Degradation and detection of fox (Vulpes vulpes) scats in Tasmania: evidence from field trials
W. E. Brown A C D , D. S. L. Ramsey B and R. Gaffney AA Invasive Species Branch Department of Primary Industries, Parks, Water and Environment, GPO Box 44 Hobart, Tas. 7000 Australia.
B Arthur Rylah Institute for Environmental Research, Department of Environment and Primary Industries, 123 Brown Street, Heidelberg, Vic. 3084, Australia.
C Present address: Save the Tasmanian Devil Program, Wildlife Management Branch, Department of Primary Industries, Parks, Water and Environment, GPO Box 44 Hobart, Tas. 7000, Australia.
D Corresponding author. Email: Bill.Brown@dpipwe.tas.gov.au
Wildlife Research 41(8) 681-690 https://doi.org/10.1071/WR14152
Submitted: 25 July 2014 Accepted: 2 February 2015 Published: 30 March 2015
Abstract
Context: The Tasmanian Government is attempting to eradicate foxes from Tasmania and carnivore-scat surveys using humans and dogs combined with DNA testing are the main methods of detection. Understanding the rate that scats degrade is a key component for estimating the power of monitoring for detecting cryptic predators and will contribute to a broader understanding of the use of scat monitoring for informing eradication programs.
Aims: To estimate the degradation rate of fox scats and derive an estimate of the abundance of scats available to observers monitoring for fox presence.
Methods: In total, 486 fresh fox scats were placed at nine sites within three bioregions in Tasmania and left to degrade for up to 126 days. Scats were observed periodically by both humans and dogs to determine when they became unrecognisable and/or undetectable.
Key results: Recognition of scats by humans declined faster in summer than in winter and did not vary systematically among bioregions. Median survival times of scats were 19 days in summer and 26 days in winter. Recognition of scats by dogs was higher in summer than in winter, with dogs recognising scats past the time they became unrecognisable to humans. Using estimates of scat degradation derived from human observers, the equilibrium abundance of detectable scats within a fox home range was estimated to be 179–243 scats. However, the abundance of detectable scats on linear features subject to monitoring was estimated to be 10–15 scats.
Conclusions: Using our estimate of the abundance of scats on linear features, the current distribution of fox scats detected in Tasmania may not be as anomalous as has been suggested by others. However, fox detection from scats will be highly dependent on deposition patterns and distribution of scats on linear features and this should be critically reassessed in Tasmania.
Implications: Fox scats are not expected to exhibit systematic regional differences in degradation rates that might have an impact on monitoring strategies. Estimates of the abundance of scats detectable by observers are critical for assessing the effectiveness of scat-monitoring programs. We advocate that a rigorous assessment of future scat-monitoring programs in Tasmania be undertaken to determine their power to detect foxes.
Additional keywords: European red fox, faeces, survival analysis.
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