BIRDS OF EAGLE MOUNTAIN, JOSHUA TREE NATIONAL MONUMENT, CALIFORNIA A. TOWNSEND PETERSON, Committeeon EvolutionaryBiology, The Universityof Chicago, Chicago, Illinois60637 The Little San Bernardino Mountains of Riverside and San Bernardino Countiesin southernCalifornia support a peninsulaof oak-pine woodland runningsoutheast from the higherSan BernardinoMountains (Figure 1). In spiteof the continuityof the woodland connectingthe two ranges,the birds of the Little San BernardinoMountains are remarkablydifferentiated from populationsto the west. Three subspeciesrequiring woodland are endemic to the range: a Mountain Quail, Oreortyxpictus russel!i, a Plain Titmouse, Parus inornatusmohavensis, and a Bushtit,Psaltriparus minimus sociabilis (Miller 1946), and another, a ScrubJay, Aphelocomacoerulescens cana, is endemic to the nearby Eagle Mountains (Miller 1946, Pitelka 1951). Miller (1946), Pitelka (1951), and Miller and Stebbins (1964) discussed three alternativehypotheses for the originof thesedifferentiated populations. (1) The peninsularestricts gene flow from populationsto the west. (2) The differentiatedpopulations represent intergrades or hybridsbetween popula- tions in the San Bernardino Mountains to the west and the Providence Mountainsto the northeast.(3) A thirdhypothesis is one of faunalrelaxation. Becauseas recently as 8000 years ago the Mojave Desert contained pin- yon-juniper woodland (Wells and Berger 1967, Van Devender 1977), dif- ferentiatedpopulations in the Little San Bernardino Mountains and other mountainranges farther east may representremnants of what was once a continuous distribution (Grinnell and Swarth 1913, Miller and Stebbins 1964). Hence, they may showtraits that are eitherancestral or intermediate owing to historicalgenetic interchange. Information on populationsof these speciesin the bits of woodland be- tween the Little San Bernardino Mountains and the Providence Mountains is criticalto assessingthe latter two hypotheses.The Eagle Mountains,the BullionMountains, the Old Woman Mountains,and othersprovide elevated landscapes(Figure 1). Of these,only the EagleMountains are known to hold pinyon woodland,and this habitatis restrictedto a smallarea (approx. 150 ha) around the peak of EagleMountain itself, in JoshuaTree NationalMonu- ment. EagleMountain reaches a heightof 1631 m, with a broad,flat valleyat approximately1460 m. Sparse woodlandsof Single-leafPinyon (Pinus monophy!!a), California Juniper (Juniperus californica), and Scrub Oak (Quercusturbinella) occur above 1400 m. Eagle Mountain is isolatedfrom the nearestwoodland habitat in the Little San BernardinoMountains by about 33 km of desert, the lowestpoint being Cottonwood Pass (914 m). In the 1940sand 1950s, scientistsfrom the Museumof VertebrateZoology (MVZ), Universityof Californiaat Berkeley,led by Alden H. Miller, studied the vertebratesof the Monument.They visitedEagle Mountain twice (in May and October 1945) and assembledrepresentative series of specimensfrom the area. DennisRainey and RichardLoomis of CaliforniaState University at Long Beach apparentlyworked in the area brieflyin the early 1960s. In 1986, George San Miguel of the Monument staffvisited the area on several Western Birds 21:127-135, 1990 127 BIRDS OF EAGLE MOUNTAIN occasionsand recordedseveral important sightings. To my knowledge,these trips consistutethe only ornithologicalwork on the birdsof Eagle Mountain prior to my visits.Information on other vertebratesknown from EagleMoun- tain was summarizedby Miller and Stebbins(1964). The purposeof this study is to summarizethe existinginformation on the avifaunaof EagleMountain. This paper representsan attemptto understand the historicalprocesses leading to the differentiationof Mojave Desertedge forms of a number of bird species. METHODS As part of studiesof the residentScrub Jays (Aphelocornacoerulescens cana), I climbed Eagle Mountain four times: 13 May 1987, 14 May 1987, 14-15 March 1988, and 26-27 May 1988, eachtime with one other person, for a total of 102 observer-hours.Observations from visitsto the area by other ornithologistsare also summarized. To check the validityof the five forms describedas differentiatedin the region [Mountain Quail, Scrub Jay, Plain Titmouse, Bushtit, and Bewick's Wren (Thryornanesbewickii)], I made comparisonsof museumspecimens in the collectionsof CaliforniaState Universityat Long Beach (CSULB) and the Museum of VertebrateZoology (MVZ). At MVZ, the three specimensof the Scrub Jay from the Eagle Mountainswere comparedwith other specimens from adjacent areas of the same age and sex, and collectedin the same seasonand approximatelythe same years. At CSULB, I used the extensive seriesfrom the Little San BernardinoMountains collected by DennisRainey and RichardLoomis to replicatethe comparisonsof Miller (1946), againcon- trollingfor variation due to age and sex, and year and seasonof collection. RESULTS Listedbelow are the speciesobserved by the MVZ teams and by Rainey and Loomis (Miller and Stebbins 1964, A.H. Miller's field notes from the Field Note Collectionat MVZ), by GeorgeSan Miguel (pers.comm.), and by myselfand my fieldcompanions. Habitat usage of speciesbreeding in the Lit- tle San BernardinoMountains is categorizedinto plant zonesfollowing Miller and Stebbins(1964): P, pinyon; Y, yucca;C, creosote.I do not describethe habitatusage of speciesthat apparentlydo not breed in the region. Species presumedor known to breed on the mountainare indicatedby an "x" or ..... , respectively. Red-tailed Hawk (Buteo jamaicensis). Single birds seen 13 May 1987 and 26 May 1988 soaringover peak. PYCx. Golden Eagle (Aquilachrysaetos). Pair seenflying by north base20 Oct 1945. PYCx. Gambel'sQuail (Callipeplagambelii). Seen 16 May and 19 Oct 1945. A covey of>20 flushed26 May 1988 at Conejo Well. PYCx. Mountain Quail (Oreortyxpictus). Collected 16 and 20 May, and seen 19 Oct. 1945. PYx. MourningDove (Zenaidamacroura). Several hundred seen flying to and from Conejo Well on 26 and 27 May 1988. PYCx. 128 BIRDS OF EAGLE MOUNTAIN Great Horned Owl (Bubo uirginianus).One heard callingat dawn on 27 May 1988. PYCx. Long-earedOwl (A$iootus). Seen 19 Feb (year?)at 1370 m (Raineyand Loomis,in Miller and Stebbins 1964). P. LesserNighthawk (Choralelies acutipennis). Seen at dusk on 26 May 1988. YCx. A•:)w atz Mtns • GraniteMts,,/•be•n .•? • •% • o• Sa•B e• t• • • o, Turtle Mtns %Granite Mtn Eagle Mtn SCALE 25kin Figure1. Topographyof the southernMojave Desert. The 1000 m contourline is shown.The blackrectangle on the insetmap of Californiashows the approximate area coveredby the map. 129 BIRDS OF EAGLE MOUNTAIN White-throated Swift (Aeronautes saxatalis). Seen 19-20 Oct 1945, 13-14 May 1987, 14-15 Mar, and 26-27 May 1988, with the recentrecords being of groupsof 5-20 individuals.Several times, especially on 26 May 1988, seenentering cavities on cliffswhich may have been nest sites.PYCx. Anna'sHummingbird (Calypte anna). Collected20 Oct and seen21 Oct 1945, 17 Mar 1986, 13 May 1987, and 26-27 May 1988. Abundant26-27 May 1988, with manyaggressive encounters observed, but only one of >50 individualshad a gorget; two others had a few dark feathers on their throats. Costa'sHummingbird (C. costae).Seen 17 Mar 1986 at west base of mountain. PYCx. Acorn Woodpecker(Melanerpes formiciuorus). An apparentlyimmature vagrant of the Arizonaform (M. f. aculeatus)collected 19 Oct 1945 (Miller 1947). Ladder-backedWoodpecker (Picoides scalaris). Seen 19 Oct 1945, 17 Mar 1986, and singleindividuals seen 13 May 1987 and 26 May 1988. PYx. Northern (Red-shafted)Flicker (Colapresauratus). Seen 19-21 Oct 1945. WesternWood-Pewee (Contopussordidulus). Seen 14 May 1945. Western Flycatcher(Empidonax difficilis). One individualseen on 13 May 1987; abundant26-27 May 1988. None heard calling,so all probablyrepresent migrants. Say'sPhoebe ($ayornis saya). Seen 17 Mar 1986 at westbase of mountain.PYCx. Ash-throatedFlycatcher (Myiarchus cinerascens). Seen 17 Mar 1986 at baseof moun- tain. PYCx. WesternKingbird (Tyrannus verticalis). Three individualsseen 26-27 May 1988. PYCx. Violet-greenSwallow (Tachycinetathalassina). Seen 19-20 May 1945. ScrubJay (Aphelocomacoerulescens). Collected on 16 May, 19 and 20 Oct 1945. On 16 May 1945, a broodof fledglingswas observed.One to five individualsseen 13 May 1987 and 14-15 Mar 1988. P'. CommonRaven (Corvuscorax). Singleindividuals heard over peak on 13 May 1987, 14 Mar, and 26 May 1988. PYCx. Mountain Chickadee (Parusgambeli). Seen Nov 1986. Bushtit(Psaltriparus minimus). Collected 16, 19-21 May 1945, and observedseveral timesdaily 13-14 May 1987, 14-15 Mar and 26-27 May 1988. P'. CactusWren (Campylorhynchusbrunneicapillus). Seen 18-21 Oct 1945, and com- monly at base of mountain 13-14 May 1987 (nestfound), 14 Mar and 26-27 May 1988. PYC'. Rock Wren ($alpinctesobsoletus). Seen 20-21 Oct 1945, 17 Mar 1986. PYCx. CanyonWren (Catherpesmexicanus). Seen 19 Oct and collected20 and 21 Oct 1945; seen commonly17 Mar 1986, 13-14 May 1987, 14 Mar and 26-27 May 1988. PYx. Bewick'sWren (Thryomanesbewickii). Collected on 16 May and 18-21 Oct 1945; seencommonly 13-14 May 1987, 14-15 Mar, and 26-27 May 1988. Recentlyfledg- ed young found 16 May 1945. PY'. Ruby-crownedKinglet (Regulus calendula). Seen 19 Oct 1945, 17 Mar 1986. Blue-grayGnatcatcher (Polioptila caerulea). Seen 16 May 1945, and commonly 13-14 May 1987, 14-15 Mar, and 26-27 May 1988, apparentlyon territories.PYx. Townsend'sSolitare (Myadestes townsendi). Seen 19 Oct 1945. Hermit Thrush (Catharusguttatus). Seen 19 Oct and collected20 Oct 1945. 130 BIRDS OF EAGLE MOUNTAIN