Do Control Interventions Effectively Reduce the Impact of European Red Foxes on Biodiversity and Agricultural Production in Australia? (systematic review)
The European red fox (Vulpes vulpes) is listed as one of the IUCN’s top 100 worst invasive alien species. The species occurs naturally throughout most of the northern hemisphere, and was introduced into Australia in the 1870s, where it has become one of this country’s most widespread pest animals, having major environmental and agricultural impacts through predation on native wildlife and livestock. Despite the huge impact foxes have on the environment and the millions of dollars they cost the economy each year, there are no recommended levels of fox control within Australia. The need to evaluate the effectiveness of control methods, particularly the main methods of poisoning with 1080-laden baits, shooting and trapping, in different situations has been identified. Such information will have value at regional, state and national scales, informing local management or policy decisions, and has the potential to influence state and national policies and guidelines on fox management for reducing impacts on conservation values and agricultural production.
To systematically search and collate published and unpublished evidence in order to address the question: “Do control interventions effectively reduce the impact of European red foxes on conservation values and agricultural production in Australia?”
The secondary objectives are:
- “Do environmental and geographical factors (e.g. ecosystem, habitat, land-use, temperature, rainfall, longitude, island/mainland populations, food resources) alter the effectiveness of fox control for reducing impacts?”
- “Do operational level variables (e.g. density of foxes, size of controlled area, previous control history, duration/effort/timing of control, fencing of controlled area, bait/poison application method, bait type) alter the effectiveness of fox control programmes for reducing impacts?”
Electronic searching was completed using the following databases, catalogues and web-engines: Agricola, Alltheweb, Australian Digital Theses Program, BIOSIS, CAB Abstracts, ConservationEvidence.com, COPAC, CSIRO Library Network Catalogue, Digital Dissertations Online, Dogpile, English Nature’s “Wildlink” catalogue, Google Scholar, Index to Theses Online, ISI Web of Knowledge (inc. ISI Web of Science and ISI Proceedings), Science Direct, Scirus (all journal and web sources), Scopus and Wildlife and Ecology Studies Worldwide (NISC). Publications on 28 statutory and non-statutory organisation websites were conducted. Bibliographies of articles viewed at full text were searched for relevant additional articles. Personal contact with recognised experts and practitioners in the field of fox control and wildlife/ agricultural protection in Australia was used to retrieve further recommendations and data.
Any studies that examined the change in impact of foxes on either agricultural production or conservation values in Australia after the implementation of control programmes using the three main techniques of 1080 lethal baiting, shooting, or trapping were included. Appropriate experimental design with spatial and temporal controls was a pre-requisite to be accepted. Studies that measured the impact of control on fox abundance alone were not included.
Data collection and characterisation
The inclusion criteria were met by sixteen articles only. Of these studies, fourteen reported on the impact of foxes on varying conservation values, while the remaining two studies measured impacts on agricultural production (typically lamb production). All of the studies involved the use of baiting with 1080, with a small number also conducting shooting and trapping. One study used electrified fencing in addition to the conventional baiting and shooting techniques.
Although all included studies reported on a change in abundance and /or survival of prey species after a control intervention, the dissimilarity in monitoring techniques (density vs indices of abundance, population vs individual survival), the inconsistency in the application of the control intervention, and the range of measured outcomes precluded the use of any formal meta-analysis statistical techniques. No study reported on the cost benefits of control intervention, and only two studies investigated the cost effectiveness of their control method.
The two studies investigating the impact of fox predation on agricultural production both concluded there was a response in lamb production after control intervention, however the extent of this response varied. The fourteen studies that reported on the impact of foxes on conservation values investigated an array of prey species, mainly native wildlife, in a diverse range of locations and habitats. Many native species showed a positive response in either individual or population survival after the control intervention, however there were some species which showed either no response or a negative response to fox removal. Of the two introduced species that were investigated, the non-native House mouse (Mus musculus) showed no response after fox control, however there was a positive response in population numbers of the rabbit (Oryctolagus cuniculus), although when fox control ceased these populations did not necessarily remain suppressed suggesting rabbit populations exceeding some critical density were not regulated by foxes.
Poisoning with 1080-laden baits was the major control tool used by all included studies, however there were inconsistencies in its application, in part mirroring the changing knowledge of baiting effectiveness and best practice over time. The two studies that investigated cost effectiveness compared different baiting strategies to achieve a pre-determined management outcome, and their results have had a major impact on the way conservation baiting programmes are now conducted in Australia.
Although fox predation has been recognised as a serious threat, especially to populations of native wildlife, the complexity of the interactions with other processes has made the collection of detailed information very difficult. On examination of the studies included in this review, only a broad set of evidence-based management guidelines can be formed. Frequent, broad-scale application of 1080-laden baits is the most effective approach to controlling fox impact currently available in Australia, however land managers will need to assess their objectives and available resources before formulating their own management programmes, then continually improve these practices through monitoring and learning.
Robust density/ damage relationships for foxes in both agricultural and conservation landscapes remain elusive and this in turn hinders more definitive bioeconomic decision making. Deriving such relationships would require costly experimental evaluations, nonetheless, opportunities and innovations for examining such relationships should not be overlooked in ongoing fox research programmes. This review also recommends further research into the implications of mesopredator release and strategies that address the simultaneous management of all predators, the re-evaluation of the efficacy of conventional baiting programmes, the improvement in lethal techniques giving consideration to welfare and ethical aspects, and the improvement and refinement of non-lethal techniques.
There is a profusion of fox management programmes conducted across Australia, but so little of the resulting information and outcomes are reported in the public arena, and an even smaller number are published in the peer reviewed literature. Managers are urged to conduct their programmes in as a controlled and replicated way as possible, and to publish their outcomes so they can be incorporated into the high quality evidence-base necessary for land managers and policy makers to make informed decisions when managing the impact of foxes.
The European red fox (Vulpes vulpes) has been listed as one of the IUCN’s top 100 worst invasive alien species (Lowe et al., 2000). The species occurs naturally throughout the northern hemisphere, from North America through Europe, Asia, and the northernmost parts of Africa (Saunders et al., 1995). While native to North America, European red foxes were introduced to other areas of the continent and subsequently interbred with native stock. Australia contains the only southern hemisphere introduction of the species (Saunders et al., 1995). This systematic review will be restricted to operations undertaken to control fox populations in Australia only.
The fox was introduced into Victoria, southern Australia, in the 1870s for hunting purposes, and rapidly spread throughout the majority of all mainland states (Rolls, 1969). In 2001, they were detected in the island state of Tasmania for the first time, despite previous introduction attempts (Saunders et al., 2006). The fox is now one of the most ubiquitous pest animals in the country, and its pattern of spread and current distribution closely mirror that of the introduced rabbit (Jarman, 1986). Fox density varies across the country, being absent from the northernmost tropical areas, to 4.6- 7.2 km-2 in the northern Tablelands of NSW, and up to 12 km-2 in Victoria’s largest city, Melbourne (Saunders et al,. 1995).
Predation by foxes has been listed as a key threatening process under the Australian Government’s Environment Protection & Biodiversity Conservation Act 1999 (DEH website). The fox has major environmental impacts in Australia, as a predator of smaller native mammals, ground-nesting birds and turtles, and may be partly responsible for several extinctions (e.g. Lunney 2001). They also cause production losses in the agricultural sector due to predation on stock, particularly newborn lambs (Saunders et al., 1995). Millions of dollars are spent each year in Australia to perform control operations on fox populations. AUD$37 million per year has been estimated for the economic costs of control and production losses, with environmental impacts raising that figure to AU$227 million (McLeod, 2004). Fox control operations are conducted for threatened species and livestock protection, and are carried out on over 10.5 million ha of land per year (Reddiex et al., 2004). The main control method used is ground-based poisoning with 1080-laden baits; other frequently used methods are aerial baiting, trapping, shooting, and den ripping and fumigation (Reddiex et al., 2004). Immunocontraceptives have been investigated, but a product usable for control operations has not been developed.
There are no recommended levels of fox control within Australia. Most States and Territories have legislative requirements for landholders to undertake fox management, most supported by region-wide management plans, although enforcement is not usual (Saunders et al., 1995). The Australian Government’s Threat Abatement Plan for Predation by the European Red Fox (1999) states, “the main priority during the life of the plan is to support on-ground control programs necessary to ensure recovery of endangered species”, but does not provide any recommended control levels. The Invasive Animals Cooperative Research Centre has set an operational target of reducing fox and wild dog impacts by 10% (AU$27 million per year) as part of its Terrestrial Products and Strategies Program (Invasive Animals CRC website).
Using systematic review methodology, the most common interventions (poison baiting, trapping and shooting) used to control European red foxes to reduce impacts on biodiversity and agricultural production in Australia will be critically appraised (Table 1). The review will consider the best available evidence of the effectiveness of control methods in different situations. Other questions within this topic, including the effectiveness of different control interventions and the reduction of impacts on wildlife and domestic stock in countries other than Australia, will not be addressed in this review; however, such information will be collated and catalogued.
The review will limit bias through the use of comprehensive literature searching (both published and unpublished), specific inclusion criteria, and formal assessment of the quality and reliability of the studies retrieved. Subsequent data synthesis (qualitative and/or quantitative) will summarise evidence, guiding the formulation of appropriate evidence-based management guidelines and highlighting gaps in research evidence.
This review should be of use to practitioners carrying out, or advising on, fox control for Australian natural resource and environmental management organisations (statutory and non-statutory), and ultimately local authorities and landholder groups. It will have value at regional, state and national scales, informing local management or policy decisions, and has the potential to influence state and national policies and guidelines on fox management for reducing impacts on biodiversity and agricultural production.