Distribution and Seasonal Movements of Bendire's Thrasher in California

Home , Chemehuevi Wash, Deserts of California, Lanfair Valley, Piute Mountains, Ward Valley (California)

WESTERN BIRDS

Volume 20, Number 3, 1989

DISTRIBUTION AND SEASONAL MOVEMENTS OF BENDIRE'S THRASHER IN CALIFORNIA

A. SIDNEY ENGLAND, Departmentof Wildlifeand FisheriesBiology, University of California, Davis. California 95616 WILLIAM E LAUDENSLAYER,JR., U.S. D. A. ForestService, Forestry Sciences Laboratory,2081 E. SierraAvenue, Fresno, California 93710

The ecology and distribution of Bendire's Thrasher (Toxostorna bendirei)have been little studiedand are poorlyunderstood. Garrett and Dunn (1981:280) classifiedthe speciesas a "fairlycommon but very local summer resident on the Mojave Desert" in southern California. Californiabreeding populations are known primarily from the eastern Mojave Desert and scattered locations in and around Joshua Tree NationalMonument in the southernMojave Desert (Johnson et al. 1948, Miller and Stebbins1964, Garrett and Dunn 1981), areas frequently visitedby bird watchersand naturalists. However, recordsfrom other parts of the Mojave and Colorado deserts suggest that breeding populationsof Bendire'sThrasher may be more widely distributedthan currentlyrecognized. Also, the preferredbreeding habitat in Californiais relativelywidespread. This habitatis typicallydescribed as Mojavedesert scrubwith either JoshuaTrees (Yucca brevifolia), SpanishBayonet (Y. baccata), Mojave Yucca (Y. schidigera), cholla cactus (Opuntia acanthocarpa,O. echinocarpa,or O. rarnosissirna),or other succulents (Grinnelland Miller 1944, Bent 1948, Garrett and Dunn 1981). Remsen(1978) consideredthe total Californiabreeding population of Bendire'sThrasher to be under 200 pairs, and the specieshas been placedon the list of Bird Speciesof SpecialConcern by the California Departmentof Fishand Game (Remsen1978). It was placedon this list becausepopulations are smalland locallydistributed and believedto be threatenedby off-roadvehicle use, overgrazing,and harvestingof Joshua Treesand other speciesof yucca. In this paper, we report the resultsof a 2-year studyof the breedingseason distributionand movement patterns of Bendire's Thrasher in California. Our findingsare basedon a reviewof historicalrecords and field surveysdesigned to (1) documentmore accuratelythe extent of Western Birds 20: 97-123. 1989 97 BENDIRE'S THRASHER IN CALIFORNIA known breedingpopulations in the easternand southernMojave Desert, (2) reinvestigatethe presenceof breedingpopulations at sitessuggested by historical records, (3) locate previously undocumented breeding locations,and (4) characterizeseasonal movement patterns in California.

METHODS

Review of Historical Records We compiled over 350 distributionrecords of Bendire's Thrashers from four primary sources: (1) Middle and Southern Pacific Coast regional reports in Audubon Field Notes/American Birds, volumes 1-42, (2) VertebrateSpecies Distribution Data and museumrecords on file with the California Desert District Office of the Bureau of Land Management (BLM), Riverside, (3) published scientific literature on Bendire'sThrasher, and (4) field notes of severalornithologists including ourselves. BLM data were gathered by employees and contractors working on the California Desert Plan Program between 1975 and 1979, and most of these observationshave never been published. These BLM recordsalso includedata transcribedfrom labelson specimensand egg sets in major ornithologicalcollections in California. We have not personallyexamined documentation for most publishedand unpublished recordsand some could be erroneous. However, most are by reliable observersand have previously been accepted by regional editors of American Birds, Garrett and Dunn (1981), or peer-reviewedjournals, and fit within patternsfor the species. Breeding-SeasonSurvey Techniques We established44 transectsalong existing roads during 1986 and 1987 (Figure1); 23 transectswere surveyedboth yearsof our field study, and the other 21 transectswere surveyedonly one year (seeAppendix). The location and distributionof our transectswere designedto maximize coverage of areas we considered to represent potentially suitable breedinghabitat. We concentratedour effortsin relativelydiverse plant communities dominated by Joshua Trees, Mojave Yucca, Spanish Bayonet, and cholla cactus. We conductedonly a few surveysat lower elevations where breeding Bendire's Thrashers would be extremely unlikely. Detailed maps and descriptionsof each transectare on file with the CaliforniaDepartment of Fish and Game, Sacramento. Individualtransect surveys were conductedon days with wind <15.0 km/hr, began approximately one-half hour after sunrise, and usually continueduntil mid-afternoon. We coveredour routesby vehicle,with stopsat 0.4- to 4.8-km intervals. Within a transect,the distancebetween stops was variable and depended on vegetation characteristics,local topography, and whether we detected Bendire's Thrashers at nearby stops. Samplepoints were placedcloser together in apparentlysuitable habitatwith JoshuaTrees, yuccas, and chollaand in areasnot previously known to support Bendire's Thrashers. Such adjustments allowed extensivecoverage of large areas.

98 BENDIRE'S THRASHER IN CALIFORNIA

At eachstop, we recordedtime and weatherconditions, and noted dominantplants, presence or absenceof washvegetation, and types of humandisturbance. The locationof the pointwas marked on a U.S. GeologicalSurvey topographic map (scale 1:24,000 or 1:62,500),and

NORTHERN

Tecop••

EASTERN

WESTERN '"'- xX,• • ,ma •o • ',, J

ß ß RH•__•///I .." ...... '. CENTRAL I SB Viet,or ville ST

LosAngeles Joshua Tree Natlona) Monument

o ©Blythe

Borrego$1ale Park , 40km ,

Figure1. Locationsof Bendire'sThrasher transects surveyed in 1986 or 1987. Transectsare identified with two-letter initials that correspond to abbreviations in Table5. Solidline, the Mojave-ColoradoDesert boundary; dashed lines, subdivisionsof the MojaveDesert.

99 BENDIRE'S THRASHER IN CALIFORNIA

Table 1 Historical Breeding-Season (mid-March through July) Observations and Specimen Records of Bendire's Thrashers in the Mojaveand Colorado Desertsa, t•

Date Locality Number Referencec

EasternMojave Desert c/ 24 Mar 1976 Granite Mtns., SB 1 JVR (AB 30:892, 1976) 11 Apr 1977 Wash on S side I pair SWC (BLM) Granite Pass, SB 11 Apr 1977 CottonwoodWash, 1 adult SWC (BLM) Granite Mtns., SB 22 Apr 1977 CottonwoodWash, 1 adult SWC (BLM) Granite Mtns., SB 24 Apr 1978 CottonwoodWash, 2 KJ fide SWC Granite Mtns., SB (pers.comm.) 16 May 1976 ShadowValley, SB 1 JVR (BLM) 24 May 1975 Salt Creek, 25.0 mi. 1 SWC (pers. N Baker, SB comm.) 29 May 1978 PowerlineRd. 1+1 singingmale PM (pers.comm.) N of Clark Mtn., SB EarlyJune Near Clark Mtn., SB 1 GMc (AFN16:448, 1962) 14 Jun 1976 Granite Pass,SB 1 adultw/food Cardiff (BLM) 14 Jun 1976 Granite Pass, SB 1 adult Cardiff (BLM) 11 Jul 1977 Halloran Summit, SB 1 adult SWC (BLM) SouthernMojave Desert Apr 1974 AroundYucca Valley, SB 2 pairs ASm, GSS (AB 28:950, 1974) 13 Apr 1974 SaltonView, JTNM, RIV 1 singingmale JM (AB 28:950, 1974) May 1896 Warren'sWell, fairlycommon Heller (1901) YuccaValley, SB May 1975 JTNM, RIV 2 USFWS BBS May 1984 Near Pioneertown,SB I TMe (pets. comm.) 7 May 1916 Near Victorville,SB I adultmale MVZ 54556; Pierce (1919) 10 May 1981 Near CottonwoodSpring, 2 RMc (pets. JTNM, RIV comm.) 13 May 1973 Near CottonwoodSpring, 1 AB 27:821, JTNM, RIV 1973 22 May 1969 Near Victorville 1 w/food GSS (AFN 23:627, (StoddardMtn.), SB 1969) 25 Mar 1978 JTNM, RIV 1 DZ (AB 32:1056, 1977) 6 Jun 1981 Near Pioneertown, SB 1 EAC (AB 35:979, 1981) Jun-Jul 1975 Near YuccaValley, SB 6 FH (AB 29:1034, 1975) 8 Jul 1986 Near LucerneValley, SB 3 RMc (AB 40:1256, 1986)

lOO BENDIRE'S THRASHER IN CALIFORNIA

Table 1 (Continued)

Date Locality Number Referencec

CentralMojave Desert 1 Apr-20 SuperiorValley N of 5 singing ASE May 1981 Barstow,SB males Western Mojave Desert 4 Apr 1981 CaliforniaCity, KE 1 GWP (AB 35:864, 1981) 7 Apr 1979 Near Lancaster,LA 1 singing JD (pers.comm.; male AB 33:806, 1979) 18 Jun 1982 KelsoValley, KE 1 singing BrE (AB 36:1017, male 1982) Northern Mojave Desert 23 May 1970 OasisRanch, 1 GMc (AB 24:645, FishLake Valley,MON 1970) 23 May 1977 MesquiteSprings, 1 GMc (AB 31:1048, DVNM, INY 1977) 28 May 1977 FurnaceCreek Ranch, 1 KG (AB 31:1048, DVNM, INY 1977) 1 Jun 1974 StovepipeWells, 1 JVR (AB 28:853, DVNM, INY 1974) Colorado Desert 14 Mar 1952 Hwy. 95 8.0 mi. 1 GMo (pers.comm.) N Vidal Jct., SB 19 Mar 1953 Lake HavasuRd. 1 GMo (pers.comm.) 5.0 mi. E Hwy. 95, SB 19 Mar 1983 Palm Spring,SD 1 EAC (AB 37:913 1983) 31 Mar 1953 Hwy. 95 8.0 mi. 1 GMo (pers.comm.) N Vidal Jct., SB 8 Apr 1885 PalmSprings, RIV 1 Stephens(1919) 16 Apr 1980 Mouthof Whitewater 1 RMc (AB 34:816, Canyon, RIV 1980) 18 Apr 1950 BetweenVidal Jct. and 2 GMo (pers.comm.) Lake Havasu Rd., SB 25 Apr 1974 Near Twentynine 2 pairs GLB (AB 28:950, Palms,SB 1974) 26 Apr 1952 BetweenVidal Jct. and 1 GMo (pers.comm.) Lake HavasuRd., SB 27 Apr 1951 BetweenVidal Jct. and 2 GMo (pers.comm.) Lake Havasu Rd., SB 30 Apr 1972 BrockRanch, IMP 1 singing AB 26:812, 1972 male 6 May 1980 ChollaGarden, 2 RMc (pers.comm.) JTNM, RIV 7 May 1984 W of Dale Dry Lake, SB 1 RMc (pers.comm.) 7 May 1984 ClarksPass E of 2 RMc (pers.comm.) 29 Palms, SB 9 May 1947 Hwy. 95 <8.0 mi. S of 1 GMo (pers.comm.) Lake Havasu Rd., SB

lol BENDIRE'S THRASHER IN CALIFORNIA

(Continued)

Date Locality Number Referencec

12 May 1984 TwentyninePalms, SB 1 RMc (pers.comm.) 17 May 1951 Hwy. 62 E of 1 GMo (pers.comm.) Vidal Jct., SB 22 May 1897 Whitewater,R1V 1 EH (Grinnell1915) 22 May 1951 BetweenVidal Jct. and 1 GMo (pers.comm.) Lake Havasu Rd., SB 23 May- PintoBasin, JTNM, RIV 2 RMc (pers.comm.) 8 Jun 1985 28 May 1950 Hwy. 62 betweenEarp 1 GMo(pers. comm.) and Vidal Jct., RIV 29 May 1949 Hwy. 95 <8.0 mi. S of 1 GMo(pers. comm.) Lake Havasu Rd., SB 30 May 1950 Hwy. 95 at Lobeck's 1 GMo(pers. comm.) Pass, Sawtooth Mtn., SB 1 Jun 1948 Hwy. 95 <8.0 mi. S of 1 GMo(pers. comm.) Lake Havasu Rd., SB 2 Jun 1950 BetweenVidal Jct. and 2+ GMo(pers. comm.) Lake Havasu Rd., SB 11 Jun 1947 Hwy. 95 S of 2 GMo (pers.comm.) ChemehueviWash, SB 19 Jun 1951 BetweenVidal Jct. and 1 GMo(pers. comm.) Lake HavasuRd., SB 19 Jun 1963 NearNeedles, SB 5 RS, AW (AFN 18:536, 1964) 25 Jun1951 BetweenVidal Jct. and 1 GMo(pers. comm.) Lake HavasuRd., SB aExcludesapproximately 200records from area previously recognized asthe primary range of Bendire'sThrasher in theeastern Mojave Desert (Figure 3). bAbbreviations:Localities--DVNM, DeathValley National Monument; IMP,Imperial Co.; INY, InyoCo.; JTNM, Joshua Tree National Monument; KE, KernCo.; LA, LosAngeles Co.; MON, MonoCo.; RIV, RiversideCo.; SB, SanBernardino Co. References--ASE,A. SidneyEngland; ASm, Arnold Small; AW, Art Wang;BBS, Breeding Bird Survey; BLM, Bureauof LandManagement; BrE, Brett Engstrom; DZ, DavidZumata; EAC, Eugene A. Cardiff;EH,-E. Heller; FH, FredHeath; GLB, Gordon L. Bolander;GMc, Guy McCaskie; GMo,Gale Monson; GSS, G. ShumwaySuffel; GWP, Gary W. Potter;JD, JonDunn; JM, JoeMorlan; JVR, J. V. Remsen;KG, KimballGarrett; K J, KentJohnson; MVZ, Museumof VertebrateZoology, Univ. Calif., Berkeley,; PM, PaulMack; RMc, Robert McKernan; RS, RichStallcup; SWC, Steven W. Cardiff;TMe, Tony Metcalf; USFWS, U.S. Fishand Wildlife Service. CReferencesto American Birds (AB) or AudubonField Notes (AFN) are not included in the Literature Cited. dSubdivisionsandboundaries ofthe Mojave and Colorado deserts areillustrated inFigures 1 and 3.

102 BENDIRE'S THRASHER IN CALIFORNIA the elevationwas interpolatedfrom the map. At each stop,we playeda taped recordingof a Bendire'sThrasher song to elicit responsesfrom nearbybirds. Eachplayback session was approximately5 minuteslong and consistedof 60 secondsof songfollowed by 60 secondsof silence, 30 secondsof song, 60 secondsof silence,30 secondsof song at low volume,and endedwith 60+ secondsof silence. Sheppard(1970) had found this playback protocol to be effective for locating LeConte's Thrashers (Toxostoma lecontei). During the playback session,we recordedthe number of individualsfor all speciesin the family Mimidae and whetherthe detectionwas visualor auditory. In 1986, we usedthe song playbacktechnique at 445 points on 38 transectsin the Mojave Desertand at 27 pointson four transectsin the ColoradoDesert. These data were collectedbetween 26 April and 4 May and between31 May and 8 June. In 1987, we conductedsurveys between 8 May and 23 May at 292 pointson 25 transectsin the Mojave Desert.

RESULTS AND DISCUSSION

BreedingPhenology The breedingschedule of Bendire'sThrashers in Californiais known primarilyfrom nestsand breedingpairs observed only once. Recordsof singingBendire's Thrashers indicate that territorialbehavior begins when birdsfirst returnto breedingareas beginning in mid-Marchand continues throughmid-June, by whichtime mostyoung from firstnests are fledged (Figure2). Presumedfirst clutcheshave been observedfrom late March throughthe end of April (Figure2). Nestlingsfrom first clutcheshave been recordedfrom early May throughearly June, and fledglingsleave the nestbetween late April and mid-June. The datesfor variousbreeding phenologymilestones are consistentwith observationsin Arizona(Brown 1901). The only breedingattempt in Californiaobserved repeatedly was one followed in Kelso Valley in the western Mojave Desert (R. Saval, pers. comm.; Table 2; Figure 2). The nest containedtwo chickson 13 June but was empty on 17 June, and an adult with a singlefledgling was observedon 22 June. On 3 July Saval discovereda secondnest with four eggswithin 100 m of the firstnest. On 19 Julytwo adultsand two nestlingswere observedat the secondnest. This record is the only evidenceof multiplebroods for California,but secondand even third nestingsare well known from Arizona (Brown 1901). For each stagein the nestingcycle for whichrecords exist, the earliest California observations are in the Colorado Desert and the latest are from the westernMojave Desert (Figure2). This pattern suggeststhat breedingbegins earlier in the southeastand progressesacross the desert to the northwest. However, the number of records in the Colorado Desert and the western Mojave Desert is inadequateto permit a firm statementthat thispattern is real, and the singlesinging male observedin Februaryin the Colorado Desert (Table 3; Figure 2) may have been a migrant.

103 BENDIRE'S THRASHER IN CALIFORNIA

Only five nestswith eggshave been foundin California. Three nests containedfour eggs each; the other recordsdid not report clutch size. Brown (1901) indicatedthat in Arizona most clutcheshave 3 eggs,4-egg clutchesare the typicalupper limit, but 5-eggclutches are known. Breeding-SeasonDistribution in the Desertsof California Our analysisof the breeding-seasondistribution of Bendire'sThrasher in California is presentedbelow for five geographicalsubdivisions of the Mojave Desert and for the Colorado Desert. The boundariesbetween theseregions are shownin Figure 1. Eastern Mojave Desert. The best-knownand largestbreeding area for Bendire'sThrasher in California has been the eastern Mojave Desert (Table 2; Figure 3). The existence of this population was first

2O ß Eastern,southern, and 18- central Mojave Desert 16- -• [] WesternMojaveDesert 14- [] ColoradoDesert 12- 10- SingingMales

O • 4 •- 2

r'• 0 I ' ' I ' ' ' ' I ' ' I ' ' ' ' I ' ' ' I ' ' ' O ',"-' 2 O Eggsin Nest 2.dC,,,tch\ Ill II 0ß I ' ' I ' ' ' ' I ' ' ' I 1 ' ' ' I ' ' 1= [ ' I I

• 2 z 0 • NestlingsI ' ' I ' ' ' ' i ' ' ' I ' ' ' ' li• ' ' ' I ' '=-:- ' 8

6 Fledglings 4

0 i i i i i i i i i 8 15 22 1 8 15 22 29 5 12 19 26 3 10 17 24 31 7 14 21 28 5 12 19 26

FEB MAR APR MAY JUN JUL

Week Beginning

Figure2. Breedingphenology of Bendire'sThrashers in the desertsof California based on historical records.

104 BENDIRE'S THRASHER IN CALIFORNIA

Table 2 Confirmed Breeding Records of Bendire's Thrasher from California a

Date Locality Number Referenceb

EasternMojave Desertc 22 Apr- LanfairValley, SB 1 pair + SWC (pers. 28 May 1976 4 nesfiings comm.) 12-14 May SW edgeof 1 pair+4 SWC (BLM; AB 1978 LanfairValley, SB nestlings 33:94, 1979) 14 May 1938 2.0 mi. NNE of 2 juveniles Johnsonet al. Cima, SB (1948) 15 May 1938 2.0 mi. NNE of 1 pair + 4 Johnsonet al. Cima, SB juveniles (1948) 15 May 1987 13.0 mi. SE Ivanpah,SB 1 pair + BAC (NRC) 3 juveniles 26 May 1980 Cima Rd. 2.25 mi. 1 pair + BM, AS (pers. N 1-15, SB 4 nestlings comm.) 27 May 1972 Near Cima, SB adults+ SWC (BLM) juveniles 24 Apr- 2.5 mi. SE of Cima, SB 1 pair + F_AC(BLM; NRC) 29 May 1976 1 nestling 29 May 1976 5.5 mi. SSE of Cima, SB 1 pair + Cardiff(BLM) 4 juveniles 30 May 1976 6.0 mi. NW of Cima, SB 1 pair + Cardiff(BLM) 1 juvenile 30 May 1976 7.5 mi. SE of Cima, SB 1 pair+ Cardiff(BLM) 1 juvenile 3 Jun 1979 WatsonWash, SB 1 juvenile SWC. (pers comm.) 4 Jun 1979 LanfairValley, SB 1 adult+ SWC (pers. 4 juveniles comm.) 11 Jun 1978 LanfairValley, SB 1 pair + BAC, SJN (BLM; 2 juveniles AB 33:93, 1979) 12 Jun 1976 12.0 mi. SE of 4 nestlings SWC (NRC) Ivanpah,SB 12 Jun 1976 13.5 mi. N of Goffs, SB 2 pairs+ Cardiff(BLM) 1 juvenile 12 Jun 1976 13.25 mi. ESE of 1 pair + Cardiff(BLM) Cima, SB 2 juveniles 12 Jun 1976 13.25 mi. ESE of 1 juvenile Cardiff(BLM) Cima, SB 13 Jun 1976 10.0 mi. S of 1 pair + Cardiff(BLM) Mountain Pass,SB 1 juvenile SouthernMojave Desert 11 Apr 1920 Victorville,SB 4 eggs SBCM 5987; Pierce (1921) 26 Apr 1920 Victorville,SB 1 female+ Specimen; 3 juveniles Pierce(1921) 26 Apr 1975 1.0 mi. NW 1 pair + JAD (NRC) YuccaValley, SB 3 juveniles

105 BENDIRE'S THRASHER IN CALIFORNIA

Table 2 (Continued) Date Locality Number Reference

11 May 1987 2.5 mi. N Belle 1 pair + Campground, 1 juvenile AB 41: 1488, JTNM, SB 1987) 28 May 1974 HiddenValley 1 pair + RR (AB 28: Campground, 3 juveniles 950, 1974) JTNM, SB 1 Jun 1974 Ryan Mtn., JTNM, RIV 1 pair + RR (AB 28: 4 juveniles 950, 1974) Central Mojave Desert 12 May 1982 SuperiorValley N of 1 adult + ASE (AB 36: Barstow, SB 3 nestlings 1017, 1982) 3 Jun 1981 SuperiorValley N of 1 pair + ASE Barstow, SB 2 juveniles Western Mojave Desert 13 Jun- KelsoValley, KE 1st nest + RSa 19 (pers. Jul 1987 2 nestlings comm.;AB 41: 2nd nest + 1488, 1987) 4 eggs Colorado Desert 1 Apr 1920 TurtleMtns., SB Eggset SBCM 1632 5 May 1985 Corn Springs,RIV 1 adult+ 3 RMc (pers. juveniles comm.) 24 May 1953 Hwy. 95 12.0 mi. 3 juveniles GMo (pers. N Vidal Jct., SB comm.) 29 May 1949 9.0 mi. N VidalJct., SB 3 juveniles GMo (pers. comm.) aAbbreviations: Localities--JTNM, Joshua Tree National Monument; KE, Kern Co.; RIV, Riverside Co.; SB, San Bernardino Co. References--AMC, Alan Mo Craig; AS, Andy Sanders; ASE, A. Sidney England; BAC, Barbara A. Carlson; BLM, Bureau of Land Management;BM, Bev Macintosh;EAC, EugeneA. Cardiff; GMo, Gale Monson;JAD, JamesA. Davis;MVZ, Museumof VertebrateZoology, University of California,Berkeley; NRC, Nest Record Card, Laboratory of Ornithology, Cornell University; RMc, Robert McKernan; RR, Richard Rowlett; RSa, Rick Saval; SJN, Sheldon J. Newberger; SWC, Steven W. Cardiff. bReferencesto American Birds (AB) or AudubonField Notes (AFN) are not included in the Literature Cited. CSubdivisionsand boundariesof the Mojave and Coloradodeserts are illustratedin Figures1 and 3.

106 BENDIRE'S THRASHER IN CALIFORNIA documented by Johnson et al. (1948), and ornithologists and bird watchers continue to return to the area in search of this species. We located approximately 200 historical records for the eastern Mojave Desert, all but 10 in the area extendingsouth from the south side of Clark Mountain, over Cima Dome, through a few canyons in the Mid

Probablebreeding range • Bishop .[]Previouslywell-documenled dislnbullonIn Ihe eastern Mojave Desert m Prevmouslyunknownor poorly documented dlstribullon

Olher breeding-seasonrecords' ß H•storlcalbreeding-records ß Historicalbreeding-season records ß Breedrag-seasonobserval•ons durlnõ 1986-87 survey

'An open symbolindicates Ihal the locationo[ the observatmon•spoorly descnbed. NORTHERN

ß '• • Tecopa',

• o • RJdgecres?• .... "E.ASTERh /[½ gaker•'.

WESTERN .&• ...... /' " ...... CENTRAL• b•'•'

40km• •Sanan Dle•• leto • ••EICentroEl • Y Figure 3. Breedingrange of Bendire'sThrasher in the Mojave Desert basedon historicalrecords and the resultsof our study. Historicalrecords for the Colorado Desert are also shown.

107 BENDIRE'S THRASHER IN CALIFORNIA

Hills, and through Lanfair, Gold, Round, and Pinto valleyson the south sideof the New York Mountainsand Mid Hills to northernFenner Valley. Seven historical records were from the area near Granite Pass between the Granite and Providencemountains and the adjacentbajadas (Table 1). We locatedonly four recordsfrom suitablebreeding habitat for the area north or west of Cima Dome, with the most noteworthybeing of a pair on the north side of Clark Mountain (Table 1). The bird observedat Salt Creek was in habitatapparently unsuitable for breedingand its statuswas not known. However, this specieswas not found at the site during biweeklysurveys conducted from November1977 throughJanuary 1979 (A. S. England,unpublished data). We conductedsong playbacksurveys on 10 transectsin the eastern Mojave Desert in 1986 and on five transects in 1987 (Table 5). Bendire'sThrashers were presentat 36 of 73 sample points within the traditionallywell-known breeding range of the species(Table 5). On the LanfairValley transect, we foundbirds in southernIvanpah Valley, on the north sideof the New York Mountains,and farther souththan previously recordedalong Lanfair Road into upper FennerValley. We alsodetected this species at 8 of 12 sample points in suitable habitat on the ProvidenceMountains transect along the flanksof thesemountains. This thrasher was relativelycommon on the transectalong the north side of Clark Mountain and on the Shadow Valley transect west of Clark Mountain and north of Cima Dome. On the basis of these results, we have concludedthat this relativelywell-known population of Bendire's Thrasheris more widely distributedthan previouslydocumented (Figure 3).

ß Winterresidents (i.e., present _> 10 days) [] Allother observations

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Month

Figure 4. Monthly distributionof California observationsof Bendire'sThrashers awayfrom knownbreeding locations (Tables 3 and 4). Birdspresent at a location in more than 1 month were counted as one observation for each month detected.

108 BENDIRE'S THRASHER IN CALIFORNIA

Table :3 Desert Recordsfor Bendire's Thrasher in the Nonbreeding Season(August through mid-March) a

Date Days/• Number Locality Referencee

MojaveDesert c/ 13 Aug 1978 1 2 RoundValley, e SB SWC (BLM) 13 Aug 1985 1 1 PintoValley, e SB SWC (pers. comm.) 13-14 Aug 2 1 CedarCanyon Rd., SWC (pers. 1985 Mid Hills,e SB comm.) 22 Aug 1978 1 6 LanfairValley? SB ASE 28 Aug 1978 1 2 LanfairValley, e SB SWC (pers. comm.) 29 Aug 1985 1 1 LanfairValley, e SB LSUMZ 126499 29 Aug 1985 1 1 LanfairValley, e SB LSUMZ 126521 29 Aug 1985 1 1 LanfairValley? SB LSUMZ 126597 29 Aug 1985 1 1 Lanfair Valley,e SB LSUMZ 126598 30 Aug 1978 1 1 LanfairValley, e SB SWC (BLM) 30 Aug 1985 1 1 LanfairValley, e SB LSUMZ 126599 1 Sep 1980 1 6 Kelso,Mid EAC fide SWC Hills? SB (pers.comm.) 10 Sep 1978 1 1 Lanfair Valley?SB SWC (BLM) 8 Oct 1978 1 2 LanfairValley, e SB BAC (BLM) 8 Oct 1978 1 1 LanfairValley, e SB SWC (AB 33: 216, 1979) 12 Oct 1985 1 1 Near Lancaster,LA FH (AB 40: 160, 1986) 13 Nov 1973 1 1 Near Lancaster,LA AB 28:109, 1974 17 Nov 1968- 15 1 MorongoValley, SB JS, RMa (AFN 1 Dec 1968 23.' 110 and 522, 1969) 19 Nov 1978 1 1 LanfairValley, e SB BAC (BLM) 17 Dec 1983- 80 1 Near Lancaster,LA JD (AB 38:358, 5 Mar 1984 1984) Winter 1 1 Salt Lake, INY RMS (AB 33:94, 1977-78 1979) 1 Jan 1966 1 1 7.0 mi. E of LACM 66090 lied Mtn., lie 29 Feb 1984 1 1 LanfairValley, e SB SWC (pets. comm.) Colorado Desert 1 Nov 1964- 88 1 S end of Garrett and 27 Jan 1965 Salton Sea, IMP Dunn (1981) 12 Nov 1967 1 1 Near Niland, IMP EAC (AFN 22:90, 1968) 17 Dec 1973- 46 1 Bard, IMP RS (AB 28:693, 1 Feb 1974 1974);Rosenberg et al. (in press)

109 BENDIRE'S THRASHER IN CALIFORNIA

(Continued)

Date Daysb Number Locality Referencec

14 Feb 1987- 2 2f Chemehuevi RMc (AB 41: 15 Feb 1987 Wash, SB 331, 1987) 2 Mar 1968 1 1 Near Niland, IMP GSS, DAG (AFN 22:479, 1968) aAbbreviations:Localities--IMP, ImperialCo.; INY, lnyo Co.; KE, Kern Co.; LA, LosAngeles Co.; SB, San Bernardino Co. Reference$--ASE, A. Sidney England; BAC, Barbara A. Carlson; BLM, Bureau of Land Management;DAG, David A. Gaines; EAC, EugeneA. Cardiff;FH, Fred Heath; GSS, G. ShumwaySuffel; JD, Jon Dunn; JS, Jay Sheppard;JVR, J. V. Remsen; LACM, Los Angeles County Museum;LSUMZ, LouisianaState University Museumof Zoology;RMa, RalphManke; RMc, RobertMcKernan; RMS, RobertM. Stewart; RS, Rich Stallcup;SWC, StevenW. Cardiff; bNumberofconsecutive daysbetween the first and last observations ata location. CReferencesto American Birds (AB) or Audubon Field Notes (AFN) are not includedin the Literature Cited. titheboundary between the Mojave and Colorado deserts isillustrated inFigures 1 and 3. eKnown breedinglocation. flncludesone singing male.

Table 4 CaliforniaRecords for Bendire'sThrashers outside the Mojaveand Colorado Desertsa,b

Date Daysc Locality Reference•

11 Jan- 40 Goleta,StB ABi (AB 38:358, 1984) 19 Feb 1984 14 Jan 1959 1 Near Shandon,SLO Garrettand Dunn (1981) 14 Jan- 32 Palos Verdes BL (AB 40:335, 1986) 14 Feb 1986 Peninsula,LA 26 Jan- 56 Near Lakeview,RIV AMC (AB 39:211, 1985) 22 Mar 1985 28 Jan- 35 Coronado,SD JC (AB 39:211, 1985) 3 Mar 1985 16 Feb- 29 Otay Mesa,SD MO (AB 39:211, 1985) 16 Mar 1985 4 Apr 1970 1 ImperialBeach, SD GMc (AB 24:645, 1970) 17-18 Apr 1980 2 FarallonIslands, SF BrB (AB 34:812, 1980) 1 May 1982 1 San LuisObispo, SLO FRT (AB 36:894, 1982) 19 May 1984 1 FarallonIslands, SF JP (AB 38:955, 1984)

110 BENDIRE'S THRASHER IN CALIFORNIA

Table 4 (Continued)

Date Daysc Locality Reference•

14 Jul 1975 1 FarallonIslands, SF DeSanteand Ainley (1980) 21 Jul 1985 1 Irvine,ORN DRW (AB 39:963, 1985) 30 Jul- 4 SanPedro, LA IPL, JD (AB 31:224, 1977) 2 Aug 1976 1 Aug 1977- 251 Courfiand,SAC RS (AB 32:254, 396, and 8 Apr 1978 1052, 1978) 8 Aug 1976- 247 Courfiand,SAC AP (AB 31:219, 371, and 11 Apr 1977 1045, 1977) 17 Aug- 57 Pt. Loma,SD DP (AB 35:227, 1981) 12 Oct 1980 21 Aug 1983 1 SantaClara River SDR (AB38:247, 1984) Estuaw,VEiN 25-29 Aug 1979 5 Goleta,StB PL (AB 34:202, 1980) 25 Aug 1978- 188 Courfiand,SAC AP (AB 33:211 and311, 28 Feb 1979 1979) 27 Aug 1964 1 SolanaBeach, SD GMc, JS (McCaskieet al. 1967) 30 Aug 1983 1 SantaBarbara CD (AB 38:247, 1984) Island,StB 1 Sep 1976 1 Malibu,LA TC (AB 31:224, 1977) 2-5 Sep1973 4 FarallonIslands, SF DeSanteand Ainley (1980) 14 Sep 1973 1 ImperialBeach, SD HK (AB 28:109, 1974) 15 Sep-1 Oct 1979 17 Pt. Mugu,VEN BB (AB34:202, 1980) 15-16 Sep1979 2 SanClemente PJ(AB 34:202, 1980) Island,SD 16 Sep1988 1 Gaviota,StB PK (AB43:169, 1989) 18 Sep1968 1 PalosVerdes RS,GSS (AFN 23:110, Peninsula,LA 1969) 29 Sep1973 1 SanNicolas LJ,JD (AB28:109, 1974) Island,StB EarlyOctober 1966 1 [] CapitanState RMW(AFN 21:78, 1967) Park, StB 1-2 Oct1964 2 ImperialBeach, SD GMc,GSS (McCaskie etal. 1967) 4 Oct1970 1 ImperialBeach, SD GMc (AB25:110, 1971) 4-11 Oct1973 8 SanDiego, SD JWD(AB 28:109, 1974) 7 Oct-2Dec 1980 57 Malibu,LA BE(AB 35:227, 1981) 10 Oct1912 1 LosAngeles, LA MVZ23259; Miller (1913) 15 Oct1988- 148 Acampo(Lodi), SJ DGY(AB 43:164 and 363, 11 Mar1989 1989) 16 Oct1975 1 ImperialBeach, SD JD(AB 30:128, 1976) 16 Oct1975- 168 Courfiand,SAC AP,RS (AB 30:122 and 31 Mar1976 763, 1976) 17 Oct1975 1 SantaBarbara LJ,KG (AB 30:128, 1976) Island,StB 21 Oct1973 1 ImperialBeach, SD GSS(AB 28:109, 1974) 31 Oct1987- 123 Acampo(Lodi), SJ GE,DGY (AB 42:131 and 1 Mar1988 318, 1987) 8 Nov1973- 85 ImperialBeach, SD JD(AB 28:109 and 693, 31 Jan1974 1974) 111 BENDIRE'S THRASHER IN CALIFORNIA

Table 4 (Continued) Date Daysc Locality Reference•

9-12 Nov 1978 4 Pt. MuguState TC (AB 33:216, 1979) Park, VEN 12 Nov 1978 1 ImperialBeach, SD EC (AB 33:216, 1979) 16 Nov 1962 1 ImperialBeach, SD GMc (McCaskieand Banks 1964) 27 Nov 1974 1 Near San Diego,SD SW (AB 29:123, 1975) 9 Dec 1984- 49 Lake Perris,RIV AMC (AB 39:211, 1985) 26 Jan 1985 17 Dec 1978- 84 ImperialBeach, SD EC (AB 33:315, 1979) 10 Mar 1979 20 Dec 1969 1 ImperialBeach, SD AFN 24:455, 1969 21 Dec 1968 1 ImperialBeach, SD CSULB 3742; JS (AFN 23:522, 1969) 21 Dec 1984- 34 Goleta,StB RAH (AB 39:211, 1985) 23 Jan 1985 21 Dec 1985- 57 Acampo(Lodi), SJ TM, ML (AB 40:327, 1986) 15 Feb 1986 24-27 Dec 1979 4 San Pedro, LA HF (AB 34:308, 1980) aAbbreviations:Localities--LA, Los Angeles Co.; ORN, OrangeCo.; RIV. RiversideCo.; SAC, SacramentoCo.; SD, SanDiego Co.; SF,San Francisco Co.; SJ,San Joaquin Co.; SLO,San Luis ObispoCo.; StB,Santa Barbara Co.; VEN, VenturaCo. References--AB,Allyn Bissel; AMC, Alan M. Craig;AP, ArvillParker; BB, BruceBroadbrooks; BE, BarbaraElliott; BL, Barbara Lachina;BrB, BryantBainbridge; CD, CharlesDrost; CSULB, California State University, Long Beach;DGY, David G. Yee;DP, Dennis Parker; DRW, Douglas R. Willick;EAC, Eugene A. Cardiff; EC, ElizabethCopper; FRT, Fern R. Tainter;GE, Gil Ewing;GMc, Guy McCaside;GSS, G. ShumwaySuffel; HF, Ha] Ferris;HK, HarryKrueger; IPL, IsabelP. Ludlum;JC, JimCoatsworth; JD, JonDunn; JP, J. Pennimon;JS. Jay Sheppard; JWD, John W. DeWitt;KG, KimballGarrett; LJ, Lee Jones;ML, MikeLippsmeyer; MO, MartyOrell; MVZ, Museumof VertebrateZoology, Universityof California,Berkeley; PJ, PaulJorgensen; PK, Pat Kelly;PL, PaulLehman; RAH, RobbA. Hamilton;RMW, Russ and Marion Wilson; RS, Rich Sta]lcup; SDR, Steve and Diane Ross; SW,Susan Wise; TC, TerryClark; TM, Tim Manolis. ballobserations areof single birds. CNumberof consecutivedays between the first and last observations at a location. dReferencesto American Birds (AB) or AudubonField Notes (AFN) are not included in the Literature Cited.

112 BENDIRE'S THRASHER IN CALIFORNIA

We also discovereda previouslyunreported population of Bendire's Thrasherssoutheast of Essexalong the Old Woman Mountainstransect (Table5; Figure3). In 1986 and 1987, we detectedthe speciesat 10 of 13 samplepoints above an elevationof 850 m. On the adjacentWard Valley transect,we found three birds in this elevationalrange on the south side of the Piute Mountains (Table 5). The habitat in the Old Woman and Piute mountainslacked Joshua Trees but had fairly dense standsof Mojave Yuccaand other succulents.The thrasherpopulation apparentlyextended from the southside of the Piute Mountainsat least to the center of the Old Woman Mountains. We did not locate Bendire's Thrashers along either the California Valley or the KingstonMountains transects (Table 5). The plant species compositionappeared to be suitablefor the thrasherat both sites,but the soil in CaliforniaValley was rockydesert pavement and the topography along the KingstonMountains transect was extremelysteep with rocky soils. Southern Mojave Desert. Historicalbreeding-season records for this portion of the Mojave Desert are centered around three general locations: Lucerne Valley/Victorville, Yucca Valley/Pioneertown, and Joshua Tree National Monument (JTNM). We located five historical recordsof Bendire'sThrashers in the Lucerne Valley/Victorvillearea (Tables 1 and 2), includingthe first two verified nestingsreported in California,but the specieshas been recordedin this area onlytwice since 1920 (Table 1). We found only one historicalrecord that confirmed breedingin the YuccaValley/Pioneertown area (Table2), but breedingin thisarea is alsosuggested by irregularand repeatedobservations of birds in apparentlysuitable habitat (Table 1). Our literaturereview yielded eight historical records for JTNM (Tables 1 and 2); three records confirmedbreeding by Bendire'sThrashers in JTNM (Table2), wherethe speciesis consideredto be scarce(McCaskie 1973) or occasional(Miller and Stebbins1964). In 1986 and 1987, we conductedsong playback surveys on four transectsin the LucerneValley/Victorville area (Table5; Figure1). We did not find Bendire'sThrashers on the StoddardMountain transect, wherethe specieswas reported on 22 May 1969 (Table1; Figure1), or on the nearby Goat Mountaintransect (Table 5). Both transectswere throughareas with either JoshuaTrees or Mojave Yucca, but the StoddardMountain area had beenheavily used by off-roadvehicles, and the soilat Goat Mountainwas very rocky. At both sites,the habitathad widelyspaced Joshua Trees, Mojave Yucca, and CreosoteBush (Larrea tridentata)with few othershrubs and only sparse annual growth. We did locateBendire's Thrashers both yearson the SidewinderMountain and Apple Valleytransects (Table 5). The habitatin southeasternApple Valley was a relativelyrich mixture of JoshuaTrees and cholla cactus. The areahas been partially developed, and houses were scattered along the transect.The SidewinderMountain transect crossed an undeveloped area with few obvioussigns of human use. The habitatwas a diverse mixtureof shrubswith numerousJoshua Trees, Mojave Yucca, and cholla cactus.

113 BENDIRE'S THRASHER IN CALIFORNIA

114 BENDIRE'S THRASHER IN CALIFORNIA

115 BENDIRE'S THRASHER IN CALIFORNIA

In the YuccaValley/Pioneertown area, we conductedsurveys on three transectsin 1986 and on two in 1987 (Table 5; Figure 1). Bendire's Thrasherswere not observedon the YuccaValley transect; this transect crosseda heavilydeveloped residential area with scatteredJoshua Trees on remainingundeveloped lots and as landscapeplants around homes. We did not find Bendire'sThrashers on either the Landersor the Pipes Canyon transectsin 1986, but did locate them on both in 1987 (Table 5). The numberof points on each transectwas increasedin 1987 to includeareas not sampledthe first year, and in both casesthe 1987 observationswere at new points. Two birds observed on the Pipes Canyon transectwere found near the intersectionof Highway 247 and Pipes Wash, west of the Landerstransect. Three birdsobserved on the Landerstransect in 1987 were on the uplandsdue east of Pipes Wash. Thus both transectsappeared to intersectthe same smallpopulation of thrashers. All five locations with Bendire's Thrashers were in habitats with JoshuaTrees and chollacactus. The pointsin PipesWash also had large Catclaws(Acacia greggii), but the two birdsobserved there were at the edge of the wash on nearby hillsides. Mojave Yucca was common alongthe Landerstransect, and houseswere scatteredalong the route. We usedthe playbacktechnique to samplethrashers at 41 pointsalong the JTNM transectin 1986 (Table5; Figure 1) and found the thrasherto be much more common than expected. We locatedbirds at 17 points, and 13 of the pointswhere we did not find them were at low elevations in the Colorado Desert either in Pinto Basin or south of the Cottonwood Pass entrance to JTNM. The habitat at most sites occupied by the thrasher had relativelydense standsof Mojave Yucca and few or no Joshua Trees. Central Mojave Desert. Bendire'sThrashers were first reportedfrom this regionin 1981 at a sitewest of Lane Mountainnear SuperiorValley (Table 1), and breedingwas confirmedthere in 1981 and 1982 (Table2). We conductedsong playbacksurveys in Superior Valley along Copper City Road and near Goldstonein 1986 and found three birdsin Superior Valley (Table 5). Both sites were relatively small, isolated stands of Joshua Tree woodland. •Vestern Mojave Desert. Our literature review documented three historicalbreeding-season records of Bendire'sThrashers in the western regionof the MojaveDesert (Table 1). Two were earlyApril observations of probablemigrants. The other was a mid-Junesighting of a singing male in JoshuaTree woodlandin KelsoValley on the easternslope of the Sierra Nevadawest of Red Rock Canyon State Park. Breedingin Kelso Valleywas confirmedin 1987 (Table2). Much of the western Mojave Desert supportsJoshua Tree woodland that appears suitablefor Bendire's Thrashers, but observationsof birds are curiouslylacking. Therefore,we concentratedmuch of our effort in this region, sampling152 pointson 16 transectsin 1986 and 99 points on 10 transectsin 1987 (Table5). Despitethis intenseeffort, we located only one Bendire'sThrasher (Table5). This silentindividual was seen on 11 May 1987 in upper ButterbreadCanyon, one ridge east of Kelso Valley. The ButterbreadSpring transect included sample points in Kelso 116 BENDIRE'S THRASHER IN CALIFORNIA

Valley,but we didnot observe thrashers there. The breedingrecord for KelsoValley and otherobservations in the areasuggest that Bendire's Thrashersmay breed either sparsely or sporadicallyin theseand possibly othercanyons on the southeasternslope of the SierraNevada northwest of Mojave(Figure 3), but are otherwiseabsent from the westernMojave Desert. Northern Mojave Desert. Prior to our study, the only recordsof Bendire'sThrashers from this portion of the Mojave Desert were four observationsof presumedmigrants found between23 May and 1 June (Table1; Figure3). Theseobservations were recordedaround Memorial Day in DeathValley National Monument and at OasisRanch in FishLake Valley. All were at desert oasesregularly visited by bird watchers searchingfor vagrants. We conductedsong playback surveysfor Bendire's Thrashers in JoshuaTree woodlandalong two transectsin the northernMojave Desert in 1986 and along four in 1987 (Table5). The thrasherwas present both years on the Lee Flat transect east of Lone Pine (Figure 3). Althoughbreeding has not beenconfirmed there, it is stronglysuggested by detectionsat 7 of 16 surveypoints in apparentlysuitable habitat, presencein 2 consecutiveyears, and unsolicitedsinging. Bendire's Thrasherswere not foundin similarvegetation at nearbysites. Colorado Desert. Most historical breeding-season records of Bendire's Thrashers in the Colorado Desert were from the northern edgesnear the boundarywith the Mojave Desert (Figure3). The only exceptionswere of singlebirds observed at Brock Ranchin southeastern ImperialCounty and at Palm Spring in Anza-BorregoDesert State Park (Table 1; Figure 3). Approximately81% of all breeding-seasonrecords were betweenmid-March and May when they couldhave been of either locallybreeding individuals or springmigrants (Tables 1 and 2). Garrett and Dunn (1981) regardedthis speciesas transientin the Colorado Desert. We locatedfour historicalbreeding records confirming that this speciesdoes breed in the Colorado Desert (Table 2; Figure 3). Garrett and Dunn (1981:280) reported "unsubstantiatedreports of nestingon the creosote desert to the west of the Colorado R. between Needles and Blythe." The sourceof this statementmay have been a figureillustrating the Arizona distributionof Bendire'sThrasher in The Birds of Arizona (Phillipset al. 1964) that indicatedsummer records exist in Californiafor the area between Needles and Blythe. These observationswere not mentionedin the accompanyingaccount for the species. G. Monsonand A. R. Phillips(pers. comm.) provided us with 19 recordsfrom the late 1940s and early 1950s supportingthese observations(Tables 1 and 2), includingtwo observationsof juvenilesnorth of Vidal Junction. These records,an egg set collectedin the nearbyTurtle Mountains(Table 2), and a February 1987 observationin ChemehueviWash of two birds includinga singingmale (Table 3), suggestat least sporadicnesting in ChemehueviValley and adjacentareas. The hypothesisthat nestingin this regionis sporadicis supportedby the fact that Daniels(1979a,b) did not report Bendire'sThrashers during winter and breeding-birdsurveys in Chemehuevi Wash. 117 BENDIRE'S THRASHER IN CALIFORNIA

In 1986, we conductedsong playback surveys for Bendire'sThrashers on four transectsin areasand habitatswhere birdshad been reportedbut failed to locate any. We did find one Bendire'sThrasher near Chiriaco Summit in the Colorado Desert at the beginningof the JTNM transect (Figures1 and 3). The habitat there was a dense and diversestand of desert scrub visuallydominated by Palo Verde (Cercidium floridurn), Ocotillo (Fouquieria splendens),and chollacactus.

Movement Patterns in California

An immature female Bendire's Thrasher collected on 21 June 1961 in pine-fir foreston Mt. Charleston,Clark Co., Nevada(Austin and Bradley 1965), indicates that movements away from breeding habitats begin immediatelyafter the end of the breedingseason. Birdsseen duringlate May and earlyJune in habitatnot suitablefor breedingmay be late spring migrants,unsuccessful breeders, or post-breedingdispersers wandering away from breedinghabitats (e.g., four recordsin the northern Mojave Desert, Table 1). Only 28 historicalrecords exist for Bendire'sThrasher in either the Mojave or Colorado desertsbetween 1 Augustand 15 March (Table 3), and these include only six observations after 1 Septemberin knownbreeding areas. Thus, existingrecords suggest that a few birds linger on the breedinggrounds past August(Table 3). This numbermay be higherthan currentlydocumented because the birdsare not vocal and are fairly secretiveat this time of year, so may be easily missed,and few ornithologistsor bird watchersvisit the desertfrom July throughFebruary. Most birds that breed in California presumablymigrate southeastto wintering grounds in southern Arizona, southwestern New Mexico, Sonora, and Sinaloa (A.O.U. 1983). However, 53 historicalCalifornia recordsof Bendire'sThrasher outside the Mojave and Coloradodeserts (Table4) demonstratethat some individualsmove west or northwestfrom breedingareas in Californiaor elsewhere. Nearly all recordsfrom the nonbreedingseason (August through mid-March) and away from breeding areas are for sitesclose to the coast(Tables 3 and 4). Fall migrantsfirst appear in coastalCalifornia in mid-July(Table 4; Figure4), and coastal and desert records indicate that fall movements continue until October or early November. These migrantsoverlap with a few birdsthat spendall or part of the winterin California(Tables 3 and 4; Figure4). Over 35% of winter records for Bendire's Thrashers in California were of birds present for more than 10 days and could have been winter residents rather than migrants (Tables 3 and 4; Figure 4). Most remarkablewere recordsof presumablythe samebirds that returnedeach winter to Courtland,Sacramento County, for 4 consecutiveyears and to Acampo,San JoaquinCounty, for 3 of 4 years(Table 4). After the first year they were reported, these birds were first observedeach year between August and October and were last observedbetween mid- Februaryand mid-April(Table 4). Other individualsrepeatedly observed duringthe winter were usuallylast seen in early to mid-March(Tables 3 and 4), but a few lingered to mid-April (Table 4). Winter recordsat 118 BENDIRE'S THRASHER IN CALIFORNIA

Lancaster,the southend of the Salton Sea, and near Bard suggestthat a few birdsmay winterin the Californiadeserts. In view of the scarcityof winter recordsfor the state, Bendire'sThrasher shouldbe considereda rare and possiblysporadic winter resident in California. Springmigration begins by February,when birdsoccasionally appear in the southern Colorado Desert (Table 3), and continuesthrough April and May, when a few recordsexist for coastalCalifornia. The end of springmigration may overlapwith movementsby early post-breeding dispersersand unsuccessfulbreeders.

Habitat Relationships Historical records of breeding Bendire's Thrashers in the eastern Mojave Desert all fall between680 and 1708 m. We found birdsfrom 575 m at Chiriaco Summit in the Colorado Desert to 1775 m on Lee Flat in the northernMojave Desert. The typicallower elevational limit of probablybreeding birds was approximately 950 m. Six possiblybreeding birds were found between 800 and 925 m near the transition between the Mojaveand Coloradodeserts along either the JTNM, Ward Valley,or Old Woman Mountains transects. Two birds observed below 750 m were also along the JTNM and Ward Valley transects. All observationsabove 1525 m were either at Lee Flat or near KeysView in JTNM. Our field surveysconfirmed that Joshua Trees, Mojave Yucca, or Spanish Bayonet are at all Mojave Desert locations with probably breedingBendire's Thrashers. The compositionof the perennialshrub layer was highly variable. Dominant shrub speciesat most sites were Creosote Bush, Cheese Bush (Hymenoclea salsola), Nevada Squaw-tea (Ephedra nevadensis),Burro Bush (Ambrosia dumosa), and Big Galleta Grass(Hilaria rigida). In most cases,the shrubswere diverse,including California Buckwheat (Eriogonum fasciculatum), Spiny Hopsage (Grayia spinosa), Cooper Desertthorn (Lycium cooperi), Anderson Desertthorn (L. andersonii), ratany (Krameria sp.), Bladdersage ($alazaria mexicana), and goldenbush(Happlopappus sp.) as other common species. Bendire's Thrashers also occurredwhere the vegetation consistedof Blackbrush(Coleogyne ramosissima) with scatteredjunipers (Juniperus osteosperma, J. occidentalis, or J. californica), Joshua Trees, and chollacactus. Locationswith this type of perennialvegetation included HalloranSummit, the road to Keys View in JTNM, and Clark Mountain near Keany Pass. Although the vegetationon Lee Flat had a sparse overstoryof JoshuaTrees, the understorydiffered from that at other sites, consistingprimarily of Shadscale(Atriplex confertifolia), Spiny Hopsage,Winterfat (Eurotia lanata), and Spiny Menodora(Menodora spinescens). Historical records from higher elevationsin the eastern Mojave Desert indicate that Bendire's Thrashers also breed in areas dominated by Big Sagebrush (Artemisia tridentata) with scattered junipers. Desert washesdominated by Catclawin the easternMojave Desert are typicallyconsidered the habitatof CrissalThrashers (Toxostoma dotsale)

119 BENDIRE'S THRASHER IN CALIFORNIA

(e.g., Garrett and Dunn 1981). Historicalrecords suggest that Bendire's Thrashersalso use this vegetation, especiallyat lower elevations. We found Bendire'sThrashers in washesdominated by Catclaw on only three occasions, but at least two of these observations were of birds that apparentlyflew into the wash from adjacenthabitat in responseto the songplayback.

CONCLUSIONS

Most Bendire'sThrashers leave breedingareas by the end of July; a few individualsmay remain into Augustor later. Most migrantsmove to wintering groundsto the southeast. However, occasionalindividuals, from either Californiaor elsewhere,move north and west and spend all or a portionof the winterin coastalCalifornia. Springmovements begin in Februaryand early March, and singingbirds begin to appear on the breedinggrounds in late March and early April. The easternMojave Desert near Cima Dome and Lanfair Valley and the southernMojave Desert at JTNM are the two primarybreeding areas for Bendire's Thrashers in California. However, this species is more widely distributedduring the breedingseason than previouslyrecorded. The easternMojave population extends considerably farther to the north, east, and souththan previouslyknown and includesa newly discovered disjunctpopulation in the Old Woman Mountains. Birds in JTNM are more widespreadand the populationappears to be more contiguousthan generally recognized. Elsewhere in the Mojave Desert, Bendire's Thrashersare restrictedto widely scatteredlocations supporting either JoshuaTrees, other speciesof yuccas,or chollacactus. Large tractsof desert,especially in the westernMojave Desert, support one or more of these plant speciesbut lack populationsof Bendire'sThrasher. The habitat variableslimiting the distributionof this specieshave yet to be quantifiedwith the detailnecessary to understandits complexdistribution. Observationsover severalyears in Superiorand Kelsovalleys suggest that these small isolated populationsare either permanent and previously undetectedor persistonly a few years. Additionalstudies could (1) locate new populations, (2) determine population sizes, and (3) establish whether small isolatedpopulations are permanent or undergoregular extinctionand recolonization. Bendire'sThrashers do breed very locally and sporadicallyin the Colorado Desert, where they are restrictedto habitatswith arborescentspecies such as Palo Verde. This type of habitatis similarto that occupiedby this thrasherin Arizona. Researchis neededto clarifythe breedingdistribution and habitatuse of this species in the Colorado Desert.

ACKNOWLEDGMENTS

Partialfunding was providedby the CaliforniaDepartment of Fish and Game and Bureauof Land Management. DanielW. Andersonserved as projectsponsor at the Department of Wildlife and FisheriesBiology, Universityof California, Davis. DanielW. Anderson,Kristin H. Berry, StevenW. Cardiff, GordonGould,

120 BENDIRE'S THRASHER IN CALIFORNIA

Larry D. Foreman, Tim Manolis, J. V. Remsen, Jr., Charles van Riper III, Kent Smith, Philip Unitt, and Jerry Verner provideduseful comments on either our initial studydesign or earlier drafts of this paper. Jay M. Sheppardshared his knowledgeabout the use of recordedsongs to locate thrashersand helped us designthe samplingprotocol. StevenW. Cardiff, Alan M. Craig, Paul Mack, Bev Mclntosh, Robert McKernan, Gale Monson, Allan R. Phillips, and Rick Saval providedinformation on recentrecords from their field notes. Karen English-Loeb prepared the original versionsof Figures I and 3. Janet Williams prepared Figures2 and 4 and revisedFigures 1 and 3.

LITERATURE CITED

AmericanOrnithologists' Union. 1983. Check-listof North AmericanBirds. 6th ed. Am. Ornithol. Union, Washington,D.C. Austin, G. T., and Bradley,W. G. 1965. Bird recordsfrom southernNevada. Condor 67:445-446. Bent, A. C. 1948. Life histories of North American nuthatches, wrens, thrashers,and their allies. U.S. Natl. Mus. Bull. 195. Brown, H. 1901. Bendire's Thrasher. Auk 18:225-231. Daniels,B. E. 1979a. Winter bird-populationstudy 81. Palo verde desertwash. Am. Birds 33:42. Daniels,B. E. 1979b. Breedingbird census150. Palo verdedesert wash. Am. Birds 33:94. DeSante, D. F., and Ainley, D.G. 1980. The avifauna of the south Farallon Islands,California. StudiesAvian Biol. 4. Garrett, K., and Dunn, J. 1981. Birds of Southern California: Status and Distribution. Los AngelesAudubon Soc., Los Angeles. Grinnell, J. 1915. A distributionallist of the birds of California. Pac. Coast Avifauna 11. Grinnell, J., and Miller, A. H. 1944. The distributionof the birds of California. Pac. Coast Avifauna 27. Heller, E. 1901. Notes on some little-known birds of southern California. Condor 3:100. Johnson,D. H., Bryant, M.D., and Miller, A. H. 1948. Vertebrateanimals of the Providence Mountains area of California. Univ. Calif. Publ. Zool. 48:221-376. McCaskie,G. 1973. The springmigration: SouthernPacific Coast region. Am. Birds 27:821. McCaskie,R. G., and Banks, R. C. 1964. Occurrenceand migrationof certain birds in southwestern California. Auk 81:353-361. McCaskie, G., Stallcup, R., and DeBenedictis, P. 1967. The distributionof certain Mimidae in California. Condor 69:310-311. Miller, L. 1913. A specimenof Bendire Thrasher in the San Diegan Region. Condor 15:41. Miller, A. H., and Stebbins,R. C. 1964. The Lives of Desert Animals in Joshua Tree NationalMonument. Univ. of Calif. Press,Berkeley. Phillips,A., Marshall,J., and Monson, G. 1964. The Birdsof Arizona. Univ. of Ariz. Press,Tucson.

121 BENDIRE'S THRASHER IN CALIFORNIA

Pierce,W. M. 1919. Another Californiarecord of the BendireThrasher. Condor 21:123. Pierce, W. M. 1921. The Bendire Thrasher nesting in California. Condor 23:34. Remsen, J. V., Jr. 1978. Bird speciesof special concern in California: an annotatedlist of decliningor vulnerablebird species. Calif. Dept. Fish and Game, WildlifeMgt. BranchAdmin. Rept. 78-1. Rosenberg,K.V., Ohmart, R.D., Hunter, W.C., and Anderson, B.W. In press. Birdsof the Lower ColoradoRiver Valley. Univ. of Ariz. Press,Tucson. Sheppard, J. M. 1970. A study of the LeConte's Thrasher. Calif. Birds 1:85-94. Stephens,F. 1919. Unusualoccurrences of BendireThrasher, Fork-tailed Petrel and Western Goshawk. Condor 21:87.

Accepted 14 September 1989

APPENDIX

The locationsof Bendire'sThrashers detected during the 1986-87 surveysare describedbelow by region of the desert. Each transectname and abbreviationis followedby the date(s)of the survey(s)and the number of Bendire'sThrashers heard, observed,and the total detected. For example, the Cima Dome transect was surveyedon 28 April 1986; six Bendire'sThrashers were heard, seven were observed, and a total of 10 were detected. Only the points or portions of transects where the thrasher was detected are described. SB, San Bernardino County;RIV, RiversideCounty. EasternMojave Desert Cima Dome (CD)--(28 Apr 1986: 6, 7, 10; 21 May 1987: 2, 2, 2)•ima Rd., SB; from 4.0 km SE of Interstate15 to 3.5 km NW of KesslerPeak. Clark Mountain (CNI)--(28 Apr 1986: 9, 3, 9)--Transmissionline road over KeanyPass on N sideof Clark Mtn., SB; from 5.0 km NE of ExcelsiorMine Rd. to 1.8 km E of Keany Pass. Halloran Summit (HS)--(28 Apr 1986: 3, 5, 5; 21 May 1987: 4, 5, 6)--Graded dirt road beginningat Halloran Summit, SB, on S side of Interstate 15; proceedingNE for 3.5 km then SE for 5.5 km. Lanfair Valley (LV)--(29 Apr 1986: 6, 6, 11; 19 May 1987: 6, 13, 15)--Ivanpah Rd., SB. One bird observedon N slopeof New York Mtns., 6.5 km SE of Ivanpah. Remainderdetected in LanfairValley from 11.0 km NNE of Cedar CanyonRd. to 13.3 km N of Golfs. Old Woman Mountains (OW)--(30 Apr 1986: 9, 9, 12; 17 May 1987: 6, 7, 9)--Sunflower Springs Rd., SB; from 13.2 km SE of Essexto 1.5 km NE of SunflowerSpring. Also, on ungradedroad intersectingSunflower Springs Rd. 0.7 km NNE of Weaver'sWell for 2.6 km towardsWillow Spring. Providence Mountains (PNI)--(29 Apr 1986: 6, 6, 9; 18 May 1987: 4, 3, 5)--Black Canyon Rd., SB; from 1.0 km SE of Hole-in-the-Wall,S for 6.8 km. Also, along transmissionline road over FoshayPass from 0.2 km E of the passto the E for 5.4 km.

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Shadow Valley (SV)•28 Apr 1986: 7, 1, 7)--ExcelsiorMine Rd., SB; from 9.6 km NNE of intersectionwith transmissionline road over Keany Pass (Clark Mtn.) to the NNE for 6.4 km. Ward Valley(WV)•30 Apr 1986: 3, 2, 3)--Transmissionline roadE of Litfie Piute Mtns., SB; at Township7N, Range 19E, NW 1/4 Section29. Also, on pipelineroad alongSE sideof PiuteMtns. at Township7N, Range18E, SE 1/4 Section 14 and SE 1/4 Section 15. Southern Mojave Desert Apple Valley(AV)•4 Jun 1986: 0, 1, 1; 14 May 1987: 1, 5, 5)--Desert View Rd., SB; from 3.2 km W of High Rd. to 0.8 km W of MilpasRd. Joshua Tree National Monument (JT)--(2 May 1986: 12, 12, 19)--One bird on gradeddirt road into Lost PalmsCanyon, 1.5 km N of ChiriacoSummit, RIV. CottonwoodSprings Rd./Pinto BasinRd., RIV; from 1.1 km SW of Cottonwood Springto 1.3 km SSEof intersectionwith BlackEagle Mine Rd.; at NationalPark Servicehousing near CottonwoodSpring; and along dirt road from Pinto Basin Rd., NW for 7.2 krn to Smoke Tree Wash at Township4S, Range 11E, NW 1/4 Section 31. General vicinity of White Tank, Jumbo Rocks, and Ryan campgrounds,RIV, at the followinglocations: 4.7 km SE and 0.4 km SE of White Tank Campground;5.5 km NE, 1.9 km NE, and 1.4 km NW of JumboRocks Campground;and 1.2 km WNW of Ryan Campground.Also, on SaltonView Rd. 1.3 km W of Keys View, RIV, and on MonumentRd. in SB at Township1S, Range 7E, SW 1/4 Section26. Landers (LA)--(16 May 1987: 1, 3, 3)--Yucca Mesa Rd. 6.1 km N of Highway62, and La BrisaDr. 1.4 and 2.0 km W of YuccaMesa Rd. Pipes Canyon (PC)•16 May 1987: 2, 1, 2)--Pipes Wash, SB; 0.4 km NW and 0.4 km SE of intersectionof Highway 247 and Pipes Canyon Rd. Sidewinder Mountain (SI)--(5 Jun 1986: 4, 4, 5; 15 May 1987: 1, 1, 2)--Ungradedroad from Highway247 over SidewinderMtn., SB, at the following locations:Township 6N, Range 1W, NW 1/4 Section 29; and Township6N, Range2W, NE 1/4 Section26 and NW 1/4 Section22. Northern Mojave Desert Lee Flat (LF)•7 Jun 1986: 3, 1, 3; 9 May 1987: 9, 6, 9)--Saline Valley Rd., Inyo Co.; 2.4 km NE of intersectionwith White Mtn. Talc Rd. Also, alongWhite Mtn. Talc Rd., Inyo Co.; from 2.7 km NW of intersectionwith SalineValley Rd. NW for 5.1 km.

Central Mojave Desert Copper City Road (CR)--(27 Apr 1986: 4, 1, 4)--Copper City Rd./Randsburg-BarstowRd., SB; from 9.9 km NNW of intersectionwith Irwin Rd., NNW for 5.3 km. WesternMojave Desert Butterbread Spring (BS)•11 May 1987: 0, 1, 1)--Graded dirt road through ButterbreadCanyon, Kern Co.; one bird 6.9 km NW of ButterbreadSpring at Township29S, Range 35E, NW 1/4 Section7.

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Bendire's Thrasher, Acampo, California, 3 November 1989 Photo by David Yee

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