Summer Birds of a Lodgepole-Aspen Forest in the Southern Warner Mountains, California

SUMMER BIRDS OF A LODGEPOLE-ASPEN FOREST IN THE SOUTHERN WARNER MOUNTAINS, CALIFORNIA

DAVID W. WINKLER, 3317 White Oak Court, Sacramento, California 95825 GAYLE DANA, 123 Marina Boulevard, San Francisco, California 94123

The Warner Mountains occupy a narrow strip approximately 15 km wide and 160 km long runningnorth and southin extreme northeastern Californiaand southeasternOregon. Geologicallythe rangeis the west- ernmost of the basin rangeswhich file eastwardinto Nevadaand Utah and is characterizedby tilted fault blocks of lake bed sedimentsinter- bedded with volcanic sediments and basalt (Oakeshott 1971). In con- trast, affinitiesof its borealavifauna lie most closelywith the adjacent Sierra Nevada and CascadeRanges (Miller 1951, Johnson 1970). The flora of the Warner Mountains is largely a mosaicof Great Basinand Sierra Nevada forms (D. Taylor pers. comm.). Summersin the range are hot and dry with occasionaland local thunderstorms,and winters are cold with relatively sparseprecipitation in at least the southernpor- tion. Little has been publishedon the birds of the Warner Mountains (Johnson 1970, 1975; Maillard 1927; Miller 1941, 1951). Distribution- al data and indications of relative abundancesof speciespresent are scatteredand incomplete. The interrelationshipsof the bird speciesand the influenceswhich the area'sunique geography and flora havehad on bird communitiesin the rangeare just beginningto be explored. During the summerof 1975 a mappingcensus was carried out on the birdsof a decadentstand of LodgepolePine (Pinuscontorta) and QuakingAspen (Populustremuloides) in the Skunk CabbageCreek drainageof the extreme southernWarner Mountains. The study wasundertaken to gather data on bird distribution in the southernarea of the rangeand the importanceof varioushabitat typesto individualbird species.

STUDY AREA AND METHODS

The Skunk CabbageCreek study area (Figure 1) consistedof 27.2 ha (about 67 acres) in the southernmostforested area of the range (41ø 10'N, 120ø 10'W). The plot wasa rectangle594 m longand 457 m wide,the longside of whichfaced southeast into the smallvalley through which Skunk CabbageCreek flows. The study area rangedin altitude from 2390 m up to 2450 m. The longaxis of the plot ran approximately parallelto the contourof the area,and the averageslope was an esti- mated 15%. The forests in the Skunk CabbageCreek area are generally patchy and broken with hillsidesof sagebrush(Artemisia) interspersedwith mule-ears(Wyetbia) and lupines (Lupinus). The low areasaround the creekare dominatedby perennialbog vegetationwith clumpsof willows

Western Birds 8:45-62, 1977 45 SUMMER BIRDS OF WARNER MOUNTAINS

(Salix)and often extensive areas of corn-lily(Veratrum). The soils on the higherareas are generally light, sparse and veryrocky, whereas the soilsof the creeksidebogs and meadows are dark and heavy. The Skunk CabbageCreek area has had a historyof relativelylittle disturbance. The majorhabitat alteration has been periodic summer grazing, and the

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Figure1. Locationmap of the SkunkCabbage Creek study plot. Contourinter- valswithin the plotboundary are forty verticalfeet. 46 SUMMER BIRDS OF WARNER MOUNTAINS area has not been logged. In the early 1960s a stock driveway was con- structedup the valleyjust downslopefrom the presentstudy area. There hasnot been a major fire in the areafor at least 130 years. Vegetationtypes on the plot (Figure 2) were classifiedas to percent composition of Lodgepole Pine and Quaking Aspen. Each vegetation type wasfurther describedby the techniquesproposed by Emlen (1956) by samplingat randomly chosensites within areasof each vegetation type. (Copiesof these more detailed descriptionsare availablefrom Winkler on request.) Although our initial descriptionof the vegetation usedseven different categoriesof vegetation,several of theseclasses were lumped together for usein analysisof the bird populationson the plot. The following brief descriptionspertain to these lumped cate- gories. LodgepoleForest (9.0 ha, 33% of total vegetationcover): Pure stands of lodgepoleare the densesthabitat on the plot, with limited visibility, little sub-canopylight and no appreciableground cover. As aspenoc- curs in greater proportions, the lodgepole forest becomes more open with sparseground coverand a shallowlitter layer. Mixed Forest (5.4 ha, 20% of cover): Forest with approximately equalproportions of aspenand lodgepoleis heterogenousin aspect,with tall pines interspersedfreely with stunted aspen. Ground coverand litter layers are better developedhere than in the lodgepoleforest. Aspen Forest (9.5 ha, 35%): This vegetationoccurs in two different types of potential significanceto avian habitat selection. The dense aspen is the least extensiveof the two and is characterizedby apparently healthy trees growing to 6-7 m in height and forming a continuous canopy. The open aspen is more common and seemsto be the type from which the aspencomponents in mixed habitatsare derived. Ground cover is best developedin the closedaspen and is very sparsein open aspen. Large amounts of litter are found in both habitats, reachinga maximum in open aspenwhere the density of downed trees and slash often makeswalking difficult. The treesin the openaspen are typically sickly in appearance;their foliage is often sparseand pale in color. In- sectinfestations often reachepidemic proportions in standsof this type. The principal insect pest appearsto be the larvaeof the tortricid moth, Sparganotbiscaliforniana. By mid-July a large number of the trees in the open aspenwere sheddingmany leaves,apparently due solelyto insect infestation. Sagebrush(3.0 ha, 11%): This habitat is typically composedof heavystands of Artemisia, often with considerableWyetbia and Lupinus. Open Areas (0.3 ha, 1%): In this habitat the substrateis almost con- tinuousrock and the predominantvegetation is low herbs. This designa- tion is usedfor areaswith small sagebrushplants as long as the sagebrush is not dominant. Even with the latter provision,the distinction between

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49 SUMMER BIRDS OF WARNER MOUNTAINS open areasand other vegetationtypes is often unclear,and in the initial descriptionof the vegetationwe resortedto the use of suchcategories as "rock-sage"and "rock-aspen"in an attempt to expressthe intermedi- ate nature of certain areasof vegetation. A grid of 46 m squareswas superimposed on the plot by markingthe cornersof eachsquare with a codedcombination of plasticsurveyor's tape. Censuseswere conductedby walkingleisurely along rows between grid markersand recordingeach contact on a tracingpaper overlayof the plot grid. The overlay was marked with a unique symbolfor each speciesand accessorysymbols for the behaviorin which the bird was engaged(see International Bird CensusCommittee 1970). A running summation of the location and number of all contactsfor all species was maintained. To maximize coveragetime during the most produc- tive morning hours and to minimize inequalitiesin observercoverage, the censuswas usually divided between two observerswho alternated halves of the plot each day. An equivalentof ten censuseswere con- ducted between 30 June and 26 July. Each censusinvolved an average of about six observer hours. Most speciesfor which sufficientdata were collectedcould easily be categorizedby habitat preferenceand/or the approximatenumber of breedingpairs on the plot basedon superimpositionof the spec.ies map on the vegetationmap. At least three speciespresented problems in analysisdue to their ubiquitousand abundantoccurrence. These species, Pine Siskin,Evening Grosbeak and Red Crossbill,were analyzed by de- terminingthe numberof contactsfor eachspecies in eachhabitat type.

RESULTS Table i presentsa list of bird speciesencountered on the Skunk CabbageCreek study area along with categorizationsof ecological char- acteristicsand avifaunalaffinities for each. The categorizationsof forag- ing and predominantfood aretaken from Johnson (1975:557) or from Bent (1937-1968). When more than one food is listed, the first listed is deemedto be of predominantimportance to breedingbirds of the species. Designationsof residenceand migratory status are based on Maillard (1927) and Grinnell and Miller (1944). The abbreviationsand their in- terpretationsare as follows:"LV" representslocal visitors, species that are thoughtto havebred in the vicinityand visitedthe plot duringor immediatelyafter breeding. "MV" designatesmigrant visitors, species that breddistant from the plot andonly visitedthe plot in the courseof their annualmigrations. "B" representsbirds that arethought to have bred on the plot. "R" is usedto signifyspecies that probablystay on or verynear the plot throughoutthe entireyear. "AM" representsal- titudinalmigrants, those which migrate to contiguouslower elevations 50 SUMMER BIRDS OF WARNER MOUNTAINS in winter. Some altitudinal migrantsmay leavethe breedinggrounds only when conditionsare severeenough to force them away. "M" sig- nifies speciesthat are latitudinal migrantsand typically leavethe area for wintering areas to the south before the onset of severeclimatic conditions or food limitations. These classificationsare among the most subjectivemade in the study, for little is known of the winter movements of birds in the Warner Mountains, and it is often difficult to characterizethe migratory patternsof all individualsin a population with a singledesignation. The approximatenumber of pairsper km2 wasestimated by comput- ing the number of pairs per ha of the species'preferred habitat and multiplying by one hundred. The "hole-nesting"category includes only speciesthat nest in cavities in trees. Although a Rock Wren nestedin a stump cavity, this species is not treated as a hole-nester,for it typically nestsin holes among rocks (Bent 1948). The determinations of avifaunal affinities are based on the lists in Miller (1951) and Johnson (1975). Habitat preferenceswere determinedby evaluationof the species mapssuperimposed on the vegetationmap. As shouldbe evidentfrom Table 1, the analysescarried out on the Pine Siskin, Red Crossbilland EveningGrosbeak revealed no habitat preferences.Habitat preferences are indicated in Table i in the following manner. Habitat types for which a speciesis judged to exhibit primary habitat preferenceare in- dicatedby X's appearingin columnsbeneath the habitat type headings. Numbersin parenthesesindicate the numberof recordsin a habitat type when there are very few records. The X's for Lazuli Buntingand White- crownedSparrow are intentionally placedin an intermediateposition between sageand aspenin an effort to expressthe interface nature of the preferredhabitat of thesetwo species.

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SPECIES ACCOUNTS The assignmentof any speciesto a restrictedhabitat type is some- what subjective.The followingnotes for selectedspecies clarify the evidencefor each determinationand provideadditional details.

RUFOUS HUMMINGBIRD: Observed around the major concentrationsof nectar-bearingplants from 9 July on. No adult maleswere observed. CALLIOPE HUMMINGBIRD: Appeared with the first large concentrationof hummingbirdson 19 July. WILLIAMSON'S SAPSUCKER: Nested in an aspengrove approximately 6 km north of the study plot at Pattersonand probably nestedadjacent to the plot. BLACK-BACKED THREE-TOED WOODPECKER: Probably nested in the pure lodgepoleforest west of the plot. This speciesoccurred on the study plot in November 1974 (H. Newhousepers. comm.). This observation,coupled with the fact that our only record.for this specieson the plot was on 21 August sug- geststhat this speciesmay shift its feeding activitiesinto aspenareas following the breeding season. EMPIDONAX SPP.: No members of this group were examined in the hand; therefore, no definite specificidentifications were made. On the basisof appearance, behavior (type of tail wag) and call note, we strongly suspectthat E. wrigbtii was presentin the lower sage-aspenareas. Two Empidonax nestswere found in the upper lodgepoleforest on the branchesof LodgepolePines less than 2 m off the ground. These nests probably did not belong to the wrigbtii-like individualswhich we observedpredominantly in the lower aspenand were very likely the nestsof oberbolseri. TREE SWALLOW: Visitor to open aspenonly. Probably nested adjacent to the plot and known to nest in aspenat Patterson,6 km to the north. CLARK'S NUTCRACKER: Only seen flying over the plot or once perched high in a LodgepolePine. Probablynested in the alpinecountry to the north and visited the area after breeding, for this conspicuousspecies was not seen until 21 July. ROCK WREN: One nest with three young was found in an aspenstump on the extreme northeasterncorner of the plot on 25 July. This pair presumablyspent most of its time out of the plot, as this was the only date the specieswas observed in that part of the area. The other two pairswere restrictedto rocky openingsin the lodgepoleand mixed forests. A Rock Wren was observedsinging from the limbsof a LodgepolePine approximately10 m off the groundon 20 July. AMERICAN ROBIN: Four nestswere found, all in aspensabout 3 m off the ground. One with two eggsand one with three eggson 9 July, the latter with two young by 19 July. A third nesthad three youngon 22 July. The contentsof the fourth nest were not examined. This speciesseems to be reliant on openingsin the forest for nesting. MOUNTAIN BLUEBIRD: Two of the five pairs nested in dense aspen and movedinto open aspenfeeding their young once the young had fledged. WARBLING VIREO: Two nestsfound adjacentto the plot: One about 8 m up in a 10 m aspenand one near the top of a 2 m aspen. The latter had two eggs in it on 10 July, both of which were apparentlyrobbed, as the nestwas abandoned by 20 July. LAZULI BUNTING: Occurred in the open aspenon the northeastern corner of the plot, first appearing 18 July. The singingmale in this area was probably a post-breedingwanderer from localitiesto the north or downslope(Erickson 1968, Pough 1957). 55 SUMMER BIRDS OF WARNER MOUNTAINS

CASSIN'S FINCH: This speciestended to move into the lower areasof open aspen as the summer progressed. During the last censusperiods many of the con- tacts for this speciesin the open aspeninvolved adult birds in the companyof small groupsof fledglings. PINE SISKIN: Although this specieswas seen in small groups(3-5 individuals) throughout the breedingseason, there is no reasonto doubt the likelihood of its breeding,for territorial defenseis very lax in this species(Palmer 1968), and the circling flights of maleswere observed. RED CROSSBILL: No definite evidenceof nestingwas obtained for this ex- ceptionallysporadic species. Although crossbills were observed in all foresttypes, it is probable that nestingactivities, if any, were carried out in the lodgepole forest. The specieswas observedin large numbersthroughout the censusperiod, but large flocks (20-50 individuals)were not observeduntil 18 July. At least two apparently juvenal plumagedbirds were observedin the company of at least one adult in an aspenin the open aspenarea on 10 July. Breedingactivity for the Red Crossbillhas neve? been reportedfrom the WarnerMountains (Johnson 1975). DARK-EYED JUNCO: One ground nest found in open aspencontained four eggson 10 July and on 20 July there were three young with one egg still un- hatched. CHIPPING SPARROW: A territorial encounterbetween this and the preceding specieswas observedin the lodgepole-mixedforest interfaceon 21 July. BREWER'S SPARROW: Three of the four pairs occupiedpatches of sagebrush, whereasthe fourth occupiedthe most open area of the aspenwith a con- spicuoussagebrush understory. In a study of finches in the mountainsof southernCalifornia, Cody (1974: 231-240) hypothesized that similarities in the songs of the Dark-eyed Junco, ChippingSparrow, and Black-chinnedSparrow (Spizella atrogularis) have evolved to maximize the efficiency of maintenance of interspecific territoriality between these species. Our data from the Warners(Figure 3) indicate that the territories of the Dark-eyed Junco, Chipping Sparrow, and Brewer'sSparrow are broadly overlappingin the Skunk CabbageCreek area. The songsof the former two species were often indistinguishable,whereas the songof the Brewer'sSparrow was very distinctive. If the similaritiesin songbetween the junco and the Chipping Sparrow have evolved as a mechanismfor the maintenance of interspecific territoriality, the mechanism does not seem to be working in the populations we studied. WHITE-CROWNED SPARROW: A common breeder in the sage-meadowin- terface immediately downslopefrom the study area; only portionsof two territories reachedthe plot. A female with a well-developedegg in the lower oviduct was capturedand releasedon 9 July.

One unofficial censuswas made on the study area on 21 August. At this time flocks of White-crowned,Chipping, and Brewer'ssparrows, all with young, were presentin the lower open aspenarea along with three Townsend'sWarblers (Dendroica townsendi) and four Solitary Vireos (Vireo solitarius). Apparently,as the summerprogresses and youngare fledged,the lower aspenarea takes on increasedimportance as a feeding area for both breedingbirds and migrants. The major food item for many of thesebirds in the aspenwas mostlikely tortricid moth larvae. 56 SUMMER BIRDS OF WARNER MOUNTAINS

Table 2. Potential indicatorsof community structureand function on the Skunk CabbageCreek study plot. See text for details.

HABITAT TYPE Lodge- Over- Open Sage Aspen Mix pole all % latitudinal migrants 100 100 47 58 46 60 % latitudinal + altitudinal migrants 100 100 80 83 69 84 % tree cavity nesters 0 0 40 17 23 24 % primary insectivores 100 0 67 58 54 68

% Boreal affinity 0 5o 79 82 lOO 75

Table 2 containsa habitat-specificbreakdown of some potential indicatorsof communityorganization. In the computationof the values in this table, only those birds thought to breed on the study area are considered.The unidentifiedEmpidonax flycatchers were left out of the computationof "% Borealaffinity". We have consideredprimary insectivoresto be those specieswhich include insectsor other inverte- bratesas a great majority of their diets during the breedingseason. In the analysisof this characterwe have relied a great deal on published accounts,especially the classicseries by Bent (1937-1968) and the re- cent work of Johnson(1975:557). It is possiblethat some of the finchesshould have been includedin the categoryof primaryinsecti- vore in view of their propensityto take large numbersof invertebrate prey during times of peak invertebrateabundance and nestlingprotein demand. Interhabitat avifaunalsimilarities were estimatedby dividingthe numberof speciesshared by both habitatsby the total numberof bird speciesin both habitats. Similarity valueswere calculatedboth with (St) and without (Sp) five "generalist"species (Mountain Chickadee, EveningGrosbeak, Pine Siskin, Red Crossbilland Dark-eyedJunco). Similarityvalues for aspenand mixed forests(St=.42, Sp=.21), lodgepole and mixed forests(St=.53, Sp=.30), and lodgepoleand aspenforests (St=.33, Sp=.13) were the only valuesgreater than zero. The un- identified Empidonax were omitted in the calculationsof similarity values.

57 SUMMER BIRDS OF WARNER MOUNTAINS

DISCUSSION

In this studywe chosea modifiedspot-mapping technique following the standardsproposed by the International Bird CensusCommittee (op. cit.) becausewe were more interestedin generalspatial relation- shipsthan in absoluteabundance (for the latter see Emlen 1971). We encounteredseveral difficulties with the techniqueswe employed,in- cludingambiguities in the code usedfor censusgrid cornersand inabil- ity to see corner stakes on steep terrain with any appreciableground cover. Another sourceof difficulty involvesthe coded designations usedfor vocalizations:it is best to determinefrom the outsetprecisely how each vocalizationtype in a species'vocal repertoire is to be record- ed (e.g.,whether as a flight call,territorial call, song, etc.). In the lodgepole and denseaspen forests, the very poor visibility of birds and grid corner markersmay haveintroduced a biasin the data for somespecies. This is a factor which must constantlybe kept in mind during use of the spot-mappingtechnique. Overcomingthis obstaclewould probably be possibleif a grid with smallersquares was used, allowing a more thoroughcoverage of the habitat. Additionally,since many of the con- tacts registeredin denseforest involve vocalizations,efforts shouldbe madeto proceedmuch moreslowly in the denseareas of a plot. The major deviation of our study from the majority of bird community studiesis the lack of quantitativedescription of the vegetation. From the beginningwe intended to correlateindividual species distri- butions with habitatsin only a generalway. If more detailed correla- tions with specific habitat parametersare desired,the techniquesem- ployed by James(1971) and Andersonand Shugart (1974) seemto be the best yet developed. Among the traits yon Haartman (1957, 1971) associateswith the hole-nestinghabit is the tendency for hole-nestingbirds to be residents. To meet intense competition for nest holes and potential nest sites, it is to the advantageof hole-nestingspecies to be present on the breeding groundsas early as possible. This predictionis upheldby our data, as only two (29%) of the sevenhole-nesting breeders are migratory ("M" only). This proportionis well below the plot meanand the proportions for any of the other habitats. Flack (1976) and Lawrence (1967) have pointed out the importanceof soft-woodedtrees, especially aspen,for hole-nestingspecies. The drilling of nest holesis often impossiblefor many hole-excavatingspecies in the trunksand branches of tree specieswith relatively hard wood. Flack hasalso indicated that hole-nesterswill excavate cavities more readily in trees whose wood has been softened by insect infestation or disease. LodgepolePine has exceptionallyhard bark (H. Newhousepers. comm.). On the basis of these observationsone would predict the highestproportion of hole-

58 SUMMER BIRDS OF WARNER MOUNTAINS nestingspecies to be in the aspenon the Skunk CabbageCreek plot. This is preciselythe relationshipobserved (Table 2). The aspencontains proportionally more primary insectivoresthan do any of the other forestedvegetation types on the plot (Table 2). Additionally, the highestnumber of species(15) occursin the aspen. Deciduousforests harbor more invertebratesper weight of twigs than do coniferousforests (yon Haartman 1971). This relationship,coupled with the observation that insects seemed to be more numerous in the aspenthan in any other vegetationtype duringthe summerof our study, tend to supportthe possibilitythat the higherproportion of primary insectivoresin the aspenis a real responsein the avifaunato higherprey concentrationsin that habitat. Whether higherinsectivore levels in the aspen is a condition to be expected every breedingseason depends on whether prey levels in that habitat are equally high in all years and whether the insectivorepopulations respond to varying prey levels through differential fecundity or migration. It is interestingthat King- ery (1970, 1971, 1973) reportshigher nestingactivity in lodgepole mixed with aspenthan in pure lodgepolein a seriesof censusesfrom Colorado. As winter comesto the study area, marked changesin the avifauna must result. With the ground coveredwith snow, the breedersin the open areasmust leave,and it is not surprisingthat all the breedersfrom theseareas are migratory. In the forestedareas considerably more cover and above snow forage is available,and there is a reducedproportion of migrants. Additionally, many of the migrantsin these areasare altitudinal migrantsand possiblyonly leavethe high countrywhen weath- er and food conditionsare at their worst. As cold weatherapproaches, insect populationscollapse and most primary insectivoresmust leave: of the breedingprimary insectivores,fifteen (88%) are either latitudinal or altitudinal migrants. The similaritiesbetween the avifaunasof the differenthabitat types (see Results)are certainlynot surprising,and they reinforcethe notion that discontinuitiesin forest characteristicsare perceivedsimilarly by both birdsand people. Reviewsof the birds of aspenforests (Flack 1976) and coniferous forest (Wiens1975) of North Americahave recently appeared. Com- parisonwith these reports on a speciesby speciesbasis would be redun- dant, for, with minor exception,these accounts reinforce our conclu- sionsregarding habitat preference.Comparisons with the work of John- son (1975) havestrengthened our impressionthat the avifaunaof our study area is little different from that of comparableareas in the adjacent Sierra Nevada. This affinity with the Boreal avifauna of the west declinessteadily from the fauna of the lodgepoleforest downthrough the forestedtypes and reachesa low in the open areaavifauna. Not

59 SUMMER BIRDS OF WARNER MOUNTAINS surprisingly,the open areaavifauna has been derivedfrom the surround- ing Great Basinaustral areas. It is interestingthat many speciesknown to breed in the northern Warners(e.g., WesternFlycatcher, Gray Jay and Golden-crownedKinglet) do not occurin areasof similar habitat in the southernpart of the range. This observationsuggests that these mountainsmay have been colonizedby Boreal populationsfrom the north and that the avifauna of the southern Warners is relatively im- poverished. The initial findingsof this study have potentiallysignificant land managementimplications. The decadentstands of aspenare apparently of great importancein maintainingthe bird populationson the plot. Not only is aspenimportant as a sourceof potentialnest sites for hole- nestingspecies, but it appearsthat the insect populationsassociated with the aspenare veryimportant for both breedingbirds and transients. Aspen standsprobably become more susceptibleto diseaseand in- sectinfestation as they grow older. As a result, it may seemsenseless to many land managersto retain old and relativelyunattractive stands of aspenwhich may act as potentialreservoirs of infestationfor neigh- boring stands. At least somedecadent stands, however, must be maintained until land managementpersonnel better understandthe require- mentsof bird populationsthat aspenstands of varyingages can satisfy overthe variationsof the changingseasons and year to year fluctuations. Much the sameconsiderations apply to lodgepoleforest. The manage- ment of forestsfor heterogenousage composition should be giventhe highestconsideration in weighingmanagement alternatives until more is known about the relationshipbetween bird populationsand the state of their habitat.

ACKNOWLEDGMENTS The completionof this projectwould havebeen impossible without the support of the U.S. Forest Service,Warner Mountain Ranger Dis- trict, Modoc National Forest. Conversationswith Ron Escofio and Hank Newhousewere extremely helpful. We would like to expressour sin- cerestthanks to Hank and all his family for providingus with our home away from home in Cedarville. Many thanksto Rob, Joe, Paul,Robin, Harry, and Hank for helpingus pack into Skunk CabbageCreek. Spe- cial thanks to Harry for his assistanceduring the project's completion. Partsof this paper were presentedat the WesternRegional Forest Ser- vice biologists'meeting in San Franciscoin February, 1976; many thanksto Dave Dunawayfor his assistancewith arrangementsthere. We

6O SUMMER BIRDS OF WARNER MOUNTAINS would like to thank Christine Weigenfor help with the figures and Robert L. Rudd, Ned K. Johnsonand Alan Craigfor many perceptive and stimulatingcomments on the manuscript. Any remainingerrors •.rc otlr own.

LITERATURE CITED Anderson,S. H. and H. H. Shugart,Jr. 1974. Habitat selectionof breedingbirds in an east Tennesseedeciduous forest. Ecology 55:828-837. Bent, A. C. 1937-1968. Life historiesof North Americanbirds. U.S. Natl. Mus. Bull. 167, 170, 174, 176, 179, 191, 195, 196, 197, 203,211,237. Cody, M. L. 1974. Competitionand the structureof bird communities.Monogr. Population Biol. No. 7, Princeton Univ. Press,Princeton, N.J. Emlen, J. T., Jr. 1956. A method of describingand comparingavian habitats. Ibis 98:565-578. Emlen, J. T. 1971. Population densitiesof birds derived from transect counts. Auk 88:323-342. Erickson,M. M. 1968. Lazuli Bunting. Pages111-132 in Bent, A. C. Life his- tories of North American cardinals,grosbeaks, buntings, towhees, finches, sparrows and their allies. U.S. Natl. Mus. Bull. 237. Flack, J. A.D. 1976. Bird populationsof aspenforests in westernNorth Ameri- ca. Ornithol. Monogr. 19. Grinnell, J. and A. H. Miller. 1944. The distribution of the birds of California. Pac. Coast Avif. 27. International Bird Census Committee. 1970. Recommendations for an international standard for a mapping method in bird censuswork. Aud. Field Notes 24: 722-726. James, F.C. 1971. Ordination of habitat relationshipsamong breeding birds. Wilson Bull. 83:215-236. Johnson, N. K. 1970. The affinities of the Boreal avifauna of the Warner Moun- tfins, California. Occ. PapersBiol. Soc. Nev. 22:1-11. Johnson,N. K. 1975. Control of number of bird specieson montaneislandsin the Great Basin. Evolution 29:545-567. Kingery, H. E. 1970, 1971, 1973. Breedingbird censuses. Lodgepole pine forest with aspen. Aud. Field Notes 24:760-761. Am. Birds 25:991-992, 27:998. Lawr4nce,L. deK. 1967. A comparativelife-history study of four speciesof woodpeckers. Ornithol. Monogr. 5. Maillard, J. 1927. The birds and mammals of Modoc County, California. Proc. Calif. Acad. of Sci., Ser. 4, 16:261-359. Miller, A. H. 1941. A review of centers of differentiation for birds in the west- em Great Basin region. Condor 43:257-267. Miller, A. H. 1951. An analysis of the distribution of the birds of California. Univ. Calif. Publ. Zool. 50:531-644. Oakeshott, G. B. 1971. California's changinglandscapes. McGraw-Hill, New York, N.Y. Palmer, R. S. 1968. Pine Siskin. Pages424447 in Bent, A. C. Life historiesof North American cardinals,grosbeaks, buntings, towhees, finches, sparrows and their allies. U.S. Natl. Mus. Bull. 237. Pough,R. H. 1957. Audubon westernbird guide. Doubleday, GardenCity, N.Y. 61 SUMMER BIRDS OF WARNER MOUNTAINS yon Haartman, L. 1957. Adaptation in hole-nestingbirds. Evolution ! !: 339-347. yon Haartman, L. 1971. Population dynamics. Pages391-459 in Farner, D. S. and J. R. King,eds. Avianbiology, vol. 1. AcademicPress, New York, N. ¾. Wiens,J.A. 1975. Avian communities,energetics, and functionsin coniferous forest habitats. Pages226-265 in Proc. Symp. on Managementof forest and rangehabitats for nongamebirds. U.S. ForestService Gen. Technical Report WO-1.

Accepted 29 June 1977

Sketch by David W. Winkler