WESTERN BIRDS Volume 21, Number 1, 1990 BREEDING DISTRIBUTION OF THE BLACK SWIFT IN SOUTHERN CALIFORNIA KEVIN S. FOERSTERand CHARLES T. COLLINS, Departmentof Biology,Califor- nia State University,Long Beach,California 90840 (presentaddress of Foerster:U.S. Fishand WildlifeService, San FranciscoBay NationalWildlife Refuge, P.O. Box 524, Newark, California 94560) The BlackSwift (Cypseloidesniger) is sparselydistributed over wide por- tions of western North America from British Columbia and southwestern Alberta south to southernCalifornia and east to Colorado (A.O.U. 1983). Elsewhereits range includesMexico, Central America south to Costa Rica, and the Greater Antilles.Within this range, it has a discontinuousdistribu- tion, with nestsfound on sea cliffs (Vrooman 1901), in sea caves (Legg 1956), behind mountain waterfalls(Smith 1928, Knorr 1962), on moist in- land cliffs (Michael 1927), and in limestonecaves (Davis 1964). The winter range of the migratorypopulation in westernNorth America is presumedto be southern Mexico (Friedmann et al. 1950). The nestand egg of the BlackSwift were discoveredby A.G. Vrooman (1901) alonga seacliff west of Santa Cruz, California.Vrooman, an amateur egg collector, was searchingfor cormorant eggs along the cliff when "suddenly,right from under the pole and not more than three or four feet from my hand, a BlackSwift flew out and down towardthe waterand passed around the angle toward the ocean." The nest was situatedin a smallcrevice linedwith mud and tuftsof grass.Even though a secondnest was found four yearslater (Vrooman 1905), the recordwas subject to widespreadskepticism from within the ornithologicalcommunity. It was not until 1915 that the record was widely accepted,following a visitto the site and a subsequent apologyfrom W. L. Dawson(1915) in an articleentitled "The Nestingof the BlackSwift--A Vindication."Subsequently, Black Swifts were alsofound breedinginland behind waterfalls(Michael 1927, Smith 1928). Knorr (1961) conducteda 10-year surveyof the geographicaldistribution of BlackSwifts in Coloradoand proposeda setof ecologicalrequirements for BlackSwift breeding. Even so, there has been a notableabsence of surveysin other parts of the species'range of the distributionof nest sitesand com- parisonswith Knorr'sproposed nest-site requirements. In thisstudy we ex- amine the characteristicsof breedingsites and the populationsize of Black Swiftsbreeding in southernCalifornia. Western Birds 21:1-9, 1990 1 BLACK SWIFT IN SOUTHERN CALIFORNIA METHODS Field work was conducted from March to early September in 1985 and from late April to early Septemberin 1986, which included the period of residencyof Black Swiftsin the area. Black Swiftsoccur in southernCalifor- nia between April and October with the extreme dates representing the passageof migrants (Garrett and Dunn 1981). The breeding period, from egg layingto fledging,is from May to September(Foerster 1987, Collinsand Foersterunpubl. data). We conductedour field surveysin the San Gabriel, San Bernardino, and San Jacinto Mountains of southern California (Figure 1). Each potentialnesting site was rated accordingto the presenceor absence of Black Swiftsand Knorr's (1961) ecologicalcriteria. Detailed descriptionsof all confirmednest site localities examined in this study, along with their eleva- tions and ecologicalfeatures are presentedbelow. The locationsof all poten- tial nest siteswhere Black Swiftswere not detectedduring this study are listed in Appendix 1. RESULTS AND DISCUSSION Distribution Within southern California, the Black Swift is a local and restricted breeder. Hall (1948) reported the first Black Swift nest in southern California near Hemet, RiversideCounty. Other previouslyknown nestingsites are Sturtevant Falls in the San Gabriel Mountains (McCaskie 1974, Remsen 1978), Big Falls in the San Bernardino Mountains (McCaskie 1969, Remsen 1978), and on the lower North Fork of the San Jacinto River (Collins and Sheppard unpubl. data). Over the two seasonsof thisstudy, we surveyed50 separatewaterfalls and found Black Swiftsnesting at six sites(Figure 1). All sites were located in mountain canyons with riparian habitat along the streams. The sites are as follows: 1. SturtevantFalls--The falls are located in Santa Anita Canyon at a top elevation of 645 meters, approximately 15 km northeastof downtown Los Angeles. Water flows year round over the 20-meter falls. The plant communitiesin this area are Chamise Chaparral and Scrub Oak Chaparral (Hanes 1976). A single nest was situated on the south side of the falls, approximately7 meters above the base. Since the early 1970s, periodic surveyshave revealed from one to three pairs of swiftspresent during the nestingseason, although only a singlenest was locatedin any of theseyears (Collins unpubl. data). 2. WolfskillFalls--This site is locatedin WolfskillCanyon within the San Dimas ExperimentalForest at a top elevation of approximately550 meters. This area is protected and regulatedby the Forest Service of the United States Department of Agriculture.Water flows year round over a seriesof three waterfalls.The largest(20-meter) and highestupstream fall servedas the nestingsite. A singlenest was locatedon the north sideof the fall, about4 metersabove the base. The major plant communitiesin the area are Chamise Chaparral and Scrub Oak Chaparral. The herbaceousvegetation in the immediate vicinity of the site consistsprimarily of monkeyflower(Mirnulus 2 BLACK SWIFT IN SOUTHERN CALIFORNIA cardinalis).A freshwateralga, Vaucheriasp., dominatesthe rock surfacesof the waterfall. 3. Big Falls--This siteis locatedabout 2.5 km northeastof ForestHome in the San BernardinoMountains at a top elevationof 1950 meters.The water flowsyear round, as thisstream is a major snowmelt drainagefor the southwestside of Mount San Gorgonio.The plant communitiesin this area are Western Coniferous Forest and Mixed Chaparral (Minnich 1976). Hazardousfalling rock and sheerinaccessibilitylimited the studyto the lowest of five waterfallsthat drop 150 meters into Mill Creek Canyon. The single nestfound was locatedin a smallcrevice 10 metershigh on the eastside of the falls. 4. Lawler Falls--Thesepreviously unnamed falls are located150 meters downstreamfrom the crossingof Highway 243 over the North Fork of the San JacintoRiver. The elevationat the top of the fallsis approximately1620 meters.The water flowsyear round over and behindseveral large boulders SanGabrielMtns.SanBernard d Figure 1. Locationsof BlackSwift breedingsites in the southernCalifornia moun- tains. 1, SturtevantFalls; 2, WolfskillFalls; 3, Big Falls;4, Lawler Falls;5, Four Falls; 6, StrawberryGrotto. The stippledarea indicatesthe generaloutline of the mountain ranges. 3 BLACK SWIFT IN SOUTHERN CALIFORNIA wedged into the bottom of the canyon. The placement of the boulders createsa waterfall8 metershigh with a cave 10 metersdeep. A minimum of sevenpairs of BlackSwifts nested in 1985 and again in 1986. The surround- ing vegetationis Mixed Conifer Forest dominatedby Coulter Pine (Pinus coulteri) and Ponderosa Pine (P. ponderosa). 5. Four Falls--This site is located on the North Fork of th• San Jacinto Riverapproximately 8 km downstreamfrom LawlerFalls at a top elevationof 755 meters. It consistsof a seriesof four waterfallson property of the Lake Hemet Municipal Water District. The falls range in height from 3 to 15 meters.The one probablenest site was locatednear the upper fallsin 1971 (Collinsand Sheppard unpubl. data) and in 1985 (this study). The plant communitynear this west-facingslope is ChamiseChaparral (Vogl 1976). A large grottowith numerousferns can be found near the middlefalls. This may be the same area describedby Hall (1948). Several nests were photographedhere in the 1950s (D. Bleitz pers. comm.). 6. StrawberryGrotto--This site is located 1.5 km downstreamfrom the crossingof TollgateRoad over StrawberryCreek in Idyllwild. The top eleva- tion of the fallsis approximately1402 meters.The water flowsthrough a hole betweentwo overhangingboulders that createa small cave. This fall is sub- ject to wide fluctuationsin water quantity, but generally the flow is year- round (M. Hamilton pers. comm.). The plant community in this area is Manzanita Chaparral (Vogl 1976). We found single nestsin two different locationsin 1985 and 1986. Grinnell (1908) first reported seeing Black Swiftsflying in StrawberryValley in the early 1900s. However, no nestswere located in the area until our study. StrawberryGrotto is the southernmost known breedingsite of Black Swiftsin California. Habitat Characteristics We surveyeda total of 50 waterfallsin southernCalifornia for the presence or absence of five ecologicalfeatures. These are summarizedfrom Knorr (1961) as follows: 1. Water. Water is presentat every nestingsite, varyingin degreefrom a rushingtorrent to a mere trickle. 2. High relief. The nestingsite must have a commandingposition above the surroundingterrain so that swiftsflying out from the nestare automatical- ly at potentialforaging altitude above the surroundingvalley. 3. Inaccessibility.The sitemust be inaccessibleto terrestrialmarauders and accessibleonly to winged animals or humans with climbinggear. 4. Darkness.The nestis in a positionsuch that the sunwill not shineon an occupied nest. 5. UnobstructedFlyways. The flyway in front of the nestmust be free of obstructions. All six nestingsites had the five ecologicalrequirements. Fifty-six percent of all the waterfallssurveyed had all five requirements(Table 1). While all of Knorr'sfive ecologicalrequirements were met by