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ROBERT L. WILKERSON AND RODNEY B. SIEGELTABLE 2. Number of blocks surveyed, Burrowing Owl pairs found, and population estimate for each geographic region surveyed during 2006-2007 that was alsosurveyed in 1991-1993 by DeSante et al. (2007). For each region and elevational subregion, we considered our “best estimate" of the number of pairs in 2006-2007to be the larger of a) the extrapolated estimate of pairs, based only on results from randomly-selected blocks, or b) the actual number of pairs counted, poolingdata from randomly-selected blocks and historic breeding blocks._________________________________ All blocks ___________________________________________Random blocks onlyRandom & “BestTotal area historic breed- Square No of Random Square No. of Estimated estimate”ofof region ing blocks km pairs blocks km pairs no. of no. ofRegion (km2) surveyed surveyed found surveyed surveyed found pairs (SE) pairs (SE) aNorthern Central ValleyLowland 10,900 37 822 12 22 497 0 0 12Upland 8,975 11 252 0 11 252 0 0 0All 19,875 48 1,074 12 33 749 0 0 12Middle Central ValleyLowland 16,400 174 3,903 339 59 1,265 34 502 (209) 502 (209)Upland 10,858 25 433 43 12 236 0 0 43All 27,258 199 4,336 382 71 1,501 34 502 (209) 545 (209)Southern Central ValleyLowland 18,650 121 2,902 204 63 1,544 72 968 (342) 968 (342)Upland 13,025 43 714 32 18 323 3 145 (118) 145 (118)All 31,675 164 3,616 236 81 1,867 75 1,113 (460) 1,113 (460)San Francisco Bay Area InteriorLowland 4,903 69 1,592 98 20 447 0 0 98Upland 6,275 21 515 14 12 290 1 21 (21) 21 (21)All 11,178 90 2,107 112 32 737 1 21 (21) 119Central-western InteriorLowland 5,325 20 308 8 17 276 0 0 8Upland 11,225 24 477 13 13 233 2 76 (51) 76 (51)All 16,550 44 785 21 30 509 2 76 (51) 84Southwestern InteriorLowland 1,250 12 301 37 3 75 1 17 (17) 37Upland 5,050 56 1,265 113 8 173 0 0 113All 6,300 68 1,566 150 11 248 1 17 (17) 150Coachella ValleyLowland 1,615 10 245 12 4 100 1 16 (16) 16 (16)Upland 2,350 10 251 37 4 100 0 0 37All 3,965 20 496 49 8 200 1 16 (16) 53[6]
DISTRIBUTION AND ABUNDANCE OF BURROWING OWLS IN CALIFORNIATABLE 2. Continued._________________________________ All blocks ___________________________________________Random blocks onlyRandom & “BestTotal area historic breed- Square No of Random Square No. of Estimated estimate”ofof region ing blocks km pairs blocks km pairs no. of no. ofRegion (km2) surveyed surveyed found surveyed surveyed found pairs (SE) pairs (SE) aImperial ValleyLowland 2,810 12 301 499 5 126 254 5,701 (2,244) 5,701 (2,244)Upland 1,780 3 53 22 2 50 17 707 (140) 707 (140)All 4,590 15 354 521 7 176 271 6,408 (2,384) 6,408 (2,384)a For each subregion we considered our “best estimate” of the number of Burrowing Owl pairs to be the larger of a) the extrapolated estimate of pairs, based only on results fromrandomly-selected blocks, or b) the actual number of pairs counted, pooling data from randomly-selected blocks and historic breeding blocks. We then summed the “bestestimate” for each subregion to obtain “best estimates” for each region.assigned to observers for sampling in year one(2006) based on the firing order. All random andhistoric blocks not sampled in 2006 wereassigned to be surveyed in 2007. Most blockswere sampled during one of the two years inour survey period. In the few instances that ablock was surveyed during both years(generally because volunteer observers becameinterested in “their” blocks during 2006 andindependently chose to resurvey them in 2007),we used data from the first survey year (2006) inour analysis.DATA COLLECTIONAdhering to the strategy developed by DeSanteet al. (2007), we relied largely upon volunteerobservers, many associated with local CaliforniaAudubon Society chapters, to collect our fielddata in the regions that were surveyed during1991-1993. We also deployed a crew of full-timefield biologist technicians to a) survey some ofthe blocks in regions where the number ofvolunteer observers was inadequate toreasonably survey all the selected blocks, and b)survey all of the selected blocks in the Sonoran,Mojave, and Great Basin regions, wherepotential volunteers were very scarce.Volunteer surveyors and IBP field crewssurveyed blocks using the field methodologydeveloped for the 1991-1993 survey (DeSante etal. 2007). For most regions, surveyors wereinstructed to visually scan all of the area in theirblocks at least once during morning (dawn to10:00 AM) or late-afternoon (4:00 PM to dusk)during the two-month period between May 15and July 15, when breeding Burrowing Owls arelikely to be feeding nestlings or recently-fledgedyoung. The survey season was shifted twoweeks earlier in the Western and Eastern MojaveDesert, Sonoran Desert, Southwestern Interior,and the Coachella and Imperial Valley regions toaccount for phenological differences amongareas.We provided surveyors with 1:24,000 scaletopographic maps with survey block boundariesand clearly marked locations of any owls knownor suspected to have bred anytime since 1981.Surveyors delineated the extent of appropriatehabitat in their block, visually scanned all areasof appropriate habitat for owls, and plotted thelocations of any detections on their maps. Foreach detection location, observers provided a[7]
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WETLAND BIRDS OF GHANAAvicennia afr
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