Feral predator control for life beyond the fence
By Dr David Roshier, Senior Ecologist (Research), Dr Andrew Carter, Wildlife Ecologist, Dr Michael Smith, South West Regional Ecologist, and Dr John Kanowski, Chief Science Officer.
Feral cats and foxes are the primary threat to small to medium-sized Australian mammals, with over 60 species rated as extremely or highly susceptible to these predators (Woinarski et al. 2014; Radford et al. 2018). Conservation of these species requires the elimination or heavy suppression of foxes and cats.
AWC has established a network of feral predator-free areas (or ‘safe havens’) at eight properties in southern and central Australia that currently support a dozen threatened mammal species, with further species to be added in the next few years.
AWC’s long-term objective
AWC’s long-term objective is to have populations of species susceptible to feral predators living ‘outside the fence’. Such a strategy, if successful, has the potential to greatly expand the area of habitat available to those species. However, implementation of this strategy is predicated on two conditions:
That source populations of susceptible species are available for reintroduction (the safe haven program is important in this context); and
That densities of feral predators can be reduced to sufficiently low levels to safely allow reintroduction of susceptible species.
Meeting the second condition requires both the development of targeted control methods (i.e., baits) and the capacity to robustly monitor densities of feral predators so we can confidently determine the impact of the control measures.
In recent years, control methods have improved for feral predators. The introduction of canid pest ejectors (CPEs) has assisted with controlling foxes, while considerable effort has gone into developing baits that are attractive to feral cats. Field trials of machines that detect and spray poison on feral cats and foxes are also underway in Australia (Read et al. 2019). However, unless we can robustly measure densities of feral cats and foxes, we can’t be sure that deployment of any control measure has a meaningful impact on their populations. Without that, we cannot commit to releasing threatened species into landscapes that still support feral predators.
Methods and outcomes from AWC’s extensive feral predator research in the Kimberley are now being applied in NSW.
Feral predator ecology research
Over the last decade, AWC has undertaken a series of ground-breaking research projects aimed at understanding the ecology of feral cats and foxes, their impacts on native animals, and how those impacts might be mitigated. The initial research was conducted primarily in the Kimberley and resulted in a series of papers on feral cats and their management in the savannas of northern Australia (e.g., MacGregor et al. 2014, 2017).
Since 2015, AWC’s feral predator research program has shifted to Scotia Wildlife Sanctuary, in western New South Wales. Here, Drs David Roshier and Andrew Carter have conducted intensive camera- trap monitoring across 14,000 hectares while simultaneously tracking a large number of cats and foxes fitted with GPS collars. The purpose of the research has been to determine the movement patterns of foxes and cats and to use this information to refine statistical methods for estimating population density of these predators (see, e.g., Carter et al. 2019).
A major finding of AWC’s research is that feral cats travel vast distances. Each colour represents a single cat’s movements across the landscape at Scotia.
Developing robust feral animal density estimates
Most current methods for estimating animal density from camera trap data are not easily implemented, while those methods that are easy to implement produce results that are not particularly robust. In contrast, we have been looking to develop robust operational methods. In particular, we have been trying to develop a method that doesn’t rely on the identification of individual cats and foxes from camera trap images which is time-consuming and unreliable. Instead, the methods we have been developing (with statistical consultant, Dr Joanne Potts) utilise information on the movements of foxes and cats in a landscape. This greatly simplifies data collection and analysis, and unifies the estimation process for similar- sized species.
Recently, we have used this approach to examine the responses of feral cats and foxes to implementation of fox control in the study area at Scotia. Fox control commenced in October 2017 and fox (and cat) activity – the number of camera ‘hits’ – has remained low since (noting the region has been in severe drought). These data have been converted to density estimates so we have a reproduceable measure rather than an index of activity. In 2021, we plan to implement cat control via aerial bait delivery in the study area at Scotia, and will use the same approach to determine the response of feral predators to this baiting program.
Elsewhere, we are building on this research to better understand the ecology of cats and foxes in other biomes. Since 2018, Dr Carter has worked with AWC ecologists in the Pilliga State Conservation Area and National Park, in central-west New South Wales, to catch and track cats and foxes, and measure their density in the landscape.
A major finding of AWC’s research is that feral cats travel vast distances. Each colour represents a single cat’s movements across the landscape at Pilliga.
The long-term objective is to inform development of an ‘outside the fence’ reintroduction strategy at this site. Research in the Pilliga is part of the ‘Reintroduction of Locally- extinct Mammal Species’ project being run by AWC in partnership with NSW National Parks and Wildlife Service, as part of the New South Wales Government’s Saving our Species program. The research is revealing: at both Scotia and the Pilliga, many cats are travelling over long distances (tens to hundreds of kilometres). This finding has major implications for attempts to control cats at a local scale.
Measuring outcomes on a large scale
AWC is extending the design and statistical methods developed at Scotia to measure the outcomes of large-scale aerial baiting of foxes and cats at Mt Gibson Wildlife Sanctuary in Western Australia, ahead of proposed ‘outside the fence’ reintroductions. AWC ecologists, led by Dr Michael Smith, have established two large grids of camera traps at Mt Gibson: the first across a 32,000 hectare ‘treatment’ grid of camera traps and a second camera grid across a 13,000 hectare ‘control’ area that will remain unbaited.
The team will then measure the density of cats and foxes in both areas before and after bait delivery to determine the effectiveness of the baiting and the exact densities that are achieved.
Assuming we effectively reduce cat and fox density, AWC will attempt to re-establish populations of the locally extinct Western Quoll (Dasyurus geoffroii) outside the fenced area. We also hope that with effective control of introduced predators, some of the mammals reintroduced to the fenced area at Mt Gibson will be able to establish populations in the broader landscape.
Carter A, Potts JM, Roshier DA (2019) Toward reliable population density estimates of partially marked populations using spatially explicit mark-resight methods. Ecology and Evolution: https://doi.org/10.1002/ece3.4907 McGregor HW et al. (2014) Landscape management of fire and grazing regimes alters the fine-scale habitat utilisation by feral cats. PLoS ONE 9: e109097. McGregor HW et al. (2017) Habitat preference for fire scars by feral cats in Cape York Peninsula, Australia. Wildlife Research 43, 623-633 Radford J et al. (2018) Degrees of population-level susceptibility of Australian terrestrial non-volant mammal species to predation by the introduced red fox (Vulpes vulpes) and feral cat (Felis catus). Wildlife Research doi.org/10.1071/WR18008 Read J et al. (2019) Target speciﬁcity of the Felixer grooming “trap”. Wildlife Society Bulletin 43, 112–120 Woinarski JCZ, Burbidge AA, Harrison PH (2014) The Action Plan for Australian Mammals 2012. CSIRO, Melbourne.