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Le Conte's thrasher

Toxostoma lecontei

USFWS: No status
CDFG: Species of Special Concern

Background

Distribution, Abundance and Trends. Le Conte's thrasher is an uncommon resident of the deserts of the American southwest and northwestern Mexico. It is found in the San Joaquin Valley and in the Mojave and Colorado deserts of California and Nevada southward into northeastern Baja California, and farther south into central and coastal Baja California. It also occurs in the Sonoran Desert from extreme southwest Utah and western Arizona south into western Sonora, Mexico. Within this range, distribution is patchy. Its elevational distribution is generally between sea level and 1,150 meters; though in Death Valley it occurs down to -81 meters, and in the Mojave Desert it is known up to approximately 1,600 meters. The species requires undisturbed substrate for foraging under desert shrubs. Agriculture and urban development have eliminated considerable former habitat in the San Joaquin Valley, portions of the Mojave Desert, Imperial and Coachella valleys, the Las Vegas area, and south and west of Phoenix. Based on false-infrared satellite imagery of 243 historic localities in the U.S. as of 1993, at least 26% no longer had suitable habitat patches within 3 km.

Its typical habitat consists of sparsely vegetated desert flats, dunes, alluvial fans, or gently rolling hills having a high proportion of one or more species of saltbush (Atriplex spp.) and/or cylindrical cholla cactus (Opuntia spp.) 0.9 - 1.9 meters high. It also occupies other desert habitats with similar structural profiles but lacking saltbush/shadscale or cholla cactus. In its typical habitat, shrubs are well scattered with contiguous or closed cover usually less than 15 meters in any direction, even along the sides of arroyos. The ground is generally bare or with sparse patches of grasses and annuals forming low ground cover (average height less than 30cm.). It is rarely found in habitats consisting entirely of creosote bush (Larrea). The majority of shrubs rarely exceed 2.5 meters in height, except for isolated desert trees, yuccas, or tall, thin shrubs such as ocotillo. Substrates are typically sandy and rarely composed of a large proportion of rock or of deep silty clays. The habitat requires accumulated leaf litter under most plants as diurnal cover for most arthropod prey. Surface water rarely exists anywhere within several kilometers of most territories except temporarily following infrequent rains.

Typical territories rarely have topographical relief greater than 10 - 20 meters, although many broad canyon floors with large flood plains and poorly vegetated sides are acceptable. Narrow, boulder-strewn canyons with little or no sand deposition are used infrequently. The species commonly uses small arroyos, depressions, or streambeds traversing more level terrain with associated larger saltbush/shadscale and other desert shrubs. It is also uses the vegetated margins of large, rolling sand dunes. Crissal and California thrashers prefer nearly continuous cover of shrub or riparian vegetation; both occupy habitats with far more contiguous or closed cover that is far denser and usually taller than any vegetation typically inhabited by Le Conte's thrasher.

For nesting, Le Conte's thrasher prefers thick, dense, and thorny shrubs or cholla cactus. Cholla cactus and saltbush were used in 85% of 289 nest sites throughout the distribution of the species. The remaining 15% were in a large variety of desert shrubs, small trees, and yucca.

Within the Plan area, there are historical records in the Natural Diversity Database and a few recent records. Historic records (the date follows the location in parentheses) include the mouth of Whitewater River Canyon (1930), Desert Hot Springs (1968), Edom Hill (1984), Andreas Canyon alluvial fan (1923), Mecca (1908), Indio (1924), Cabazon (1916), Whitewater River east of Palm Springs Airport (1920), 2 miles west of Thousand Palms (1921), Palm Canyon wash (1923), Whitewater River in Indian Wells (1919), and Shavers Valley (1986). Many of these areas have been impacted by development. Records since 1990 include 4 records for the Desert Hot Springs area, 2 of which are west of Highway 62, a record for the area below Cottonwood Canyon (west of Whitewater Canyon), a record for the area south of I-10 and west of Gene Autry Trail, a record for the Willow Hole ACEC area, a record for Pushwalla Canyon, a record for the Thousand Palms Oasis area, and a record for Indian Wells. These historical and current records suggest a widespread distribution of the species in the Plan area, where there is appropriate habitat. This would include most of the non-mountainous areas that have not been disturbed by urbanization or agriculture.

No data is available on population density in the Plan area. However, average density in Maricopa, California was 4.63 pairs/km2. Other density estimates have ranged from less than one pair per square kilometer to 1.7 pairs/km2. Other estimates have been 6 pairs/mi2, or 2.3 pairs/km2, (Engels, 1940), and 10 pairs/mi2, or 3.86 pairs/km2 in one study area in the San Joaquin Valley and 0 - 5 pairs/mi2, or 0 - 1.93/ km2, throughout the range (Sheppard, 1970). The home range limits vary with time and interactions with neighbors, if any; pairs may occupy about 40 - 100 ha in aggregate over a period of a few years.

Threats and Limiting Factors. The primary threat to the species is loss of habitat due to conversion to urban, agricultural, or other uses. Other threats may include degradation of habitat from ORV shooting, alteration of habitat from fire, pesticides in habitat near agricultural areas, predation of young by house cats, and collisions with cars.