BIRD POPULATIONS - Birdpop.org

BIRD POPULATIONSA journal of global avian biogeographyVolume 10 2010 (2009-2010)Bird Populations 10:1-36© The Institute for Bird Populations 2010ASSESSING CHANGES IN THE DISTRIBUTIONAND ABUNDANCE OF BURROWING OWLSIN CALIFORNIA, 1993-2007 1ROBERT L. WILKERSON AND RODNEY B. SIEGEL 2The Institute for Bird PopulationsP.O. Box 1346Point Reyes Station, CA 94956-1346Abstract. The Western Burrowing Owl (Athene cunicularia hypugea) has declined in recentdecades across much of its range, including California, where it is classified as a Species ofSpecial Concern. During 2006-2007, we surveyed the entire breeding range of the species inCalifornia, except the Channel Islands. Relying largely on volunteers, we surveyed 8605km x 5km blocks, and documented exact locations of 1,758 pairs. Using data fromrandomly-selected blocks, we extrapolated a statewide, breeding-season population of9,187 (SE = 2,346) pairs. For all of the species’ California range, except the Modoc Plateauand the Mojave and Sonoran deserts, we compared results with those of DeSante et al.(2007) using identical methods and study area boundaries during 1991-1993. Our 2006-2007estimate of 8,128 (SE = 2,391) pairs was 10.9% lower than the previous estimate, but thedifference was not statistically significant. The major patterns of Burrowing Owl occurrenceacross California appeared to be relatively unchanged since 1993, although non-significantdeclines were apparent in numerous regions. Burrowing Owls appear to have declinedparticularly sharply in two urban areas: the San Francisco Bay Area and Bakersfield. Oursurveys of previously unsurveyed portions of the species’ California range yielded few orno owls in the Modoc Plateau/Great Basin, Northern Mojave/eastern Sierra Nevada,eastern Mojave, and Sonoran Desert regions (excluding the Palo Verde Valley) but detectedlarger aggregations in the Palo Verde Valley and the western Mojave Desert region.Key words: Burrowing Owl, California, Athene cunicularia, citizen scienceEVALUAR LOS CAMBIOS EN LA DISTRIBUCIÓN Y ABUNDANCIA DELBÚHO LLANERO EN CALIFORNIA, 1993-2007Resumen. El Búho Llanero (Athene cunicularia hypugea) ha disminuido en las últimasdécadas en gran parte de su distribución, incluyendo a California, donde está clasificadocomo una especie de interés especial. Durante el periodo 2006-2007, encuestamos a todo elrango reproductivo de la especie en California, con la excepción de las Channel Islands.____________________1Submitted: 20 April 2010; accepted 11 June 20102Corresponding author: rsiegel@birdpop.org[1]