AVIS-IBIS

Birds of Indian Subcontinent

METHODS TO CORRECT FOR DENSITY INFLATION BIASES IN HAWAIIAN HAWK SURVEYS USING ATTRACTANT CALLS

Publication Type:Journal Article
Year of Publication:2007
Authors:Klavitter, JL, Marzluff, JM, Bednarz, JC
Journal:Journal of Raptor Research
Volume:41
Issue:2
Date Published:2007
ISBN Number:0892-1016
Keywords:Accipitridae, Buteo, Buteo solitarius
Abstract:ABSTRACT Point-count surveys with playback recordings have been used to estimate density and abundance for Hawaiian Hawks (?Io; Buteo solitarius) on Hawaii. Playbacks are necessary for effective surveys, but attract hawks toward the observer prior to their detection. This attraction inflates estimates of density and abundance based on distance analytical techniques. We quantified movement of radio-tagged Hawaiian Hawks and evaluated six methods to adjust estimates to account for attraction. We evaluated methods by comparing density estimates determined by spot mapping to adjusted point counts at two study sites (Kona Forest, Puu Waawaa) during 1998 and 1999 on Hawaii. By spot mapping, we estimated densities of 0.59 and 0.76 hawks/km2 at the Puu Waawaa and Kona Refuge study sites, respectively. We adjusted for (1) lack of response, (2) attraction to calls, (3) attraction and lack of response, (4) view obstruction, (5) view obstruction and lack of response, and (6) movement prior to detection. All methods were effective in adjusting density at the two study areas, but simply subtracting the mean distance moved from estimated distances (attraction) provided nearly identical density estimates to spot mapping. We describe a simple computer simulation routine to accomplish this task for future Hawaiian Hawk surveys.ABSTRACT Point-count surveys with playback recordings have been used to estimate density and abundance for Hawaiian Hawks (?Io; Buteo solitarius) on Hawaii. Playbacks are necessary for effective surveys, but attract hawks toward the observer prior to their detection. This attraction inflates estimates of density and abundance based on distance analytical techniques. We quantified movement of radio-tagged Hawaiian Hawks and evaluated six methods to adjust estimates to account for attraction. We evaluated methods by comparing density estimates determined by spot mapping to adjusted point counts at two study sites (Kona Forest, Puu Waawaa) during 1998 and 1999 on Hawaii. By spot mapping, we estimated densities of 0.59 and 0.76 hawks/km2 at the Puu Waawaa and Kona Refuge study sites, respectively. We adjusted for (1) lack of response, (2) attraction to calls, (3) attraction and lack of response, (4) view obstruction, (5) view obstruction and lack of response, and (6) movement prior to detection. All methods were effective in adjusting density at the two study areas, but simply subtracting the mean distance moved from estimated distances (attraction) provided nearly identical density estimates to spot mapping. We describe a simple computer simulation routine to accomplish this task for future Hawaiian Hawk surveys.
URL:http://dx.doi.org/10.3356/0892-1016(2007)41[81:MTCFDI]2.0.CO;2
Short Title:Journal of Raptor Research
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