BIRD POPULATIONS - Birdpop.org

ROBERT L. WILKERSON AND RODNEY B. SIEGELrather they occupied a variety of relatively aridhabitats including brushland, desert scrub, andnatural grasslands, and appear to be clusteredon the outskirts of urban development.Large confidence intervals make comparingour statewide population estimate with that ofDeSante et al. (2007) during 1991-1993 difficult,especially since the difference in the estimates isrelatively small. Three quarters of owl pairs inour aggregated population estimate reside in thedensely occupied Imperial Valley, where thestandard error associated with our regionalestimate is well over 2,000 pairs. Thus, the lackof precision in this single regional estimatecould easily mask a real statewide decline, or forthat matter, potentially even obscure a statewideincrease. Future survey efforts could perhapsminimize the problem of low statistical powerby focusing monitoring efforts on smaller areasselected for high owl population density orother factors, and sustaining those efforts formultiple successive breeding seasons.Our survey of the “new” survey regionscovering the Modoc Plateau/Great Basin,Mojave Desert, and Sonoran Deserts representsthe first systematic survey of Burrowing Owlsacross vast portions of California. We foundBurrowing Owls to be distributed heterogeneouslyamong these regions, with few or noowls in the Modoc Plateau/Great Basin, NorthernMojave/Eastern Sierra Nevada, EasternMojave, or Sonoran Desert regions (excludingthe Palo Verde Valley). However, we found muchlarger aggregations of burrowing Owls in theWestern Mojave region, and in one small area ofthe Sonoran Desert—the Palo Verde Valley.CONSERVATION IMPLICATIONSA comprehensive conservation strategy forBurrowing Owl in California is underdevelopment by California Department of Fishand Game and its partners (Burkett andJohnson, 2008). Here we provide a fewconservation-related conclusions and recommendationsthat stem directly from our results:1) Despite the apparent robustness of thepopulation in the Imperial Valley, smallerpopulations elsewhere in the state, particularlyin and near urban areas, appear to havecontinued to decline since the 1991-1993 survey.2) The vast majority of the state’s breedingBurrowing Owls continue to nest on privatelands; any meaningful conservation efforts musttherefore engage private stakeholders.3) Across much of California, Burrowing Owlnesting remains closely associated with thepresence of ground squirrels, another factor thatmust be considered in developing successfulconservation measures.4) In a few key areas, particularly theImperial Valley and the Palo Verde Valley,Burrowing Owls are not closely associated withground squirrels, and instead rely heavily on thebanks of concrete and earthen water conveyancestructures for nesting sites. Comprehensiveconservation planning for Burrowing Owl inCalifornia must take into consideration theimportance of these artificial structures.5) Although Burrowing Owl detections werescarce across most of the land area of the newlysurveyed Modoc Plateau/Great Basin andsouthern California desert regions, substantialpopulations persist in the Sonoran Desert (PaloVerde Valley) and the western Mojave Desertregions (particularly in and around theAntelope, Apple, and Lucerne valleys). Weestimate the western Mojave Desert region tocontain ~6% of California’s breeding BurrowingOwls, superseded in numerical importance tothe statewide population only by the ImperialValley and the Southern Central Valley regions.Successful conservation planning for this speciesmust address the particular needs of these substantialdesert populations (Wilkerson andSiegel, in press).6) A statewide conservation strategy willlikely need to incorporate a statewidemonitoring program to assess the effectivenessof conservation measures. Our study demonstratesthe potential value of citizen-scienceparticipation in single-species studies, particularlyof raptors or other highly charismaticspecies like Burrowing Owls that are relativelyeasy to find and identify. While many of ourvolunteer observers were highly skilled birders,and in some cases, even wildlife professionals,others had little or no birding experience. With afairly modest investment of time and money forrecruiting, training, and supporting volunteersurveyors, we were able to extend our surveyacross a vast area. Engaging citizen-scientists inmonitoring could reduce the cost and extend thescope of any owl monitoring project, and mayalso yield less tangible benefits — participants in[32]