Confirmed Nesting of an Indigo with a Lazuli Bunting in Kern County

NOTES

CONFIr NESTING OF AN INDIGO WITH A LAZULI BUNTING IN KERN COUNTY, CA-nORNIA

SEAN P. ROWE and DANIEL S. COOPER, Kern River ResearchCenter, P.O. Box 990, Weldon,California 93283 (currentaddress of Cooper:Dept. of EarthSciences, Universityof California,Riverside, California 92521)

The NatureConservancy's Kern RiverPreserve, located along the SouthFork Kern River(elev. 2640 feet)near Weldon, Kern County,California, comprises 1100 acres of the largestremaining example of cottonwood/willowriparian forest in California. Since1986, 320 acresof formerlygrazed pasture have been planted with Red Willow ($alix laevigata),Fremont's Cottonwood (?opulus fremontii), and Mulefat (Baccharis salicifolia)as part of the preserve'sriparian restoration program. The Kern River ResearchCenter has been monitoring breeding birds on the restorationplots and in the natural forest since 1988. On 28 May 1996, while surveyingbirds on the Kern River Preserve,Cooper locateda femaleLazuli Bunting (Passerina amoena) building a nestin a smallRed Willow. Rowe checkedthe neston 31 May and notedthat it appearedfinished. No adultbunting was seen in the area and the nestwas not checkedto determinethe contents.On 5 June,Cooper noted the femaleLazuli incubating two buntingeggs and a singleBrown-headed Cowbird (34olothrus ater) egg. The cowbirdegg was removed from the nest,shaken vigorously, and returnedto the nest.While checkingthe nest Cooperobserved a maleIndigo Bunting (P. cyanea)singing ca. 15 m distant.The femaleLazuli flushed from the nestand joined the maleIndigo, both calling and flying quicklyfrom tree to tree aroundthe nestas Cooperapproached. The male was all deepblue, as istypical of a pureadult male Indigo, and showed no evidenceof being a hybridLazuli x Indigo.We visitedthe nestagain on 12 June,when only one bunting eggand one cowbird egg remained. Visits on 23 and25 Junefound the pairbringing foodto a singlenestling estimated six to sevendays of age (on 25 June)on the basis of pinfeathersjust breaking through the sheaths.No eggsremained in the nest.The nest was intact and showedno sign of disturbancebut was inactivewhen Rowe returnedon 29 June.With an incubationperiod of 11 to 13 daysand a nestlingperiod of 9 to 12 days(Payne 1992) and fromthe estimatedage of the nesfiingon 25 June, the youngbunting should have fledged between 26 and 29 June.Although the nest showedno evidenceof depredation,we were not ableto locateeither the youngor adultsbuntings on 29 June. The nest was locatedon a 20-ha riparianrestoration plot that was plantedwith cottonwoodand RedWillow in 1992. Mean tree densityon the plot was268 treesper hectare;mean tree height was 5.5 m witha meanstem diameter of 11.9 cm. Mean canopycover on the plotwas 23%, meanbrush cover was 4.3%, andmean forb cover was 54.1% (Kern River ResearchCenter unpubl. data). The nest was placed 2 m abovethe groundin a fork of a horizontalbranch in a youngRed Willowapproxi- mately4 m in height.The tree standsin a relativelyopen grassy area at the edgeof the restorationplot amongseveral dozen similar willows spaced ca. 4 m apart. This areadiffers from the restof the restorationplot in that the treesare smallerand that thereare fewcottonwoods, except for severalold (50-100 years)ones along the edge of the plot ca. 15 m distant.A heavilygrazed pasture is locatedadjacent to the plot. The IndigoBunting has undergone a dramaticrange expansion in the southwest- ern U.S. duringthe last40 years(Johnson 1994). The firstbreeding record in the Southwestwas in 1944 near Flagstaff,Arizona (Dearing and Dearing 1946). Indigo Buntingsnow breedlocally in Utah, Arizona,and southernCalifornia (AOU 1983, Payne 1992). The first recordof the IndigoBunting in Californiawas of a male collectedat Mecca,Riverside County, in 1908 (Thompson1964). By the 1950s only

Western Birds 28:225-227, 1997 225 NOTES a handfulof recordshad beenreported in the state.In more recentyears, however, territorialmales have been regularlyreported throughout southern California. The firstbreeding record for Californiawas of a maleIndigo mated to a femaleLazuli in SoledadCanyon in Los AngelesCounty in 1956 (Bleitz 1958). Even with the abundanceof breeding-seasonrecords of territorialIndigos throughout California, verylittle has been published on nestingby the speciesin the state,and we were able to locatedrecords of only 15 instancesof nestingby mixedor pure pairs(Table 1). There is some uncertaintyas to whetheranthropogenic habitat changeshave influencedthe expansionof the IndigoBunting into the southwesternU.S. Rosenberg et al. (1991) suggestedthat the species'invasion of the lowerColorado River valley is, in part, a resultof human-inducedhabitat changes. They citedhighest densities of Indigosin recenfiyburned riparian areas where willow and saltcedar (Tamarix) have regenerated.Johnson (1994), however,suggested that the rangeexpansion of the IndigoBunting throughout the Southwestin unrelatedto anthropogenichabitat alterations.He reasonedthat the IndigoBunting is usingboth undisturbednatural habitatsas wellas secondarygrowth caused by humanactivities, and that the habitat which IndigoBuntings currenfiy use was availablelong beforeexpansion into the regionand wasmuch more extensive.

Tab!• 1 Reportsof Indigoand Mixed Indigox LazuliBunting Pairs Nesting in California

Male/ Year Fernale• Location Source

1956 I/L SoledadCanyon, Los Angeles Co. Bleitz(1958) 1973 I/L SpringCanyon, near Santee, San Diego Co. Unitt(1984) 1977 I/? N. of Needles,San Bernardino Co. Rosenberget al. (1991) 1979 I/L Ukiah,Mendocino Co. Am. Birds33:895, 1979 1981 l/I MorongoValley, San Bernardino Co. Am.Birds 35:980, 1981 1982 I/I MorongoValley, San Bernardino Co. Am.Birds 36:1017, 1982 1984 I/? SanLuis Obispo, San Luis Obispo Co. Am. Birds38:1063, 1984 1984 I/L Olerna,Marin Co. Shuford(1993) 1991 I/L LakeCuyarnaca, San Diego Co. Am. Birds45:1162, 1991 1992 I/L CajonPass, San Bernardino Co. Am. Birds46:1180, 1992 1992 I\X\L/L CajonPass, San Bernardino Co. Am. Birds46:1180, 1992 1993 I/L FishCanyon, Angeles Nafi. Forest, K. Campbell LosAngeles Co. (pers.comm.) 1995 l/L GoatRock, Alameda Co. Am. Birds49:978, 1995 1995 I/L Whittier,Los Angeles Co. L. Schmahl (pers.comm.) 1996 I/L KernRiver Preserve, Kern Co. thisstudy

Indigo Bunting;L, Lazuli Bunting.

226 NOTES

With respect to California, we concur with Johnson's(1994) conclusionthat anthropogenichabitat changes probably played little or no role in the rangeexpansion of the Indigo Bunting.Given the extent of riparian habitatdestruction in Californiaduring the past 100 years,it seemsreasonable to assumethat muchless second-growthhabitat suitable for IndigoBuntings occurs in the statethan naturally occurredprior to large-scalehuman-induced habitat alterations. Although anthropogenichabitat changes certainly influence the distributionof IndigoBuntings on a local level,as on the lowerColorado River and in the Kern RiverValley, it seemslikely that the ultimatereasons behind the IndigoBunting's range expansion are unrelatedto human-caused habitat modifications. In the Kern River Valley,the IndigoBunting, along with a few Indigo x Lazuli hybrids,is an uncommonbut regularsummer resident, with as many as 20 singing maleson territorybetween early May and mid-August.Highest densities of Indigosin the valleyoccur between the fluctuatingeastern border of IsabellaReservoir and the town of Onyx.Although most territorial male Indigo Buntings in the Kern RiverValley useyoung (

LITERATURE CITED

AmericanOrnithologists' Union. 1983. Check-listof North AmericanBirds, 6th ed. Am. Ornithol. Union, Lawrence, KS. Bleitz,D. 1958. IndigoBunting breeding in LosAngeles County, California. Condor 60:408. Dearing,H., and Dearing,M. 1946. IndigoBuntings breeding in Arizona.Condor 48:139-140. Johnson,N. K. 1994. Pioneeringand naturalexpansion of breedingdistributions in western North American birds. Studies Avian Biol. 15:27-44. Payne,R. B. 1992. IndigoBunting, in The Birdsof NorthAmerica, No. 4 (A. Poole, P. Stettenheim,and E Gill, eds.).Acad. Nat. Sci., Philadelphia. Rosenberg,K. V., Ohmart, R. D., Hunter,W. C., and Anderson,B. W. 1991. Birds of the Lower ColoradoRiver Valley. Univ. of Ariz. Press,Tucson. Shuford,W. D. 1993. The Marin CountyBreeding Bird Atlas. Bushtit Books, Bolinas, CA. Thompson,W. L. 1964. An earlyspecimen of the IndigoBunting from California. Condor 66:445. Unitt, P. 1984. The birdsof San DiegoCounty. San DiegoSoc. Nat. Hist. Memoir 13.

Accepted $ August 1997

227