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CRISSAL THRASHER (Toxostoma Crissale) Sam D

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CRISSAL THRASHER (Toxostoma Crissale) Sam D II SPECIES ACCOUNTS Andy Birch PDF of Crissal Thrasher account from: Shuford, W. D., and Gardali, T., editors. 2008. California Bird Species of Special Concern: A ranked assessment of species, subspecies, and distinct populations of birds of immediate conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists, Camarillo, California, and California Department of Fish and Game, Sacramento. Studies of Western Birds No. 1 CRISSAL THRASHER (Toxostoma crissale) Sam D. Fitton Criteria Scores Population Trend 10 Range Trend 0 Population Size 7.5 Range Size 10 Endemism 0 Population Concentration 0 Threats 10 Year-round Range County Boundaries Water Bodies Kilometers 80 40 0 80 Year-round range of the Crissal Thrasher in California, where restricted to limited regions of the Mojave and Colorado deserts. Outline of the overall range is generally stable, though numbers have declined at least moder- ately. 316 Studies of Western Birds 1:316–320, 2008 Species Accounts California Bird Species of Special Concern SPECIAL CONCERN PRIORITY (San Bernardino, Riverside, and Imperial coun- ties), and at Fort Yuma (Imperial County); Palm Currently considered a Bird Species of Special Springs and the Coachella Valley (Indio, Thermal, Concern (year round), priority 3. Included on and Mecca), Riverside County; and Alamoria, both prior special concern lists (Remsen 1978, 3rd Imperial County (Grinnell and Miller 1944). priority; CDFG 1992). These authors considered numbers of this thrasher at the western periphery of its California range to REEDING IRD URVEY TATISTICS B B S S be “small,” but the species to be “fairly common” FOR CALIFORNIA where mesquite habitat was well developed. Data inadequate for trend assessment (Sauer et al. 2005). RECENT RANGE AND ABUNDANCE IN CALIFORNIA GENERAL RANGE AND ABUNDANCE Although this species is now known from more Distributed in widely scattered patches of appro- areas, the general outline of its range in California priate habitat throughout the southwestern por- has probably changed little since 1944 (see map). tions of the United States from southeastern Recent documentation of occurrence west to California east through southern Nevada, south- Borrego Valley, San Diego County; west and western Utah, northern Arizona, and southwest- north to the Granite, New York, and Clark moun- ern New Mexico to western Texas and south tains, the Kingston Range, and Mesquite Lake, to south-central Mexico and northeast Baja San Bernardino County; and north to the vicinity California (AOU 1998). Three to four subspecies of Tecopa and Shoshone, Inyo County, appears are currently recognized (AOU 1957, Davis and to reflect increased observer coverage rather than Miller 1960, Phillips 1986). Toxostoma crissale a true range extension (Garrett and Dunn 1981, coloradense is the breeding resident subspecies in Cody 1999, J. Sterling pers. comm.). Since the California, where more than half of its range lies. mid-1970s, R. McKernan has likewise found In the United States, this thrasher is apparently this species in microphyll woodland and riparian most abundant in central-southern New Mexico washes scattered throughout southeastern San and the westernmost finger of Texas (Sauer et al. Bernardino and eastern Riverside and Imperial 2005). In California, it is most numerous along counties in the area between the Salton Sea and the Colorado River and less so to the west and Colorado River. Examples of occupied areas are north (Garrett and Dunn 1981). Palen Valley, McCoy Wash/Spring, Chuckwalla Well, Milpitas Wash, Blue Mountain, Mammoth SEASONAL STATUS IN CALIFORNIA Wash, Augustine Pass, Homer Wash, Ward Valley, Year-round resident; breeds from February to late Chemehuevi Wash, and Camino (R. McKernan July (Cody 1999). unpubl. data). The center of abundance in California contin- HISTORIC RANGE AND ABUNDANCE ues to be the riparian habitat along the Colorado River (Rosenberg et al. 1991, Patten et al. 2003). IN CALIFORNIA This despite conversion to unsuitable agricultural Grinnell and Miller (1944) described the range lands, row crops, and orchards, which by 1986 of the Crissal Thrasher (Toxostoma crissale) in left only 25% of the historic floodplain riparian California as all along the Colorado River, west forest (Rosenberg et al. 1991). Remaining suitable through the Imperial and Coachella valleys to habitat has been degraded by altered flood and fire Palm Springs, and the east slope of the Providence regimes and by changes to the plant species com- Mountains. These authors did not mention any position (Rosenberg et al. 1991). In the Salton appreciable range or habitat loss that had occurred Sea area, habitat loss, degradation, and fragmenta- up to that time. This thrasher was found from 190 tion, from agricultural and urban development ft (58 m) below sea level near the Salton Sea up to and invasive tamarisk (Tamarix spp.), has resulted 4500 ft (1372 m), possibly up to 5400 ft (1646 in this thrasher becoming increasingly local and m), in the Providence Mountains. Breeding, “uncommon” (Patten et al. 2003). There are prob- however, is chiefly below 500 ft (152 m; Grinnell ably fewer than 10 pairs in the disjunct population and Miller 1944). Typical breeding locations were on the floor of Borrego Valley, where the mesquite Providence Mountains, San Bernardino County; habitat is threatened by lowering of the water table Colorado River, from Needles to Pilot Knob as a result of human water use (Unitt 2004). Along Crissal Thrasher 317 Studies of Western Birds No. 1 the Amargosa River near Tecopa, Inyo County, C. Cody 1999). In a desert wash within the Granite McCreedy (pers. comm.) recently found densities Mountains, San Bernardino County, Cody (1999) of Crissal Thrashers higher than expected for that often found territories discontiguous with conspe- northern desert wash habitat. cific territories centered over the wash but sepa- rated by seemingly unsuitable habitat. ECOLOGICAL REQUIREMENTS The Crissal Thrasher forages on the ground using its long, curved bill to probe through fri- Rangewide, this species occupies a relatively large able soil and sift through leaf litter in search of variety of desert riparian and scrub habitats from prey. In an investigation of 32 stomach samples, below sea level to over 6000 ft (1800 m). In Rosenberg et al. (1991) found 21 arthropod and California, the range of habitats is more restricted two plant taxa. The relative abundance of different but still quite broad. The common factor, regard- food items varied seasonally, with indices of insect less of habitat type and species of shrub, is abundance in winter only 12% of that in summer dense, low scrubby vegetation. In California, this (Anderson et al. 1982). Beetles were most impor- thrasher occupies predominately riparian scrub tant throughout the year, whereas other prey were or woodland at lower elevations (e.g., Colorado taken as available—caterpillars in fall, winter, River valley), and the low, dense scrub associated and spring, maggots in summer, grasshoppers in with arroyos at higher elevations in the Mojave late summer, and ants in winter (Rosenberg et Desert, normally at or near the upper reaches al. 1991). Thrashers also occasionally take small of desert scrub vegetation and below the piñon- lizards (Bent 1948). They consume fruits, ber- juniper foothill woodland of the slopes above ries, and seeds to a minor degree, mostly from (Garrett and Dunn 1981, Cody 1999). Dominant October to April (Cody 1999). Water is often species of shrubs or small trees in occupied habitat present at occupied sites, and while the species is include mesquite (Prosopis spp.), Catclaw (Acacia known to drink water, its presence is not thought greggii), Ironwood (Olneya tesota), palo verde to be a critical habitat component (Dobkin and (Cercidium spp.), willows (Salix spp.), sagebrush Granholm 1990, Cody 1999). (Artemisia spp.), Desert Almond (Prunus fascicu- Some movement in elevation (Engels 1940) latum), Desert-thorn (Lycium cooperi), Bitterbrush and seasonal shifts in habitat use (Anderson et (Purshia tridentata var. glandulosa), saltbush al. 1982, Rice et al. 1983, Rosenberg et al. 1991) (Atriplex spp.), and tamarisk (Hunter et al. 1988, have been noted. Rosenberg et al. (1991) reported Rosenberg et al. 1991, Cody 1999, R. McKernan that population densities tended to increase slight- in litt.). These plant species are often found in ly in tamarisk and Screwbean Mesquite (Prosopis loose sandy soil or alluvium (Grinnell and Miller pubescens) in late summer and fall, when declines 1944). In addition, this thrasher uses agricultural were first noted in the thrasher’s primary habitat edges (e.g., citrus orchards) for foraging when of Honey Mesquite (P. glandulosa), but they were adjacent to native habitat patches where they nest uncertain whether this indicated later breeding and forage (Rosenberg et al. 1991). in suboptimal habitats or actual habitat shifts by Nests are most often placed in the densest por- thrashers. Rice et al. (1983) found greater use of tions of shrubs (Engels 1940), averaging approxi- tamarisk and cottonwood habitats in spring and mately 1 m above the ground, usually with a por- of willow in fall. tion of the nest plant over the nest (Cody 1999). The factors that primarily regulate this thrash- These well-concealed nest sites may help reduce er’s population are unknown. In general, however, nest predation and provide cover from the sun overall population size likely is regulated by the (Rosenberg et al. 1991, Cody 1999). Two broods extent of various types of breeding habitat (Cody are typically produced per season in the Colorado 1999). River valley, but the short winter season may allow for a third brood; birds in higher elevations may THREATS not raise a second brood (Cody 1999). This thrasher is strongly territorial and main- The extent and severity of threats to this species tains its territories year round in most areas, have not been well studied. However, the loss though some movement in the nonbreeding and degradation of this thrasher’s requisite habi- season has been noted in some populations (Cody tats—riparian areas, desert washes, and patches 1999).
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