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Observer Differences in the North American Breeding Bird Survey
John R. Sauer, Bruce G. Peterjohn and William A. Link
Vol. 111, No. 1 (Jan., 1994), pp. 50-62
Published by: American Ornithological Society
Stable URL: http://www.jstor.org/stable/4088504
Page Count: 13
You can always find the topics here!Topics: Binomials, Population trends, Null hypothesis, Aviculture, Birds, Population dynamics, Statistical estimation, Population estimates, Breeding, Censuses
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Because count data collected in many bird surveys are only an index to population size, factors that can influence the counts must be identified and incorporated into analyses. Observer quality is often ignored in analyses of population changes from survey data, but observers differ in methods and capabilities and, hence, tend to count different numbers of birds. We assess the consequences of between-observer differences in counts for estimation of population trends in the North American Breeding Bird Survey. Observer differences in numbers of birds counted were found in 50% of the 369 species we examined. For many species, observers in later years tended to count more birds than observers in earlier years, suggesting an increase in observer quality over time. Analysis of population trends from 1966 through 1991 indicates that failure to include observers as covariables in the analysis results in an overly optimistic view of population trends.
The Auk © 1994 American Ornithologists' Union