Detecting rare carnivores using scats: Implications for monitoring a fox incursion into Tasmania

Abstract

The ability to detect the incursion of an invasive species or destroy the last individuals during an eradication program are some of the most difficult aspects of invasive species management. The presence of foxes in Tasmania is a contentious issue with recent structured monitoring efforts, involving collection of carnivore scats and testing for fox DNA, failing to detect any evidence of foxes. Understanding the likelihood that monitoring efforts would detect fox presence, given at least one is present, is therefore critical for understanding the role of scat monitoring for informing the response to an incursion. We undertook trials to estimate the probability of fox scat detection through monitoring by scat‐detector dogs and person searches and used this information to critically evaluate the power of scat monitoring efforts for detecting foxes in the Tasmanian landscape. The probability of detecting a single scat present in a 1‐km2 survey unit was highest for scat‐detector dogs searches (0.053) compared with person searches (x¯≅0.015) for each 10 km of search effort. Simulation of the power of recent scat monitoring efforts undertaken in Tasmania from 2011 to 2015 suggested that single foxes would have to be present in at least 20 different locations or fox breeding groups present in at least six different locations, in order to be detected with a high level of confidence (>0.80). We have shown that highly structured detection trials can provide managers with the quantitative tools needed to make judgments about the power of large‐scale scat monitoring programs. Results suggest that a fox population, if present in Tasmania, could remain undetected by a large‐scale, structured scat monitoring program. Therefore, it is likely that other forms of surveillance, in conjunction with scat monitoring, will be necessary to demonstrate that foxes are absent from Tasmania with high confidence.

Evaluation of camera placement for detection of free‐ranging carnivores; implications for assessing population changes

“…Similarly, van Hespen, Hauser, Benshemesh, Rumpff, and Lahoz‐Monfort (2019) demonstrated through simulation modelling that small changes in environmental factors, budget constraints and monitoring design can affect the chances of a monitoring programme successfully achieving its intended outcomes. These are crucial considerations for developing effective monitoring programmes, yet there are relatively few examples in the published peer‐reviewed literature where power analysis has been used to inform carnivore monitoring (but see Ramsey et al., 2017; Travaini et al., 2010; van Hespen et al., 2019).…”

Can evolutionary theories of dispersal and senescence predict postrelease survival, dispersal, and body condition of a reintroduced threatened mammal?

“…However, wild individuals are harder to source and their removal may compromise established wild populations, especially for threatened species (Todd et al, 2002). Wild quolls from Tasmania are not expected to have an appropriate predator response to foxes on the mainland (Jones et al, 2004); this is due to foxes being absent or occurring at very low densities in Tasmania (Ramsey et al, 2018) and a lack of co‐evolution of the two species (Woinarski et al, 2015).…”

Jackal in hide: detection dogs show first success in the quest for golden jackal (Canis aureus) scats

“…Scats have been used in a number of well-known and universal methodologies for a variety of species and with various specific non-invasive monitoring objectives (Foran et al 1997;Delahay et al 2001;Baines et al 2013;Ramsey et al 2017). In our study, detection dogs successfully found and indicated golden jackal scats with an accuracy of 73%.…”

“…In contrast, we assume that humans are not able to distinguish reliably between golden jackal scats and those from closely related canid species, especially in areas of coexistence with the red fox (Vulpes vulpes), a species widespread all over Europe. Moreover, humans have a much smaller overall detection success than dogs (Böcker 2016;Ramsey et al 2017;Grimm-Seyfarth et al 2019).…”