CRISSAL THRASHER (Toxostoma Crissale) Sam D

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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 counties), 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). Territory sizes vary from a low of 5 ha in of mesquite—is an ongoing and primary threat optimum mesquite thicket to a high of 8–10 ha (Laudenslayer et al. 1992). For example, where in less-preferred habitat (Laudenslayer et al. 1992, highest reported densities for this species in

318 Species Accounts California Bird Species of Special Concern

California occur along the Colorado River, much development. The increase in species such as the of the riparian habitat has been converted to agri- Common Raven (Corvus corax) and American culture, a smaller amount to urban development. Crow (Corvus brachyrynchus) could augment nest Riparian habitat restoration is ongoing along predation rates on Crissal Thrashers. Common the Colorado River, and Crissal Thrashers have Ravens have been seen along the Colorado River been documented using these revegetated areas walking through and perched on riparian habitat (Rosenberg et al. 1991, Cody 1999). Further, the in an obvious attempt to find prey (W. Boarman stabilization and channelization of the Colorado pers. comm.). River has been credited with increasing the amount of Screwbean Mesquite, which forms a Management and Research plant community suitable for this species. This Recommendations positive development, however, has been partially • countered by clearing and burning of important Maintain and restore dense, low scrub mesquite stands north of Blythe (Rosenberg et al. (especially <3 m) in riparian, desert wash, 1991). Regardless, it is unlikely that the increase and higher-elevation thrasher sites. • in suitable mesquite and restored habitats has off- Map the full extent of potential habitat and set the large amount of habitat lost to agriculture its occupancy by thrashers. • and urban development (Rosenberg et al. 1987, Use marked populations to determine the 1991). species’ ability/tendency to move within Invasion of riparian areas by the exotic invasive and between habitat areas. • tamarisk has the potential to impact this species. Determine the importance of the popula- However, this thrasher has been documented tions along the Colorado River, the species’ using tamarisk habitat in the lower Colorado center of abundance in the state, in geneti- River as well as to the east in Arizona, New cally linking other populations away from Mexico, and Texas (Hunter et al. 1988). By con- the river. • trast, the loss of mesquite to tamarisk results in Initiate demographic studies to determine the loss of Crissal Thrashers in the Salton Sea area population viability and the primary factors (Patten et al. 2003), indicating that this species that influence it (e.g., patch size, habitat may respond variably within California to invasive type). • woody plants and loss of Honey Mesquite. The Study the effect of tamarisk invasion in quality—for reproduction and survival—of native riparian areas on breeding density, various versus non-native tamarisk habitats has not been components of reproductive success (e.g., studied. clutch and brood size, nest success), and site Though the Crissal Thrasher is apparently fidelity. • more vagile than other sickle-billed thrashers Study the potential impact of various dis- (Laudenslayer et al. 1992), increasing distances turbances with particular attention to off- between occupied habitat patches could leave road vehicle use. • these occupied areas functioning as population Evaluate whether habitat restoration pro- islands and make birds more prone to extirpation vides suitable habitat by making compari- (Soulé 1987). sons (e.g., breeding density, nest success, It is likely that this species is vulnerable to site fidelity) with reference sites. Use results certain types of disturbance. Desert washes and to provide specific restoration and manage- riparian areas are often the locations of off-high- ment recommendations. way vehicle trails (Remsen 1978). High-intensity Monitoring Needs recreation use along these narrow corridors could negatively affect this species. Disturbance to this The state’s breeding habitat should be mapped and species’ habitat by livestock could change its struc- monitored for changes in areal extent. Current ture enough to render it unsuitable for thrasher monitoring strategies (i.e., Breeding Bird Survey use. As elsewhere in California, desert habitats and Christmas Bird Count) are inadequate for this have been changed by the addition of non-native species because of its patchy and/or linear distribu- annual plants, which may reach abundances that tion and its early commencement of breeding (i.e., increase the risk and intensity of fire, the effects of peak singing). Standard extensive monitoring pro- which are unknown for this thrasher. tocols (e.g., point count surveys) should be used Some native and non-native predators have and adjusted for space and timing issues specific to increased as a result of agricultural and urban Crissal Thrashers. A subset of breeding populations

Crissal Thrasher 319 Studies of Western Birds No. 1 should be intensively monitored annually state- Engels, W. L. 1940. Structural adaptations in thrashers wide using territory mapping and nest monitoring, (Mimidae: genus Toxostoma) with comments on stratified by habitat type, to determine long-term interspecific relationships. Univ. Calif. Publ. Zool. trends in breeding numbers and nest success. 42:341–400. Garrett, K., and Dunn, J. 1981. Birds of Southern Cali- Acknowledgments fornia: Status and Distribution. Los Angeles Audubon Soc., Los Angeles. This species account was greatly improved by reviews Grinnell, J., and Miller, A. H. 1944. The distribution of by B. Anderson, T. Gardali, and W. D. Shuford. Brief the birds of California. Pac. Coast Avifauna 27. comments by J. Sterling were also beneficial and appre- Hunter, W. C., Ohmart, R. D., and Anderson B. W. ciated. C. McCreedy provided summaries of recent field 1988. Use of exotic saltcedar (Tamarix chinensis) by data and assisted in obtaining data on habitat change. birds in arid riparian systems. Condor 90:113–123. R. McKernan provided many sightings documenting the occurrence of this species between the Salton Sea Laudenslayer, W. F., Jr., England, A. S., Fitton, S., and and Colorado River. Saslaw, L. 1992. The Toxostoma thrashers of Califor- nia: Species at risk? Trans. W. Section Wildl. Soc. 28:22–29. Literature Cited Patten, M. A., McCaskie, G., and Unitt, P. 2003. Birds American Ornithologist’s Union (AOU). 1957. Check- of the Salton Sea: Status, Biogeography, and Ecology. list of North American Birds, 5th ed. Am. Ornithol. Univ. Calif. Press, Berkeley. Union, Baltimore. Phillips, A. R. 1986. The Known Birds of North and American Ornithologists’ Union (AOU). 1998. Check- Middle America. Part 1. A. R. Phillips, Denver. list of North American Birds, 7th ed. Am. Ornithol. Remsen, J. V., Jr. 1978. Bird species of special concern Union, Washington, DC. in California: An annotated list of declining or vul- Anderson, B. W., Ohmart, R. D., and Fretwell, S. D. nerable bird species. Nongame Wildl. Invest., Wildl. 1982. Evidence for social regulation in some riparian Mgmt. Branch Admin. Rep. 78-1, Calif. Dept. Fish & bird populations. Am. Nat. 120:340–352. Game, 1416 Ninth St., Sacramento, CA 95814. Bent, A. C. 1948. Life histories of North American Rice, J., Ohmart, R. D., and Anderson, B. W. 1983. nuthatches, wrens, thrashers, and their allies. U.S. Habitat selection attributes of an avian community: Natl. Mus. Bull. 195. A discriminant analysis investigation. Ecol. Monogr. California Department of Fish and Game (CDFG). 53:263–290. 1992. Bird species of special concern. Unpublished Rosenberg, K. V., Ohmart, R. D., Hunter, W. C., and list, July 1992, Calif. Dept. Fish & Game, 1416 Ninth Anderson B. W. 1991. Birds of the Lower Colorado St., Sacramento, CA 95814. River Valley. Univ. Ariz. Press, Tucson. Cody, M. L. 1999. Crissal Thrasher Toxostoma( crissale), Rosenberg, K. V., Terrill, S. B., and Rosenberg, G. H. in The Birds of North America (A. Poole and F. Gill, 1987. Value of suburban habitat to desert riparian eds.), no. 419. Birds N. Am., Philadelphia. birds. Wilson Bull. 99:642–654. Davis, J., and Miller, A. H. 1960. Family Mimidae, in Sauer, J. R., Hines, J. E., and Fallon, J. 2005. The North Check-list of Birds of the World (E. Mayr and J. C. American Breeding Bird Survey, results and analysis Greenway Jr., eds.), vol. 9. Mus. Comparative Zool., 1966–2004, version 2005.2. USGS Patuxent Wildl. Cambridge, MA. Res. Ctr., Laurel, MD. Available at www.mbr-pwrc. Dobkin, D., and Granholm, S. L. 1990. Crissal Thrasher, usgs.gov/bbs/bbs.html. in California’s Wildlife, vol. II, Birds (D. C. Zeiner, Soulé, M. E., ed. 1987. Viable populations for conserva- W. F. Laudenslayer Jr., K. E. Mayer, and M. White, tion. Cambridge Univ. Press, New York. eds.), pp. 534–535. Calif. Dept. Fish & Game, Unitt, P. 2004. San Diego County bird atlas. Proc. San Sacramento. Diego Soc. Nat. Hist. 39.

320 Species Accounts