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RESEARCH ARTICLE
Contents Vol 32(3)

A method for estimating wildlife detection probabilities in relation to home-range use: insights from a field study on the common brushtail possum (Trichosurus vulpecula)

Stephen J. Ball A D , David Ramsey B , Graham Nugent A , Bruce Warburton A and Murray Efford C
+ Author Affiliations
- Author Affiliations

A Landcare Research, PO Box 69, Lincoln, New Zealand.

B Landcare Research, Private Bag 11052, Palmerston North, New Zealand.

C Landcare Research, Private Bag 1930, Dunedin, New Zealand.

D Corresponding author: Stephen_J_Ball@yahoo.com.au

Wildlife Research 32(3) 217-227 https://doi.org/10.1071/WR03125
Submitted: 22 December 2003  Accepted: 21 February 2005   Published: 22 June 2005

Abstract

Using field data from brushtail possums (Trichosurus vulpecula), we present a method for modelling wildlife detection probabilities. Whereas detection functions typically (e.g. for distance sampling) describe the probability of direct human observations of animal subjects, we adapted this approach for cryptic species where observation depends on animals being caught in traps. Specifically, we characterised the probability of individual brushtail possums being caught by leg-hold traps in an area of farmland and native forest in New Zealand. Detection probability was defined as the per-individual, per-trap, per-night probability of a possum being captured, and was modelled as a function of home-range utilisation. Radio-telemetry was used to define the home-range distributions of 18 possums, and a combination of scanning radio-receivers and movement-activated video-cameras recorded instances when radio-collared possums encountered and stepped on the trigger of leg-hold traps (inactivated by being wired open). We estimated a 5% chance of trapping individual possums with a single leg-hold trap located in the centre of their home range for one night (median value across possums). Furthermore, this probability decreased rapidly as a function of distance, so that at 120 m from the centre of the home range there was less than a 1% chance of trapping success per possum per night. The techniques developed in this study could be applied to a wide variety of species and sampling methods.


Acknowledgments

Thanks go to Blair Brown for the collection and processing of much of the data used in this study. We acknowledge Murray and Linda Harmer for the use of their property near Mt Somers, New Zealand. Geoff Graham and Ian Trethowen were essential in the development of the automatic tracking system and scanning radio-receivers used in this study. Steve Hough provided the idea for (and construction of) a switch-activated light for the detection of would-be trapping events. Thanks to Steve Ferriss for assistance with data-handling in the ArcView Geographic Information System. This work was undertaken partly in Alford Forest under NZ Department of Conservation concession permit. All work with possums was carried out under Landcare Research Animal Ethics Committee permit 02/05/01.


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