Observer differences in the North American Breeding Bird Survey

The Auk
By: , and 



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.

Publication type Article
Publication Subtype Journal Article
Title Observer differences in the North American Breeding Bird Survey
Series title The Auk
DOI 10.2307/4088504
Volume 111
Issue 1
Year Published 1994
Language English
Publisher American Ornithological Society
Contributing office(s) Patuxent Wildlife Research Center
Description 13 p.
First page 50
Last page 62
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