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Tailoring point counts for inference about avian density: dealing with nondetection and availability

Natural Resource Modeling

By:
, , , , , and
DOI: 10.1111/nrm.12024

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Abstract

Point counts are commonly used for bird surveys, but interpretation is ambiguous unless there is an accounting for the imperfect detection of individuals. We show how repeated point counts, supplemented by observation distances, can account for two aspects of the counting process: (1) detection of birds conditional on being available for observation and (2) the availability of birds for detection given presence. We propose a hierarchical model that permits the radius in which birds are available for detection to vary with forest stand age (or other relevant habitat features), so that the number of birds available at each location is described by a Poisson-gamma mixture. Conditional on availability, the number of birds detected at each location is modeled by a beta-binomial distribution. We fit this model to repeated point count data of Florida scrub-jays and found evidence that the area in which birds were available for detection decreased with increasing stand age. Estimated density was 0.083 (95%CI: 0.060–0.113) scrub-jays/ha. Point counts of birds have a number of appealing features. Based on our findings, however, an accounting for both components of the counting process may be necessary to ensure that abundance estimates are comparable across time and space. Our approach could easily be adapted to other species and habitats.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Tailoring point counts for inference about avian density: dealing with nondetection and availability
Series title:
Natural Resource Modeling
DOI:
10.1111/nrm.12024
Volume
27
Issue:
2
Year Published:
2014
Language:
English
Publisher:
Wiley
Contributing office(s):
Southeast Ecological Science Center
Description:
15 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Natural Resource Modeling
First page:
163
Last page:
177
Number of Pages:
15