Modeling co-occurrence of northern spotted and barred owls: accounting for detection probability differences

Biological Conservation
By: , and 



Barred owls (Strix varia) have recently expanded their range and now encompass the entire range of the northern spotted owl (Strix occidentalis caurina). This expansion has led to two important issues of concern for management of northern spotted owls: (1) possible competitive interactions between the two species that could contribute to population declines of northern spotted owls, and (2) possible changes in vocalization behavior and detection probabilities of northern spotted owls induced by presence of barred owls. We used a two-species occupancy model to investigate whether there was evidence of competitive exclusion between the two species at study locations in Oregon, USA. We simultaneously estimated detection probabilities for both species and determined if the presence of one species influenced the detection of the other species. Model selection results and associated parameter estimates provided no evidence that barred owls excluded spotted owls from territories. We found strong evidence that detection probabilities differed for the two species, with higher probabilities for northern spotted owls that are the object of current surveys. Non-detection of barred owls is very common in surveys for northern spotted owls, and detection of both owl species was negatively influenced by the presence of the congeneric species. Our results suggest that analyses directed at hypotheses of barred owl effects on demographic or occupancy vital rates of northern spotted owls need to deal adequately with imperfect and variable detection probabilities for both species.
Publication type Article
Publication Subtype Journal Article
Title Modeling co-occurrence of northern spotted and barred owls: accounting for detection probability differences
Series title Biological Conservation
DOI 10.1016/j.biocon.2009.07.028
Volume 142
Issue 12
Year Published 2009
Language English
Publisher Elsevier
Publisher location Amsterdam, Netherlands
Contributing office(s) Patuxent Wildlife Research Center
Description 7 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Biological Conservation
First page 2983
Last page 2989
Country United States
State Oregon
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