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A hybrid double‐observer sightability model for aerial surveys
Author(s) -
Griffin Paul C.,
Lubow Bruce C.,
Jenkins Kurt J.,
Vales David J.,
Moeller Barbara J.,
Reid Mason,
Happe Patricia J.,
Mccorquodale Scott M.,
Tirhi Michelle J.,
Schaberl Jim P.,
Beirne Katherine
Publication year - 2013
Publication title -
the journal of wildlife management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.94
H-Index - 111
eISSN - 1937-2817
pISSN - 0022-541X
DOI - 10.1002/jwmg.612
Subject(s) - aerial survey , statistics , cervus elaphus , abundance estimation , observer (physics) , covariate , abundance (ecology) , environmental science , geography , mathematics , computer science , ecology , cartography , biology , physics , quantum mechanics
Raw counts from aerial surveys make no correction for undetected animals and provide no estimate of precision with which to judge the utility of the counts. Sightability modeling and double‐observer (DO) modeling are 2 commonly used approaches to account for detection bias and to estimate precision in aerial surveys. We developed a hybrid DO sightability model (model M H ) that uses the strength of each approach to overcome the weakness in the other, for aerial surveys of elk ( Cervus elaphus ). The hybrid approach uses detection patterns of 2 independent observer pairs in a helicopter and telemetry‐based detections of collared elk groups. Candidate M H models reflected hypotheses about effects of recorded covariates and unmodeled heterogeneity on the separate front‐seat observer pair and back‐seat observer pair detection probabilities. Group size and concealing vegetation cover strongly influenced detection probabilities. The pilot's previous experience participating in aerial surveys influenced detection by the front pair of observers if the elk group was on the pilot's side of the helicopter flight path. In 9 surveys in Mount Rainier National Park, the raw number of elk counted was approximately 80–93% of the abundance estimated by model M H . Uncorrected ratios of bulls per 100 cows generally were low compared to estimates adjusted for detection bias, but ratios of calves per 100 cows were comparable whether based on raw survey counts or adjusted estimates. The hybrid method was an improvement over commonly used alternatives, with improved precision compared to sightability modeling and reduced bias compared to DO modeling. © 2013 The Wildlife Society.