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RESEARCH ARTICLE
Contents Vol 109(2)

Do observer differences in bird detection affect inferences from large-scale ecological studies?

David B. Lindenmayer A C , Jeff T. Wood A B and Christopher MacGregor A
+ Author Affiliations
- Author Affiliations

A Fenner School of Environment and Society, The Australian National University, Canberra, ACT 0200, Australia.

B Statistical Consulting Unit, The Australian National University, Canberra, ACT 0200, Australia.

C Corresponding author. Email: david.lindenmayer@anu.edu.au

Emu 109(2) 100-106 https://doi.org/10.1071/MU08029
Submitted: 12 June 2008  Accepted: 21 January 2009   Published: 26 May 2009

Abstract

Use of multiple observers in large-scale bird surveys is often unavoidable. But how significant are observer differences in bird detection? Do observer effects significantly influence inferences about environmental factors on birds? We conducted a field experiment to quantify differences between observers in the detection of birds at Booderee National Park, south-eastern Australia. We also re-analysed a large dataset from an observational study where multiple observers had participated in bird surveys. We identified highly significant observer differences for estimates of bird species richness and the probability of detection of three exemplar taxa. We demonstrated that observer effects would not substantially alter inferences we made about relationships between bird species and vegetation type or burning history. We believe that four features of our survey design and protocol limited the magnitude of observer effects on environmental inferences: (1) high levels of replication of classes of field sites – critical for relative comparisons of site (vegetation) types; (2) pre-survey screening to ensure that only experienced ornithologists participated in surveys; (3) repeat sampling of field sites by a different observer on a different day to reduce the impacts of observer heterogeneity and ‘day’ effects; and (4) precluding surveys during poor weather or long after dawn, also to limit ‘day’ effects.


Acknowledgements

Mr Mason Crane, Mr Damian Michael, Dr Rebecca Montague-Drake and Mr Lauchie McBurney are key personnel that have made major contributions to the ongoing research at Booderee National Park. This study was made possible through the dedicated support of volunteers from the Canberra Ornithologists Group. In particular, Bruce Lindenmayer, Jenny Bounds, Martin Moffat, Terry Munro, Peter Fullager, Mike Doyle, Ian Anderson and Peter Roberts have been wonderful supporters of our field-based projects for well over a decade. The work at Booderee National Park has been supported by the Federal Department of Environment, Water, Heritage and the Arts, the Federal Department of Defence and the Australian Research Council. Permission to work on indigenous land was granted by the Wreck Bay Aboriginal Community. Rachel Muntz helped admirably with many key aspects of this study. Comments by three anonymous referees greatly improved earlier versions of this paper.


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