Review of existing Red Fox, Feral Cat, Feral Rabbit, Feral Pig and Feral Goat control in Australia. II. Information Gaps

Final report
Ben Reddiex, David M. Forsyth.
Department of the Environment and Heritage, 2004

Executive Summary

Project and client

Red foxes, feral cats, feral rabbits, feral pigs, and feral goats separately and in various combinations are believed to be responsible for the extinction or decline of a wide range of native species and for adverse changes in ecological communities in Australia. Predation by foxes and feral cats are key threatening processes under the Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act), whilst competition with native species and land degradation by feral rabbits, feral pigs and feral goats are also listed as key threatening processes under that Act. The belief that pest animals have caused declines in native species (and damage production values) is reflected in legislation and has led to many attempts to control the pests. Many agencies and organisations including Federal, State and Local governments commit significant resources managing these species. However, there is limited hard evidence that this management has led to a reduction in threats and to a reversal in the decline.

The Department of the Environment and Heritage (DEH) commissioned the Arthur Rylah Institute for Environmental Research to undertake a project aimed at increasing the understanding on whether control of foxes, feral cats, feral rabbits, feral pigs, and feral goats lead to a reduction in threats to native species and ecological communities. The project is being completed in three stages. The first stage detailed an audit of 1306 existing pest animal control programs in Australia (Reddiex et al. 2004). This, the second stage, identifies gaps in knowledge on control activities and recommends priorities for filling these gaps. Other stages include the development of protocols for monitoring pest species, and designing a process to determine priority ranking for control of pest animals in order to minimise threats to native species and ecological communities.

Objectives

The objectives of this report are to:

  • Identify gaps in existing information on control activities, especially in relation to the success in reducing/removing pest species, and in subsequent recovery of native species/ecological communities, especially those listed under the EPBC Act, across Australia.
  • Identify the native species perceived to be threatened by foxes, feral cats, feral rabbits, feral pigs, and feral goats, for which there is still limited information on results of pest control activities.
  • Recommend priorities for filling gaps in existing knowledge, by both experimental control and monitoring of existing control activities, to cover as large a range of threatened species as possible, especially those native species perceived to be threatened by foxes, feral cats, feral rabbits, feral pigs, and feral goats.
  • Design specific control experiments that include varied levels of control and the consequences for a range of native species and ecological communities, in particular, those that are difficult to target through monitoring of existing control activities, and include the cost of conducting these experiments.

Methods

  1. We considered both the amount and reliability (Reddiex et al. 2004) of knowledge available for the following four areas:
    • Monitoring techniques; are there techniques for monitoring changes in relative and/or absolute abundance of the pest animal as a consequence of control?
    • Effectiveness of control; are there control programs or research studies documenting the effectiveness of the commonly-used control techniques in terms of changes in the abundance of the pest animal and/or residual densities?
    • Costs of control; have the costs of the commonly-used control techniques been documented?
    • Benefits of control for native species/ecological communities; have the benefits of pest animal control for native species and ecological communities been investigated in a reliable manner?
  2. Based on (1), we identify the native species for which there is limited information on the benefits of pest animal control. We focused on the benefits of control for EPBC Act listed threatened species known or perceived to be threatened by the pest animal species, and then identified any other species/ecological communities for which information was available.
  3. Our priorities for filling information gaps were as follows. First, if there were no adequate methods for monitoring changes in the abundance of the pest animal then the development of monitoring techniques was given the highest priority. Given that adequate monitoring techniques are available, the next highest priority was obtaining reliable information on the benefits of pest animal control for native species/ecological communities.
  4. Since the most reliable information is obtained from a designed experiment, we proposed one experiment to identify the benefits (or not) of (i) feral goat, (ii) feral pig, (iii) feral rabbit, and (iv) fox control for native species/ecological communities. We give indicative costs for conducting the experiment. The actual costs will depend on the area(s) where the work is conducted, and the charge-out rates of the organisations involved in the work. Our costs should be used for broad budgeting purposes only.

Results and Discussion

  1. The first stage of this review (audit of existing pest animal control programs in Australia; Reddiex et al. 2004) found that there was little reliable knowledge about the benefits of fox, feral cat, feral rabbit, feral pig and feral goat control for EPBC Act listed threatened species. Few control programs monitored changes in the pest species targeted for control and the native species of interest. In addition, monitoring designs rarely included non-treatment areas or were randomly allocated, and few had assessed the species/habitat of interest prior to control. However, experimental studies have provided some information on the benefits of control for some species known to be threatened by foxes (see Reddiex et al. 2004; Robley et al. 2004).
  2. The highest priority for filling these gaps in knowledge for each species are as follows:
    • Feral goats; assessing the benefits of feral goat control for native plant species.
    • Feral pigs; assessing the benefits of feral pig control for ground disturbance, native plant species and below-ground processes.
    • Feral rabbits; assessing the relationship between feral rabbit density and their impact on native plant species.
    • Foxes; assessing the benefits of fox control for native fauna species.
    • Feral cats; developing techniques for estimating relative and absolute abundance of feral cats.
  3. Experiments are proposed for reliably evaluating the benefits of control for feral goats, feral pigs, feral rabbits, and foxes. An experimental assessment of the benefits of feral cat control for native species/ecological communities should not be undertaken until adequate methods are available for estimating the abundance of feral cats. Each experiment should run for at least five years before being reviewed in the light of both results and environmental variables (e.g., rainfall) that are likely to influence the results. We strongly recommend that monitoring designs are based on an underlying modelling framework, thereby ensuring the correct information is collected for system models. Experiments can then continually update system models and decrease the amount of time it takes to improve the reliability of management decisions.
  4. Until study sites are identified the costs of these experiments should be considered indicative for long-term budgetary purposes. The start-up costs of these experiments ranged from c. $325K (for feral goats) to c. $2.1 million (for foxes), and annual costs ranged from c. $250K (for feral goats) to $1.8 million (for foxes). The large costs reflect the need for experimental designs that can reliably demonstrate the benefits of pest animal control. Failure to adopt the elements of experimental design outlined here will lead to the continued accumulation of unreliable knowledge and an inability to predict the effects of pest animal control.

Recommendations

  1. The proposed experiments evaluating the benefits of feral goat, feral pig, feral rabbit, and fox control should be undertaken as funding permits. The experimental design should not be compromised in order to reduce the costs of the experiments: it would be preferable for just one experiment to be adequately funded rather than several experiments inadequately funded.
  2. Research to develop methods for estimating the relative and absolute abundance of feral cats, and the absolute abundance of foxes should be funded.