BIRD POPULATIONS - Birdpop.org

DISTRIBUTION AND ABUNDANCE OF BURROWING OWLS IN CALIFORNIATABLE 3. Comparison of Burrowing Owl regional population estimates extrapolated from randomly-selectedblocks for regions that were surveyed during both the 1991-1993 and 2006-2007 surveys. Although we presentextrapolated population estimates for all regions here, in many cases the extrapolated number of pairs basedon random blocks only was not judged to be the “best estimate” of the regional population._______________________1991-1993 survey _______________________2006-2007 surveyNo. of random Extrapolated No. of random Extrapolated Change in Percent changeblocks no. of blocks no. of estimated in estimatedRegion surveyed pairs (SE) surveyed pairs (SE) no. of pairs no. of pairsNorthern Central ValleyLowland 22 231 (153) 22 0 -231 -100%Upland 2 0 11 0 0 n/aAll 24 231 (153) 33 0 -231 -100%Middle Central ValleyLowland 163 577 (122) 59 502 (209) -75 -13.0%Upland 28 17 (17) 12 0 -17 -100%All 191 594 (139) 71 502 (209) -92 -15.5%Southern Central ValleyLowland 41 1,000 (410) 63 968 (342) -32 -3.2%Upland 11 396 (182) 18 145 (118) -251 -61.4%All 52 1,396 (592) 81 1,113 (460) -283 -20.3%Entire Central Valley 267 2,221 (884) 185 1,615 (669) -606 -27.3%San Francisco Bay Area InteriorLowland 86 41 (20) 20 0 -41 -100%Upland 25 0 12 21 (21) +21 n/aAll 111 41 (20) 32 21 (21) -20 -51.2%Central-western InteriorLowland 14 0 17 0 0 n/aUpland 16 31 (27) 13 76 (51) +45 +145.2%All 30 31 (27) 30 76 (51) +45 +145.2%Southwestern InteriorLowland 4 100 (100) 3 17 (17) -83 -83%Upland 10 127 (81) 8 0 -127 -100%All 14 227 (181) 11 17 (17) -210 -95.2%Coachella ValleyLowland 5 0 4 16 (16) +16 n/aUpland 6 0 4 0i 0 n/aAll 11 0 8 16 (16) +16 n/aImperial ValleyLowland 15 6,429 (1,135) 5 5,701 (2,244) -728 -11.32%Upland 1 142 2 707 (140) +565 +397.9%All 16 6,577 7 6,408 (2,384) -163 -2.6%SOUTHERN CENTRAL VALLEYWe surveyed 81 randomly-selected blocks and83 historic breeding blocks in this region (Fig. 4).Surveys of random blocks yielded 75 BurrowingOwl pairs, and surveys of historic breedingblocks yielded 161 pairs, for a total of 236 pairs.Owls were considerably more abundant in thesouthern portion of this region than in thenorthern portion. We found Burrowing Owls inonly one survey block in Madera County(though it had 12 pairs), and our detections werenearly as sparsely distributed in Fresno andKings counties. We found substantial concentrationsonly in Tulare and Kern counties. As inthe other Central Valley regions, the greatmajority of owls we found were in lowlandblocks; in the upland blocks covering the Sierrafoothills we found owls in just one block in each[11]