Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats

Visibility bias in aerial survey: mark–recapture, line-transect or both?

Jeff Laake A , Michelle J. Dawson B and Jim Hone B C
+ Author Affiliations
- Author Affiliations

A National Marine Mammal Laboratory, AFSC, NMFS, Seattle, WA 98115, USA.

B Institute for Applied Ecology, University of Canberra, Canberra, ACT 2601 Australia.

C Corresponding author: jim.hone@canberra.edu.au

Wildlife Research 35(4) 299-309 https://doi.org/10.1071/WR07034
Submitted: 19 March 2007  Accepted: 12 December 2007   Published: 27 June 2008


Mark–recapture and line-transect sampling procedures both provide estimators for visibility bias in aerial surveys, and have coexisted in the literature for decades. Mark–recapture estimators of abundance tend to be negatively biased in this context as a result of unmodelled heterogeneity. Line-transect sampling can also be negatively biased if detection probability on the line is less than 1.0. Numerous papers have described hybrid approaches using mark–recapture and line transect methods but there have been some subtle but important differences that may not be apparent to the practitioner. We have used wild horse survey data collected in south-eastern Australia and some imaginary data to highlight these subtle differences. We demonstrate the advantage of using the hybrid approach, which uses the strengths of both mark–recapture and line-transect procedures by fitting a detection function (with p(0) = 1) to the line-transect data to estimate the shape of the detection function, and uses a separate detection function for the mark–recapture data to estimate the intercept (p(0)).


We thank the pilot, P. Potroz, and the Australian Alps Liaison Committee and the University of Canberra for funding. The New South Wales National Parks and Wildlife Service provided logistic support. We thank Alex Zerbini, Kim Goetz, David Anderson and two anonymous reviewers for their insightful comments that led to useful improvements in the manuscript.


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� MJD previously published as M. J. Walter.

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