RISK ASSESSMENT
for the import and keeping of
exotic vertebrates in australia
Mary Bomford
Bureau of Rural Sciences
Canberra, Australia
© Commonwealth of Australia 2003
ISBN 0-9750443-3-8
This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth available from the Department of Communications, Information Technology and the Arts. Requests and inquiries concerning reproduction and rights should be addressed to the Commonwealth Copyright Administration, Intellectual Property Branch, Department of Communications, Information Technology and the Arts, GPO Box 2154, Canberra ACT 2601 or at http://www.dcita.gov.au/cca.
The Commonwealth of Australia acting through the Bureau of Rural Sciences has exercised due care and skill in the preparation and compilation of the information and data set out in this publication. Notwithstanding, the Bureau of Rural Sciences, its employees and advisers disclaim all liability, including liability for negligence, for any loss, damage, injury, expense or cost incurred by any person as a result of accessing, using or relying upon any of the information or data set out in this publication to the maximum extent permitted by law.
Editor: Penny Olsen, School of Botany and Zoology, Australian National University.
Credit for cover photographs: Adelaide Zoological Gardens (zebra, lemur, ocelot); Queensland RLPB (cane toad); Department of Agriculture, Western Australia (starling); New South Wales Agriculture (feral cat).
Design: Big Island Graphics, Canberra
Preferred way to cite this publication: Bomford, M. (2003) Risk Assessment for the Import and Keeping of Exotic Vertebrates in Australia. Bureau of Rural Sciences, Canberra.
Contents 3
Foreword 5
Summary 6
Key points 6
Factors influencing establishment in the wild 6
Factors influencing feasibility of eradication 8
Factors influencing pest potential 9
Using the risk assessment model to determine a species’ VPC Threat Category 10
Terminology 11
Introduction 12
Section 1: 14
Review of factors affecting the potential of an exotic vertebrate to establish and become a pest 14
1.1 Probability an escape or release will occur 14
1.1.1 Factors affecting the probability of escape or wilful release 14
1.1.2 Risk assessment significance of potential to escape from captivity 15
1.2 Probability escaped or released individuals will cause harm 15
1.3 Probability escaped or released individuals will establish a free-living population 15
1.3.1 Predicting establishment success 17
1.3.2 Uncertainty in predicting establishment success 32
1.4 Probability of eradication 33
1.4.1 Criteria for determining feasibility of eradication 33
1.4.2 Practical considerations for meeting eradication criteria for exotic species 36
1.4.3 Risk assessment significance of probability of eradication 37
1.5 Probability exotic species will become a pest 38
1.5.1 Types of damage caused by exotic pests 38
1.5.2 Predicting pest status 42
1.5.3 Factors contributing to uncertainty in assessing pest potential 49
Section 2: 52
The risk assessment procedure to determine VPC Threat Categories for exotic vertebrates 52
2.1 Information requirements for species risk assessments 52
2.2 Introduction to the risk assessment model 59
2.3 Risk assessment 60
2.4 Decision process 68
2.5 Limitations of the risk assessment model for assessing VPC Threat Categories 70
Acknowledgements 72
References 72
Appendices
Appendix A: Introductions of exotic vertebrates to Australia 88
Appendix B: Climate match data for mammals and birds introduced to mainland Australia 94
Appendix C: CLIMATE matching model 100
Appendix D: Major agricultural commodities that could be damaged by exotic animals 103
Tables
Table 1: Establishment success rates for exotic mammal and bird species 17
Table 2: Proportion of exotic mammals and birds that are pests 44
Table 3 : Commodities that could be damaged by a wild population of an exotic species 55
Table 4: Calculating Total Commodity Damage Score 66
Table 5: Score sheet for risk assessment model 68
Table 6: VPC Threat Categories 70
Table A1: Exotic vertebrate introductions to Australia 88
Table B1: Climate matches for mammals successfully introduced to mainland Australia 94
Table B2: Climate matches for mammals unsuccessfully introduced to mainland Australia 96
Table B3: Climate matches for birds successfully introduced to mainland Australia 97
Table B4: Climate matches for birds unsuccessfully introduced to mainland Australia 98
Table C1: The 16 climate parameters in the CLIMATE_program 100
Figures
Figure C1: Climate match maps for the Burchell’s zebra 101
Figure D1: Major agricultural commodities in Australia [not included] 103
Foreword
Exotic vertebrates (mammals, birds, reptiles and amphibians) introduced into Australia can establish wild pest populations that harm agriculture and forestry costing hundreds of millions of dollars annually. They can also cause untold harm to Australian native species and ecosystems. Exotic grazing and browsing species already present in Australia, such as rabbits and goats, compete with stock and native animals for food and water and cause severe land degradation through overgrazing and destruction of regenerating trees and shrubs. Exotic predators, such as cats and foxes, can kill, maim or harass native species or livestock. Exotic birds, such as starlings, compete for nest holes and food with native birds.
Unfortunately, there is a risk that new exotic species could establish as wild pests in Australia. These could be species that are already being kept in captivity, for example as companion animals or as display animals in zoos, or they could be animals that are imported into Australia in the future. If such animals escaped, or were illegally released, into a favourable environment, they could start to breed in the wild and spread to new locations. Once they are widespread, eradication becomes virtually impossible.
Not all exotic species pose the same level of threat for establishing a wild pest population. Is it possible to distinguish between species that pose a high risk and those that pose a lower risk? This report addresses this question and, based on a review of world scientific literature and an analysis of past exotic vertebrates to Australia, concludes that there is a suite of factors that separates high and low-risk species. This information is used to construct a scientifically based risk assessment model to evaluate the risk that an exotic species released into the wild will establish a wild population, and if it does, the risk that it will become a pest.
The Bureau of Rural Sciences produced this report for the Vertebrate Pests Committee as part of the National Feral Animal Control Program, a Natural Heritage Trust initiative. The report provides information and guidance that will assist the Commonwealth and State and Territory Governments assess and manage the risks posed by the import and keeping of exotic vertebrates. To encourage acceptance and use of the model as a basis for assessing the risk posed by the import and keeping of exotic vertebrates, comment has been sought from State, Territory and Commonwealth Government agencies throughout its development. The scientifically based model presented in this report will help government policy makers, quarantine officials and wildlife managers reduce the risk that new exotic species will establish and cause harm.
Peter O’Brien
Executive Director
Bureau of Rural Sciences
Summary
Key points
At least 25 exotic mammals, 20 birds, one amphibian and four reptiles have already established wild populations on mainland Australia and at least eight more exotic species have colonised offshore islands.
Many of these introduced species are pests that have adverse impacts on agriculture and the environment. This is not just a legacy from the past. There is a risk that additional species now kept in captivity, or newly imported species, may find their way into the wild, establish and become pests.
Risk assessment processes for importing and keeping exotic animals now have an important role to play in reducing the likelihood of new species establishing and causing adverse impacts in Australia. Risk assessment involves identifying hazardous events, in this case the establishment of new exotic vertebrate pest species in Australia, and estimating the likelihood that such events will occur and the probable consequences if they do.
This report evaluates literature reviews and research on past introductions of mammals and birds into Australia and overseas to determine which factors have the most significant influence on whether introduced species succeed or fail to establish exotic populations. In addition, the attributes of established species that become pests of primary production or the environment are compared with the attributes of non-pest species. The results of these analyses are used to develop a more quantitative model for risk assessment for use by government agencies and the Vertebrate Pests Committee. This exotic vertebrate risk assessment model has a sound scientific basis and a transparent decision mechanism.
There are several layers of risk associated with the importing and keeping of exotic species. The likelihood of escape or wilful release depends on such elements as the security of premises, keeping restrictions, and keeper and community attitudes. Also, there is always the chance that individual animals that find their way to freedom may cause harm, for example, if they are powerful carnivores, destructive or poisonous. The major risk factors are the potential to establish in the wild, the potential failure to eradicate and the potential to become a pest.
Factors influencing establishment in the wild
Worldwide about one-third of bird species and two-thirds of mammal species released into new environments establish exotic wild populations. On the Australian mainland, 42% of introduced exotic bird species and 69% of introduced exotic mammal species have established permanent wild populations.
Based on the success or failure of past introductions of exotic mammals and birds to Australia, a number of factors were identified that influence whether an exotic species released in Australia will establish in the wild. These factors need confirmation by rigorous scientific studies, all have exceptions, and chance events play a large part. Despite this uncertainty, together they can be used to predict the likelihood that a new species will establish:
• Introduction effort — the release of large numbers of animals at different times and places enhances the chance of successful establishment. For introductions of exotic birds and mammals to Australia, the number of individuals released, the number of introduction sites and the number of introduction events is correlated with introduction success. The threshold minimum population size for successful invasion is not known for most species. An approximate estimate is that if less than about 20 individuals are released, in many circumstances survival is unlikely. Small numbers of released animals are more susceptible to extinction from such factors as increased risk of predation, not finding a mate, or competition with native species. Chance events, such as random fluctuations in the proportions of males and females, accidents, fires and floods are also likely to drive small populations to extinction. Nevertheless, despite this general principle of small numbers of animals being less successful, there are many examples of less than ten individuals, and sometimes even single pairs, establishing exotic populations. Repeated releases over an extended period increase the chance of successful invasion simply because the release experiment is repeated many times, under different biotic and abiotic conditions, for example, in different climates and seasons and with variations in the fitness of released animals.
• Climate match — For exotic birds and mammals introduced to Australia, the better the match between the climate in a species’ overseas geographic range and Australian climates, the greater the risk of establishment.
• Extent of geographic range — The larger the overseas geographic range size the greater the risk of establishment success for exotic birds and mammals in Australia.
• History of invasiveness — A history of establishing exotic populations elsewhere in the world increases the risk of establishment for exotic birds and mammals introduced to Australia. However, when predicting a species’ establishment potential, this criterion must be used with caution. Many species have not had the opportunity to demonstrate their invasive potential because they have not been released in new environments.
• Mammals vs birds — Exotic mammals have a higher establishment success rate than exotic birds both in Australia and overseas.
• Taxonomic group — Exotic gamebirds (Order: Galliformes) have a lower establishment success rate than other bird taxa on the Australian mainland, but they have done well on offshore Australian islands and overseas. Otherwise, taxonomic grouping gives little indication of a species’ likelihood of establishing. Often a species will be highly successful at establishing exotic populations whereas close relatives that are also introduced to the same environments repeatedly fail or do poorly.
• Body mass — There is a correlation between female body mass and establishment success for exotic birds introduced to Australia and New Zealand.
• Fecundity — Number of broods produced per season is correlated with establishment success for exotic birds introduced to Australia.
• Sedentary vs migratory — Non-migratory exotic birds introduced to New Zealand and non-migratory exotic mammals introduced to Australia are more successful at establishing exotic populations than migratory species.
• Generalist vs specialist diet — Nearly all established exotic birds and mammals in Australia and overseas have broad diets, suggesting that dietary generalists may be more successful invaders than dietary specialists with restricted diets. However, as few species with specialist diets have been introduced to Australia, this hypothesis is largely untested.
• Commensal with humans — All the exotic bird and mammal species that have successfully established in Australia are able to live in heavily human-disturbed habitats in their overseas geographic ranges, suggesting that species able to live commensally with humans may be successful invaders. However, as few species that are not human commensals have been introduced to Australia, this hypothesis is largely untested.
• Wild vs captive — Wild-caught animals are more successful at establishing exotic populations than are captive-bred animals.
• Recent vs past — Historical timing of introductions is correlated with establishment success for exotic birds in Australia with more recent introductions being more successful.
• Location of introduction — Animals released in disturbed habitats may be more likely to establish than animals released in undisturbed habitats.
Factors influencing feasibility of eradication
Eradication is the permanent removal of all wild living individuals of a species from a defined area. While there have been many eradications of introduced mammals from islands, no eradication campaign against any widely established exotic vertebrate species has ever been successful on any continent, despite numerous large-scale attempts and the huge potential benefits of success.