Observer error in identifying species using indirect signs: analysis of a river otter track survey technique

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Title: Observer error in identifying species using indirect signs: analysis of a river otter track survey technique
Author: Evans, Jonah Wy
Abstract: Indirect signs of species presence (e .g . , tracks , scats , hairs ) are frequently used to detect target species in occupancy , presence /absence , and other wildlife studies . Indirect signs are often more efficient than direct observation of elusive animals , making such signs well suited for long -term and broad -scale monitoring programs . However , error associated with misidentification of indirect signs can be high , and should be measured if meaningful inferences about population parameters are to be made . This study addressed the need for systematic approaches to estimate and minimize variation due to observer error in identifying indirect signs . I reanalyzed data from 4 replicates of a presence /absence survey of northern river otters (Lontra canadensis ) that had been conducted by Texas Parks and Wildlife Department (1996 -2003 ) . Sixteen observers had recorded tracks at sample points under bridges (n = 250 ) distributed throughout 27 counties in the Piney -Woods ecoregion of east Texas . My objectives were to 1 ) determine if observers were a source of bias in the survey , 2 ) estimate the proportion of error associated with track identification skill , and 3 ) evaluate the use of an international certification procedure that measured observer tracking skill . The null hypothesis that observers had no effect on the variation in reported sign was rejected . Indeed , binary logistic regression tests indicated that observers were significantly associated with variation in reported track presence . Observers were not randomly distributed among bridge sites , and therefore were significantly correlated with 4 habitat variables that may have influenced heterogeneity in otter occupancy and probability of detection (watershed , vegetation -type , water -type , bridge -area ) . On average , experienced observers (n = 7 ) misidentified 44 % of otter tracks , with a range of 0 % to 100 % correct detection . Also , 13 % of the tracks of species determined to be 'otter -like' were misidentified as belonging to an otter . During the certification procedure , participants misidentified the tracks of 12 species as otter . Inaccurate identification of indirect signs is a likely source of error in wildlife studies . I recommend that observer skill in identification of indirect signs be measured in order to detect and control for observer bias in wildlife monitoring .
URI: http : / /hdl .handle .net /1969 .1 /5853
Date: 2007-09-17

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Observer error in identifying species using indirect signs: analysis of a river otter track survey technique. Available electronically from http : / /hdl .handle .net /1969 .1 /5853 .

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