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Literature in Review

Palm Springs (Round-tailed) Ground Squirrel

Spermophilus tereticaudus var. chlorus

USFWS: No official status
CDFG: Species of Special Concern

Background

Distribution, Abundance and Trends. The Palm Springs ground squirrel is a subspecies of the round-tailed ground squirrel which occurs in the Coachella Valley associated with sandy substrates. Within the Plan area, the current and historical distribution for the Palm Springs ground squirrel is from San Gorgonio Pass to the vicinity of the Salton Sea (Grinnell and Dixon 1918). Individuals of this species have been observed at the south end of La Quinta near Jefferson Ave. and along the Coachella Canal near Box Canyon. The range of this species in the eastern part of the Plan area is not well known. The Plan area includes all of the known range for the Palm Springs subspecies of the more widely distributed round-tailed ground squirrel.

The Palm Springs ground squirrel is typically associated with sand fields and dune formations (Bradley and Deacon 1971), although it does not require active blow sand areas. This small ground squirrel seems to prefer areas where hummocks of sand accumulate at the base of large shrubs that provide burrow sites and adequate cover (Grinnell and Dixon 1918, C. Barrows pers. comm.). Various authors have referred to the use of mesquite habitat by round-tailed ground squirrels (Allen 1895, Elliot 1904, Grinnell and Dixon 1918, Vorhies 1945, Drabek 1973, Dunford 1975). Although numerical data were not presented McDonald (1999) reported relatively high densities of Palm Springs ground squirrel in a mesquite hummock and active sand field habitat at the east end of the Indio Hills. In surveys for this Plan, Dodero (1995) reported observing this squirrel at Willow Hole in the central portion of the dune as well as at the southern periphery, at the edge of mesquite clumps. He also reported that these squirrels are most abundant at Willow Hole in the dune area where the transition from desert dune to Sonoran creosote scrub takes place. Barrows (2001) suggests that they are most abundant in more mesic sand dune habitats, often associate with mesquite hummocks. They may also be found in areas where sandy substrates occur in creosote bush scrub and desert saltbush or desert sink scrub that supports herbaceous growth. In addition to wind blown sand habitats, they may occur in areas of more coarse sands, associated with washes. According to Mark Fisher of the University of California Deep Canyon Desert Research Center, the Palm Springs ground squirrel used to occur on this reserve in sandy patches associated with washes and was reported from 1979 to 1984 (see known locations data for this species). He indicated that this ground squirrel has not been observed in the Deep Canyon area since the 1980's when the sandy substrates were removed by a large flood event and have not been restored

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Very little quantitative data is available to describe the population density for this species throughout the Plan area. Density estimates for the species in Arizona range from 5.3/ha on a 63 hectare site in southcentral Arizona (Drabek 1970) to 40/ha on a crowded site (Dunford 1977). It is likely that densities in the Coachella Valley would be less than in Arizona where average annual rainfall and vegetation density are relatively higher. Based on input from various observers, including members of the SAC, areas where the Palm Springs ground squirrel occurs in relatively high density have been identified. This squirrel occurs in good populations in the vicinity of Snow Creek, from Fingal to Windy Point; it has also been observed further west near Cabazon. It occurs around the Whitewater river channel north and west of Palm Springs, including the Whitewater River Floodplain Preserve. It has been observed along the Mission Creek wash and likely occurs in suitable habitat in the southern parts of Desert Hot Springs. Habitat, including mesquite hummocks and sand dunes, at the Edom Hill-Willow Hole Preserve/ACEC has been described as high quality for this species (Dodero 1995) and many individuals were observed there during surveys for the Plan. Data on the number of individuals of Palm Springs ground squirrel along a 1 km. transect at the Willow Hole-Edom Hill preserve have been collected during annual monitoring surveys for the fringe-toed lizard (CNLM 2000); the mean number of squirrels per survey per year ranges from 2 to 7 squirrels from 1990 to 1994 and from 4 to 10 squirrels from 1998 to 2000. From the Willow Hole-Edom Hill ACEC it can be found in sandy habitats east toward the Coachella Valley Preserve. It occurs in good numbers on the dunes of the Coachella Valley Preserve. It is also common on the sand dunes at the east end of the Indio Hills.

Habitat is still present for this ground squirrel on the so-called Big Dune south of Interstate 10, although surveys for this species have not been conducted in this area because it is private land without access.

The Palm Springs ground squirrel occurs in small colonies widely scattered in suitable sandy habitats (Ryan 1968). According to Jaeger (1961) 10 to 15 animals per square mile is probably an average number. From trap data in the creosote-palo verde habitat, Ryan (1968) estimated 1.1 individual/acre during 30 April-2 May, 2.3 individuals/acre during October, and 1.1 individual/acre during January. Drabek (1973) found mean home range estimates of 0.74/acre for adults and 0.77/acre for juveniles.

The burrows of the Palm Springs ground squirrel are typically located at the base of a large creosote bush or other shrub, often on a small mound or hummock. The entry is several inches across leading to tunnels that are not usually deep nor over five or six feet in length (Jaeger 1961). Young are born in March or April in litters of four to twelve. In winter, they remain in their underground burrows for much of the time. They feed on seeds and green leaves of desert plants, including the stems of Mormon tea (Ephedra sp.), leaves and beans of mesquite, cactus fruit, ocotillo blossoms, and agricultural crops but may occasionally take small lizards (including flat-tailed horned lizards) and insects; they have also been observed to feed on carrion.

Threats and Limiting Factors. Threats to the Palm Springs ground squirrel in the Plan area include loss of habitat as a result of urbanization and agricultural development, including the loss of mesquite hummocks due to lowered water tables, and related impacts. As ground dwelling small mammals, they are susceptible to impacts from off-road vehicles and other surface disturbances that could crush their burrows. At the urban interface, impacts from domestic pets (cats and dogs) and small predator populations could pose a threat. As they seem to prefer open areas with adequate visibility, invasive exotic plants such as Saharan mustard (Brassica tournefortii) and Russian thistle (Salsola tragus) may reduce habitat suitability. This species has been observed crossing two and four-lane roads; in high traffic areas, however, roads within suitable habitat could increase mortality significantly. While the Palm Springs ground squirrel does not require active blow sand areas, maintenance of their habitat will depend on protection of ecosystem processes associated with sand dunes.

Special Considerations. Within the Plan area, other species of concern whose habitat overlaps with that of the Palm Springs ground squirrel include flat-tailed horned lizard, Palm Springs pocket mouse, Coachella Valley fringe-toed lizard, Coachella Valley milkvetch, Coachella giant sand treader cricket, Coachella Valley Jerusalem cricket, and burrowing owl.