Within-site variability in surveys of wildlife populations

By: , and 



Most large-scale surveys of animal populations are based on counts of individuals observed during a sampling period, which are used as indexes to the population. The variability in these indexes not only reflects variability in population sizes among sites but also variability due to the inexactness of the counts. Repeated counts at survey sites can be used to document this additional source of variability and, in some applications, to mitigate its effects. We present models for evaluating the proportion of total variability in counts that is attributable to this within-site variability and apply them in the analysis of data from repeated counts on routes from the North American Breeding Bird Survey. We analyzed data on 98 species, obtaining estimates of these percentages, which ranged from 3.5 to 100% with a mean of 36.25%. For at least 14 of the species, more than half of the variation in counts was attributable to within-site sources. Counts for species with lower average counts had a higher percentage of within-site variability. We discuss the relative cost efficiency of replicating sites or initiating new sites for several objectives, concluding that it is frequently better to initiate new sites than to attempt to replicate existing sites.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Within-site variability in surveys of wildlife populations
Series title Ecology
DOI 10.2307/1939433
Volume 75
Issue 4
Year Published 1994
Language English
Publisher Wiley
Contributing office(s) Patuxent Wildlife Research Center
Description 12 p.
First page 1097
Last page 1108