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Abstract
Accurate and precise estimates of numbers of animals are vitally needed both to assess population status and to evaluate management decisions. Various methods exist for counting birds, but most of those used with territorial landbirds yield only indices, not true estimates of population size. The need for valid density estimates has spawned a number of models for estimating
p, the ratio of birds detected to those present. Wildlife biologists can be assisted in evaluating these methods by appreciating several subtleties of
p: (1)
p depends upon the duration of the count, (2)
p has two independent components,
availability of cues and
detectability of cues, (3) detectability is a function of both the
conspicuousness of cues (e.g., vocalizations, conspicuous movements) and the
abundance of cues, and (4) discontinuous production of cues lowers availability, which has a direct and sometimes profound effect on
p. Two recently-updated methods of estimating
p, double-observer sampling and distance-sampling, are better suited to estimating detectability, while two others, double sampling and removal sampling, are better suited to estimating availability. While none of the four offers a complete solution at present, hybrids are under development, and a technique that can yield estimates of availability and detectability from survey data may be available in the near future.
Parent Publication
Keywords
abundance of cues,
availability,
bird survey,
census,
conspicuousness,
detectability,
detection probability,
distance sampling,
double sampling,
double-observer sampling,
index ratio,
point count,
removal sampling
Citation
McCallum, D. Archibald. 2005. A conceptual guide to detection probability for point counts and other count-based survey methods. In: Ralph, C. John; Rich, Terrell D., editors 2005. Bird Conservation Implementation and Integration in the Americas: Proceedings of the Third International Partners in Flight Conference. 2002 March 20-24; Asilomar, California, Volume 2 Gen. Tech. Rep. PSW-GTR-191. Albany, CA: U.S. Dept. of Agriculture, Forest Service, Pacific Southwest Research Station: p. 754-761
