen et al. 1998).

Fire and Invasive Grasses

Millions of acres of shrublands and grasslands across the West have been invaded by cheatgrass, red brome (B. madritensis, B. rubens), and other exotic annual grasses (Pellant and Hall 1994; Salo 2004). In western shrublands and grasslands, continuous fuel provided by annual grasses has fostered the spread of fires far larger than those that occur in areas dominated by native vegetation (Brooks and Pyke 2001; Keane et al. 2008; Balch et al. 2013; Brooks et al. 2016). Many areas of the West are now locked in a grass/fire cycle, wherein fire-adapted annual grasses facilitate intensified fires, which kill sagebrush and other fire-intolerant native competitors, and thereby promote even greater spread of annual grasses (D'Antonio and Vitousek 1992; Brooks et al. 2004; Balch et al. 2013).

Research in the NCA on the Snake River Plain in southwestern Idaho indicated that the grass/fire cycle has caused large-scale habitat loss for black-tailed jackrabbits and thereby negatively affected golden eagles (Kochert and Pellant 1996; USDI 1996). Golden eagle reproduction in the NCA was initially negatively impacted by declines in jackrabbits following major wildfires and loss of shrub cover in the 1980s and 1990s but then rebounded after a few years as a result of eagles shifting to alternate foraging habitats and prey, including Piute ground squirrels (Marzluff et al. 1997; Kochert et al. 1999; Heath and Kochert 2016). However, conversion of shrublands to exotic annual grasses was associated with wider annual fluctuations in Piute ground squirrel numbers (Yensen et al. 1992; Van Horne et al. 1997), lower population densities, and lower body masses compared with shrub and native grass habitats (Steenhof et al. 2006). Thus, continued conversion of the native

Ground Squirrels—15 sagebrush and bluegrass community to cheatgrass will likely negatively affect Piute ground squirrel populations (Yensen et al 1992).

Preventing or interrupting loss of prey habitat to the grass/fire cycle could be crucial to the conservation of golden eagles in the western U.S. (USFWS 2016b). Conservation of ground squirrels and other prey is largely concordant with existing strategies for preserving or restoring habitat for protected wildlife species, such as greater sage-grouse (Centrocercus urophasianus) and Brewer's sparrows (Spizella breweri) (e.g., GBBO 2010; RISCT 2012; BLM 2015). However, at finer scales it is possible that management prescriptions to benefit these species differ from those that are optimal for ground squirrels and other golden eagle prey.

Invasive annual grasses, intense wildfire, and continued habitat conversion, are likely to further isolate and restrict ground squirrel populations (Yensen and Sherman 2003). Thus, maintaining ground squirrel populations will largely depend on conservation of occupied habitat, particularly for the sagebrush-steppe species that exist as a series of small, isolated populations (Yensen and Sherman 2003).

Lead and Anticoagulant Rodenticide Exposure

Shooting of ground squirrels is considered widespread and shot ground squirrels typically contain sufficient lead fragments to sub-lethally or lethally poison scavenging golden eagles and other raptors (Knopper et al. 2006; Haig et al. 2014; Herring et al. 2016). Lead poisoning (i.e., lead toxicosis) from ingestion of lead ammunition in carcasses is a known cause of golden eagle deaths (USFWS 2016b). Lead is a neurotoxicant, and lead toxicosis can present a wide range of physiological and neurological responses including mortality (Haig et al. 2014). Lead exposure can also increase the risk to golden eagles of accidental trauma and the likelihood of a fatal collision with vehicles or structures (Herring et al. 2017).

Population control of Belding’s ground squirrels on alfalfa fields was identified as a source of lead contamination to golden eagles that fed on shot carcasses (Herring et al. 2016). Belding’s ground squirrel numbers can be prolific in some agricultural areas (Whisson et al. 1999) where they were the primary prey for breeding golden eagles (Bedrosian et al. 2017). Lethal control efforts associated with agriculture and recreation should consider the potential impact of lead ammunition and poisons (e.g., ARs) on non-target wildlife, including golden eagles. Lead exposure from shooting ground squirrels could be reduced by collecting and disposing of shot carcasses, or by using non-lead ammunition (Knopper et al. 2006).

First and second generation ARs used to control ground squirrel populations also pose a risk to golden eagles (Ratner et al. 2014), particularly near agricultural areas where their use is more prevalent (Herring et al. 2017). Second generation ARs may have a higher likelihood of bioaccumulation, and thus secondary poisoning to golden eagles, than first generation ARs (Rattner et al. 2014). Although relatively little is known regarding AR poisoning in golden eagles, ARs have been identified in postmortem examinations of golden eagles in California (Kelly et al. 2014) and a wide range of harmful physiological and behavioral effects from AR poisoning in birds have been identified (reviewed in Herring et

Ground Squirrels—16 al. 2017). These include bleeding from body openings and excreta, irregular posture, and lethargy. Raptors with secondary exposure to ARs can bleed to death from minor wounds such as those commonly inflicted by prey (Erickson and Urban 2004; Murray 2013). Anticoagulant rodenticide poisoning may separately, and in combination with lead exposure, increase the risk of golden eagles dying from trauma-related injuries (Herring et al. 2017).

First generation ARs require multiple doses over several days to be ingested by ground squirrels before they are lethal (Rattner et al. 2014). Second-generation ARs are capable of killing ground squirrels in a single dose, and there is also evidence that they persist longer in vertebrate livers than first-generation ARs. Therefore, the risk to golden eagles from second generation ARs is considered to be greater than with other rodenticides (Herring et al. 2017). Non-ARs such as bromethalin, cholecalciferol, and zinc phosphide, do not accumulate in soft tissues and are less likely to have secondary poisoning effects (Rattner et al. 2014). New regulations on the use of second generation ARs may have the effect of decreasing their use, and thus risk to golden eagles, while increasing the use of first generation ARs and non-ARs (Rattner et al. 2015). We caution that the use of any poisons to control ground squirrels may negatively affect non-target wildlife species, including golden eagles.

Climate Change

Climate change may have direct and indirect effects on ground squirrel populations. A decrease in the lower elevation range of Belding’s ground squirrels was correlated with earlier spring snowmelt and greening of vegetation in California (Eastman et al. 2012). Alongside this temporal trend, body size increased, indicating some degree of phenotypic plasticity in response to environmental change. In addition, increased midday temperatures may increase the time ground squirrels spend in burrows (Loehr and Risser 1977) and decrease their availability to golden eagles. Species of ground squirrels that are less abundant and more geographically restricted may be even more vulnerable to climate change.

Information Gaps

• Most information on the use of ground squirrels as prey by golden eagles comes from breeding season diet studies (Bedrosian et al. 2017) and the degree to which nonbreeding eagles (sub-adults and floaters) feed on ground squirrels is poorly understood.

• Basic biological information on ground squirrels (e.g., morphology, physiology, reproduction) is well documented (Yensen and Sherman 2003); however, there is far less information on ecology and population dynamics for the majority of species. For example, little is known regarding the biotic and abiotic factors that affect population dynamics, or how anthropogenic sources of disturbance impact populations (Yensen and Sherman 2003).

Ground Squirrels—17

• More information is needed regarding effects of habitat loss and modification on ground squirrel populations resulting from fire and invasive annual grasses, grazing practices, conifer encroachment, agricultural conversation, and climate change.

• Shooting and poisoning as population control measures can expose golden eagles to contaminants (i.e., lead and anticoagulant rodenticides; Herring et al. 2017), yet little is known regarding the intensity and distribution of these hazards across large landscapes. Increased reporting and investigation of trauma-related golden eagle deaths is needed to understanding the population-level impacts of contaminants ingested from ground squirrels and other small mammals.

• Ground squirrel species can be difficult to distinguish from one another in the field and recent taxonomic revisions have split multiple species with implications to conservation and management. For example, Piute ground squirrels and Merriam’s ground squirrels are no longer considered subspecies of Townsend’s ground squirrels; Helgen et al. 2009) and therefore may not be poisoned using zinc phosphide without updated pesticide labels (O’Hare 2006). It is important that public information resources are updated to reflect current species distinctions and geographic distributions.

Ground Squirrels—18 References

Allison, T.D., J.F. Cochrane, E. Lonsdorf, and C. Sanders-Reed. 2017. A review of options for mitigating take of golden eagles at wind energy facilities. Journal of Raptor Research 51(3):319–333.

Andelt, W.F., and S.N. Hopper. 2016. Managing Wyoming ground squirrels. Colorado State University Extension. http://extension.colostate.edu/topic-areas/natural- resources/managing-wyoming-ground-squirrels-6-505/ (last accessed 1 April 2016).

Arnell, W.B. 1971. Prey utilization by nesting Golden Eagles (Aquila chrysaetos) in central Utah. Master's Thesis. Brigham Young Univ. Provo, UT.

Bagne K.E., M.M. Friggens, S.J. Coe, and D.M. Finch. 2014. The importance of assessing climate change vulnerability to address species conservation. Journal of Fish and Wildlife Management 5(2):450–462.

Balch, J.K., B.A. Bradley, C.M. D'Antonio, J. Gomez-Dans. 2013. Introduced annual grass increases regional fire activity across the arid western USA (1980–2009). Global Change Biology 19(1):173–183.

Bedrosian, G., J.W. Watson, K. Steenhof, M.N. Kochert, C.R. Preston, B. Woodbridge, G.E. Williams, K.R. Keller, and R.H. Crandall. 2017. Spatial and temporal patterns in golden eagle diets in the western United States, with implications for conservation planning. Journal of Raptor Research 51(3):347–367.

Betts, B.J. 1990. Geographic distribution and habitat preferences of Washington ground squirrels. Northwestern Naturalist 71(2):27–37.

Betts, B.J. 1999. Current status of Washington ground squirrels in Oregon and Washington. Northwestern Naturalist 80(1): 35–38.

BLM (Bureau of Land Management). 2015. Record of decision and approved resource management plan amendments for the Great Basin Region, including the Greater Sage- Grouse Sub-Regions of Idaho and southwestern Montana, Nevada and northeastern California, Oregon, Utah. Prepared by US Department of the Interior, Bureau of Land Management, Washington, D.C.

Bronson, M.T. 1980. Altitudinal variation in emergence time of golden-mantled ground squirrels (Spermophilus lateralis). Journal of Mammalogy 61(1):124–126.

Brooks, M.L., C.M. D'Antonio, D.M. Richardson, J.B. Grace, J.E. Keeley, J.M. DiTomaso, R.J. Hobbs, M. Pellant, and D. Pyke. 2004. Effects of invasive alien plants on fire regimes. BioScience 54(7):677–688.

Brooks, M.L., C.S. Brown, J.C. Chambers, C.M. D'Antonio, J.E. Keeley, and J. Belnap. 2016. Exotic annual Bromus invasions: Comparisons among species and ecoregions in the western United States. Pp. 11–60 in M. Germino, J.C. Chambers, and C.S. Brown (eds.).

Ground Squirrels—19 Exotic Brome-Grasses in Arid and Semi-Arid Ecosystems of the Western US: Causes, Consequences, and Management Implications. Springer International Publishing, Switzerland.

Brooks, M.L., and D.A. Pyke. 2001. Invasive plants and fire in the deserts of North America. Pp. 1–14 in K.E.M. Galley and T.P. Wilson (eds.). Proceedings of the Invasive Species Workshop: the Role of Fire in the Control and Spread of Invasive Species. Fire Conference 2000: the First National Congress on Fire Ecology, Prevention, and Management. Miscellaneous Publication No. 11, Tall Timbers Research Station, Tallahassee, Florida.

Chappell, M.A., and G.A. Bartholomew. 1981. Activity and thermoregulation of the antelope ground squirrel Ammospermophilus leucurus in winter and summer. Physiological Zoology 54(2):215–223.

Clark, T.W. 1970. Richardson’s ground squirrel (Spermophilus richardsonii) in the Laramie Basin, Wyoming. Great Basin Naturalist. 30(2): 55–70.

Cole, F.R., and D.E. Wilson. 2009. Urocitellus canus (Rodentia: Sciuridae). Mammalian Species 834:1–8.

D'Antonio, C.M., and P.M. Vitousek. 1992. Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annual Review of Ecology and Systematics 23:63–87.

Davidson, Ana D., J. K. Detling, and J. H. Brown. 2012. Ecological roles and conservation challenges of social, burrowing, herbivorous mammals in the world’s grasslands. Frontiers in Ecology and the Environment 10(9):477–486.

Davis, W. 8. 1939. The Recent mammals ofldaho. Caxton, Caldwell, ID.

Dobson, S. F., and J. O. Murie. 1987. Interpretation of intraspecific life history patterns from Columbian ground squirrels. The American Naturalist 129(3):382–397.

Elliot, C.L., and J.T. Flinders. 1991. Spermophilus columbianus. Mammalian Species 372:1–9.

Elliott, J.E., S. Hindmarch, C. A. Albert, J. Emery, P. Mineau, and F. Maisonneuve. 2014. Exposure pathways of anticoagulant rodenticides to nontarget wildlife. Environmental Monitoring and Assessment 186(2):895–906.

Erickson, W. and D. Urban. 2004. Potential risks of nine rodenticides to birds and nontarget mammals: A comparative approach. Office of Pesticides Programs, Environmental Fate and Effects Division, United States Environmental Protection Agency, Washington, D.C.

Eshelman, B.D. and C.S. Sonnemann. 2000. Spermophilus armatus. Mammalian Species. 637: 1–6.

Ground Squirrels—20 Fahrig, L., J. Baudry, L. Brotons, F.G. Burel, T.O. Crist, R.J. Fuller, C. Sirami, G.M. Siriwardena, and J. Martin. 2011. Functional landscape heterogeneity and animal biodiversity in agricultural landscapes. Ecology Letters 14:101-112.

Gavin, T.A., P.W. Sherman, E. Yensen, and B. May. 1999. Population genetic structure of the northern Idaho ground squirrel (Spermophilus brunneus brunneus). Journal of Mammalogy 80(1):156–168.

GBBO (Great Basin Bird Observatory). 2010. Nevada Comprehensive Bird Conservation Plan, ver. 1.0. Great Basin Bird Observatory, Reno, Nevada. Available online at: www.gbbo.org/bird_conservation_plan.html (last accessed January 15, 2017).

Haig, S.M., J. D’Elia, C. Eagles-Smith, J.M. Fair, J. Gervais, G. Herring, J.W. Rivers, and J.H. Schulz. 2014. The persistent problem of lead poisoning in birds from ammunition and fishing tackle. Cooper Ornithological Society 116:408–428.

Hall, E.R. 1981. The mammals ofNorth America, Vol. I. John Wiley, New York.

Hansen, R.M. 1956. Decline in Townsend ground squirrels in Utah. Journal of Mammalogy 37(1):123–24.

Helgen, K.M, F.R. Cole, L.E. Helgen, and D.E. Wilson. 2009. Generic revision in the Holarctic ground squirrel genus Spermophilus. Journal of Mammalogy 90(2): 270–305.

Heath, J.A., and M.N. Kochert. 2016. Golden eagle dietary shifts in response to habitat alteration and consequences for eagle productivity in the Morley Nelson Snake River Birds of Prey National Conservation Area. Final report for U.S. Fish and Wildlife Service, Idaho State Office, Boise, ID and U.S. Bureau of Land Management, Boise District, Boise, Idaho.

Herring G., C.A. Eagles-Smith, and M.T. Wagner . 2016. Ground Squirrel Shooting and Potential Lead Exposure in Breeding Avian Scavengers. PLoS ONE 11(12): e0167926. doi:10.1371/journal.pone.0167926.

Herring, G., C.A. Eagles-Smith, and J. Buck. 2017. Characterizing Golden Eagle risk to lead and anticoagulant rodenticide exposure: a review. Journal of Raptor Research 51(3):273–292.

Hoffmann, R.S., C. G. Anderson, R.W. Thorington, Jr., and L.R. Heaney. 1993. Family Sciuridae. Pp. 419-466 in species of the world: a taxonomic and geographic reference (D. E. Wilson and D. M. Reeder, eds.). 2nd ed. Smithsonian Institution Press, Washington, D.C

Holekamp, K.E. 1983. Proximal mechanisms of natal dispersal in Belding's ground squirrels (Spermophilus beldingi). Ph.D dissertation, University of California, Berkeley.

Holekamp, K.E., and P.W. Sherman. 1989. Why male ground squirrels disperse: a multilevel analysis explains why only males leave home. American Scientist 77(3):232–239.

Howell, A.H. 1938. Revision of the North American ground squirrels, with

Ground Squirrels—21 a classification of the North American Sciuridae. North American Fauna 56:1–256.

Hunt, W.G., R.E. Jackman, T.L. Brown, J.G. Gilardi, D.E. Driscoll, and L. Culp. 1995. A pilot Golden Eagle population study in the Altamont Pass Wind Resource Area, California. Predatory Bird Res. Group, Univ. of California, Santa Cruz.

IDHW (Idaho Department of Health and Welfare). 2017. 2017 Seasonal plague advisory for veterinarians. Division of Public Health, Bureau of Communicable Disease Prevention, Epidemiology Program. file:///H:/Science%20Literature%20Library/plague-advisory- veterinarians-2017.pdf (last accessed 25 September 2017).

IFG (Idaho Fish and Game). 2006. Idaho Comprehensive Wildlife Conservation Strategy. Appendix B: Idaho Species of Greatest Conservation Need. http://fishandgame.idaho.gov/public/wildlife/?getPage=158#comp (last accessed 23 April 2015).

IFG (Idaho Fish and Game). 2016. State Wildlife Action Plan. https://idfg.idaho.gov/swap (last accessed October 2, 2017).

IUCN (International Union for Conservation of Nature and Natural Resources). 2014. IUCN Red List of Threatened Species. http://www.iucnredlist.org (last accessed 9 January 2015).

Jenkins, S.H. and B.D. Eshelman. 1984. Spermophilus beldingi. Mammalian Species No. 221. Special Publication of the American Society of Mammalogists.

Johnson, K.H., R.A. Olson, and T.D. Whitson. 1996. Composition and diversity of plant and small mammal communities in tebuthiuron-treated big sagebrush (Artemisia tridentata). Weed Technology 10(2):404-416.

Keane, R.E., J.K. Agee, P. Fule, J.E. Keeley, C. Key, S.G. Kitchen, R. Miller, and L.A. Schulte. 2008. Ecological effects of large fires on US landscapes: benefit or catastrophe? International Journal of Wildland Fire 17:696–712.

Keller, K.R. 2015. Golden eagle nesting survey report for the central Utah study area, March–July 2015. Report submitted to the Utah Division of Wildlife Resources and Natural Resources Department, U.S. Army, Dugway Proving Ground.

Kelly, T.R., R.H. Poppenga, L.A. Woods, Y.Z. Hernandez, W.M. Boyce, F.J. Samaniego, S.G. Torres, and C.K. Johnson. 2014. Causes of mortality and unintentional poisoning in predatory and scavenging birds in California. Veterinary Record Open 0:e000028. doi:10. 1136/vropen-2014-000028.

Knick, S.T., D.S. Dobkin, J.T. Rotenberry, M.A. Schroeder, W.M. Vander Haegen, and C. Van Riper III. 2003. Teetering on the edge or too late? Conservation and research issues for avifauna of sagebrush habitats. Condor 105(4):611–634.

Ground Squirrels—22 Knight, J. and J. Parks. 2014. Ground squirrel control in Montana. Montana State University Extension, Bozeman, MT. http://store.msuextension.org/publications/AgandNaturalResources/MT201406AG.pdf (last accessed 11 April 2016).

Knopper, L.D., P. Mineau, A.M. Scheuhammer, D.E. Bond, and D.T. McKinnon. 2006. Carcasses of shot Richardson’s ground squirrels may pose lead hazards to scavenging hawks. Journal of Wildlife Management 70(1):295–299.

Kochert, M.N., and M. Pellant. 1986. Multiple use in the Snake River Birds of Prey Area. Rangelands 8(5):217–220.

Kochert, M.N., K. Steenhof, L.B. Carpenter, and J.M. Marzluff. 1999. Effects of fire on golden eagle territory occupancy and reproductive success. Journal of Wildlife Management 63(3):773–780.

Laundre, J.W 1993. Effects of small mammal burrows on water infiltration in a cool desert environment. Oecologia 94(1):43–48.

Laundre, J.W. 1998. Effect of ground squirrel burrows on plant productivity in a cool desert environment. Journal of Range Management 51(6):638–643.

Lenihan, C.M. 2007. The ecological role of the California ground squirrel (Spermophilus beecheyi). Doctoral Dissertation. University of California Davies.

Lockhart, J.M. 1976. The food habits, status and ecology of nesting golden eagles in the Trans-Pecos region of . Master's Thesis. Sul Ross State Univ. Alpine, TX.

Loehr, K.A. and A.C. Risser, Jr. 1977. Daily and seasonal activity patterns of the Belding ground squirrel in the Sierra Nevada. Journal of Mammalogy 58(3):445-448.

Marsh, R.E. 1994. Belding’s, California, and rock ground squirrels: damage prevention and control methods. Pages B151–158 in S. E. Hygnstrom, R. M. Trimm, and G. E. Larson (EDS). Prevention and control of wildlife damage. Cooperative Extension Division, University of Nebraska, Lincoln.

Marsh, R.E. 1998. Historical review of ground squirrel crop damage in California. International Biodeterioration and Biodegredation 42: 93–99.

Marti, C.D., Bechard, M., and F.M. Jaksic. 2007. Food habits. Pages 129–151 in D.M. Bird and K.L. Bildstein [EDS.], Raptor research and management techniques. Raptor Research Foundation and Hancock House, Blaine, WA U.S.A.

Marzluff, J.M., S.T. Knick, M.S. Vekasy, L.S. Schueck, and T.J. Zarriello. 1997. Spatial use and habitat selection of golden eagles in southwestern Idaho. Auk 114(4):673–687.

Mateos-Delibes, M., A.T. Smith, C.N. Slobodchikoff, and J.E. Swenson. 2011. The paradox of keystone species persecuted as pests: a call for the conservation of abundant small mammals in their native range. Biological Conservation 144:1335-1346.

Ground Squirrels—23

McKeever, S. 1966. Reproduction in Citellus beldingi and Citellus lateralis in northeastern California. Symposium of the Zoological Society, London 15:365-385.

Messick, J.P., G.W. Smith, and A.M. Barnes. 1983. Serologic testing of badgers to monitor plague in southwestern Idaho. Journal of Wildlife Diseases 19(1):1–6.

Michener, G.R., and Koeppl, J.W. 1985. Spermophilus richardsonii. Mammalian Species 243: 1–8.

Montana Natural Heritage Program. 2014. Montana Animal Species of Concern Report. Montana Natural Heritage Program and Montana Fish, Wildlife and Parks. http://mtnhp.org/SpeciesOfConcern/?AorP=a (last accessed 23 April 2015).

Morse, T.E. 1978. A description of and analysis of behavior patterns among Uinta ground squirrels. Ph.D. dissertation, Utah State University, Logan.

Murray, M. 2013. Presenting problem: Anticoagulant rodenticide toxicosis in free-living birds of prey. https://lafeber.com/vet/presenting-problem-anticoagulant-rodenticide- toxicosis-in-free-living-birds-of-prey/ (last accessed 31 August 2017).

Nadler, C.F., R.S. Hoffmann, and K.R. Greer. 1971. Chromosomal divergence during of ground squirrel populations (Rodentia: Spermophilus). Systematic Zoology 20(3):298–305.

NatureServe. 2015. NatureServe Explorer. Version 7.1 (2 February 2009). Last updated January 2015. http://explorer.natureserve.org (last accessed 15 May 2015).

Nydegger, N.C., and G.W. Smith. 1986. Prey populations in relation to Artemisia vegetation types in southwestern Idaho, pp. 152–156 in E.D. MacArthur and B.L. Welch (EDS). Proceedings-symposium on the biology of Artemisia and Chrysothamnus. U.S. Forest Service Intermountain Research Station, Ogden, Utah.

O'Hare, J.R., J.D. Eisemann, and K.A. Fagerstone. 2006. Changes in taxonomic nomenclature and conservation status of ground squirrel species: implications for pesticide labeling and use of zinc phosphide pesticide products.

Orabona, A., C. Rudd, M. Grenier, Z. Walker, S. Patla, and B. Oakleaf. 2012. Atlas of Birds, Mammals, Amphibians, and Reptiles in Wyoming. Wyoming Game and Fish Department Nongame Program, Lander. 232pp.

Patterson, B.D., G. Ceballos, W. Sechrest, M.F. Tognelli, T. Brooks, L. Luna, P. Ortega, I. Salazar, and B.E. Young. 2007. Digital Distribution Maps of the Mammals of the Western Hemisphere, version 3.0. NatureServe, Arlington, Virginia, USA.

Parmenter, R.R., and J.A. MacMahon. 1983. Factors determining the abundance and distribution of rodents in a shrub– steppe ecosystem: the role of shrubs. Oecologia 59(2- 3):145–156.

Ground Squirrels—24 Pellant, M., and C. Hall. 1994. Distribution of two exotic grasses on public lands in the Great Basin: status in 1992. Pp. 109–112 in S.B. Monsen and S.G. Kitchen (comps). Proceedings--ecology and management of annual rangelands; 1992, May 18–22; Boise ID. Gen. Tech. Rep. INT-GTR-313. U.S.D.A., Forest Service, Intermountain Research Station, Ogden, Utah.

Rattner, B.A., K.E. Horak, J.E. Elliott, R.F. Shore, and N. Van Den Brink. 2014. Adverse outcome pathway and risks of anticoagulant rodenticides to predatory wildlife. Environmental Science and Technology 48:8433–8445.

Rattner, B.A., K.E. Horak, R.S. Lazarus, S.L. Schultz, S. Knowles, B.G. Abbo, and S.V. Volker. 2015. Toxicity reference values for chlorophacinone and their application for assessing anticoagulant risk to raptors. Ecotoxicology 24(4):720–734.

Rickart, E.A. 1987. Spermophilus townsendii. Mammalian Species 268:1–6.

Rickart, E.A. 1988. Population structure of the Piute ground squirrel (Spermophilus mollis). Southwestern Naturalist 33(1):91–96.

RISCT (Range-wide Interagency Sage-grouse Conservation Team). 2012. Near-term greater sage-grouse conservation action plan. Available online at: http://www.wafwa.org/initiatives/sagebrush_ecosystem_initiative (last accessed January 15, 2017).

Salo, L.F. 2004. Population dynamics of red brome (Bromus madritensis subsp. rubens): times for concern, opportunities for management. Journal of Arid Environments 57:291– 269.

Schmalzried, J.T. 1976. Nesting and food habits of the golden eagle on the Laramie plains. Master's Thesis. University of Wyoming.

Schweiger, A., H. Funfstuck, and C. Beierkuhnlein. 2015. Availability of optimal-sized prey affects global distribution patterns of the golden eagle Aquila chrysaetos. Journal of Avian Biology 46(1):8–88.

Sherman P.W., and M.L. Morton. 1984. Demography of Belding’s ground squirrels. Ecology 65(5):1617–1628.

Sherman P.W, and M.L. Morton. 1987. Four Months of the Ground Squirrel, pp. 129-137. in H.R. Topoff (ED). The Natural History Reader in Animal Behavior. Columbia University Press, New York, New York.

Slade, N.A., and D.F. Balph. 1974. Population ecology of Uinta ground squirrels. Ecology 55(5):989–1003.

Steenhof, K., E. Yensen, M.N. Kochert, and K.L. Gage. 2006. Populations and habitat relationships of Piute ground squirrels in southwestern Idaho. Western North American Naturalist 66(4):482–491.

Ground Squirrels—25 Steenhof, K. and M.N. Kockhert. 1988. Dietary responses of three raptor species to changing prey densities in a natural environment. Journal of Animal Ecology 57(1):37–48.

Steenhof, K., M.N. Kochert, and T.L. McDonald. 1997. Interactive effects of prey and weather on Golden Eagle reproduction. Journal of Animal Ecology 66(3):350–362.

Svihla, A. 1939. Breeding habits of Townsend's ground squirrel. Murrelet 20(1):6–10.

Turner, L.W. 1972a. Autecology of the Belding ground squirrel in Oregon. Ph.D dissertation, University of Arizona, Tucson, U.S.A.

Turner, L.W. 1972b. Habitat differences between Spermophilus beldingi and Spermophilus columbianus in Oregon. Journal of Mammalogy 53(4): 914–917.

USDI (U.S. Department of the Interior). 1996. Effects of military training and fire in the Snake River Birds of Prey National Conservation Area. BLM/IDARNG Research Project Final Report. U.S. Geol. Surv., Bioi. Res. Div., Snake River Field Sta., Boise, Idaho.

USFWS (U.S. Fish and Wildlife Service). 2013. Eagle Conservation Plan Guidance: Module 1—Land-based Wind Energy, Version 2. Division of Migratory Bird Management. Washington, D.C.

USFWS (U.S. Fish and Wildlife Service). 2015. Endangered and Threatened Wildlife and Plants; 12-Month Findings on Petitions To List 19 Species as Endangered or Threatened Species. Department of the Interior. 50 CFR Part 17. https://www.gpo.gov/fdsys/pkg/FR- 2015-10-08/pdf/2015-25058.pdf (last accessed October 2, 2017).

USFWS (U.S. Fish and Wildlife Service). 2016a. Environmental Conservation Online System (ECOS). http://ecos.fws.gov/ecp/ (last accessed April 12, 2016).

USFWS (U.S. Fish and Wildlife Service). 2016b. Final programmatic environmental impact statement for the Eagle Rule revision. Department of Interior, Washington, D.C.

USGS-GAP (United States Geological Survey Gap Analysis Program). 2013. National Species Distribution Models. http://gapanalysis.usgs.gov (last accessed August 14, 2017).

Van Horne, B., G.S. Olson, R.L. Schooley, J.G. Corn, and K.P. Burnham. 1997. Effects of drought and prolonged winter on Townsend’s ground squirrel demography in shrubsteppe habitats. Ecological Monographs 67(3):295–315.

Van Horne, B., R.L. Schooley, and P.B. Sharpe. 1998. Influence of habitat, sex, age, and drought on the diet of Townsend's ground squirrels. Journal of Mammalogy 79:521–37.

Weddell, B. J. 1989. Dispersion of Columbian ground squirrels (Spermophilus columbianus) in meadow steppe and coniferous forest. Journal of Mammalogy 70(4):842–845.

Whisson, D.A., S.B. Orloff, and D.L. Lancaster. 1999. Alfalfa Yield Loss from Belding's Ground Squirrels in Northeastern California. Wildlife Society Bulletin 27(1):178–183.

Ground Squirrels—26 Whitford, W.G., and F.R. Kay. 1999. Biopedturbation by mammals in deserts: a review. Journal of Arid Environments 41:203–230.

Yensen, E., D.J. Hafner, and J.A. Cook. 1998. Conservation priorities, action plans, and conservation strategies for North American rodents. Pages 125–145 In: D. J. Hafner, E. Yensen, E., and G.L. Kirkland, Jr. (EDS). North American Rodents: status survey and conservation action plan. International Union for Conservation of Nature and Natural Resources Species Survival Commission. https://portals.iucn.org/library/efiles/documents/1998-039.pdf (last accessed January 6, 2015).

Yensen, E., and P.W. Sherman. 2003. Ground Squirrels. In Wild Mammals of North America: Biology, Management, and Conservation, 211–231. 2nd ed. Edited by George A. Feldhamer, Bruce C. Thompson, and Joseph A. Chapman. Baltimore, MD: Johns Hopkins University Press.

Yensen, E., and D.L. Quinney. 1992. Can Townsend's ground squirrels survive on a diet of exotic annuals? Great Basin Naturalist 52:269–77.

Yensen, E., D.L. Quinney, K. Johnson, K. Timmerman, and K. Steenhof. 1992. Fire, vegetation changes, and population fluctuations of Townsend’s ground squirrels. American Midland Naturalist 128(2): 299–312.

Yuskavitch, J. 2017. Stories: heavy metal. Earth Island Journal. http://www.earthisland.org/journal/index.php/eij/article/heavy_metal/ (last accessed 5 September 2017).

Zegers, D.A. 1984. "Spermophilus elegans.”Mammalian Species. 214:1–7.

Ground Squirrels—27 Appendix 1: Body sizes of ground squirrels in the western United States.

Species Body Length cm (in) a Body Mass g (oz) a Belding’s ground squirrel 30 (12) 340 (12.0) (U. beldingi) Columbian ground squirrel (U. columbianus) 41 (16) 812 (28.6) Merriam’s ground squirrel (U. canus) 27 (11) 325 (11.5) Piute ground squirrel 27 (11) 325 (11.5) (U. mollis) Richardson’s ground squirrel (U. richardsonii) 36 (14) 469 (16.5) 30 (12) 425 (15.0) (U. armatus) Wyoming ground squirrel 25–38 (10–15) b 250–400 (9–14) b (U. elegans) a Data source from NatureServe (2015) unless otherwise noted. b Andelt and Hopper (2016).

Ground Squirrels—28 Appendix 2: Conservation Status of Ground Squirrels in the western United States.

NatureServe Conservation Status (Year State Conservation Species Reviewed) a Status Belding’s ground squirrel US: Secure (1996) (Urocitellus beldingi) CA: Not Ranked ID: Apparently Secure NV: Secure OR: Secure UT: Possibly Extirpated (1996) Columbian ground US: Secure (1996) squirrel ID: Secure (U. columbianus) MT: Secure OR: Apparently Secure / Secure WA: Secure Merriam’s ground US: Apparently Secure (1998) IDb: Species of Greatest squirrel ID: Critically Imperiled Conservation Need / (U. canus) NV: Vulnerable / Apparently Secure Protected Nongame OR: Not Ranked Piute ground squirrel US: Secure (1998) BLM Landb: Sensitive (U. mollis) CA: Not Ranked species in ID ID: Imperiled IDc: Protected Nongame NV: Apparently Secure / Secure Oregon: Not Ranked UT: Apparently Secure / Secure (1998) Richardson’s ground US: Secure (1996) squirrel IA: Vulnerable (U. richardsonii) MN: Not Ranked MT: Secure ND: Not Ranked SD: Secure (1996) Uinta ground squirrel US: Secure (1996) MTd: Potential Species (U. armatus) ID: Apparently Secure of Concern MT: Vulnerable / Apparently Secure WYe: Nongame UT: Secure WY: Vulnerable / Apparently Secure (1996) Wyoming ground squirrel US: Secure (1996) MT: Potential Species (U. elegans) CO: Secure of Concern ID: Vulnerable IDb: Species of Greatest MT: Vulnerable / Apparently Secure Conservation Need / NE: Possibly Extirpated Protected Nongame NV: Secure WY: Nongame OR: Possibly Extirpated UT: Vulnerable WY: Vulnerable / Apparently Secure (1996) a NatureServe 2015. b IFG 2016. c IFG 2006. d Montana Natural Heritage Program 2014; e Orabona et al. 2012.

Ground Squirrels—29