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Costa's Hummingbird: Its Distribution and Status

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Costa's Hummingbird: Its Distribution and Status WESTERN BIRDS Volume 20, Number 2, 1989 COSTA'S HUMMINGBIRD: ITS DISTRIBUTION AND STATUS WILLIAM H. BALTOSSER, Departmentof Bioloõyand Museum of Southwestern Bioloõy,The Universityof New Mexico, Albuquerque,New Mexico 87131. AlthoughCosta's Hummingbird (Calypte costae) is a commonspecies of the arid Southwest,its status remains poorly understoodor poorly documentedin muchof itsrange. This is due in partto the femaleand young of thisspecies being frequently inseparable in the fieldby sightfrom those of Black-chinned(Archilochus alexan&i), Ruby-throated(Archilochus colu- bris), and, to a certainextent, Anna's (Calypteanna) hummingbirds.The problemis further compounded by recentrange expansions and by apparent resurgenceinto some areas of historicoccurrence where, until recently, there had beenfew recordssince the late 1800s. Aidsto identificationrecently publishedby Baltosser(1987) and the referencescited therein provide suffi- cientinformation to identifyvirtually any birdin the hand and even many seen at closedistances. In addition,the call of Costa'sHummingbird is diagnostic(Stiles 1971) and being learned by many observers.In time, therefore,some of the inherentmystery associated with this and similar speciesmay dissipate. The Check-listof North American Birds (A.O.U. 1983) liststhe breeding distributionof Costa's Hummingbird as extending from central California (north to Monterey, Merced, and lnyo counties),southern Nevada, and southwesternUtah (BeaverdamMountains) south to southernBaja Califor- nia (includingthe ChannelIslands off Californiaand islandsoff bothcoasts of Baja California), Sonora (includingTiburon and San Esteban islands), southern Arizona, and southwesternNew Mexico. The same sourcelists the winter range as southernCalifornia and southernArizona south to Sinaloa, casuallynorth to southwesternBritish Columbia (VancouverIsland, sight record), western Washington (actual data lacking--assumed to occur), Oregon, central Nevada (ToiyabeMountains), and northern Utah, and east to centralTexas (Hays Co., alsosight records east to AransasCo.). Here I documentthe statusand distribution(including seasonal aspects) of Costa's Hummingbird and report extensionsto its known range. WesternBirds 20: 41-62, 1989 41 COSTA'S HUMMINGBIRD METHODS The statusof Costa'sHummingbird as presentedis based on over 500 distinctlocalities of occurrence(i.e., areasseparated by 10-20 km) and on over 1,500 recordsconsisting of three typesof data, which I have arranged hierarchically(specimens, photographs, and sightrecords). Presentation of the data in this way shouldenable readers to formulatetheir own opinion regardingthe species'status and, I hope, will inducesome to fill in gapsor to validate occurrences at more definitive levels. I have placedthe mostfaith in specimenevidence (museum abbreviations explainedin the acknowledgments),which includesstudy skinsor, in some instances,select rectrices plucked and preservedfrom birdsthat were subse- quently released (e.g., many of the Guadalupe Canyon recordsfrom ex- treme southwesternNew Mexico) or voice recordings(e.g., recordingsfrom the San Franciscoarea by L. F. Baptista).Photographs can occasionallybe misleading,so I have not equated them with specimens.The problems associatedwith sightrecords have been discussedby Van Tyne (1956) and Zimmerman(1973); sightrecords suffer primarily from their lack of tangible evidencefor subsequentscrutiny. I have thereforerelegated them to the least definitivecategory of verification.Most sightrecords I includeare of adult males, althoughsome of adult femalesand young males showingmetallic purple/violet fleckson their chinsor sightrecords in conjunctionwith call notes (heard but not recorded) have occasionallybeen included. Throughout,I presentthe most fundamentalaspects of the distribution and statusof the speciesfirst, then discussperipheral and vagrant occur- rencesor, in somecases, the apparentresurgence of the speciesinto an area following an absenceof decades. Distributionalaccounts are arranged by state/provinceand depictedby region and degree of verification.Mapped locations,based on recordsthrough 1987, are as accurate as logistically possible,with more than 90% of all localitiesplotted. The relativelyfew records not depicted were lumped with adjacent localities(i.e., locations within ca. 10-20 km). Stipplingis usedto signifythe normalrange of the species,while occurrencesoutside shaded areas are of a more peripheral nature. Maps showingseasonal aspects of occurrence(Appendices A-D), while computerizedby degreeof verification,have not been depictedin this way becauseit was not feasibleon maps of this scale. BREEDING The breedingrange of Costa'sHummingbird (Figure 1) occupiesmuch of the Lower Sonoranand limitedportions of the Upper Sonoranlife zonesof western North America. The speciesnests from below sea level (Death Valley, California)to about2000 m in somedesert mountain ranges (Garrett and Dunn 1981). A. W. Anthony'sreport of nestingto 2,273 m (7500 feet) in the Sierra San Pedro Martit of Baja CaliforniaNorte, cited by Brewster (1902) and Grinnell (1928), is exceptionalif accurate. Breedingoccurs earlier in southernregions such as Baja CaliforniaSur, where it extendsfrom late January through March (Brewster1902). At in- termediate latitudes the nesting period is o•ten the same (e.g., many 42 COSTA'S HUMMINGBIRD southernCalifornia and southernArizona records) or slightlydelayed (e.g., Monson 1951). At higher latitudes,as from the easternMojave Desert and OwensValley to the lower slopesof the White Mountains,nesting may ex- N o 500 I I I Figure 1. Breedingrange of Costa'sHummingbird based on actualevidence (dots) and on extrapolation(shaded areas). 43 COSTA'S HUMMINGBIRD tend from early March throughlate July (Garrettand Dunn 1981). Extreme dates range from 17 January on Santa Margarita Island in Baja California Sur, where Bryant observeda nestcontaining large young (Brewster1902), to early July at SabinoCanyon, Pima Co., southernArizona (young in nest, Witzeman and Stejskal1987) and to mid-july at Bixby Canyon, Monterey Co., along the Californiacoast (LeValley and Evens 1981). Nestingin peripheralareas such as Bixby Canyon is frequentlydelayed in comparisonto that within the normal range of the species.In other areasof peripheralnesting such as GuadalupeCanyon (CochiseCo., Arizona, and Hidalgo Co., New Mexico), nestingextends into early June (Baltosser1986, 1989). Many if not most nestingattempts after late April I suspectto be second nestings,and thus peripheral nestingsperhaps representattempts after subsequentdispersal to new areas. DISTRIBUTION California Costa'sHummingbird is resident, although during late fall and early winter in relativelylow numbers,along the coastfrom southeasternSanta Barbara County souththrough San Diego County, with some birdsresident in the southernand southeasterndesert regions of San Bernardino, Riverside,and Imperial counties (includingthe Colorado River Valley) (Figure 2). From mid-Februaryto early April the speciesoccurs in all of the formerareas (in- cludingoffshore islands), but by thistime numbershave been augmentedby birdsreturning from winteringareas. By mid-Aprilthe speciesis alsofound in the mountains of the eastern Mojave Desert (KingstonRange, Ivanpah Mountains, New York Mountains, and ProvidenceMountains) and north to centraland northernInyo County (the OwensValley and the lowerslopes of the White Mountains),with a few birdsin theseareas lingering into July and perhaps longer. The statusof the speciesin centraland northernCalifornia is in a stateof flux. In the past,the specieswas believed to be restrictedto the hillsalong the westernedge of the San JoaquinValley northto StanislausCounty, where it nests (McCaskie el al. 1979). Grinnell and Miller (1944), however, cited recordsas far northwestas Hayward (1875) and Oakland (1890), Alameda County, and withinthe lastdecade many Costa'sHummingbirds have been sightednorth of StanislausCounty. Recentrecords for centraland northern Californiaare mostfrequent duringwinter (possiblesampling bias resulting from ChristmasBird Counts)and springand clusteraround the San Fran- ciscoBay and Montereyareas. There are numerousrecent records of spring vagrants,post-breeding vagrants, and winter vagrantsalong the coastfrom Santa Cruz County north to Del Norte County and inland as far east as Mariposa, Placer, and Nevada counties and north to Siskiyou County. Costa'sHummingbirds have now been reported from all but 19 of the 58 Californiacounties, being absentfrom areas in the northeastat the edge of the Great Basinand, with the exceptionof a singlebird in YosemiteNational Park, MariposaCounty (LeValleyand Evens1983), from the SierraNevada. While the nonbreedingrange of Costa'sHummingbird in northernCalifornia has spreadbeyond the westernedge of the San Joaquin Valley, virtuallyall COSTA'S HUMMINGBIRD of theserecords are of vagrants;the specieshas not yet extendedits normal breedingrange to the northwest. o 500 I I I km DEGREE OF VERIFICATION ß SPECIMEN 'G PHOTOGRAPH 0 SIGHT Figure 2. Distributionof Costa's Hummingbird in the southwesternUnited States showingthe normal occurrenceof the species,all seasonscombined (shaded areas), and its documented presence (dots). Filled circles, specimens;half-filled circles, photographs;open circles, sightings. 45 COSTA'S HUMMINGBIRD Nevada Costa'sHummingbird is probablynot a true winter residentin Nevada, contraryto the A.O.U. (1983), as there are no Decemberor January records. By early February, however, a few individualsarrive, and
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