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Home , California thrasher, Carrizo Plain, Crissal thrasher, Sage thrasher

THE OF : AT RISK?

WILLIAM F. LAUDENSLAYER, jR., U.S. Forest Service, Pacific Southwest ~esearchStation, 208 1 East Sierra Avenue, Fresno, CA 937 10

A. SIDNEY ENGLAND, Department of Wildlife and Fisheries Biology, University of California, Davis, CA 956 16

SAM FITTON, U.S. Bureau of Land Management, Bakersfield Distria, 800 Truxton Avenue, Bakersfield, CA 9330 1

LARRY SASLAW, U.S. Bureau of Land Management, Bakersfield District, 800 Truxton Avenue, Bakersfield, CA 9330 1

1992 TRANSACTIONS OF THE WESTERN'SEGTION OF THE WILDLIFE SOCIETY 28:22-29

Abstmct: Four of the 10 described species of Toxostoma breed in California- (T.redivivum), Bendire's thrasher (T. bendirei), (T. crissale), and Le Conte's thrasher (T. fecontei). Urbanization, agricultural development, fire management, and livestock grazing are among the land uses that affect large tracts of the habitats occupied by these species. Other uses generally impact smaller areas. None of these species are likely to be eliminated from the California avifauna in the forseeable fiture. However, they are potentially susceptible, in varying degrees, to localized extirpations because (1) they occur at low densities, (2) portions of their ranges are Eragmented, and (3) only the Bendire's thrasher is known to regularly move long distances. Thus, in addition to direct habitat loss and degredation, California, Crissal, and Le Conte's thrashers may be susceptible to population declines following habitat fragmentation. Similarly, other species, subspecies, and populations of the California breeding avifauna with similar life history traits could suffer comparable declines. This potential is especially high among the numerous tam of nonmigratory shrubland . Shrubdwelling species have generally been overlooked by wildlife biologists and land managers. A systematic review, survey, and monitoring of the California avifauna is needed to identify taxa and populations that may become threatened.

The genus Toxostoma is comprised of 10 species of grazing in desert scrub has altered plant species thrashers found in ; the majority of these composition (Wagner 1978). The scale of these changes breed in the arid southwestern and Mexico can vary from a few acres (e.g., mineral extraction) to (AOU 1983). California (T. redivivum), Le Conte's (T. hundreds of thousands of acres (e.g., fire suppression, lecontei), and Crissal thrashers (T. crissale) are year- livestock grazing). round residents in California while Bendire's thrasher Soule et al. (1988), working in San Diego County, (T.bendirei) breeds in California, but generally winters have documented a previously unreported factor affecting in southern and northwestern Mexico. The shrubland birds in California-habitat fragmentation, habitats used by these birds are generally shrub- generally by housing developments, followed by local dominated, ranging from sparse desert scrub to dense extirpation of isolated populations. They observed that and woodlands with a shrub understory. some native birds are lost as patches become isolated and Shrublands, including desert shrublands, cover a vegetation is altered. The probability of localized larger proportion of the state (approximately 39% of 10 1 extinction depends on the size of remaining patches, million acres) than any other major structural type (e.g., distance to other patches, and time since fragmention. marsh, , woodland, or forest) (CDF'FP 1988). One ofthe birds that Soul6 et al. (1988) found susceptible Yet these habitats have received little attention from to local extinction was the California thrasher. wildlife ecologists and land managers. This treatment Our objective in this paper is to examine the status undoubtedly is due to the perception that the economic andpotential threats to the four Toxostomathrashers that value, species diversity, and endangerment of shrubland breed in California. This review is based on existing wildlife is low. Nonetheless, human activities have literature and unpublished data collected by @e authors affected shrublands for over a century. on the distribution, population status, and life history The most obvious impact has been habitat loss due characteristics of these thrashers. This analysis is timely to agricultural and urban dkvelopment. Other activities in light ofthe fragmentation effects documentedby Soule have had more subtle, but still potentially damaging et al. (1988) on California thrasher and because the other effects. For example, decades of fire suppression have three species are classified as Species of Special Concern caused a heavy accumulation of fuels (Biswell 1989), by the California Department of Fish and Game (CDFG controlled burning in late winter and early spring has 1991). Each of us has field experience with at least one shifted the timing of fire in chaparral, and livestock of these thrashers [Crissal (W.F Laudenslayer), TRANS. WEST. SECT. WILDL. SOC. 28: 1992 Toxostoma Thrashers , Laudenslayer et al. 23

l California (A.S. England), Bendire's (A.S. Englandand polycarpa) (Grimell and Miller 1944, Sheppard 1970; W.F. Laudenslayer),andLe Conte's (- S. Fitton and L. Saslaw, unpublished data). They often S. Fitton and L. Saslaw and deserts A.S. England and frequent desert washes and flats with scattered bushes W.F. Laudenslayer)]. We also are or have been directly and areas of open sandy, alkaline (Grinnell and involved with manageknent activities that affect thrasher Miller 1944), or gypsum soils (S. Fitton and L. Saslaw, habitat. unpublished data). The habitat of this species has been altered by THREATS TO THRASHER HABITAT conversion to agriculture, urbanization, oil, and gas California Thrasher development, fire, and heavy livestock grazing. California thrashers are widespread in the lowlands Agricultural development has severely reduced the and foothills of cismontane California in a variety of distribution of suitable habitat in the San Joaquin Valley habitats, similar in that all have a dense and continuous and has fragmented the remaining suitable habitat shrub cover (Grinnell 1917). They are primarily found (Fig. 1). Heavy livestock use in the San Joaquin Valley in chaparral and some river bottom thickets, but also in during droughts may also have substantially altered the 'informally kept gardens' (Grinnell andMiller 1944:351). character of the remaining thrasher habitat, thereby The primary threats to the habitat of California thrashers reducing the canopies of large shrubs used for nesting are urbanization, conversion to agriculture, and the and reducing the litter in which birds forage (S. Fitton resulting fragmentation from these events. Soule' et al. and L. Saslaw,unpublisheddata). Fire has alsoeliminated (1988) have documented that California thrashers are or fragmented the saltbush community. These same extirpated from small patches of habitat isolated by types of impacts have also occurred in desert habitats urban development in . The occupied by Le Conte's thrasher, but the extent of losses interaction between wildfires and habitat fragmentation appears to be considerably less relative to available has not been studied directly, but the combination could habitat thanthose taking place in the San Joaquin Valley. . eliminate this species from patches that might otherwise Urbanization has also been an important factor in habitat support populations. For the first 2-3 years following a loss in the Antelope, Mojave River, and Coachella fire, California thrashers are either eliminated or their Valleys (K.L. Garrett, pers, comm.). numbers are severely depressed (A.S. England, unpublished data, Moriarty et al. 1985). Population Crissal Thrasher recovery begins approximately five years after a fire but This thrasher is found in desert riparian and desert does not reach peak abundance until after 20 years. Thus, wash habitats where dense thickets of shrubs or low trees an isolated population could be eliminated unless screen the ground (Grinnell and Miller 1944). recolonized from another site. Characteristic shrubs include mesquite (Prosopis sp.), California thrashers may persist in developed areas desert ironwood (Olneya tesota), catclaw acacia (Acacia where some nativevegetation is retained or where dense, greggii), willows (Salix sp.), sagebrush (Artemisia sp.) non-native shrubbery compensates, to some extent, for (Grimell and Mdler 1944), and thickets of the exotic the loss of larger tracts of suitable habitat (Grimell and salt-cedar (Tamarix sp.) where mixed with mesquite Miller 1944, W.F. Laudenslayer, pers. obs.). The birds (Hunter et al. 1988). Soils tend to be of loose or also do not show any 'aversion to lawns and other open (Grimell and Miller 1944). spaces' adjacent to dense shrubs (Woods writing in Bent In California away from the Colorado River, Crissal 1948:407). Thus, developed areas adjacent to isolated 'thrasher is restricted to small patches of habitat often fragments of native habitat could become more suitable isolated from other suitable habitat such as washes for the species as landscaping matures. within pinyon-juniper woodlands (e.g., Clark Mountain in the eastern Mojave Desert). Large portions of suitable habitat in the lower Colorado River Valley have been Le Conte's Thrasher converted to agriculture. Livestock grazing and off- This thrasher is widespread in the Mojave and highway vehicle use may present problems to this ,' Colorado deserts but in the San Joaqyn Valley is now but evidence is lacking. restricted to only a small portion of its former range (Figure I). In the deserts, it is found in open desert scrub, Bendire's Thrasher alkali desert scrub, and desert succulent shrub, as as This thrasher breeds in habitats generally described Jo~huatree (Yucca brevifolia) dominated habitats as flat desert floor with clumps of cholla (Opuntia sp.) or (Sheppard 1970). Ih the San Joaquin Valley, it is found yucca (Yucca sp.) (Grinnell and Miller 1944). In primarily in habitats dominated by saltbush (Atriplex California, it is typically found in Mojave desert scrub 24 Toxostoma Thrashers Laudenslayer et al. TRANS. WEST. SECT. WILDL. SOC. 28: 1992

/ LEGEND C<--7 Saltbrush Distribution - 1937 MERCED ....." ..:..:,: .. Known Occupied Habitat - 1992

Fig. 1. Presumed historic (1937) Le Conte's thrasher habitat, based on the distribution of saltbush (Afriplex polycarpa) (Piemeisel and Lawson 1937), and known occupied Le Conte's thrasher habitat (1992) in the San Joaquin Valley (S. Fitton and L. Saslaw, unpublished data) TRANS. WEST. SECT. WILDL. SOC. 28: 1992 Toxostoma Thrashers Laudenslayer et al. 25 with a considerable ground cover of grasses and other 1983 above) and the Palos Ver&s Peninsula, annuals, and a variety of understory shrubs generally County, Calif. (Garrett and Dunn 1981). However, the associated with Joshua Trees. These shrubs include latter record may indicatea remnant breeding population, Spanish Bayonet (Yucca baccata), Mojave Yucca (Y. possibly extirpated, rather than a wandering bird (K.L. schidigera), various species of cholla (Opuntia Garrett, pers. comm). Historically, this thrasher was acanthocarpa, 0. echinocarpa, or 0. ramosissima) or found in the (W. Anderson, pers. cornrn.) other succulents, or junipers (Juniperus sp.) (England but they are no longer found there and may be unable to and Laudenslayer 1989). recolonize from nearby populations (Anderson 1983). In California, Bendire's thrasher is restricted to The species has not been recorded from the Channel disjunct locationswell isolatedfrom one another (England Islands even though extensive suitable habitat exists and Laudenslayer 1989). Historically, the perceived (Garrett andDunn 198 1). It has not been recorded on the threats within the California breeding range have included , where all the migratory members of the mining, yucca harvest, and livestock grazing. Mining family Mimidae [northern (Mimus continues today, but yucca harvesting, relatively common polyglottos), gray catbird (Dumetella carolinensis), in the 1970s, now appears to be very limited. The total (Toxostoma rufum), Bendire's thrasher, number of acres where yuccas have been removed for all and sage thrasher (Oreoscoptes montanus)] have been purposes in the last 10 years lies somewhere between reported (DeSante and Ainley 1980,Pyle and Henderson 2,000 to 4,000 acres (K. McMullan pers. comm.). 1991). Livestock use, at current levels, does not appear to be California thrashers also are generally not found on causing declines in thrasher numbers (Boyer and the deserts away from their :limited breeding localities' Wessman 1980). (Garrett and Dunn 1981:282). Beedy and Granholm (1985) indicate that California thrashers are residents of DISTRIBUTION AND MOVEMENT PATTERNS the foothillsand never migrate into the higher mountains. Highly vagile species are easily capable of long Vagrant California thrashers have not been reported distance movements across areas of unsuitable habitat. from the lower Colorado River Valley (Rosenberg et al. Species with low vagility may not cross even a short gap 1991),Arizona (Monson andPhillips 198l),Utah (Behle to another visible patch of suitable habitat. A tendency andPerry 1975,Hayward etal. 1976), or the Great Basin to not move across unsuitable habitat is a life history trait (Ryser 1985). Soul6 et al. (1988) indicate that these that makes it difEicult for recolonization to occur after a thrashers persist in large, isolated canyons, but are found disturbance has eliminated an isolated population. only in those small canyonsthathavebeen recently isolated, An examination of U.S. Fish and Wildlife Service suggesting that birds do not easily move between habitat records for the four species of Toxostoma thrasher under patches. Thus, the literature indicates that California study revealed that (1) few individuals have been banded thrashers are quite sedentary and their capacity to move and (2) all recoveries have been in the same 10-minute even relatively short distances is extremely limited. block where the individual was originally banded. This latter observation suggests that California, LeConte's, Le Conte's Thrasher and Crissal thrashers may have weak dispersal abilities; This thrasher is considered resident (Merriam 1895, Bendire's thrasher is a migratory species. The following Engels 1940, AOU 1957, 1983), and Sheppard (1970) discussion briefly summarizesother existing information reports that it is very territorial through much of the year. on the movement patterns of these species. In California, it occurs in two disjunct geographic areas. Outside the Mojave and Colorado Deserts, it is found in California Thrasher the southern San Joaquin Valley of Kern County, and in Th~sspecies is considered resident (AOU 1957, and on the Carrizo of San Luis 1983), 'quite sedentary' (Garrett and Dunn 1981:282), Obispo and Santa Barbara Counties. Birds have also and nonmigratory (Engels 1940), although McCaskie et recently been found in the vicinity of Avenal, Kings al. (1979) state that they wander locally in winter. County (Morlan and Erickson l988), and elsewhere in California thrashers are generally found in California the Kettleman Hills, Fresno County (Yee et al. 1990, S. north toHumboldt, Shasta, and Sisltiyoucountieswest of Fitton and L. Saslaw, unpublished data). On the deserts, the Cascades-Sierra Nevada axis and the deserts, and in east of the Sierra Nevada, the range of the species extends northwestern Baja California. They are casual in north to Mono and Inyo counties, southern Nevada, southwestern Oregon around Medford (AOU 1983573). southwestern Utah, and western and south-central Extralimital. records are known f~omMedford, Arizona south to northeastern Baja California and Oregon (Roberson 1980) (but see informationfrom AOU northwestern Sonora; and in westcentral Baja California 26 Toxostorna Thrashers . Laudenslayer et al. TRANS. WEST. SECT. WILDL. SOC. 28: 1992

Table 1. Average counts of birds from 10-minute point Table 2. Spring densities @airs/ 40 ha) of thrashers and counts in chamise chaparral, Glenn County, California other common species in the Mojave and Colorado (1983-1985, A.S. England, unpub. data) deserts of southern California (based on breeding bird surveys published in AmericanBirds in 1977 and 1978). Time Since Last Burn , and Species Sample Size Mean 2 SE Plot Type and Species Mean 2 SE

Less than 5 years Plots with Bendire's thrasher (n=6) Wrentit 54 1.27 + 0.20 Ash-throated flycatcher California thrasher 54 0.20 + 0.06 Bendire's thrasher Sage sparrow 54 2.67 t 0.29 Black-throated sparrow Cactus wren Greater than 20 years Gambel's quail Wrentit 20 3.05 + 0.24 Mourning dove California thrasher 20 0.67 + 0.10 Sage sparrow 20 0.76 t 0.17 Plots with Crissal thrasher (n=9) Ash-throated flycatcher Black-tailed gnatcatcher (AOU 1983573). Le Conte's thrasher is possibly a Crissal thrasher resident ortransient along the edge of thelower Colorado Gambel's quail River Valley, but therearevery few records from localities House finch within the floodplain (Rosenberg et al. 1991). In Mourning dove California, Garrett and Dunn (1981) note that this Verdin thrasher has been found 'near Niland andBardl,Imperial White-winged dove County, 'which suggests at least a slight movement away from thebreeding localities,' and near Moreno, Riverside Plots with Le Conte's thrasher (n=12) County, which is 'clearly extralimital' (Garrett andDunn Ash-throated flycatcher 9.85 + 2.89 1981:282-283), but only a few miles west of known Black-tailed gnatcatcher 9.32 3.00 breeding localities in San Gorgonio Pass near Banning. Black-throated sparrow 5.00 + 1.54 In Arizona, 'a specimen from Union Pass between Gambel's quail 19.75 & 11.01 Kingman and Davis Dam may have been a vagrant or House finch 7.08 3- 3.48 migrant' (Monson and Philips 1981: 124). Le Conte's Le Conte's thrasher 3.87 + 1.60 thrashers have not been recorded from .the Farallon Mourning dove 26.48 1 11.84 Islands (DeSante and Ainley 1980, file and Henderson Verdin 12.56 + 4.07 1991), Northern California (McCaskie et al. 1979), the GreatBasin(Ryser 1985), (Arnold 1984), Oregon, or Washington (Roberson 1980). Le Conte's thrashers summer and winter and a migrant exhibiting fall and are generally resident, and the existing data suggest they spring movements, with post-nesting birds wandering do not regularly move long distances. into adjacent lowlands. There is a record Erom Furnace Creek Ranch (McCaskie 1988) and a fall record from Crissal Thrasher DeathValley Junction (Garrett and Dunn 198 1) but the This species is considered resident (AOU 1957, authors do not indicate if the latter bird was a fall 1983, Bradley andDeacon 1967, Rosenberg 1991). It is migrant, a juvenile, or if breeding habitat is nearby. No primarily sedentary,but some populations exhibit seasonal Crissal thrashers have been recorded from the Farallon elevational movements (Engels 1940), and there is local Islands (DeSante and Ainley 1980, ble and Henderson movement between habitats (Bradley and Deacon 1967, 1991); the Great Basin (Ryser 1985), althoughBehle and Rosenberg et al. 1991). In Arizona, these thrashers are Perry (1975) reported these thrashers as uncommon considered fall migrants ,(Monson and Phillips 1981), residents in southwestern Utah, as in Oregon and and the species is morehientif~lin the Verde Valley, Washington (Roberson 1980). Crissal thrashers generally Arizona, in winter than in summer (Mearns 1886). appear to be resident, but do exhibit a regular pattern of Wauer (1973) reports that the species is a resident in seasonal movements by some portion of the population. TRANS. WEST. SECT. WILDL. SOC. 28: 1992 Toxostomo Thrashers . Laudenslayer et al. 27

Bendire's Thrasher POTENTIAL FOR LOCAL EXTIRPATIONS OR This speciesis the only migratory Toxostomathrasher ENDANGERMENT that breeds in California. It is known to breed from California Thrasher southeastern California, northwesternArizona, southern This species has a wide distribution, threats are Nevada, southern Utah, southeastern Colorado, and relatively localized, and birds have a limited ability to use westernand central New Mexico, south to central Sonora. residential edges. Therefore, extinction of the species is Birds winter from southern Arizona and southwestern unlikely for the forseeable future. Because the species New Mexico south through Sonora to southern Sinaloa. occurs at low densities and has low vagility, it is Casual wintering birds are found north to central susceptable to localized extirpation resulting from Californiaand north-central Utah (AOU 1957,1983). In population declines after habitat fragmentation. This California,breeding Bendire's thrashers occur in isolated impact has already been reported fiom southern California populations (see figure 3 in England and Laudenslayer by SoulCet al. (1988), but shouldalsobe expectedin other 1989). These thrashers are capable of extensive expanding urban zones such as the Sierra Nevada movement, having been recorded on the Farallon Islands foothills and the San Francisco Bay Region. Additional five times (Pyle and Henderson 1991), as a vagrant in information is needed on dispersal ability to determine northern Utah (Behle and Perry 1975), as a rare and whether developments such as major freeways or losses irregular visitor in winter and spring in the lower Colorado of riparian corridors might be effective barriers to River Valley (Rosenberg et al. 1991); and numerous movement. times, mainly in the fall, in coastal southern California (K.L. Garrett, pers. comm.). Bendire's thrasher is a Le Conte's Thrasher relatively strong flier and capable of negotiating long For the same reasons as described for the California distances in its migration. Thus, difficulties in invading thrasher, extinction of this species is unlikely in the or reinvading suitable habitat are more likely to be forseeablefuture. Because of low vagility, susceptability related to the probability of finding suitable habitat than to habitat fragmention, and habitat changes previously to the capability of flying to such areas. described, the amount ofmitable habitat in the San Joaquin valley has been greatly reduced, and localized THRASHER DENSITIES extirpation and isolation of subpopulations are likely to . Considerable recent evidence from studies in continue. Similarly,populations in the Antelope, Mojave conservation biology and island biogeography suggest River, and Coachella Valleys have probably suffered that species occurring at relatively low densities are similar, undocumented declines. Additional data on among the first to be locally extrpated after fragmentation distribution, habitat distribution, habitat preferences, (e.g., Pimmet a]. 1988, SoulC et al. 1988). Thrashers are and dispersal ability of desert populations is needed generally found at low numbers relative to other bird before the potential for fragmentation effects in the species inhabiting similar vegetation. In charnise deserts can be evaluated. chaparral (Table I), mean California thrasher counts were 5-6 times lower than counts for wrentits (Chamaea Crissal Thrasher fasciala) and over 10 times lower than sage sparrows This bird is widely distributed in the Southwest and (Amphispiza belli) in prime habitat for that species. appears to be capable of more movement than either of Bendire's, Crissal, andLe Conte's thrashers also occurred the species previously discussed. The risk of extinction at low densities relative to other common birds breeding of the species in California appears low. However, on the same plots in the Mojave and Colorado deserts of because it is found in small, isolated patches of habitat, southern California (Table 2). Le Conte's thrasher localized extinctions could easily occur. densiees from near Maricopa in the San Joaquin Valley were 10 pairs per square mile (1.54 pairs140 ha) (Sheppard Bendire's Thrasher 1970). These sites are thought to be areas of 'very high Bendire's thrashers are capable of long-&stance density' because, in most of the species' range, densities movements and reestablishment should local extirpations usually range from 0 to 5 pairs per square mile (0-0.77 occur. This species occurs over an extensive range and, pairs140 ha)(Sheppard 197036). SiriceSheppard'swork because of their ability to move across distances, the risk in the late 1960s, densities in the San Joaquin have of extirpation in California is extremely low, and the risk declined except in a few core areas (S. Fitton and L. of localized extinctions persisting through time is not Saslaw, unpublished data). expected to be high as long as the habitat is intact. 28 Toxostoma Thrashers . Laudenslayer et al. TRANS. WEST. SECT. WILDL. SOC. 28: 1992

CONCLUSIONS Beedy, E.C., and S.L. Granholm. 1985. Discovering One of the tenets of modern conservation biology is Sierra birds. Yosemite Natural History Association the sound management and preservation of genetic and Sequoia Natural History Association, Yosemite diversity. Implementing this principle requires looking National Park, Calif. 229pp. beyondthe level of speciesto subspecies and populations. Behle, W.H., and M.L. Perry. 1975. Utah birds: check- Taxa that are endemic to an area, especially of relatively list, seasonal and ecological occurrence charts and small geographic extent, may also be subjected to higher guides to bird finding. Utah Natural History Mu- probabilitiesof extinction. Many birds found in California seum Publ., Univ. of Utah, Salt City. 143pp. and adjacent areas of Baja California exhibit a high Bent, A.C. 1948. Life histories of North American degree of endemism. A review of the Subfamily nuthatches, wrens, thrashers, and their allies. U. S. Emberizinae (AOU 1957 and 1983) indicates that of the National Museum Bulletin 195. 475pp. 20 species of towhees and sparrows that breed in the Biswell, H.H. 1989. Prescribed Burning in California state, 10 (50 percent) have at least 1 endemic subspecies. Wildlands Vegetation Management. University of Of the 60 subspecies that breed in California, 31 (52 California Press, Berkeley and Los Angeles. 255pp. percent) are endemic and represent 2 1percent ofthe total Boyer, K.B.,and E.V. Wessman. 1980. Comparison of number described for North America. This high degree small vertebrate populations on the grazing lands of of endemism reflects a high degree of genetic the Eastern Mojave Desert, California. U. S. Bureau differentiation which may be related to low vagility. of Land Management, California Desert Plan Pro- Even less is known about the detailed distribution and gram, Riverside, Calif. Final Report. 110 pp. movement patterns of subspecies than is known about Bradley, W.G., and J.E. Deacon. 1967. The biotic species. communities of southern Nevada. Nevada State A systematic review, survey, and monitoring of the Museum Anthropological Paper No. 13, part 4. California avifauna is needed to further identify the laxa 295pp. with distributions, habitat requirements, life history CDFG. 1991. Bird and Mammal Species of Special characteristics, and potential threats that make them Concern. (May 1990). California Department of susceptible to endangerment. This program needs to be Fish and Game, Nongame Bird and Mammal Divi- implemented quickly to preserve options as the human sion, Sacramento, Calif. 2pp. population of the state and areas necessary to support it CDFFP. 1988. California's Forests and Rangelands: grow. Growing Conflict over Changing Uses. California Department of Forestry and Fire Protection, Forest ACKNOWLEDGEMENTS and Rangeland Resources Assessment Program, DonaldH. Behrens, DavidL. Connell, Diana Craig, Sacramento, Calif. 348pp. + appendices. and Henry Hansen reviewed an early version of this DeSante, D.F., and D.G. Ainley. 1980. The avifauna of paper and their comments greatly improved the the South Farallon Islands, California. Studies in manuscript. We also appreciate the reviews of Kimball Avian Biology No. 4. 104pp. L. Garrett, Tim Manolis, Garland Mason, and Michael England, A.S., and W.F. Laudenslayer, Jr. 1989. Dis- A. Patten for their insightful comments and tribution and seasonal movements of Bendire's recommendations on an earlier version of the manuscript. Thrasher in California. Western Birds 20:97-123. Finally, we thank Charlie Price for his work on the Engels, W.L. 1940. Structural adaptations in thrashers figure. (Mimidae: genus Toxostoma) with comments on interspecific relationships. University of California LITERATURE CITED Publications in Zoology 42:341-400. AOU. 1957. Check-list of North American birds. 5th Garrett, K., and J. Dunn. 1981. Birds of Southern edition. American Ornithologists' Union, Balti- California: Status and distribution. Los Angeles more, Md. 691pp. Audubon Society, Los Angeles. 408pp. . 1983. Check-list of North American birds 6th Grinnell, J. 19 17. The niche-relationships of&e Califor- edition. American Ornithologists' Union, Wash- nia Thrasher. Auk 34:427-433. ington, D.C. 877pp?' ,and A.H. Miller. 1944. The distribution of the Anderson, W. 1983. The Sutter Buttes: a naturalist's birds of California. Pacific Coast Avifauna 27. view. The Natural Selection, Chico, Calif. 326pp. Hayward, C.L., C. Cottam, A.M. Woodbury, and H.H. Arnold, K.A. ed. 1984. Checklist of the Birds of Texas. Frost. 1976. Birds of Utah. Great Basin Naturalist 2nd edition. Texas Ornithological Society, Austin. Memoir No. 1. 147~~ TRANS. WEST. SECT. WILDL. SOC. 28: 1992' Toxostoma Thrashers . Laudenslayer et al. 29

Hunter, W.C., RD. Ohmart, andB.W. Anderson. 1988. Pimm, S.L., H.L. Jones, and J. Diamond. 1988. On the Use of exotic saltcedar (Tamarix chinensis)by birds risk of extinction.American Naturalist 132:757- in arid riparian systems. Condor 90: 113-123. 785. McCaskie, G. 1988. Southern Pacific Coast Region. Pyle, P., and R.P. Henderson. 1991. The birds of American ~irds40:482. SoutheastFarallon Island: Occurrence and seasonal , P. DeBenedictis, R Erickson, and J. Morlan. distribution of migratory species. Western Birds 1979. Birds of Northern California: an annotated 22:4 1-84. field list. Golden Gate Audubon Society, Berkeley, Roberson, D. 1980. Rare birds of the West Coast. Wood- Calif. 84pp. cock Publications, Pacific Grove, CA. 496pp. Mearns, E.A. 1886. Somebirdsof Arizona. Auk 3:289- Rosenberg,K.V.,R.D. Ohmart, W.C. Hunter,andB.W. 307. Anderson. 1991. Birds of the Lower Colorado River Merriam, C.H. 1895. The LeConte Thrasher, Valley. University ofArizonaPress, Tucson. 4 16pp. Harporhynchus lecontei. Auk 12%-60. Ryser, F.A., Jr. 1985. Birdsofthe Great Basin: anatural Monson, G. and A.R. Phillips. 1981. Annotated check- history. University of Nevada Press, Reno. 604pp. list of the birds of Arizona. University of Arizona Sheppard, J. 1970. A study of the LeConte's Thrasher. Press, Tucson. 240pp. California Birds 1:85-94. Moriarty, D.J., RE. Farris, D.K Noda, and P.A Stanton. SoulC, M.E., D.T. Bolger, A.C. Alberts, J. Wright, M. 1985. Effects of fire on a coastal sage scrub bird Sorice, and S. Hill. 1988. Reconstructed dynamics community. The Southwestern Naturalist 30:452- of rapid extinctions of chaparral-requiring birds in 453. urban habitat islands. Conservation Biology 2:75- Morlan, J., and R. Erickson. 1988. Supplement to the 92. Birds of Northern California. Pages 85-97 in Wagner, F.H. 1978. Livestock grazing and the livestock McCaskie, G., P. DeBenedictis, R. Erickson, and J. industry. Pages 121-145 in H.P. Brokaw, ed. Wild- Morlan. Birds ofNorthern California: an annotated life and America: Contributions to an Understand- field list. Golden Gate Audubon Society, Berkeley, ing of American Wildlife and its Conservation. Calif. 97pp. Council on Environmental Quality, Washington, Piemeisel, RL., and F.R. Lawson. 1937. Types of D.C. 532pp. vegetation in the San Joaquin Valley of California Wauer, R.H. 1973. Birds ofBig Bend National Park and and their relation to the beet leafhopper. U.S. vicinity. University of Texas Press, Austin. 223pp. Department AgricultureTechnicalBulletinNo. 557. Yee, D.G., B.E. Deuel, and S.F. Bailey. 1990. Middle 28~~. Pacific Coast Region. American Birds 44:493.