Breeding Distribution and Habitat Preference of the Gray Vireo In

CALIFORNIA

BIRDS

Volume 3, Number 4, 1972

BREEDING DISTRIBUTION AND HABITAT PREF. ERENCE OF THE GRAY VIREO IN NEVADA

Ned K. Johnson

In the northernportion of the breedingrange of the Gray Vireo (Vireo vicinior)in Nevada,published records of occurrenceare based on sevenspecimens from four localitiesand sight recordsfrom an additional five stations scattered over southern Nye, southern Lincoln, and Clark counties(Linsdale, 1936; Miller, 1946; Gullionet al., 1959; Haywardet al., 1963; and Johnson,1965). The present note summarizes the aforementioned records and adds new informa- tion on occurrenceat five localities,one of which extendsthe known breedingdistribution of the speciesapproximately 50 milesto the north (Fig. 1). Thesedata document the occurrenceof the Gray Vireo to the northern limits of the Mohave Desert in Nevada. All but two of the specimens(number shown within parentheses)in the following tabulaUonare storedin the Museumof VertebrateZoology where theix identifications have been verified. Dates and initials of observer are indicatedafter sight records.Gullion et al. (I959)provided no datesor supplementarydetail for their sightrecords; therefore these placesof supposedoccurrence may not be breedinglocalities and they are queriedon the map. NYE COUNTY: GrapevineMountains-Wood Ca•on (1, not examined); Phinney Canyon, 6000 ft, at 3 mi E GrapevinePeak (1): Phinney Canyon, 6700 - 6900 ft, at 2• mi E and I mi S GrapevinePeak (singingon territory, 18 and 20 May, 1971; NK•). Nevada Test Site, Pahute Mesa-Shoshone Mountain area (1, not examined).1• mi SW Oak Spring,$850 fi (southeastof BeltedRange; close to 37ø 15'N, 116ø 5'W) (1). Calif. Birds 3: 73-78, 1972 73 GRAY VIREO IN NEVADA

LINCOLN COUNTY: 1% mi N and l•A mi W CaseIron,6100 ft (1); Wheeler Ranch, 6600 ft, E side Highland Range (singingon territow, 22 June 1972; NKJ); 1• mi N Mount Irish Peak, 7400 ft (1); Clover Mountains,Tule Desert, and Mormon Mountains, (no dates;GWG). CLARK COUNTY: Hidden Forest Canyon, 6100 - 6500 ft, $hoepRanB•; 2• mi E Cold Cr. Field Station, 6200 ft, SpringRange (sir,ging on territow, 24 May 1971; NKJ); N side Potosi Mountain, 5800 - 6000 ft (3); Potosi Pass,

Tonopah :

37 ø ß 37ø'• LINCOLN CO Beoffy

ß•C OUNTYNYE CLARKCO.•

o 2o

ß miles ß•.__ f'.:•.:.:c.:.•.:..•• LasVegas

36 ø

Figure 1. Map of southernNevada showing known localitiesof occurmlmeof the Gray Vi•eo {Vireo vicinior}. Recordsat presumedbreeding stations axe indicatedby dots. Recordsfor localitieswhere breed"ragis uncertainam indicatedby circles.Approximate extent of woodlandandlot forest zonesin the highlandsis shownby stippling.Note the locationof manyof tho localities for vireosnear the marginsof the woodland-forestzone. 74 GRAY VIREO IN NEVADA

6300 ft (pair on territow, 24 May 1971; NKJ); % mi E and % mi S Virgin Peak, 5400 - 6100 ft, Virgin Mountains (8); •6 mi E Big Pine Spring,5400 ft, McCullough Range (two pairs on territories, 23 May 1972; NKJ); Dead Mountains (no date; GWG). Gullion et al. (1959) mention the occurrenceof the Gray Vireo at Boulde• City and in Las Vegas Valley; these records presumablypertain .to transients. From theselocality data, and from noteson ecologicoccurrence, I cansummarize the statusof this speciesin Nevada.Here, aselsewhere on the MohaveDesert, the Gray Vireo usuallyoccurs at low density, occupyingremote slopes and canyonbottoms over a relativelynarrow elevationalrange between 5400 and 6600 feet (rarely to 7400 feet) at the lower edge of pi•on (Pinusmonophylla}-juniper (Juniperus osteospenna}woodland (Fig. 1). As Grinnelland Miller (1944: 386) noted, "Dry chaparral,which forms a continuouszone of twig growth from one to five feet abovethe ground"is the preferred habitat. In the Virgin Mountainsof Clark County this vireooccurred at unexpectedlyhigh density,with numbersperhaps comparable to thosereached in coastalsouthern California chaparral where Grinnell and Swarth (1913: 293) estimated 16 pairs per squaremile in chan•se(Adenostorna fasciculaturn) in the San JacintoMountains. The vireos in the Virgin Mountainsoccupied mountain-mahogany (Cercocarpusledifolius), Gambel oak (•2uercusgarnbelii), and Mexican manzanita(Arctostaphylos pungens). Gullion et al. (1959: 296) and Kay and Bradley(1968: 72-73) commenton the unusualdevelop- ment of the mixed chaparralformation in this range.Clearly, the designationof the Gray Vireo as an inhabitantof the "most arid scrub" (Barlow et al., 1970: 395) or of the arid "lowlands" (Hamilton,1958:31 l) doesnot applyin the regionunder discussion. The northernmostrecords for the species,from the foothillson the east sideof the HighlandRange near Caseltonin LincolnCounty, were obtained in an area of diverse shrubland and low woodland of spacedjuniper and sagebrush(Artemisia tridentata), where squaw apple (Peraphyllumramosissimum) and cliff rose (Cowaniastans- buryana}grew in profusionwith severalother unidentified species of smallshrubs. The Gray Vireo was numeroushere; severalmales sang along one-half mile of road. A male in active breedingcondition (singing;left testis,5 x 3 ram) was collected;it interactedwith a presumedmate. Nearby areasgrown to juniper and sagebrush,but without the other speciesof shrubs,lacked the vireo. In view of continuinginterest in habitatdistribution and sympatty of vireos(Hamilton, 1959 and 1962; Barlowet al., 1970; Williamson, 1971) I offer the followingremarks on the ecologicrelationships of 75 GRAY VIREO IN NEVADA the Gray Vireo and the SolitaryVireo {Vireo solitariusplumbms) duringthe nestingseason in southernNevada. These species are both membersof the subgenusF•reo; V. vicinioris a "thicket forager"and V. solitariusis an "arborealforager" (Hamilton, 1958: 310-311),and thus one might assumethat they couldstratify if sympatric.I have observedboth V. vicinior and V. solitariuson breedingterritories in six different mountainranges in southernNevada. The Gray Vireo has been studiedin two other rangeswhere Solitary Vireos apparent- ly do not nest.Only in the GrapevineMountains, Nye County,and on Mount Irish, Lincoln County, have the two speciesbeen found as closelyas approximatelyone-half mile. In the formerrange the Gray Vireo has been recordedalong Phinney Canyon from 6000 to 6900 feet elevationand I havefound the SolitaryVireo on the slopeabove the same canyonbetween 6900 and 7500 feet elevation.On Mount Irish I recordedthe Gray Vireo once at 7400 feet elevationand found the Solitary Vireo one-halfmile distantat 6900 feet elevation, at 7800 feet, and again at 8100 feet. In the other four mountain rangesthe SolitaryVireo alwayshas beenlocated at mid•levations one mile or more upslopefrom the sites of occurrenceof the Gray Vireo in the foothills.In suchplaces the SolitaryVireo preferseither forest of ponderosapines {Pinus ponderosa) or heavy woodlandof maturephion. Mountain-mahogany and/or Garnbel oak occasionallyis presentas a subdominant.I havenever observed overlap between the Gray Vireo and the SolitaryVireo in Nevada,but contactmay occur infrequentlywhere the chaparraland scatteredwoodland preferred by V. vicinior intermixesat its upper elevationaledge with the lower border of the ponderosapine forest or heavy pi•on woodland inhabited by V. solitariu• Dependingupon slope, exposure,and latitude (Wellsand Berger,1967), suchcontact could occurbetween approximately6500 and 7500 feet elevation. Evidentlythe habitat intermixturein certainportions of Arizona permits greatercontact of the two speciesthan is seenin Nevada toward the northern edge of 'the range of the Gray Vireo. For example,Barlow et al. (1970) reportedseveral instances of "habitat co-occupancy"of V. vieinlet and V. solitartusin Grand Canyon National Park, CoconineCounty, and presentedresults of limited experimentswith playbackof tape-recordedsongs which suggest the possibilityof interspecificterritoriality. In Nevada,not only do the distinctivehabitat preferencesof eachspecies seem to precludesuch interactions,but it is also significantthat neither-formin allopatry has ever been found on a breedingterritory in habitatthat appeared 76 GRAY VIREO IN NEVADA evenmarginally suitable for occupancyby the other form. Thus, Hamilton's(1962) thesis,that local sympatryis rarely found in membersof the samesubgenus within Vireo, seemssupported by the presentevidence. Furthermore, P. Williamson(1971) in an elegant analysisclearly has demonstratedthe existenceof species-specific foragingmovements in the Red-eyedVireo {V. olivaceous),Yellow- throatedVireo (V. flavifrons),and White-eyedVireo {V. griseus),and of important differencesin foraging sites of the sexes of V. olivaceous.Therefore, although differencesin grosshabitat prefer- encesand stratificationamong vireos may preventsubstantial contact between species,when contact does take place subfie additional differencesin behaviorand ecologycan come into play. Presumably such differences serve to reduce even further interaction and com- petition.

Figure 2. Habitat of Gray Vireo in mixed chaparral and open woodland of pi•on, juniper, serviceberry, and scrub oak on the north slope of Potosi Mountain, 6300 feet, Clark County Nevada. Photogxaph taken on 25 May 1971. Photo by Ned K. Johnson 77 GRAY VIREO IN NEVADA

Gene M. Christman drafted the final version of the map and Robert Oreduff identifiedseveral shrubs. Lynn Carpenter,Robert E. Jones,and AlexanderK. Johnsonprovided assistance and companion- ship in the field. These data were obtainedincidental to research dealingwith speciationin the SolitaryVireo, whichis supportedin part by the Committeeon Research,University of California, Berkeley.

LITERATURE CITED

Barlow, J. C., R. D. James,and N. Williams, 1970. Habitat co-occupancyamong somevireos of the subgenusVireo (Aves: Vireonidae). CanadianJ. Zool. 48: 395-398. Grinnell, J., and A. H. Miller. 1944. The distributionof the birds of California. Pac. Coast Avif. 27: 1-608. Grinnell, J., and H. S. Swarth. 1913. An accournof the birds and mammalsof the San Jacinto area of southern California. Univ. Calif. Publ. Zool. 10: 197-406. Gui!lion, G. W., W. M. Pulich, and F. G. Evenden,1959. Noteson the occurrence of birds in southern Nevada. Condor 61: 278-297. Hamilton, T. H. 1959. Adaptivevariation in the genus Yireo. WilsonBull. 70: 307-346. Hamilton, T. H. 1962. Speciesrelationships and adaptationsfor syrupartyin the avian genusVireo. Condor 64: 40-68. Hayward, C. L., M. L. Killpack, and G. L. Richards.1963. Birdsof the Nevada Test Site. Brigham Young Univ. Sei. Bull., Biol. Set. 3: 1-27. Johnson,N. K. 1965. The breedingavifaunas of the Sheepand Springranges in southern Nevada. Condor 67: 93-124. Kay, F. R., and W. G. Bradley. 1968. The occurrenceand distribution of the eastern fence lizard {Sceloporusundulatu# in southern Nevada. Herpetologica24: 72-76. Linsdale, J. M. 1936. The birds of Nevada. Pac. Coast Avif. 23: 1-145. Miller, A. H. 1946. Vertebrate inhabitantsof the pinon associationin the Death Valley region. Ecology 27: 54-60. Wells, P. V., and R. Berger. 1967. Late Pleistocene history of coniferous woodland in the Mohave Desert. Science 155: 1640-1647. Williamson,P. 1971. Feedingecology of the Red-eye•lVireo (Vireo olivaceous} and associatedfoliage-gleaning birds. Ecol. Monogr.41: 129-152.

Museumof VertebrateZoology and Department of Zoology,University of California,Berkeley, California 94 720.