j. RaptorRes. 34(3):187-195 ¸ 2000 The Raptor ResearchFoundation, Inc.

POPULATION FLUCTUATIONS OF THE HARRIS' HAWK (PARABUTEO UNICINCTUS) AND ITS REAPPEARANCE IN CALIFORNIA

MICHAEL A. PATTEN Departmentof Biology,University of California,Riverside, CA 92521 U.S.A.

RICHARD A. ERICKSON LSA Associates,One Park Plaza, Suite 500, Irvine, CA 92714 U.S.A.

ABSTRACT.--TheHarris' Hawk (Parabuteounicinctus) was consideredextirpated from California in the mid-1960s.Most sightingsin the past 30 yearswere, therefore, consideredto be escapedor released birds. The specieshas recently staged an incursioninto southernCalifornia and northern BajaCalifornia in the 1990s,involving nearly 50 individualsand local breeding.This incursionwas apparently another in a long-term seriesof population fluctuationsof the Harris' Hawk, each bringing large numbersto the north and west of its establishedrange in Arizona and Baja California. Although first recorded at the state border in the 1850s, the Harris' Hawk was not recorded as a breeder until an incursion in the late 1910s and 1920s brought hundreds to the state, including the first known breeders.Numbers declined again in the 1940s,built up again in the 1950s,and thereafterdrastically declined to the point of their absenceby the mid-1960s.Therefore, the recent incursionwas not anomalousbut rather follows historicalpatterns of occurrence,indicating that California is on the fringe of the natural range of the Harris' Hawk, with emigrationbringing birds into the stateand subsequentpopulation decreases leading again to "extirpation." KEYWORDS: Harris'Hawk; Parabuteo unicinctus; Baja California;California; population fluctuations.

Fluctuacionespoblacionales de Parabuteounicinctus y su reaparicitn en California RESUMEN.--E1gavilfin de harris (Parabuteounicinctus) fue consideradocomo extirpado de California a mediados de 1960. La mayoria de los avistamientosde los filtimos 30 aftosfueron consideradoscomo avesescapadas o liberadas.La especieha incursionadoen el sur de Californiay norte de BajaCalifornia en los aftos90, incluyendounos 50 individuosy algunoseventos de reproduccitn locales.Esta incursitn es aparentementeuna mils de las ocurridasa largo plazo por esta especie.Cada una trayendograndes nfimeros de individuos al norte y oeste de su rango establecidoen Arizona y Baja California. Aunque por primera vez fue registradoen el borde del estadoen 1850, el gavilfinde harris no fue reportado en reproduccitn hastasu incursitn en 1910 y 1920 con cientosde individuosincluyendo los primeros registrosde reproduccitn. Los nfimeros de individuosdeclinaron otra vez en 1940, aumentaron en 1950, y declinaron drfisticamentehasta considerarlos ausentes en 1960. Por lo tanto, la reciente incur- sitn no es antmala, al contrario, siguelos patronesde ocurrencia indicando que California estfien el limite del rango natural del gavilfin de harris, con su emigraci0n trayendo avesdentro del estado y la subsecuentedeclinacitn la cual conllevaa su extirpacitn. [Traducci6n de Ctsar Mfirquez]

The Harris' Hawk (Parabuteounidnctus) ranges as has been expandingnorthward in recent years from the southwestern United States southward (Bednarz et al. 1988, Bednarz 1995, Dawson 1998). through Central America to central Chile and cen- In California, the Harris' Hawk wasfound formerly tral Argentina, with a geographicallydisjunct pop- throughout the lower Colorado River Valley and in ulation on the Baja California peninsula. In the the Imperial Valley south of the Salton Sea (Grin- United States, it occurs from southern Arizona, nell and Miller 1944). By the mid-1950s,it wasex- southeastern New Mexico, and central Texas south- tirpated from California as a breeder (Remsen ward (Fig. 1; American Ornithologists' Union 1978, Walton et al. 1988), with the last definite wild 1998). Its range in Arizona, New Mexico, and Tex- bird recorded north of Blythe on 28 November

187 188 PATTENAND ERICKSON VOL. 34, NO. 3

LakeTahoe

Colorad/e•'River

California

Arizona Salton Sea

Figure1. The northwesternportion of the currentrange (the shadedarea) of the Harris'Hawk (Parabuteo un2- cznctus),modified from Bednarz (1995) and Dawson(1998). The dashedline signifiesthe formerwesterly limits of its rangein southwesternArizona and southeasternCalifornia. SEPTEMBER2000 HArems' HAwI• IN CALIFOm'4IA 189

1964 (Garrett and Dunn 1981, Rosenberg et al. mate of the magnitude of the incursion and to examine 1991). its geographicextent.

A reintroduction project for the Harris' Hawk THE 1994 INCURSION wasinitiated in California in 1979 by variousstate, federal, and private groups (Stewart1979, 1982, Despitean annual "background"escape/release Walton et al. 1988). Eight birds were releasedthat rate throughout California of >3 Harris' Hawks year and severalmore were releasedeach year un- (Bloom pers. comm., Walton pers. comm.), a dif- til 1989, for a total of 222 releases (Linthicum ferent phenomenon began 15 April 1994, when J. 1989, Linthicum pers. comm.). The first pair nest- Rudley, P. Jorgensen,and M. Jorgensenobserved ed successfullyin 1983, three pairs bred success- three adults together in Borrego Valley. Between fully in 1986 (Walton et al. 1988, Rosenberget al. 1994-96, at least 34 individuals had been found in 1991), and five nested in 1989 (Linthicum 1989, southern California (Table 1; McCaskie 1995). The Bednarz 1995). However, it is unlikely that this largest groups of birds consistedof at least eight population is viable, as birds are now infrequently individuals in the Borrego Springs region of the noted (Rosenberget al. 1991, Patten pers. obs.). Anza-Borrego Desert and up to five individuals Since the mid-1960s,virtually all recent records both at the former George Air Force Base near of the Harris' Hawk in California are of birds con- Victorville and at Boulevard (Table 1). During this sidered to have escapedfrom falconers (Garrett apparentlynatural incursion (Bednarz 1995, Mas- and Dunn 1981, Unitt 1984). In some cases,birds sey1997, Walton pers.comm.), Harris' Hawkswere have been observedwith jessesand clearly came found north of their historical range as far as Vic- from this source. In other cases,there appearsto torville in the Mojave Desert, with scatteredindi- be some tendency for natural occurrence such as vidualsreported around the Salton Sea and else- sightingsof immatures along the Colorado River where (Fig. 2). Additional birds in cismontane near Blythe in September (Roberson 1980) and valleysat Riversideand in centralSan Diego Coun- December1978 (Rosenberget al. 1991) and at the ty may or may not have been naturally occurring, south end of the Salton Sea on 25 June 1989 with individualsfar westin coastalOrange County (McCaskie 1989). Nevertheless,records of individ- and in the Antelope Valley being particularlysus- ual birds are perhapsalways suspect given that the pect given the apparent geographicextent of the speciesremains popular with falconersand reha- influx (Fig. 2). Indeed, the Orange County bird bilitated birds are occasionallyreleased, as were a showed signs of being in captivity (Bloom pers. few around the Salton Sea in the 1970s and 1980s comm., Daniels pers. comm.). This influx into southern California was con- (Walton et al. 1988). Herein, we document a major increasein sightingsbeginning in April 1994 that comitant with at least 22 individuals well north of wasapparently a natural influx involvingnearly 50 the species'normal range in northern Baja Cali- individuals throughout southern California and fornia (Table 2; Radamakerpers. comm., Wurster northern Baja California. Further, we hypothesize pers. comm.) and in adjacentnorthwestern Sonora that such incursions are the rule rather than the (Russell and Monson 1998). During this period, exceptionfor the occurrenceof this speciesin Cal- Harris' Hawks bred in California at Borrego ifornia. Springs (Massey 1997), Boulevard (Unitt pers. comm.) and Laguna Dam (McCaskie 1996, Massey METHODS 1997), and in northern Baja Californiaat Valle San For the recent incursion,we gatheredrecords and doc- Telmo (Bloom pers. comm.). Small numbershave umentation from various field observers (see Acknowl- persistedin BorregoValley as recentlyas 7 March edgments)and from files of the California Bird Records 1999 (Jorgensenpers. comm.) and in Valle San Committee. All specificdata gathered are on file at the Telmo on 31 January 1999 (Patten pers. obs.). Western Foundation of Vertebrate Zoology (WFVZ), Camarillo, California U.S.A. Recent and historical data HISTORICAL TRENDS AND CURRENT STATUS were gathered from seasonalreports for the Southern Pacific CoastRegion published in FieldNotes (now North The historical distribution of the Harris' Hawk AmericanBirds), Christmas Bird Countsand specimensat in California is not clear. The specieswas first re- the San Diego Natural History Museum (SDNHM), San Diego, California U.S.A., National Museum of Natural corded along the Colorado River on the Arizona History (USNM), Washington, D.C.U.S.A. and WFVZ. side in February 1854 (Kennerly 1859, Swarth We tabulatedand mapped these data to obtain an esti- 1914), but Elliot Couesnever recorded the species 190 PATTEN AND ERICKSON VOL. 34, NO. 3

Table 1. California records of the Harris' Hawk (Parabuteounicinctus) from spring 1994 through winter 1996-97 (Fig. 2), arranged chronologically.Birds nested at Boulevard (1994) and Laguna Dam (1996), and exhibited nesting behavior (copulations,carrying sticksand food) at Borrego Valley (1994-95), with immatures observedin 1995. Data are on file with the CBRC.

DATE (S) LOCATION MAXIMUM 15 April 1994-January1999+ San Diego County;Borrego Valley 1 June 1994-31 October 1995 San Diego County; Boulevard 26 November 1994-29 January 1995 San Diego County; Santee ? December 1994 RiversideCounty; Blythe 7-18 December 1994 Imperial County; Westmorland 10-12 December 1994 Orange County; Irvine 31 December 1994-29 January 1995 RiversideCounty; n. end Salton Sea 2-21 January 1995 San Bernardino County;Victorville 27 June-23 July 1995 RiversideCounty; Riverside 6-10 July 1995 San Diego County;Carrizo Canyon 3 April 1996 San Diego County;Escondido 5 April 1996 San Bernardino County;Vidal Wash 25 March-30 December 1996 Los AngelesCounty; Antelope Valley 29 March-April 1996 Imperial County; Laguna Dam 31 March 1996 San Diego County;Spring Valley during his extensivesurveys of the lower Colorado first for the lower Colorado RiverValley, as Cooper River Valley in the 1870sand 1880s.It apparently (1870) made no specificmention of encountering was not recorded at the Colorado River again until this species.By the mid-1940s,it was "locally com- August (Stephens1903) and December 1902 (Wil- mon" in California (Grinnell and Miller 1944). der 1916), when individuals were noted on both There were occasionalrecords of large numbers, sidesof the river. Two specimenscollected in the although reports of 400-500 between Calexico and Rio Colorado delta of northeasternBaja California Heber, Imperial County, on 22 October 1920 bracket these records, a male along the Rio Alamo (Chambers 1921) and 250 near Calexico on 28 Au- southwestof Pilot Knob on 7 April 1894 (USNM gust 1923 (Chambers 1924) are perhapsbest con- 133726)and a subadultalong the Rio Hardy on 16 sidered tentative given that the speciesdoes not April 1905 (USNM 197921).Thus, a few birdswere travel in large flocks (Bednarz pers. comm.). in the area from the mid-1890s until the early The few recordsof the Harris' Hawk prior to the 1900s; however,following the few noted in 1902, late 1910s may have involved occasionalstrays to the species again went unrecorded in California the west of its establishedrange given its apparent for a decade. For example, Joseph Grinnell and spread into western Arizona. This species"has a party did not find the Harris' Hawk during their reputation for being somewhat nomadic" (Bed- exhaustivesurvey of the length of the lower Colo- narz et al. 1988), with straysbeing recorded north rado River Valley 14 February-15 May 1910 (Grin- to Ohio (Earl 1918) and Kansas(Bunker 1919, Sny- nell 1914). Given the paucity of records through der 1919), east to Louisiana (Coombs 1892), and this period, Grinnell (1915) consideredthe species west to Utah and Nevada (Palmer 1988). The spe- to be only a "summer visitant" to the Colorado cies has bred opportunistically even at the fringes River, based solelyon Stephens' (1903) records. of its range, including occasionalnesting in Kansas The Harris' Hawk was not documented as a (Parmalee and Stephens1964) and Louisiana(Bai- breeder in southeastern California until the late ley and Wright 1931). On a smaller scale,groups 1910s,with the first evidencefound on 25July 1916 of Harris' Hawks have been documented to invade (Wiley 1917, Bancroft1920); the first breedingev- and subsequentlynest in severalregions in south- idence for northeastern Baja California was con- ern Arizona east of its normal range (Bednarz comitant (WFVZ 83655). Thus, it is probable that 1995). Furthermore, there are two historical re- the specieshad only recently expanded its range cords of the Harris' Hawk for coastalSan Diego into the area. These breeding recordswere alsothe County, California: one collected at MissionValley SEPTEMBER 2000 H2xmus' HAWK IN CALIFORNIA 191

Colorado River

Los

SanDieg ( . ß

ß 1 individual Gulf of ß 2-3 individuals California ß 4+ individuals Approximate northern •' limitof range (Wilbur 1987)

Figure 2. Recordsof the Harris' Hawk (Parabuteounicinctus) in southern California and northern Baja California since April 1994. The double line identifies the apparent geographic limits of the 1994 incursion. Recordswithin this line are best considered naturally occurring, records falling on the line are debatable, and records well to the west or east are problematic (see text). Shading representsurban/agricultural areas. on 17 November 1912 (Grey 1913, SDNHM 1842; 3 December 1902 (Wilder 1916). These numbers the second record for California) and one ob- followed many decadesof no recordsfor the lower served at Oceanside from 1-6 November 1942 Colorado RiverValley. Elliot Couesnever recorded (Kent 1944). the speciesduring manyyears of work at Yuma and Although there are no long-term population the specieswas apparently absent again by 1910 censusdata, availabledata suggestthat the Harris' (Grinnell 1914). This dearth was followed by an Hawk has undergone four influxes into California influx in the late 1910s and early 1920s that was during the 20th century (Fig. 3). The first major apparently an order of magnitude larger than the northwesterlyexpansion was around the turn of incursionsof 1902 or 1994, asevidenced by reports the century when "10-20 [were] in the air at a of large numbers in the Imperial Valley (Chambers time" along the lower Colorado River between 1- 1921, 1924), a new westerlyoutpost for the species. 192 P^TT}•NAND EPdCICSON VOI•. 34, No. 3

Table2. BajaCalifornia records of the Harris' Hawk (Parabuteounicinctus) north of itsnormal range from fall 1993 throughfall 1995 (Fig. 2). Recordsare arrangedchronologically. Breeding has been documentedin the ValleSan Telmo, where at leastone wasstill presentas of 31 January1999 (Pattenpers. obs.); in addition,an adult wasstill presentat Leyesde Reformaon 7 November1998 (Ericksonpers. obs.). For the sakeof completenesswe also include one record from this timeframefor the Rio Coloradoin extremenorthwestern Sonora (Russelland Monson1998). See Methods for data sources (now on file at WFVZ).

DaTE (S) LOCATION MAXIMUM

5 September 1993-fall 1995+ Valle San Telmo 2 20 February 1994 20 km s. of San Quintin 3 9 April 1994 E1 Doctor (Sonora) 1 10 April 1994 Valle las Palmas 1 23 April 1994 Laguna Hanson 1 21 May 1994 Campo Christiano 3 21 May 1994-5 March 1995 Valle San Matias 5 30 May 1994 Ejido Sinaloa 1 13 November 1994-fall 1995+ Leyes de Reforma 2 13 November 1994 Valle Trinidad 1 26 March 1995 La Rumorosa 1 10 November 1995 H6roes de la Independencia 1

200

__ 100s in ImperialValley and alongColorado River by early 1920s

flocks of 10-20 and first California record in 1902 numbersbuild up to •oo flocksof 30 by 1950

first record for Colorado River (Arizon• in 1854 over 30 individuals unrecordedby Grinnell in 1910 stage influxin 50 unrecordedby Coues in late 1800s extirpated '1964

0 1840 1860 1880 1900 1920 1940 1960 1980 2000 YEAR Ftgure 3. Timeline of the fluctuatingoccurrence of the Harris' Hawk (Parabuteounicinctus) in California and the lower Colorado River Valley. SEPTEMBER 2000 HARMS' HAWK IN CALIFORNIA 193

There was apparently another influx of Harris' nia and northern Baja California, it explains nei- Hawks into California during the late 1940s and ther the magnitude nor the rapidity of the 1994 early 1950s (Bednarz 1995). During this period event. Instead, our investigation supports the hy- numbers again built to double digits (e.g., 30 at pothesisthat the speciesundergoes periodic pop- HavasuNational Wildlife Refugeon 27 December ulation fluctuationsthat result in rapid range ex- 1950) following two decadesof only a few individ- pansionsfollowed by adventitiousbreeding and, uals being regularly recorded (Rosenberg et al. typically, slow range contraction (Millsap 1981, 1991). Bednarzet al. 1988). Each expansion-retractioncy- Two major factorshave been implicatedin caus- cle differs in magnitude and may bring individuals ing the extirpation of this speciesin California. into areaswhere they had not been recorded pre- First, the sport of falconry had an upsurgein pop- viously,such as the Mojave Desert. The breeding ularity in the 1950s,and the Harris' Hawk wasand biology of the Harris' Hawk promotesrapid expan- remains a favored bird (White 1988, 1989). Rem- sion in numbers when conditions allow. While sen (1978) suggestedthat nestlingswere taken in most nest in spring (March-June), it is able to California until the population wascompletely de- breed year-roundin temperate-climatedesert hab- pleted, but there is no evidencethat falconersever itats in North America and may produce second harvested Harris' Hawks in California (Walton and third clutches (Bednarz 1987, 1995). We be- pers. comm.). Instead, birds were harvestedin Ar- lieve that most birds observed during the 1994 izona and Texas and most flown now are from cap- event originated in northern Baja California, tive breeding. Shootingwas undoubtedly common where rainfall totals at Ensenada were 140% of av- and may also have contributedsomewhat to its de- erage during winter 1991-92 and 168% in 1992- cline. 93, but were 90% average in 1993-94 (Mellink Second, habitat loss along the Colorado River pers. comm.). Perhaps two years of favorable con- from agricultural clearing and water diversionpro- ditions allowed for an increase in numbers suffi- jectswas extensive between 1930-60 (Whaley1986) cient to send birds far afield during lessfavorable and similarly occurred during this time in the Im- conditions in 1993-94, although causesare likely perial Valley (Steere 1952). In addition to direct more complex. clearing, erratic water levelsled to periodic flood- In summary,the availableevidence suggests that ing and desiccation,killing most suitablenest trees. the Harris' Hawk has alwaysbeen on the fringe of Throughout its range, the Harris' Hawk inhabits its natural range in California, with occasionalir- savannah-typehabitats in arid and semiarid areas, ruptive occurrencesinto the state every few de- including open woodland, open scrub, mesquite cades.Many stayto breed or linger for significant (Prosopisspp.) woodland, and riparian woodland periods, but eventually numbers decline as ap- bordering open spaces.Trees, especiallycotton- peared to be happening alreadyin the wake of the woods (Populusspp.), or large cacti such as the sa- influx of 1994. As noted above for Louisiana and guaro (Carnegieagigantea), are used for nesting; Kansas, this species is capable of adventitious however,this specieswill useutility polesand other breeding following a lengthy dispersal.Further- artificial structures.In recentyears, this specieshas more, the more general pattern of range expan- been steadilyincreasing its range in southeastern sion and contraction has been documented re- Arizona (Bednarz 1995, Dawson 1998) where it has peatedly in Arizona and New Mexico (Bednarz become more tolerant of human settlements. In- 1995, Dawson1998), although it is perhapsmore deed, Dawson (1998) noted that "the willingness dramatic in California given that the speciesmay of Harris' Hawk to nest in urban areas offers some not occur in the state for years at a time. hope of mitigating habitat loss to development," although post-fledgingsurvival of suchbirds is low ACKNOWLEDGMENTS (Bednarz pers. comm.). We are indebted to P.D. Jorgensen, K.A. Radamaker, Perhapssuch tolerance for urban setting is a re- R. Theriault, and T.E. Wurster for graciously providing cent advent, for if it were alwaysthe casethen the extensive summaries of field observations of the Harris' Harris' Hawk may have persistedin many areas Hawk in southern California and northern Baja Califor- nia. P.H. Bloom, B.E. Daniels, G. McCaskie, E. Mellink, where it formerly occurred. However,we feel that J. Linthicum, P. Unitt, and B.J. Walton supplied unpub- whereasthis urban tolerancemay play some small lished information and shared their views of this incur- role in the recent incursion into southern Califor- sion. California Bird Records Committee files (housed at 194 P^TTE•q AND EP,ICKSO•q VOL. 34, NO. 3

WFVZ) were an invaluable resource for information ical engineers, in 1853 and 1854: No. 3, report on about recent occurrences. R. Corado and J. Fisher birds collected on the route. Pac. RailroadRep. 10:19- (WFVZ), J.P. Dean and C. Ludwig (USNM), and P. Unitt 35. (SDNHM) provideddata about and/or allowedaccess to KENT, W.A. 1944. Rare birds seen in southern California. specimensin their care. We thank J.C. Bednarz, P.H. Condor 46:129-130. Bloom, BJ. Walton, and S.R. Wilbur for their careful re- viewsof the manuscript. LINTHICUM,J. [ED.]. 1989. Peregrine Falcon monitoring, nestmanagment, hack site,and cross-fosteringefforts, LITERATURE CITED 1989, including information regarding other field AMERICAN ORNITHOLOGISTS' UNION. 1998. Check-list of and laboratory activities.Ann. Activity Statement, San- North American Birds, 7th ed. Am. Ornithol. Union, ta Cruz PredatoryBird Res.Group, Univ. Calif., Santa Washington,DC U.S.A. Cruz, CA U.S.A. BAILEY, A.M. AND E.G. WRIGHT. 1931. Birds of southern M^SSE¾,B.W. 1997. Guide to birds of the Anza-Borrego Louisiana. Wilson Bull. 43:190-219. Desert. Anza-Borrego Desert Nat. Hist. Assoc.,Bor- BANCROFT,G. 1920. The Harris Hawk as a breeder in rego Springs,CA U.S.A. California. Condor 22:156. McCaSKiL,G. 1989. Southern Pacific Coast Region. Am. BEDNARZ,J.C. 1987. Pair and groupreproductive success, Birds 43:1366-1369. polyandry,and cooperativebreeding in Harris' Hawk. ß 1995. Southern Pacific Coast Region. FieldNotes Auk 104:393--404. 49:195-201. 1995. Harris' Hawk (Parabuteounidnctus). In A. ß 1996. Southern Pacific Coast Region. FieldNotes Poole and F. Gill [EDS.], The birds of North America, 50:330-334. No. 146. Acad. Nat. Sci., Philadelphia, PA and Am. MILLSAP,B.A. 1981. Distributional status of falconiformes Ornithol. Union, Washington,DC U.S.A. in west-centralArizona: with notes of ecology,repro- , J.W. DAWSON,AND W.H. WHALEY.1988. Harris' ductive success,and management. Bureau Land Man- Hawk. Pages71-82 in R.L. Glinski,B.G. Pendleton, age. Tech. Note 355. M.B. Moss, M.N. LeFranc, Jr., B.A. Millsap, and S.W. PALMER,R.S. 1988. Bay-wingedHawk. Pages390-394 in Hoffman [EDS.], Proc. SouthwestRaptor Manage- R.S. Palmer [ED.], Handbook of North American ment Symposiumand Workshop.Natl. Wildl. Fed. Sci. birds. Vol. 4. Yale Univ. Press, New Haven, CT U.S.A. Tech. Ser. 11. PARMALEE,P.F. AND H.A. STEPHENSß1964. Status of the BUNKER,C.D. 1919ß Harris' Hawk (Parabuteounicinctus Harris' Hawk in Kansas. Condor 66:443-445. harrisi) in Kansas. Auk 36:285. REMSEN,J.V., JR. 1978.Bird speciesof specialconcern in CIqAM}•ERS,W.L. 1921. A flight of Harris' Hawks. Condor California: an annotated list of declining or vulnera- 23:65. ble bird species.Calif. Dept. Fish and Game, Wildl. 1924. Another flight of Harris' Hawks. Condor Manage.Branch Admin. Rep. 78-1. 26:75. ROBEi•SON,D. 1980ß Rare birds of the West Coast. Wood- COOMBS,F.E. 1892. Notes on a few Louisiana birds. Auk cock Publ., Pacific Grove, CA U.S.A. 9:204--206. ROSENBERG,K.V., R.D. OHMART, W.C. HUNTER, AND B.W. COOPER,J.G. 1870. The naturalistin California.Am. Nat. ANDERSON. 1991. Birds of the Lower Colorado River 3:470-481. Valley.Univ. Ariz. Press,Tucson, AZ U.S.A. D^WSON,J.W. 1998. Harris' Hawk. Pages77-81 in R.L. RUSSELL, S.M. AND G. MONSON. 1998. The birds of So- Glinski [ED.], The raptors of Arizona. Univ. Ariz. nora. Univ. Ariz. Press, Tucson, AZ U.S.A. Press, Tucson, AZ U.S.A. SNYDEI•,L. 1919. Harris' Hawk in Kansas. Auk 36:567. EARL,J.M. 1918. Harris' Hawk in Ohio. WilsonBull. 30: STEERE,C. H. 1952. Imperial and CoachellaValleys. Stan- 15-16. ford Univ. Press, Stanford, CA U.S.A. G•RETT, K. ANDJ. DUNN. 1981. Birds of southern Cali- STEPHENS,F. 1903. Bird notes from eastern California and fornia: statusand distribution.Los AngelesAudubon western Arizona. Condor 5:75-78. Soc., Los Angeles, CA U.S.A. STEWART,G.R. 1979.Re-establishing the Harris' Hawkon GREY, H. 1913. Harris' Hawk in California. Condor 15:128. the Lower Colorado River. Unpubl. job report (proj. GRINNELL,J. 1914. An accountof the mammalsand birds W-54-R-12,job II-7), BureauLand Manage.,Yuma, AZ of the lower Colorado Valley, with especialreference U.S.A. to the distributionalproblems presented. Univ. Calif. ß 1982. Re-establishingthe Harris' Hawk on the Publ. Zool. 12:51-294. Lower Colorado River: annual report for fiscal 1982. ß 1915. A distributional list of the birds of Califor- Unpubl.job report (proj.W-54-R-14,job II-7), Bureau nia. Pac. CoastAvifauna 11. Land Manage., Yuma, AZ U.S.A. --AND A.H. MILLERß 1944. The distribution of the SWARTH, HoS. 1914. A distributional list of the birds of birds of California.Pac. CoastAvifauna 27. Arizona. Pac. CoastAvifauna 10. KENNERLY,C.B.R. 1859. Route near the thirty-fifth paral- UNITT, P. 1984. The birds of San Diego County. SanDiego lel, explored by LieutenantA.W. Whipple, topograph- Soc. Nat. Hist. Mere. 13. SEPTEMBER 2000 H•m•IS' HAWK IN CALIFORNIA 195

WALTON, B., J. LINTHICUM,AND G. STEWART.1988. Re- United States- 1987. Unpubl. report, U.S. Fish and lease and re-establishmenttechniques developed for Wildl. Serv.,Washington, DC U.S.A. Harris' Hawks-ColoradoRiver 1979-1986. Pages 318- --. 1989. Report on raptor propagatorsin the Unit- 320 in R.L. Glinski, B.C. Pendleton, M.B. Moss, M.N. ed States- 1988. Unpubl. report, U.S. Fish and Wildl. LeFranc, Jr., B.A. Millsap, and S.W. Hoffman [EDS..], Serv., Washington, DC U.S.A. WILDER, H.E. 1916. Some distributional notes on Califor- Proc. SouthwestRaptor ManagementSymposium and nia birds. Condor 18:127-128. Workshop. Natl. Wildl. Fed. Sci. Tech. Ser. 11. WILEY,L. 1917. Nesting of the Harris' Hawk in south- WHALEY,W.H. 1986. Population ecologyof the Harris' eastern California. Condor 19:142. Hawk in Arizona. RaptorRes. 20:1-15. WHITE, B. 1988. Report on raptor propagatorsin the Received30 October 1999; accepted 14 March 2000