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Managing Vertebrate Pests: Feral Goats

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Bureau of Resource Sciences
and
Australian Nature Conservation Agency
Managing Vertebrate Pests:
Feral Goats
John Parkes, Robert
Henzell
and Greg Pickles
Scientific editing by
Mary Bomford
Australian Government Publishing Service
Canberra
Commonwealth of Australia 1996
ISBN 0 644 29240 7 (set)
ISBN 0 644
35846
7
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 Australian Government Publishing Service. Requests and
inquiries concerning reproduction and rights should be addressed to the Manager, Commonwealth Information
Services, Australian Government Publishing Service, GPO Box
84,
Canberra ACT 2601.
Cover and publication design by Bob Georgeson, Bureau of Resource Sciences Design Studio.
Credits for cover photograph. Main: R. Knox, APB. Insert: P. O’Brien, BRS.
Typesetting and diagrams by Hemyk
Dekker.
The Bureau of Resource Sciences is a research bureau of the Department of Primary Industries and Energy. Its mission
is to enhance the sustainable development of Australia’s agricultural, fisheries, forestry, mineral and petroleum
resources and their industries by
providing scientific
and technical advice to government, industry and the community.
Affiliations
Authors: John Parkes, Landcare Research, New Zealand; Robert Henzell, Animal and Plant Control Commission,
South Australia; Greg Pickles, Agriculture Western Australia, Western Australia.
Editor: Mary Bomford, Bureau of Resource Sciences, Canberra.
Publication to be cited as: Parkes,
J.,
Henzell, R. and Pickles, G. (1996) Managing
Vertebrate
Pests:
Feral
Gouts.
Australian Government Publishing Service, Canberra.
AGPS Reference A61983
Produced for the Bureau of Resource Sciences by the Australiin Government Publishing Service, Canberra
FOREWORD
This publication, which is one in a series,
provides land managers with best practice
national guidelines for managing the
agricultural and environmental damage
caused by feral goats. Others in the series
include guidelines for managing feral horses,
rabbits, foxes, feral pigs and rodents. The
publication was developed and funded by
the Vertebrate Pest Program in the Bureau
of Resource Sciences. Production of the feral
goat guidelines was aided by financial
assistance from the Australian Nature
Conservation Agency’s Feral Pests Program.
To ensure that the guidelines are widely
accepted as the basis for feral goat manage-
ment, comment has been sought from State,
Territory and Commonwealth government
agriculture, environmental, and resource
management agencies. Comments were also
sought from land managers and community
and other organisations, including the
Australian Conservation Foundation, the
National Farmers’ Federation, the National
Consultative Committee on Animal Welfare,
the Australian Veterinary Association, and
four research and development corpo-
rations. The Standing Committee on
Agriculture and Resource Management has
endorsed the approach to managing feral
goat damage set out in these guidelines.
Farmers have a problem with feral goats
because they compete with livestock and
contribute to land degradation. Conservation
authorities are also concerned about the
role of feral goats in land degradation, and
their impacts on native plants and animals,
through competition, grazing and browsing.
Quarantine authorities need to manage the
risk that feral goats could be involved in
exotic disease outbreaks, such as
foot-and-
mouth disease or scrapie, should such
diseases enter Australia. On the other hand,
feral goats are valued by those who harvest
them commercially or hunt them
recre-
ationally. The authors have attempted to
take all these divergent views and objectives
into account in compiling the guidelines.
The principles underlying the strategic
management of vertebrate pests have been
described in Managing Vertebrate Pests:
Principles and Strategies (Braysher
1993).
The
emphasis is on the management of pest
damage rather than on simply reducing pest
density. The guidelines recommend that
wherever practical, management should
concentrate on achieving clearly defined
conservation or agricultural production
benefits.
These guidelines will help land managers
reduce the damage caused by feral goats to
agriculture and the environment through the
use of scientifically-based management that
is humane, cost-effective, and integrated with
ecologically sustainable land management.
Peter O’Brien
Executive Director
Bureau of Resource Sciences
. . .
Bureau of Resource Sciences/Australian Nature Conservation Agency
111
CONTENTS
FOREWORD
ACKNOWLEDGEMENTS
SUMMARY
INTRODUCTION
1.
2.
3.
4.
5.
HISTORY OF
INTRODUCTION AND
SPREAD
9
Summary
9
1.1
Goats as emergency food
9
1.2
Goats as domestic livestock
9
1.3
Establishment of feral herds
10
DISTRIBUTION AND
ABUNDANCE
11
Summary
11
2.1
World distribution of goats
11
2.2 Distribution of feral goats in Australia
11
2.3 Abundance of feral goats in Australia
13
2.4 Factors influencing distribution and abundance
14
2.5
Domestic goats in Australia
18
BZOLOGY
19
Summa y
19
3.1
Ancestry
19
3.2
Body weight
19
3.3
Breeding season 20
3.4 Population dynamics 20
3.5 Diet 22
3.6
Movements and home ranges
22
3.7 Social behaviour
23
3.8 Parasites and diseases 23
ECONOMIC AND ENVIRONMENTAL
IMPACTS
AND
COMMERCIAL
USE
25
Summa y
25
4.1
Economic losses
25
4.2 Environmental impacts
28
4.3 Resource value and commercial use
32
4.4 Implications of goat harvesting for damage control
33
COMMUNITY
ATTITUDES TO FERAL
GOAT MANAGEMENT
36
Summa y
36
5.1
Aboriginal perceptions
36
5.2 Pastoralists
36
5.3 Conservation groups
37
5.4 Animal welfare concerns
37
5.5
Domestic goat farmers
38
5.6 Goat meat industry
39
.
.
.
111
vii
6
iv
Managing
Vertebrate Pests: Feral Goats
6.
7.
8.
3.
PAST AND
CURRENT
MANAGEMENT
40
Summary
40
6.1
Past management
40
6.2 Current legal status
40
6.3
Current management
42
TECHNIQUES
TO
MEASURE
AND
MANAGE
ABUNDANCE
AND
IMPACTS
Summary
7.1
Measuring abundance
7.2
Measuring impact
7.3 Control techniques
45
45
45
49
51
THE
STRATEGIC MANAGEMENT
APPROACH AT
THE
LOCAL AND
REGIONAL
LEVEL
62
Summa y
62
8.1
Economic frameworks
62
8.2 Strategic approach
63
8.3 Defining the problem
64
8.4 Management plan
64
8.5 Implementation
74
8.6
Monitoring and evaluation
74
8.7 Case study
-
Western Australia
75
8.8 Case study
-
Flinders Ranges
78
IMPLEMENTING
A
88
Summary
88
9.1
Organising stakeholders for action
88
9.2
Around the states
89
9.3
Partnerships are needed
90
9.4 Stakeholders
91
9.5 Identifying goals
91
9.6
Government involvement
92
9.7 Facilitation of effective groups
92
10. DEFICIENCIES IN
KNO
LEDGE
AND
PRACTICE
Summa y
10.1
Introduction
10.2 Future introductions and spread
10.3 Distribution and abundance
10.4 Biology
10.5 Economic and environmental impacts
10.6
Animal welfare concerns
10.7
Current management
10.8
Techniques to measure abundance
10.9
Control techniques
10.10
Ranking conservation management units for control
10.11
Integrating risk management
10.12
Implementation
94
94
94
94
94
94
95
95
95
96
96
96
96
97
Bureau of Resource Sciences/Australian Conservation Agency
V
ACKNOWLEDGMENTS
The Vertebrate Pests Committee’s Working
Group, who oversee the preparation of the
guidelines
-
Peter Allen, Roger O’Dwyer,
Andrew
McNee,
Don Pfitzner and Jason
Alexandra
-
provided valuable input and
comments.
Special acknowledgement is given to the
following people who made helpful
comments on the draft manuscript: Ross
Blick,
Dana Bradford, Mike Braysher, Garry Grant,
Robert Hadler, Quentin Hart, Onko
Kingma,
Terry Korn, Jonathan Lee,
Sylvana Maas,
Colin
Mues, Alan
Newsome,
Peter O’Brien, Glenys
Oogjes, Glen Saunders,
Mick
Statham,
Jim
Thompson and Brian Toseland. Special thanks
to Dana Kelly who made a particularly
valuable contribution to Chapter
9
and
Appendix B, and to Mike Braysher, for his
role in organising a workshop and writing
team for this book.
Quentin Hart wrote Appendix B and both
he and Dana Bradford helped edit the
manuscript and figures and assisted in the
final collation and publication.
The draft manuscript was circulated to
the following organisations for comment:
z
Commonwealth Department of Primary
Industries and Energy
Vertebrate Pests Committee
Standing Committee on Agriculture and
Resource Management
Australia and New Zealand
Environment and Conservation
Council
-
Standing Committee on
Conservation
-
Standing Committee on the
Environment
Land and Water Research and
Development Corporation
Meat Research Corporation
Rural Industries Research and
Development Corporation
International Wool Secretariat
Australian Conservation Foundation
National Consultative Committee on
Animal Welfare
Australian and New Zealand Federation
of Animal Societies
National Farmers’ Federation
Australian Veterinary Association
Aboriginal and Torres Strait Islander
Commission
We wish to thank these groups for their
contributions. Many other people, too
numerous to acknowledge individually, also
gave us the benefit of their experiences by
commenting on drafts of the manuscript.
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
vii
SUMMARY
The introduced feral goat
(Capra
hircus)
occurs in all states and territories of Australia
except the Northern Territory. Total numbers
are estimated to be about
2.6
million. The
main concentrations are in western New
South Wales, southern Queensland, central
eastern South Australia and Western
Australia. Feral goats occur in a wide range
of habitats, although they do not do well
where dingoes are present.
Feral goats are a major environmental
and agricultural pest. They compete with
sheep for pasture and also cause land
degradation through soil damage, over-
grazing pasture plants and browsing
established trees and shrubs preventing their
regeneration. There is also a risk that feral
goats could be involved in outbreaks of
exotic diseases, such as foot-and-mouth
disease, should such diseases be introduced
into Australia. Goats damage native flora
but have a largely unknown effect on native
animals. Feral goats are also a resource,
harvested primarily for meat.
These guidelines are a comprehensive
review of the history of feral goats in
Australia, their biology, the damage they
cause, their use and past and current
management. The attitudes of conser-
vationists,
animal
welfare groups,
commercial and recreational hunters,
Aboriginal peoples and other interest groups
were sought during the development of the
guidelines. Management techniques and
strategies for feral goat management are
recommended and illustrated by case
studies. Deficiencies in knowledge,
management and legislation are identified.
Why develop national guidelines?
These guidelines for managing the impact
of feral goats have been developed under
the Vertebrate Pest Program
(VPP)
administered by the Bureau of Resource
Sciences
(BRS).
VPP funded the project with
significant assistance from the Australian
Nature Conservation Agency
(ANCA).
VPP
is producing a series of pest management
guidelines, including ones for feral horses,
rabbits, foxes, feral pigs and rodents.
The purpose of these guidelines is to
assist in the development of cost-effective
strategies to reduce the damage feral goats
cause to production and the environment.
Ideally, such strategies are based on reliable
quantitative information about the damage
caused by goats, the cost of control and the
effect of implementing control on damage
levels. In developing these guidelines the
authors have used available current
information, but in some instances land
managers responsible for feral goat
management will have to make assumptions
about feral goat impact and the efficacy and
cost-effectiveness of control techniques until
more reliable information becomes
available.
The emphasis in these guidelines is on
the strategic management of feral goats to
minimise the damage they cause to
production and/or conservation values, not
merely to kill goats. Feral goats need to be
considered as one factor in a complex and
changing ecosystem which includes a highly
variable climate, fluctuating commodity
prices, other animal and plant pests, the
number and quality of farm stock, and the
profitability of farming businesses.
Who
will
use
the guidelines?
The ‘Managing Vertebrate Pests: Feral Goats’
guidelines have been prepared primarily for
State, Territory, and Commonwealth land
management agencies to assist them to
better plan and implement programs to
manage the impacts of feral goats on all
lands. They should be read in conjunction
with the introductory book, ‘Managing
Vertebrate Pests: Principles
and
Strategies’
(Braysher 1993). In the strategic
management of all pests, it is important to
involve landholders and other interest
groups, such as commercial harvesters and
animal welfare groups, in the planning and
implementation of feral goat management.
Bureau of Resource Sciences/Australian Nature Conservation Agency 1
Hence, special emphasis is given in the
guidelines to the way landholders might
organise themselves to manage feral goats.
The
feral goat problem
Australia’s feral goats occupy about 1.21
million square kilometres, mostly in the
semi-arid and arid lands used for pastoral
farming of sheep. It is estimated that feral
goats cause a net annual loss to sheep
production of about $17.8 million, after
allowing for a net return of about $4 million
(farm gate value based on average sale
prices over the last ten years) from the sale
of about one million feral goats that are
mustered.
Feral goats also cause an unknown (but
usually assumed to be substantial) loss to
conservation values and as such are an issue
for the conservation of biological diversity.
Feral goats have been responsible for severe
or even catastrophic environmental damage
on island habitats that evolved without
browsing mammals. On mainland Australia
there are no documented examples of feral
goats severely damaging large areas in the
absence of significant populations of other
herbivores, such as sheep, cattle, rabbits
and kangaroos. But feral goats contribute
to damage to vegetation, soils, and native
fauna in the large areas of pastoral land that
are overgrazed, although their share is
generally less than that of other herbivores.
Feral goats do, however, have the capacity
to reach high densities and inflict severe
damage if left uncontrolled. Feral goats also
compete with native animals for resources.
They deplete the soil’s protective cover of
vegetation and break up the soil crust with
their hooves. They also affect trees and
shrubs by eating established plants and by
preventing regeneration of seedlings. Feral
goats also overgraze grasses and herbs when
alternative food is scarce. These impacts
undoubtedly affect ecosystem processes,
although the extent of the role of feral goats
among all the other agents of change is
difficult to quantify and may differ during
droughts and wet periods. In the
Endangered Species Protection Act
1992,
the Commonwealth Government has listed
competition
and land degradation
by feral
goats’
as a ‘Key Threatening Process’ to the
survival of native species. This Act makes
the Commonwealth, through the Australian
Nature Conservation Agency, responsible
for the preparation and implementation of
a national Threat Abatement Plan which is
expected to be completed by the end of
1996. Both the planning and the
implementation of the Threat Abatement
Plan will draw on the strategies described
in these guidelines.
Resource
value
Feral goats are a commercial resource. About
one million goats are mustered each year,
mainly for abattoir slaughter, and an
additional
30
000-40
000
are shot by field
hunters. The return to exporters from the
sale of feral goats was $29 million in
1992-93.
Landholders only receive about
$6
million annually from feral goat sales, of
which about $2 million is spent on mustering
costs. Landholders and managers in the
semi-arid pastoral lands would make more
money from grazing sheep than from the
commercial exploitation of feral goats
(based on average prices for sheep and
goats over the last ten years and an
equivalent stocking rate). The value of goats
has improved since 1992, but it may be safer
for landholders to make management
decisions based on long-term average prices,
because it is not economically desirable or
practical to switch between managing feral
goats as a pest or as a resource, in response
to short-term fluctuations in market values.
History
and biology
Feral goats were selected through the
process of domestication to have
characteristics of value to people. However,
many of these characters are the traits that
make feral goats pests. Harvested
populations of feral goats can increase by
over
50%
per annum if harvesting stops,
because goats become sexually mature at
2
Managing Vertebrate Pests: Feral Goats
an early age, have extended breeding
seasons, can conceive while still lactating,
and can produce more than one kid per
pregnancy. Their impact on the environment
is enhanced by their social nature which can
increase the intensity of their browsing; their
ability to use a wide variety of food plants
in a wide variety of habitats; and their
tolerance to drought in semi-arid areas.
Techniques to control feral goats
Techniques to manage feral goats in the
rangelands fall into two types depending on
the fate of the goats. Mustering and trapping
are used in cases where goats are intended
for commercial slaughter. It has been
estimated that on average only 3040% of
populations are removed in a muster, though
this figure can be as high as 80%. However
mustering and trapping become uneconomic
once populations are reduced to densities of
about one goat per square kilometre.
Management of these low density herds, those
in rough or densely vegetated areas, or of
remnant or
colonising
herds, relies on lethal
techniques such as aerial or ground shooting,
or trapping and on-site slaughter. The use of
radio-telemetered Judas goats can improve
the efficiency of some of these latter control
techniques. No research for biological control
of feral goats is currently being undertaken,
other than the use of dingoes on offshore
islands in Queensland.
Development of a strategic
management approach
Feral goats can be managed, and perhaps
even eradicated from some local areas and
regions, in cost-effective ways using
presently available technology. That they
are not so managed is usually because the
local landowners either see goats as a
resource or because they do not have the
organisation necessary to implement a
comprehensive management plan.
Current management is increasingly
sensitive to environmental and animal
welfare issues associated with management.
Considerable effort is expended to ensure
that techniques and methods are sensitive
to community needs.
What is the strategic management
approach?
Achieving a strategic approach to the
management of goats and other vertebrate
pests involves establishing four key
components. These are:
Defining the Problem
-
The
problem first
needs to be determined in terms of the
impact of feral goats on a valued resource,
both economic and environmental. The next
step is to quantify the impact, which may
require experimental assessment of that
damage.
Management Plan
-
In developing a
management plan, it is essential that clear
objectives are established wherever
practicable, in terms of desired production
and/or conservation outcomes. Options
for feral goat management include local
eradication, strategic management,
commercial harvesting, crisis management
or no management. In light of the
objectives, and the chosen management
option, a practicable management strategy
should be developed which uses the most
cost-effective techniques available and
allows for restrictions due to local
circumstances.
Economic frameworks need to be
developed to assist land managers to
assess the relative value of alternative
control strategies. Such frameworks
require: definition of the economic
problem; data on relative costs and
benefits of different goat management
strategies; an understanding of why the
actions of individual land managers may
not lead to optimal levels of goat control
and how such problems can
be
addressed.
Implementation
-
The most effective
approach is to coordinate management of
feral goat damage on a local and regional
level. This involves cooperative action by
land managers, both public and private, and
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
3
where relevant, government agencies and
industry.
Monitoring and Evaluation
-
Monitoring
has two aspects. Operational monitoring is
required to assess the efficiency of the
management strategy over time, particularly
to determine whether it is being carried out
in a cost-effective manner. Performance
monitoring gathers information by which
the effectiveness of the strategy in meeting
the desired long-term production or
conservation outcome can be determined.
Both forms of monitoring provide the
information to decide whether and how to
modify the management strategy.
whether this achieved the resource protection
goals in the longer term (performance
monitoring).
Local
eradication or strategic
management?
The above approach has been adopted for
these national guidelines, and the information
in this report is designed to facilitate the
development of strategies for managing goats
at the local and regional level. Models have
been presented to show the costs and benefits
of managing goats in an extensive sheep
grazing enterprise, and to encourage those
with an interest in the management of goats
and the outcomes to develop a coordinated
approach to their management.
The
reliance of many populations of goats
on artificial water supplies makes them
particularly vulnerable to control, and the
management of water is therefore likely to
be a crucial factor in the long-term control
of feral goats. This reliance may allow feral
goats to be permanently removed from local
areas where reinvasion can be prevented.
There is considerable argument about how
large these local areas might be, and
therefore how realistic eradication policies
are at large-scale or state planning levels.
Eradication of feral goats from the entire
mainland is not possible as they are
widespread and common and there are
many domestic goat enterprises which
present a continual source of reinfestation.
Implementing a management
campaign
The
crucial first step in achieving success is
to achieve concerted action by organising
individuals and groups of landowners in ways
appropriate to the scale of the goat problem.
For long-term success, it is important that land
managers have ownership of feral goat
management programs, and are involved in
‘participatory decision-making’ for solving
problems caused by feral goats on their lands.
The proper role of government in the
organisation must be carefully
focussed
so as
not to distort risk management.
If strategic management is the chosen
option, or the de facto option when
eradication is not achieved, managers must
have some understanding of the nature of
the impacts of feral goats relative to the suite
of other wild, feral and domestic herbivores.
This understanding is needed to determine
target densities of feral goats and frequency
of control.
The most financially attractive manage-
ment option where it is profitable to muster
feral goats for sale, is to capture as many goats
as possible, use the profit to further reduce
the population, and then to maintain annual
culls to sustain low goat densities. The gains
from this strategy can be made either by
increasing production from sheep or by
increasing the quality of the environment.
Each management operation should The cost-benefit arguments of local
prescribe the strategic and tactical intent, and
eradication versus this form of strategic
identify resources to be committed. The management have not been adequately
operation should be monitored at a level con s i dered because of the lack of
suitable for its scale and goals to measure information. However, isolated colonies of
what was done, where, by whom, at what feral goats can be readily and cheaply
cost (operational monitoring) and to measure eradicated using Judas goats.
4
Managing Vertebrate Pests: Feral Goats
Community
attitudes
The status of feral goats will be largely
determined by the owners or managers of the
land that harbours the animals. Some
pastoralists see goats as both a pest and a
resource that can bring in extra cash. Many
people who view feral goats mainly as pests
would prefer to eradicate them, though it is
usually acknowledged that this is generally
not achievable, and that control to low
densities may be the only feasible alternative.
Opposition to the view of goats as pests to
be eradicated or controlled comes from some
groups seeking to harvest the animals as a
commercial resource. They argue that goats
in the right place at tolerable densities should
not be classed as pests. Others simply seek
to harvest a resource while it exists but do
not oppose feral goat control.
The multiple use of feral goats leads to
conflict within the rural community as well
as within the general community. The
significant spin-offs from the game meat
export industry and recreational hunting are
politically attractive. There is active debate
among many interest groups on whether
commercial and recreational use of feral
goats is compatible with effective feral goat
management. These guidelines put this
debate in context and provide information
to land managers to help them reach
decisions to meet their own objectives.
The major animal welfare groups in
Australia recognise the problems posed by
unmanaged feral goats and accept that this
justifies their management by suitable
humane means. In particular, they seek to
phase out commercial exploitation by
muster, transport, and slaughter of feral goats
as a control method. In the interim, they
seek some agreed rules to make this process
as humane as possible. Shooting goats is
generally seen as relatively humane if
conducted according to codes of practice.
The
future
To further develop the strategic approach
to the management of feral goats, more
information in some key areas is essential.
One of the basic weaknesses in being able
to determine priorities for where to control
feral goats in many areas of Australia is the
lack of objective, quantitative data on the
impact of goats on the environment and a
means of comparing its cost in terms of
values affected with economic losses caused
by goats, such as to agriculture.
The main problems in managing feral
goats are strategic rather than tactical.
Therefore, the main deficiencies in
knowledge are associated with decisions on
whether to attempt local eradication or
strategic management; and if the latter, on
deciding target densities and control
frequencies. The available information to
justify these decisions is poor. Managers
need data on the relationship between feral
goat density and their impacts on production
and conservation values so that target
densities for management can be set and
the cost-efficiency of integrated manage-
ment systems can be determined.
Improvement in current and future
management is limited by a need to improve
knowledge and skills of control agency staff
in extension theory and adult education
principles. Lack of these skills can be a
serious barrier to the rapid adoption of best
practice management and attention to
adequate training and extension is critical.
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
5
INTRODUCTION
These
guidelines for managing feral goats
are the fifth in a series being published
under the Vertebrate Pest Program
(VPP)
of
the Bureau of Resource Sciences
(BRS)
in
cooperation with the Vertebrate Pests
Committee of Standing Committee on
Agriculture and Resource Management
(SCARM).
Their preparation was funded
mainly by BRS with significant assistance
from the Australian Nature Conservation
Agency. Other guidelines in the series are
for feral horses, rabbits, foxes, feral pigs and
rodents.
The need for a new approach to
vertebrate pest management is described in
Managing
Vertebrate Pests: Principles and
Strategies (Braysher
1993),
in which it is
explained why national guidelines for
managing pest animals were developed, the
development process, and the principles on
which pest management should be based.
The need to focus on the damage caused
by the pest and not the pest itself is stressed.
One set of guidelines for all vertebrate
pests, taking into account the links between
them, and other aspects of land manage-
ment, would be desirable and consistent
with the holistic approach to land manage-
ment advocated under the Ecologically
Sustainable Development (ESD) Strategy
and Landcare. However, this has not proved
practicable. Nevertheless all the guidelines,
including this one for feral goats, stress the
need to consider interactions between
species and other aspects of land manage-
ment.
The guidelines are principally for state
and territory land management agencies so
that they can more effectively manage goat
damage through better coordination,
planning and implementation of regional
and local management programs. The
Commonwealth also has a major interest in
the effective management of pest damage,
both through its role as a manager of
Commonwealth lands, and through several
national initiatives, such as
Landcare
and
the National Strategy for the Conservation
of Australia’s Biological Diversity. Applying
the strategic approach to the management
of goats and other vertebrate pests involves
establishing four key components as shown
in Figure 1. This approach has been adopted
for developing these national guidelines.
Chapter 1 describes the history of the goat
in Australia; Chapter 2 the distribution and
density of feral goats; and Chapter 3 their
biology.
Defining the Problem
Feral goats are a locally significant
agricultural, environmental, and conser-
vation pest. Unlike many other vertebrate
pests in Australia, many populations of feral
goats in Australia can be cost-effectively
managed using present control technologies,
with the cost of control being met by the
sale of goats plus savings in reduced
resource damage.
Chapter 4 reviews the evidence concerning
the impact they have on production and
environmental resources. These impacts are
not well quantified, and further studies are
needed to address these deficiencies.
Chapter 4 also addresses commercial use of
feral goats and its implications for their
control.
Community attitudes strongly influence
the management of goats. These are
discussed in Chapter
5.
Chapter 6reviews past and current
management of feral goats and their legal
status. Chapter
7
reviews methods for
assessing the impact of goats, goat numbers,
and the various control techniques to
manage them. The different management
options possible from using these
techniques are then discussed in Chapter 8
and three are modelled (c o m merci a l
management, strategic management, and
local eradication).
The damage caused by goats and other
pests needs to be put in context with other
factors influencing the desired outcomes
6
Managing Vertebrate Pests: Feral Goats
Strategic management of feral goats at the national level
Defining Management
problem
Plan
(Section 8.3) (Section 8.4)
z
who has the
problem
z
real or perceived
z
define harmful
impact
-
economic
-
environmental
z
measure impact
z
mapping
z
objectives
z
management
options
-
local eradication
-
strategic
management
-
crisis
management
-
no management
-
commercial
management
z
performance
criteria
z
allocating
management
units
z
management
strategy
I
I
r
I
Implementation
(Section 8.5)
Monitoring
and Evaluation
(Section 8.6)
.group action
z
assess control
-
ownership
z
compare over time
z
whole farm/district
z
techniques
z
government
z
evaluation
role of outcome
Figure
1:
The strategic approach to managing feral goat damage (after
Braysher 1993).
from the land management system.
Development of an integrated goat
manage-
ment program is described in Chapter 8.
to a total catchment plan, is advocated since
it can help significantly in managing the
risks posed by feral goats.
The conditions under which land
Management Plan
The objective of the national guidelines is
to encourage the adoption of best practice
to manage goat impact as distinct from ad
hoc measures by individuals and agencies.
Best practice is defined as the most effective
method of management within existing
social and economic circumstances. The
strategic approach is based on cooperative
action at the local and regional level,
involving land managers and others with a
major stake in the outcome of the manage-
ment. Adopting the local and regional
approach to management, preferably linked
managers, including graziers, operate are
highly volatile. A number of factors influence
the desired outcomes, including conser-
vation objectives, fluctuating commodity
prices, climatic variability (including
drought), plant and animal pests, grazing
pressure, quality of stock, animal welfare
objectives, and social factors such as the
influence of conservation organisations.
The guidelines will have met their purpose
if the strategic approach they advocate is
accepted and implemented by a significant
number of agencies and individuals. This is
a criterion of performance.
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
7
Implementation
It is important to involve all relevant land
managers and other interest groups, such
as commercial harvesters and animal welfare
groups, in the planning and implementation
of feral goat management. This is best
addressed cooperatively at the local and
regional level. These issues are reviewed in
Chapter
9.
Monitoring and evaluation
Monitoring is an essential, but often forgotten
part of goat management. Monitoring allows
managers to assess the efficiency of the
control strategy implemented and analyse its
effectiveness over time. It also provides
feedback to modify the strategy as required
to meet the objectives of the management
plan. Chapter 8 reviews monitoring and
evaluation requirements. Chapter 10 looks to
the future and addresses research and
management developments that are needed.
Vertebrate Pest Program
In the Prime Minister’s Environment
Statement of December 1992, the
Commonwealth Government provided
resources to prepare the guidelines for
managing Australia’s major vertebrate pest
species, including feral goats, and to
establish key demonstration projects to
facilitate adoption of best practice pest
management. Projects draw on the
management strategies outlined in the
relevant guidelines for each species. For
most projects, including goats, it is
anticipated that best practice will continue
to evolve based on experience gained from
undertaking strategic management. Using
the management system to refine pest
management strategies is an element of
adaptive management, or learning by doing.
The feral goat guidelines are designed to
encourage ownership of the pest problem
and the management strategy by relevant
land managers and others with a key stake
in the outcome. Accordingly, preference in
funding under the VPP has been given to
projects which involve collaboration
between a number of appropriate govern-
ment and/or non-government agencies and
involve community-based groups in their
design and implementation.
The VPP supports projects which address
the impact pests have on primary
production. The complementary Feral Pests
Program (FPP) administered by the
Australian Nature Conservation Agency
gives priority to strategic pest management
in areas primarily used for conservation.
There are strong links between the
programs, and projects which address both
agricultural and conservation damage due
to pests may be jointly funded. It is intended
that these guidelines and the results of the
VPP and FPP projects will assist state and
territory governments in their role of
providing legislative, technical and policy
support for feral goat control.
8
Managing Vertebrate
Pests:
Feral Goats
1.
History of
introduction and
spread
Summary
Goats
originally
came to Australia with the
First Fleet
in 1788.
The
present
feral goat
populations are descended from animals
introducedfor a variety of reasons
in 1788
and
subsequently. During the
y,
many liberations on islands and on the
mainland were
made by
mariners
to
ensure
emergency
supplies er, most
feral goatpopulations have a
more
domestic
ancestry.
Cashmere goats were imported
into South Australia in 1837, and in the
1860's
attempts were made to start a goat
fibre industry
using angora
and
cashmere
goats imported from Asia. This industry
collapsed
in
the 1920s. Goats, particularly
the milking
breeds, were
also taken around
Australia with settlers, railway construction
gangs,
and miners. More
recently, feralgoat
populations have established from goats
used to control weeds
in
plantation
forests
and woody weeds in inland New South
Wales and Queensland. Currentferal goat
populations reflect these mixed
origins.
1.1
Goats as emergency
food
Goats were popular transportees on long sea
voyages because they were easier to keep
alive than other potential providers of milk
and meat. They were listed in the manifests
of most Spanish and Portuguese explorers
from the 15th Century, who were responsible
for their release in the West Indies and a few
Pacific Islands (Lever 1985). This naval
tradition of liberating domestic goats as
sources of food for shipwrecked or transient
mariners continued with Captain Cook who
liberated goats on many islands, such as in
New Zealand and Hawaii (Lever 1985). It was
a practice carried on by 19th Century whalers
and sealers (Raoul Island; Parkes
1984),
and
was still
practised
in the early 20th Century
(on subantarctic islands; Rudge 1990).
Whalers, sealers and naval officers released
goats on many Australian islands during the
19th Century. Liberations by whalers or sealers
are recorded for islands off the south coast
of West Australia (Abbott 1978; Long
1988)
and on Lord Howe Island
(Pickard
1976,
and
the navy liberated goats on
Moreton
Island
in the 1860s (O’Brien 1983).
1.2
Goats as domestic
livestock
Domestic goats were landed at Sydney in 1788
with 19 animals of unstated breed being listed
on the commissary of the First Fleet (Rolls
1969).
The fate of these animals is unknown,
but the descendants of the numerous
importations that followed formed the basis
for the present feral goat populations.
Domestic goats were among the first
livestock introduced by Europeans in many
settlements around Australia. Goats were
taken to Philip Island in the early 1800s to
provide sport for the prison officers and food
for the Norfolk Islanders. They were reported
as common by 1838 (Taylor
1966),
but had
gone by 1870 (Hermes et al. 1989). Goats
were thriving in Tasmania in 1822 (Rolls
1969),
and arrived in South Australia with the first
settlers in 1836 (Hodder
1893),
and were taken
by explorers into the Flinders Ranges in the
1840s
(Aitken
1980).
‘Domestic goats were among
the first livestock introduced
by Europeans in many
settlements around Australia.
Cashmere goats were introduced to South
Australia in 1837 (Hodder
1893),
and more
serious attempts were made to start a goat
fibre industry using angora and cashmere
goats from about
1860
until 1900 (Evans 1980).
Herds were founded by the Victorian
Acclimatisation
Society in 1862 (Rolls
1969),
from which other states eventually obtained
animals. For example, 50 goats were sold to
West Australian interests on Faure Island in
about 1870 and upgraded with South African
angoras in the early 1900s (Clarke I976), and
others were sold in New South Wales in the
mid-1860s (Rolls
1969).
Bureau of Resource Sciences/Australian Nature Conservation Agency
9
1.3
Establishment of feral
herds
Domestic goats escaped, were abandoned,
or were deliberately released, and these
animals established feral herds, in a process
that continues to this day. Goat populations
that survive after being castaway on islands
are by definition feral animals.
10
Managing
Vertebrate
Pests:
Feral Goats
2.
Distribution and
abundance
Summary
Domestic goats
occur on all continents
Antarctica), but theirferal descendants are
much less
prevalent,
occurring
widely only
in Australia, New Zealand, and on many
small
islands. In 1993 there were
about 2.6
million feral goats in Australia but this
number
has
fluctuated
widely. Most feral
goats inhabit the semi-arid pastoral areas
used
for sheep
farming.
In
these areas food
is usually abundant, regular water is
provided by people, and natural predators
such as
dingoes
and feral
dogs are controlled
to
protect
the sheep.
2.1
World distribution of
goats
Domestic goats have been introduced to all
continents (except Antarctica) and live under
a wide range of climates and conditions, but
are most numerous in the tropical and dry
areas of Africa and Asia (Gall
1981).
The
world population of goats is estimated to
be 450 million (Devendra and Burns
1983).
Feral goats are also widespread but occur
in large numbers only in Australia
(Harrington
1982a)
and New Zealand (Rudge 1990).
Smaller populations are present elsewhere,
such as in Britain and Ireland (Whitehead
1972),
and on many offshore and oceanic
islands (Rudge
1984).
Goats usually only form
feral
populations where
predators
(particularly wild
canids)
are absent or scarce,
where there are large tracts of land and where
domestic goats are not of sufficient value to
people to be worth the effort to keep them
all under management.
2.2
Distribution of feral
goats in Australia
Feral goats occur in all states and in the
Australian Capital Territory, but are rare or
absent on the mainland of the Northern
Territory (Figure 2). The most extensive
populations live in semi-arid pastoral areas
of Queensland, New South Wales, South
Australia, and Western Australia where
people, through supplying water and
controlling predators to improve sheep
production, have modified the natural
habitat favourably for feral goats.
‘Feral goats
occur
in all states.
Isolated populations of feral goats occur
in the higher rainfall and agricultural areas
in Victoria, Tasmania, eastern New South
Wales, Queensland, South Australia, and
south-west Western Australia. These goats
survive mainly in areas where patches of
scrub or forest offer protection from control
by people. Not all such populations are
shown in Figure 2 as new populations are
established and old ones eliminated from
time to time.
Recolonisation
of such areas
cleared of goats is usually via escaping or
deliberately released domestic animals
rather than by dispersing feral goats (as
evidenced by the presence of ear tags on
some feral goats).
Feral goats also occur on many Australian
offshore islands (Figure
1)
(see
Rudge
1984;
Morris
1989 for partial lists). These include
islands with important conservation values,
such as Lord Howe Island
(Pickard 1976),
and
islands in the Recherche Archipelago (Morris
1989). Island populations are generally
considered to be pests but the feral goats on
North Goulburn Island provide a source of
trophy animals for a safari operation run by
the Aboriginal owners and also provide food
for the owners while they visit the island
(R.
Turner, BRS, Canberra, pers.
comm.
1994).
Feral goats have been eradicated from several
islands including Faure Island (G. Pickles,
unpublished), Bernier Island (Morris
1989),
Woody Island (Allen
1991)
and Townshend
Island (Allen and Lee 1995). The estab-
lishment of new island populations is now
less likely than in the past, especially in South
Australia where the
Animal
and
Plant
Control
Act
1986
prohibits the keeping and release
of goats on nearly all islands in that State. The
chance of natural
colonisation
of islands is
Bureau of Resource Sciences/Australian Nature Conservation Agency
11
II
1
Northern Territory
1
Queensland
I
Tasmania
Figure 2:
Distribution of feral goats in Australia
(R.
Henzell, unpublished). Additional small isolated
populations occur in northern Australia. Table lists offshore islands where goats occur.
Island
Queensland
Prince of Wales’
Curtis2
location
142”07’E
10”41’S,142”09”E
153”25’E
27”3O’S,
153”25’E
Island
South Australia
location
Kangaroo4
35’55’S,
136”4O’E
26”57’S, 153”07’E
23”3 8’S, 151”1O’E
16”08’S, 123”45’E
Great
Kep
I
High Pea
South
Northeast
Middle
OS,
2
St
North
Ma
‘S,
‘E
a
The domestic
goats
on Middle Percy and Greet
Keppel
islands are recorded
as
they
may
give rise
to
feml goat
herds in the future.
1.
Australian
Bureau
of
Animal
Health
(1979).
2.
Messersmith,
J., QDEH North
Rockhampton,
1993.
3.
Dunson
(1974).
4.
R.
Henzell,
unpublished, 1993.
5. Collins, J., APB,
Kununurra,
1993.
6. Pickles, G., AWA, Western Australia, 1995
7. Bell, M., NAQS, Darwin, 1993.
12
Managing Vertebrate
Pests:
Feral
Goats
Table
1:
Estimated numbers of feral goats between
1982
and
1994, the
change in area they occupied
since
l982,
and their average density in
1992-93
in the pastoral areas of four states.
Year
(1) Number (000)”
1982
1987
1989
1990
1991
1992
1993
1994
(2) Area occupied (000
1982
1
(3) Density
1992-93
Western
South
New
South
Queensland
Australia
Australia Wales
720 450
615
1095
2625’ 755
985 290 125 255 315
1210 480 130 330
2.2 1.6 2.2 3 .6 1.5
160
245
450
310
215
290
260
60 50
1180
The 1982 data are from Harrington
(1982a),
except for the figure for Queensland which is taken from Mitchell
et al.
(1982),
because the 1982 Queensland figure determined by Harrington was based on an extrapolation
from New South Wales data and is probably wrong. The estimates far later years are from Grigg et
al.
(1992),
Southwell
et al.
(1993)
and other sources.The estimates from 1982 were made using several methods and those
from 1987-l 993 were taken from aerial surveys (Chapter 7). The Flinders Ranges were not surveyed in the
South Australia aerial surveys from 1989 to 1993, and the
foll
owing
estimates were added to the State totals:
1989, 80 000; 1990, 120 000; 1991, 100 000; 1992, 80 000; and 1993, 60 000. Aerial survey counts
have been adjusted by a correction factor of 1.68 (Section 7.1.1).
A slight underestimate because some goat-infested pastoral areas in Queensland were not surveyed.
Includes the 1992 estimates for New South Wales and Queensland.
Aerial survey data.
Data from Western Australia and South Australia from 1993, and elsewhere from 1992.
remote as goats will swim (or even wade)
only under dire need (Mackenzie
1970; New
Zealand Department of Conservation
1995,
but perhaps not impossible because goats
have been reported to swim to obtain fresh
water.
In 1993
there were an estimated
2.6
million
feral goats in Australia. Most live in the
pastoral areas of Queensland, New South
Wales, South Australia, and Western Australia
(Table
1).
Feral goats are counted during
aerial surveys to estimate the number of
kangaroos. The proportion of goats seen
during these surveys is variable (Section
7.1 so the estimate may be biased. The
aerial surveys are also not done in some
areas of goat’s range, such as north-eastern
Queensland and the Flinders Ranges, so the
total aerial survey estimate has been
increased by approximation (Table
1).
The
numbers in the agricultural areas and on
islands are not known, but are small in
comparison;
30 000 is a
reasonable estimate.
Bureau of Resource
Sciences/Australian
Nature Conservation Agency
13
The estimated population of about
2.6 million must be in the right order or
possibly conservative, since although some
one million feral goats have been mustered
annually in recent years (Section
4.3),
this
does not appear to have significantly
reduced the national population.
‘Most of the estimated
2.6 million feral goats in
Australia live in the pastoral
areas of Queensland, New
South Wales, South Australia
and Western Australia.
The intensity of control and harvesting
differs between years resulting in fluctuations
in the numbers of goats in the pastoral areas.
The number of feral goats in these areas
increased by 260% from about 720 000 in 1982
to about 2
600
000 in the early 1990s, while
the area occupied has increased by only 23%
from 985 000 square kilometres in 1982 to
1210 000 square kilometres in the early
1990s.
2.4
Factors influencing
distribution and
abundance
The presence of food species and their
nutritional quality, the availability of water
and cover, the presence of natural and
human predators, diseases, toxic plants and
complex interactions among these factors
are known or suspected to limit the
distribution and/or density of feral goats in
Australia.
2.4.1 Food
Goats are generalist herbivores (Harrington
1986)
and the density of edible vegetation
in Australian rangelands is sufficiently high
that it rarely limits the distribution of feral
goats, However, the type and nutritional
quality of the vegetation are highly variable
and are affected by the amount and
frequency of rainfall, which in turns affects
the number of goats an area can support.
Stock
watering points
have
allowedferal goats to successfully
colonise
semi-arid rangeland
areas.
Source:
R.
HenzelI,
APCC
14
Managing Vertebrate
Pests:
Fed Goats
For example, goats do not reach high
densities in areas dominated by spinifex,
and anecdotal evidence indicates their
numbers are limited by the poor nutritional
quality of drought-affected grasslands
-
although not so much by drought-affected
shrublands (Section 2.4.2).
2.4.2 Water and droughts
During dry times goats need to drink water,
and so they occur only where water occurs
naturally or is artificially provided. An
average size goat of 33 kilograms eating one
kilogram of dry matter per day (Section
4.25) requires between 2-4.5 litres of water
per day depending on ambient temperature
and humidity and reproductive state;
lactating goats drink more (Morand-Fehr
1981). Consumption of water increases
rapidly when ambient temperatures exceed
(Norbury
1993).
‘The reduced availability
and quality of water during
droughts affects the
densities of goats.’
Some goats, particularly those in
temperate and wet climates, can obtain most
of their water requirements from their food,
and can survive in areas with no permanent
fresh water. For example, feral goats had a
stable density of ten per hectare on
Macauley
Island (in the Kermadec Group)
without access to permanent fresh water
(Williams and Rudge
1969),
and goats on
Esk Island (in the Palm Group, Queensland)
(Dunson 1974) and on several islands in the
Galapagos Group
(Dunson
1974; Merrill and
Taylor 1981) survive without access to
permanent fresh water. It may be that goats
can survive by drinking sea water. This was
reported for goats on Aldabra Atoll (Burke
1990) and at Zuytdorp Cliffs (north of
Kalbarri, Western Australia)
(G.
Pickles, APB,
Western Australia, pers.
comm.
1994). Burke
found no unusual morphological effects on
the goats’ kidneys resulting from this
behaviour, but Pickles found the Australian
goats that had drunk saltwater would die
when chased or stressed.
The reduced availability and quality of
water during prolonged droughts must affect
the densities of goats although data to show
this are limited. Some limited information
shows that recruitment into the population
is depressed in times of drought. For
example, at Fowlers Gap (near Broken Hill,
New South Wales) recruitment fell by 44%
during the 1977-78 drought
(McRae 1984),
and at Canegrass (north of the Murray River
in South Australia) recruitment of kids fell
by about 35% during the 18-month-long
drought of 1982-83, when rainfall declined
by 63% below the long-term average
(Henzell
1993). In the latter case, most or
all of the reduced recruitment was caused
by a reduction in the proportion of nannies
that were pregnant, rather than by increased
mortality among new-born kids. In contrast,
Mahood (1985) found that breeding
continued during the 1977-78 drought in
western New South Wales. The drought also
affected most adversely those individuals
with highest metabolic needs. Lactating
females were in poorest condition and the
growth rates of kids was slowed. This was
particularly evident among the faster
growing male kids whose growth rates
declined from about 120-150 grams per day
to 60 grams per day during the drought
(Henzell 1993). In contrast, individuals with
lower metabolic needs appeared hardly
affected by the drought; some mature males,
for example, were very fat even at the height
of the drought possibly because they could
save energy at times when few females were
reproductively receptive.
Perennial vegetation at Canegrass was
abundant, and provided the bulk of goats’
diet throughout a 13-year study. Perennial
plants retained enough nutritional value
during a drought to provide an adequate
maintenance ration for the goats. Unlike
annual vegetation, the perennial species
continued to provide fruit and flowers for
goats to eat during the drought. In contrast,
anecdotal reports indicated that in other areas
where perennial shrubs were less common,
such as parts of the Flinders Ranges, goats
did not fare so well in the drought.
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
15
Natural mortality must increase during
droughts as goats can become too weak to
pull themselves from mud around drying
earth dams, some refuse to leave their home
range and die of thirst when waterholes dry,
and others may fall into rock holes as the
water levels drop.
2.4.3 Natural predation
Dingoes, feral dogs and their hybrids, foxes,
wedge-tailed eagles and feral pigs are all
predators of feral goats. Dingoes and feral
dogs are the main predators and clearly
affect feral goat distribution, as they are
rarely present unless dingoes or feral dogs
are absent or regularly controlled to low
densities. There are many examples where
the presence of uncontrolled populations
of dingoes has restricted the distribution of
feral goats or where the removal of dingoes
has allowed feral goats to spread:
z Goats were present in the Kimberley
Region (Western Australia) in the 1950s
and 1960s but have now mostly gone
(Long
1988,
due in part to the reduction in dingo
control following removal of sheep in the
1970s (Seddon 1968; J. Collins, APB,
Western Australia, pers.
comm.
1993).
Similarly, feral goats were on Mumpeowie
Station (immediately north of the dingo
fence between Lakes Eyre and Frome,
South Australia) when sheep were run
there and dingoes were controlled
(D.
Barratt,
Braemar, Lucindale, South
Australia,
pers.
comm. 1979). Apart from
a few goats that immigrate through the
dingo fence and survive only when dingoes
are at low densities
(K.
Leslie, North
Flinders Soil Board, Quom, South Australia,
The presence
of dingoes
may
prevent the establishment
of feral
goats in some areas.
Source: CSIRO
16
Managing Vertebrate Pests:
Feral Goats
pers.
comm.
1993,
goats disappeared
when the station changed to cattle and
ceased controlling dingoes.
Feral goats have been present in the more
rugged parts of the North Flinders Ranges
(South Australia) since they escaped from
miners last century, but only became a
major problem after dingoes were
removed in the 1940s (R. Sprigg,
Arkaroola, South Australia, pers. comm.
1994).
Similarly, unmanaged semi-feral
populations of goats persist near station
homesteads where they presumably gain
some relief from dingoes, for example at
Rosewood Station (90 kilometres from
Kununurra, Northern Territory).
Goats were released in the Musgrave
Ranges (in the north-west of South
Australia), but failed to persist, probably
because of the presence of dingoes (R.
Read, Scientific Expedition Group, South
Australia, pers.
comm.
1990).
Dingoes were released onto Townshend
Island (Queensland) in
1993
to successfully
control feral goats (Allen and Lee 1995).
There are exceptions to the dingoes
-
no
goats rule. Feral goats and low populations
of dingoes occur in the Ngarkat Conservation
Park (in south-east South Australia); goats
and dingoes coexist in the Australian Capital
Territory; and it is possible that some of the
isolated populations of feral goats in the Great
Dividing Range (in New South Wales, Victoria,
and Queensland) are sympatric with dingoes
(see the distribution maps in Wilson et al.
1992a).
Dingoes, feral dogs,
foxes, wedge-tailed eagles
and feral pigs are all predators
of feral goats.’
The evidence for predation of goats by
other animals is mostly based on their effects
on domestic goats. Foxes killed an average
of
3.6%
(range 0.5-7.0%) of newbo rn
domestic goats in Western Australia (Long et
al. 1988;
Mawson
and Long
1992),
and foxes
and/or feral pigs killed up to 30% of kids in
a New South Wales study (Mitchell 1977).
Feral pigs are significant predators of lambs
in Australia (Pavlov and Hone 1982) and they
are likely to prey on kids. Wedge-tailed eagles
take kids, particularly where there is no cover
(Mitchell 1977). Whether any combination of
these predators (excluding dingoes) are
capable of affecting the distribution or density
of goats is unknown, however, as most seem
to only take kids, which makes it unlikely that
they have a significant effect on feral goat
population size.
2.4.4 Hunting by people
It is unclear whether hunting by Aboriginal
peoples restricted the establishment of feral
goat colonies in the early years of European
settlement. Escaped domestic animals would
have been easy prey for experienced
hunters, but it is likely that most hunting by
Aboriginal peoples ceased before dingoes
were effectively controlled. It would appear
that predation by dingoes rather than
hunting by Aboriginal peoples was the
decisive factor that limited the establishment
of feral goat herds. Feral goats still provide
a source of fresh meat for Aboriginal peoples
living in remote communities (R. Turner,
Roseworthy Campus, University of Adelaide,
Roseworthy, pers.
comm.
1995).
Feral goats are now regularly mustered
with dogs and vehicles (including aircraft),
trapped at waterholes, or shot (Ramsay
1994) and poisoned (Harrington 1982a) to
manage their numbers or limit their dispersal
(Chapter 7). This human predation is the
decisive limiting factor in the higher rainfall
agricultural areas and in the flatter, more
open range in the pastoral areas from which
dingoes have been removed. Recreational
bow and rifle hunters consider feral goats
to be an important game species in Australia.
2.4.5 Diseases and parasites
A number of potentially debilitating parasites
and diseases occur among feral goats in
Australia (Section 3.8). It is unlikely that
parasites and diseases have any major impact
on the density or distribution of feral goats in
Bureau of Resource Sciences/Australian Nature Conservation Agency
17
Table
2: Number of domestic goats (in thousands) by state and territory in Australia. Estimates
from the Australian Bureau of Statistics.
Year
QLD
NSW ACT
VIC
TAS SA
WA NT
Total
1991
54.2 246.9 0.7 55.2
15.5
26.6 48.3
1.8
449.2
1993
31.9
121.4 0.1
32.9
8.4 16.2
29.3
1.1
241.3
the dry pastoral areas, partly because the
browsing habits of goats reduces their intake
of parasite eggs (Chevis 1980) and arid
climates do not favour transmission of
pathogens. The influence of parasites and
diseases in wetter areas is less clear.
Liverflukes
(Fasciola
hepatica)
may limit the
distribution of goats in the wetter parts of
eastern Australia (P.J. Holst, unpublished data
quoted in Harrington
1982a),
although goats
in the wetter parts (over
670
millimetres
average annual rainfall) of South Australia do
not carry a heavy infestation of helminth
parasites and liverflukes (Beveridge et al.
1987). It is also speculated that the bacterial
disease, melioidosis, may contribute to the
absence of goats in the Top End of the
Northern Territory (M. Bell, Northern
Australian Quarantine Strategy, Darwin, pers.
comm.
1993) and in northern Queensland,
where it severely affects domestic goats
(Seddon
1965).
2.4.6 Poisonous plants
Despite their tolerance to many toxic plants
(Section 3.5), the presence of some plant
species may limit the distribution and/or
density of goats. The toxic tree, ironwood
(Erythrophleum
chlorostachys),
along with
dingoes and melioidosis, has been
implicated in the absence of feral goats from
the Top End of the Northern Territory (M.
Bell, NAQS, Darwin, pers.
comm.
1993).
‘Goats have a tolerance to
many toxic plants.
Thirty-five species of Australian plants (in
the genus Gastrolobium plus Acacia
georginae)
contain the potent vertebrate toxin
fluoroacetate (Aplin 1971)
-
the sodium salt
of which is the pest control poison 1080. The
distribution of these plants (Twigg and King
1991) does not generally coincide with the
distribution of feral goats (Wilson et al.
1992a),
except for the area north of the Kalgoorlie
-
Perth Highway. It has been suggested that
the absence of goats in south-west Western
Australia is due to the presence of
1080-
bearing plants (T. Oliver, APB, Western
Australia, pers.
comm.
1994).
2.5
Domestic goats
in
Australia
There were about 450 000 domestic goats
in Australia in 1991, although numbers have
since fallen (Table 2). Most are managed
for fibre production, and about 1000 tonnes
of mohair were exported in 1989 (Cribb
1991). Feral goats with the best cashmere
fibres were selected and used as foundation
stock for breeding back to angora bucks,
although this practice has declined as the
quality of domestic stock improved
(Ramsay
1994).
18
Managing Vertebrate Pests: Feral Goats
3.
Biology
Summary
Feral goats were selected through the
process
of domestication to have characteristics of
value to people. However, many of these
traits ensure that feral goats are effective
pests. Harvested populations of feral goats
can increase by over 50% per annum
if
harvesting stops, because goats become
sexually mature at an early age, have
extended breeding seasons, can conceive
while still lactating, and
can produce
more
than one kidperpregnancy. impact
on the environment is enhanced by their
gregariousness which can increase the
intensity of their browsing, and by their
ability to use a wide variety offoodplants
in a wide variety of habitats.
Feral goats in the rangelands have
unusually large
home
ranges of up to 600
square kilometres (average 380 square
kilometres) for sub-adult males.
These
are
focussed
on
permanent
water and
decrease
in
droughts when goats have to drink more
frequently.
Feral goats can carry many internal and
externalparasites, some of which can also
infest sheep. The importance of
cross-
infection is unknown, although probably
low.
The
bacterial disease melioidosis may
limit the spread of goats, and the rickettsial
disease
Q-fever
is carried
by
goats and may
be transmitted
to people.
Goats arepotential
hosts of exotic diseases such as
foot-and-
mouth disease.
3.1 Ancestry
Goats were domesticated about 9000 years
ago
(Glutton-Brock
1992) from the wild goat
(Capra aegagrus). This wild goat now
extends in a series of races or sub-species
from Turkey and Iran
(C.
a.
aegagrus
-
the
bezoar goat), and from Turkmenia to
Pakistan (C. a. blythi
-
the Sind ibex). The
taxonomic status of these races is uncertain
(Schaller
1977,
and their demographic
status is equally uncertain as agriculture and
hunting threaten many populations. The
domestic descendants of wild goats are now
divided into a large number of breeds of
uncertain genetic relationships (Mason
1981).
‘Domestication involved
selection for high reproductive
ability. Feral goats retain this
trait
-
making them difficult
to control’
Domestication involves both a cultural
process in which a wild species is integrated
into human society as property (Ducos
1989,
and a biological process in which the
owners select for desirable characters
(Clutton-Brock 1992). Domestic goats and
their feral’ descendants are gregarious, move
short distances, have wide dietary
preferences for flexibility of management,
variable coat colours so people could
recognise individuals and for aesthetic
reasons, and high productivity.
The Neolithic people who domesticated
wild goats probably selected animals which
could breed over a wide season to provide
milk and kids over more of the year. They
also probably selected goats that could
lactate for longer than wild goats, could
become pregnant while still lactating, could
regularly produce several kids per litter, and
could do all this at an early age. The feral
descendants have retained these abilities
-
which is one reason why they are difficult
to control when they become pests.
3.2 Body
weight
Feral goats weigh about 2.6 kilograms at
birth (McDonald et al.
1988,
with male kids
being heavier than females, a difference
they retain throughout their lives. Adult
goats (over three years old) from South
1
Feral animals are defined as those domesticated species which have escaped the ownership, management and control
of people and
are
living and reproducing in the wild.
Bureau of
Resource
Sciences/Australian Nature Conservation Agency
19
Australia weigh about 45 kilograms for
females and 60 kilograms for males (Henzell,
data quoted in Harrington 1982a). These
weights appear typical of animals from other
pastoral areas such as Broken Hill (McRae
1984) and White Cliffs (I.
Mahood,
unpublished data quoted in Harrington
I982a),
and are within the range of weights
for the dairy and angora breeds likely to
have been their domestic ancestors (Mason
1981).
3.3 Breeding season
The wild ancestors of domestic and feral goats
have breeding patterns typical of temperate
ungulates with a relatively narrow mating
season spread over two to three months
during autumn and winter according to
limited data collected by Schaller (1977).
Shortening daylength, fine-tuned by
temperature or rainfall-controlled food supply,
are thought to determine the onset of
breeding (Roberts 1967; Schaller 1977). The
evolutionary advantages of this breeding
system have been explained first by
temperate-region
seasonality,
so that the
median date of birth coincides with optimum
conditions for the mother and young (Sadleir
1969),
and second by the reduced effects of
predators caused by providing a glut of
potential victims (Estes 1976). This is
particularly so when the prey species has
highly developed young which follow adults
(but see Section 3.7)
(Rutberg
1987).
‘Birth coincides with
optimum conditions for the
mother and young.’
All sexually mature female goats in a herd
may come into oestrus at about the same time,
and it is thought that this is
synchronised
by
male sexual activity (Shelton 1960). Feral goats
in areas with a more-or-less regular food
supply can breed all year round (Rudge
1990),
but usually retain the ancestral distinct peak
in conceptions during the time when
daylength is shortening and have significantly
fewer conceptions in spring (Parkes 1993a)
(Table 3).
However, there are so many variations
on this basic pattern that influence of day
length must be easily overridden by other
environmental cues; for example, it is
accentuated by drought when mating is
restricted to the period January
-
March
(McRae
1984). Some populations show
secondary or occasionally sole breeding
peaks in summer (Parkes
1993a),
and one
population (studied for 18 months on Santa
Catalina Island, California) showed four
annual peaks of breeding spaced about
three months apart (Coblentz 1980).
3.4
Population dynamics
Population dynamics of feral goat herds are
determined by the difference between
recruitment (births + immigration) and losses
(deaths + emigration).
3.4.1
Population structure
Equal numbers of male and female kids are
born in most feral goat populations (Parkes
1993a; R. Henzell, unpublished data),
alth o u g h Mahood
(1985),
working in
western New South Wales, found a ratio of
male to female foetuses of 0.68 : 1.0, which
is significantly different from unity
(P<0.05).
Fortune favours females as their proportion
in many populations increases among older
age classes. There are significantly more
males in harvested populations (sex ratio =
Table 3:
Monthly pattern of conceptions
(o/o)
in goats sampled over a 12-year period at Canegrass
for 272 conceptions (R. Henzell, unpublished data).
JFMAMJJASOND
%
of
conceptions
9
14 13
6
11 11
4
6
1
4
7
14
20
Managing Vertebrate Pests: Feral Goats
1 female : 0.8 males, n = 909; McRae 1984)
than in unharvested populations (sex ratio
= 1 female
:
0.6 males, n = 1047;
P<0.01;
Williams and Rudge
1969,
showing that the
bias in favour of females is not because
males are selectively removed by mustering
or culling.
Harvesting or the culling of feral goats can
alter the natural age structure of populations.
Feral populations that are commercially
mustered in Australia are heavily biased
towards young animals, about two-thirds of
the animals being less than two years old (R.
Henzell, unpublished data). In contrast, the
goats that survived longest during the
eradication campaign on Raoul Island were
mostly elderly females, presumably because
they were more cunning than males and
young animals
(J.
Parkes, unpublished data).
3.4.2 Birth rates
Population birth rates of feral goats can be
high because of the higher proportion of
females in some populations. Females may
become pregnant in their first year and they
can become pregnant soon after giving birth
as lactation does not stop oestrus. Therefore,
they can breed twice within a year as their
gestation period is only 150 days. Twins and
triplets are common.
For example, in one area in South
Australia 41% of goats shot through the year
were females of breeding size. On average,
they produced 1.57 litters per year with an
average of 1.59 embryos per litter (R.
Henzell, unpublished data).
‘Goats can breed twice a year.’
The proportion of females breeding and
the number of multiple births shows general
patterns with maternal age. Generally, only
about 50% of first-year females breed and
rarely produce more than a single kid.
Fecundity increases with age and reaches a
maximum among females at about 21 months
(four-tooth stage) and older, but declines in
aged adults with worn teeth (Henzell 1983;
Parkes
1993a).
The reduced fecundity of old
females makes little difference to population
birth rates in harvested herds in Australia
because the proportion of older animals is
low (Section 3.4.1).
Maternal condition, generally governed
by food supply or quality, can have a
profound effect on birth rates. For example,
birth rates increased by 77% in a population
of feral goats on Raoul Island as the per
capita food supply increased during a
decade-long eradication campaign (Parkes
1984). Harvesting or culling
per se
does not
appear to increase the birth rates of
Australian populations, presumably because
few populations are at carrying capacity.
However, declining food quality during
droughts can cause a decline in breeding
(McRae 1984).
3.4.3 Natural
mortality
rates
Natural mortality of kids from birth to six
months can be high. On
Macauley
Island
(in the Kermadec Group), 35% of kids died
(Williams and Rudge
1969,
and in one
population on the North Island of New
Zealand 19% died (Rudge 1969). Estimates
of natural mortality from Australian
populations are usually confounded by
unnatural mortality from mustering or
culling. Mahood (1985) found post-natal
mortality in kids up to two months old was
45% in western New South Wales. In a South
Australian population, 38% of young kids
died from natural and human-induced
causes (Henzell 1983). Natural mortality
rates among older goats are unknown but
assumed to be 10% in later calculations.
Predation by dingoes and other animals,
lack of water and food during droughts, toxic
plants and various diseases and parasites are
known or suspected to kill feral goats. These
factors are discussed in Section 2.4.
3.4.4 Rates of increase
Feral goats have a very high potential to
increase their numbers. Subtraction of likely
natural mortality rates (38% of kids and 10%
of adults) from the known finite birth rate
of 2.02 from South Australia (R. Henzell,
Bureau of Resource Sciences/Australian Nature Conservation Agency
21
unpublished data) gives a finite rate of
increase of 1.53 or an instantaneous
exponential rate,
r
= 0.425. Such a
population would double every
1.6
years
in the absence of mortality caused by human
control efforts, or 35% would need to be
killed annually to stop it from increasing.
Mahood
(1985) recorded a maximum rate
of increase for feral goats in western New
South Wales of = 0.395 or 42% a year.
‘Feral goats have a very high
potential to increase their
numbers.’
However, there are few measurements of
natural rates of increase of feral goat
populations in Australia that are not
confounded by harvesting. Few feral goat
populations in the pastoral zone are not
harvested, and aerial surveys (Table
1)
show
that some feral populations were increasing
despite harvesting. For example, the
population increased by 18% each year
between 1987 and 1990 in Western Australia
despite an annual harvest averaging about
200 000 goats (Southwell and Pickles 1993).
3.4.5
Ecological
carrying
capacities
The ecological carrying capacity
(K)
of a feral
goat population is that density attained when
the goats reach an equilibrium with their
resources, natural predators, and competitors
in the absence of human-induced mortality
(Caughley 1980).
The equilibrium is of course
only as stable as the environment under which
the goat
-
vegetation system exists; this is
highly variable for the drought-prone pastoral
areas of Australia, and may be declining as
the rangelands degrade.
The carrying capacity for feral goats can
be very high. Goats were left for 150 years
on
Macauley
Island and when eradicated in
the 1960s were at a density of 1000 per square
kilometre (Williams and Rudge 1969).
Carrying capacity has not been measured
empirically in Australian pastoral zones
because goats are regularly mustered or
culled. Certainly, in the short term the
potential exists for average densities much
higher than the estimated l-3 goats per square
kilometre in the pastoral areas (Table
1),
and
higher than the 20-40 goats per square
kilometre which is the estimate of Kfor all
large herbivores in the semi-arid rangelands
(Section
4.2.5).
3.5
Diet
Goats are generalist herbivores that select the
highest quality food available
(McCammon-
Feldman et al.
1981).
They eat foliage, twigs,
bark, flowers, fruit and roots. They will also
eat plant litter and seeds on the ground, and
fungi. The proportions in their diet of different
kinds of food (browse, grass, herbs), and of
different species within these groups, varies
with their availability, quality and palatability
(Merrill and Taylor 1981). The reasons for
differences in intake between forage types
and species are not well understood (Becker
and Lohrmann 1992).
‘Goats select the highest quality
food and eatfoliage, twigs,
bark,
flowers, fruit and roots.’
In Australia, any one of shrubs, grasses or
herbs may comprise the principal part of
goats’ diet at different times or places (Dawson
et al. 1975; Wilson et al. 1975; Dawson and
Ellis 1979; Squires 1980; Harrington 1986).
Herbs and grasses are most eaten when they
are growing, and are more uniformly ac-
ceptable than browse because they generally
lack the secondary plant compounds that
render some shrub species relatively un-
palatable. Despite this selectivity, goats can
eat the majority of plants in the pastoral areas
of Australia, including prickly acacias, many
poisonous or bitter plants, and species
avoided by sheep and cattle.
3.6
Movements and home
ranges
Feral goats in areas with ample water and
food have small, non-exclusive home ranges
generally of about one square kilometre
with males having larger ranges than
22
Managing Vertebrate Pests Feral Goats
females. For example, on
Moreton
Island
(Queensland), male and female groups
occupied about 1.5 and 1.0 square
kilometres, respectively (O’Brien 1984),
similar to home ranges of feral goats on a
pasture/forest margin in New Zealand
(Riney and Caughley 1959) and on the
summit of Mount Haleakala (Maui, Hawaii)
(Yocum 1967).
‘Feral goats in arid areas
centre their movements about
permanent water.’
Feral goats in arid areas centre their
movements about permanent water (McRae
1984; King 1992), and have much larger,
non-exclusive home ranges. On Yerilla
Station (Western Australia) adult female,
sub-adult female, adult male, and sub-adult
male goats had average home ranges of
69,
63, 247 and 379 square kilometres
respectively, as measured by radio-telemetry
over a period of 23 months (King 1992). The
maximum individual home range was
600
square kilometres. Ranges were smaller in
drier periods, presumably because the goats
had to visit water more frequently (King
1992). The limited data provided for Broken
Hill feral goats confirm these large home
ranges (McRae 1984).
3.7 Social behaviour
Feral goats are social animals, the basic
social unit being an adult female and recent
offspring which associate in an area (the
herd range) with similar, often related,
groups (O’Brien 1988). The young males
leave these matriarchal groups and form
loose associations with similar aged males
or larger mixed-aged groups which associate
with the female’s home range during the
breeding season, but may range over larger
areas at other times (Rudge 1990). Females
that are about to give birth leave the group
and give birth in a protected spot. Kids are
fully active soon after birth, but most,
although not all, are hidden by their mothers
and only visited for feeding until, after a few
days, they join their mother on her travels
(O’Brien 1983; Rudge 1970).
3.8
Parasites and diseases
Feral goats in Australia are known to carry
22 nematode, 2 cestode, 2 trematode, 4
arthropod, and 3 protozoan parasites
(McKenzie et al. 1979; Harrington 1982a;
Beveridge et al. 1987). This is a much smaller
list than the substantial list quoted for New
Zealand feral goats (Rudge 1990). Many of
these parasites also infest domestic sheep
and of course domestic goats, although lice
afflicting feral goats are mostly specific to
goats. Sheep lice have not been reported
from feral goats, but the sheep body louse
(Bovica ovis,
formerly
Damalinia
ovis),
can
survive and apparently breed on penned
goats
(Hallam
1985). Cattle ticks
(Boophilus
microplus)
rarely occur on goats (Sangster
1990),
and have not been reported from feral
goats. Nevertheless, programs to control
these ectoparasites and other pathogens in
domestic livestock must take account of their
possible presence on feral goats. The
importance of cross-infestation between
livestock and feral goats is unknown, but it
is probably not significant. Parasites are
usually only a problem in well-watered
pastures where intensive stocking occurs,
and in these areas feral goat numbers are
generally low (see Section 2.4.5).
‘Many diseases of livestock
are known to be carried by
feral goats.
Feral goats may also be infected with a
variety of bacterial and viral diseases. Most
are not lethal, although the bacterium
Pseudomonas pseudomallei which causes
melioidosis may limit the spread of goats
(Section 2.4.5). Caseous lymphadenitis,
abscesses on the lymph nodes caused by the
bacterium
Corynebacterium
ovis, has been
reported (McKenzie et al.
1979),
but is unlikely
to be lethal (Williams 1981). Pneumonia is
occasionally found in goats, but many other
important diseases of livestock appear to be
rare (such as yersiniosis, leptospirosis, and
mycobacterial diseases such as Johne’s disease
and bovine tuberculosis).
Q-fever is widespread among feral goats
with the antibodies of the causal agent
Bureau of Resource Sciences/Australian Nature Conservation Agency
23
(Coxiella burnetti) being found in 52% of
goats tested in one survey
(Hein
and
Cargill,
unpublished data quoted in Harrington
1982a). This rickettsia is normally non-
pathogenic, but has been implicated in
abortions in goats. However, the disease is
a zoonosis and thus infected feral goats may
be a public health problem.
Many other important diseases of
livestock are known to be carried by feral
goats, but have not been reported from
Australia. Should it reach Australia, foot-
and-mouth disease seems the most likely
disease to establish in feral herds. Other
exotic diseases which feral goats could be
involved in, should they reach Australia,
include bluetongue, rinderpest, screw-worm
fly, capripox, Rift Valley fever, vesicular
stomatitis and scrapie (Henzell et al. in
press). The management responses in such
an event are described in AUSVETPLAN
Emergency Operations Manual
-
Wild Goats
(1990).
24
Managing Vertebrate Pests: Feral Goats
4.
Economic and
environmental
impacts and
commercial use
Summary
Calculable economic losses attributable
to feral
goats
in
Australia are estimated at $25 million
per annum. These are derived from a
calculated $17.8 million net loss caused by
reduced
stock production
(after
taking account
of the profit obtained
from mustering
feral
goats for sale),
$6
million contingency loss
because of the threat of exotic disease, and
$1.2 million direct cost expended by
government agencies on goat control
operations.
This
estimate does not include the
costs associated with the impact of goats on
the environment, of soil
erosion,
orpasture
degradation. No value has been calculated for
these losses. Feral goats also adversely affect
conservation values and biological diversity
by
damaging
the vegetation
and competing
with
native fauna.
Commercial
exploitation
of feral goats
provides economic benefits by supporting an
industry
worth about $29 million annually
to the
exporters
and providing full-
or part-
time jobs for
about 500
workers.
At
the
estimated national average density
over the areas they occupy of
two
per
square
kilometre,
feral goats consume about 0.35%
of the total net annual above-ground
vegetation production
in semi-arid rangelands,
and
constitute about 10% of the totalgrazing
pressure of all
large herbivores.
In
many
areas,
goats
reach
much higher densities, and are
sometimes the dominant large herbivore.
It
is
difficult to differentiate
the
particular
impact of feral goats on single species of
indigenous biota from the impacts of other
herbivores.
4.1 Economic losses
The net costs of feral goats in Australia can
be considered in four sections: the actual
public cost to manage them; the estimated
net costs to production; contingent costs
associated with exotic diseases; and the costs
due to land degradation caused by goats.
4.1.1
Public costs of goat control
The economic social cost of feral goats is
the difference between the value of net
benefits that could be obtained if the optimal
levels of feral goat control were undertaken,
and the net benefits under current levels of
control. Public expenditure on goat control
is just one factor in this equation.
State government agencies spend an
unknown amount managing feral goats,
directly on land reserved for conservation
purposes and indirectly to support private
control efforts. The amount spent reflects
the limited resources available rather than
the amount required to solve the problem.
When landholders spend money on feral
goat control to meet their legal obligations
(Section
6.3),
there are public costs
associated with reduced taxation if they can
claim the costs of goat management for land
conservation purposes (Braysher 1993).
In Western Australia, about $800 000 per
year has been spent supporting feral goat
control operations between 1991-92 and
1994-95. The Animal and Plant Control
Commission and local Soil Boards in South
Australia spent about $170 000 in 1992 on
grants, research, and extension work to
manage feral goats. Queensland spent about
$175 000 0
n
goat control and related
activities in 1994.
4.1.2 Net costs to production
Feral goats and sympatric domestic livestock
(usually sheep) in semi-arid areas have
overlapping diets. The extent of this overlap
varies between habitats and depends on the
extent to which food is limiting within
habitats. For example, dietary overlap is low
in belah (Casuarina
cristata)
-
rosewood
(Alectryon oleifolius) woodland (Wilson
et al. 1975), but high in a poplar box
(Eucalyptus populnea) area (Harrington
Bureau of Resource Sciences/Australian
Nature
Conservation Agency
25
1986,
both in western New South Wales.
Because of this dietary overlap it is generally
assumed that the two species compete for
food, particularly when food is scarce
(Harrington
1982a).
‘Feral goats persist longer
than sheep or kangaroos in
drought.’
It has been argued that dietary overlap is
not necessarily any measure of competition
when food is abundant (Choquenot 1992).
For example, rabbits and sheep do not
compete for food in chenopod shrublands
where the pasture biomass is above about
250 kilograms per hectare when factors other
than food limit both species (Short 1985;
Williams 1991). In rangelands with sheep,
rabbits and kangaroos, pasture biomass will
not exceed this threshold about 45% of the
time. Whether this threshold argument holds
for feral goat
-
sheep competition is not clear,
but the observation that goats persist longer
than sheep and kangaroos in the face of
droughts (Choquenot
1992),
suggests severe
competition when food and/or water is
limited. It is also possible, however, that
differences in these species’ abilities to survive
on poor-quality food during drought, or the
ability of goats to browse on shrubs, also
affects their survival.
Competition should also be seen within
general strategies of grazing management
that balance production risks, such as too
many herbivores leading to land
degradation, and economic risks, such as
the return from wool, within a highly
variable climate. For example, it is possible
that conservative stocking rates in good
years when food limits neither stock nor
pests might increase the economic risk of
the enterprise by not producing enough
High vegetation line resulting from feral goat browsing.
Source:
R.Henzell APCC
26
Managing Vertebrate Pests: Feral Goats
income to see it through droughts (White
1992),
although it might promote sustain-
ability by allowing perennial vegetation to
regenerate.
The net cost of the present population of
feral goats to sheep production has been
estimated (Henzell 1989) by assuming the
extent of competition, contingent costs or
benefits if goat populations are changing,
and the net income from mustering goats
and profits from sheep. All these factors vary
in space and time but updating Henzell’s
(1989) calculations for South Australia gives
an estimate of a net average cost per feral
goat to sheep graziers of $8.15 per goat
(Appendix A). This calculation takes into
account the profits pastoralists make from
mustering and selling goats. But it does not
take into account the fact that in good years
pasture may be so abundant that sheep and
goats do not compete for food. In such years
the costs due to goats will be less. Nor does
the calculation take into account the fact
that in dry years pastoralists who have not
controlled feral goats may have to sell
additional sheep at a very low price, or
destroy them, because the goats have so
denuded the range it will not support them.
These sheep will have to be replaced later
at a much higher price. The calculation uses
a farm gate price for mustered goats of
$6.
Although the current price is up to $15, at
other times it has been as low as $2, and
$6
is used as an approximate ten-year average.
Obviously, however, pastoralists will not
have the flexibility to manage feral goat
numbers according to short term fluctuations
in either pasture biomass or sale price. In
contrast such flexibility is available with
sheep stocking rates.
‘Feral goats may change
the composition of the
vegetation towards more
perennial species.’
The total average annual loss to sheep
production due to feral goats in Australia is
estimated to be about $17.8 million
(Appendix A). This figure does not include
the unknown costs due to pasture
degradation, shrub destruction, soil erosion
and losses to biodiversity attributable to
goats. The farm gate value of mustered goats
is estimated to be about $6 million
(calculated from the
$6
average farm gate
value for feral goats above, and the
approximately one million feral goats
mustered each year (Section 4.3). Given that
mustering these goats costs about $2 million,
the total profit to graziers from mustering
feral goats in Australia is about $4 million
(farm gate value averaged over the past ten
years). Further, economic studies showed
the approximate annual cost of feral goats
in Western Australia to be about $2.5 million
(Howard 1992).
In addition, feral goats are an unknown
cost to primary producers because they
cause long-term changes to the perennial
vegetation upon which livestock depend
during droughts, they have a reputation for
being first to the best feed after any rain,
they compete for water and so reduce the
number of livestock that can be carried
during droughts (or add to the cost of caning
water), and they damage fences.
Costs to other production values include
the costs to farmers owning quality domestic
goats of keeping feral males from mating
with their females, and costs to production
foresters caused by goat-damage to their
seedlings (McCarthy 1985).
4.1.3
Contingent costs of exotic
diseases
The presence of feral goats in Australia
increases the contingent cost of insuring
against the outbreak of exotic diseases of
livestock (Section 3.8). The cost, prior to the
Commonwealth’s Wildlife and Exotic
Disease Preparedness Program, was
estimated to have been $12.5 million per
year, mostly in relation to foot-and-mouth
disease. This is expected to fall to about $5
million per year as a consequence of the
eradication of some goat populations,
research and contingency planning (Henzell
1989). The current cost, including both
public and private costs, is estimated to be
about
$6
million per annum (Henzell
1989).
Bureau of Resource Sciences/Australian Nature Conservation Agency
27
4.1.4
Costs
to the environment
The economic costs of feral goats to
environmental resources or conservation
values cannot be calculated because the
nature of their impact is not always clear
(Section
4.2),
and the value of many of the
resources goats affect cannot easily be
measured in dollars. Nevertheless, the cost
is usually assumed to be considerable.
4.2
Environmental impacts
Feral goats have been responsible for severe
or even catastrophic environmental damage
to ecosystems that evolved without
browsing mammals, such as those on islands
(Parkes
1990a),
but in ecosystems adapted
to some browsing their effect is variable.
The primary causes of environmental
degradation may include mismanagement
of all the natural and domestic herbivores
(French 1970;
Dunbar 1984),
but because
feral goats can survive and reproduce in
these degraded habitats, they are often made
the scapegoats to carry the sins of all culprits
into the wilderness they alone are accused
of creating (Leviticus
16).
On mainland Australia there are no
documented examples of feral goats severely
damaging large areas in the absence of
significant populations of other herbivores,
but they contribute their share of the damage
to the vegetation, soils, and native fauna in
the large areas of pastoral land that are
overgrazed. Their share is generally less than
that of other herbivores, although this has
more to do with their later introduction than
sheep to the pastoral lands and to spasmodic
control by landowners rather than to any
inherent incapacity to reach high densities
and cause severe damage.
Because of their social behaviour, goats
can cause severe localised damage to the
environment, particularly around their camp
sites, and their agility and generalist diet
means they damage some vegetation not
accessible or palatable to other herbivores
(see Section 8.82).
4.2.1
Impact on the soil
Feral goats can deplete the soil’s protective
cover of vegetation and break up the soil
crust with their hooves
(Mahood
1983). In
droughts this leads to wind erosion, in rain
storms it leads to water erosion, and in steep
lands it can cause slips.
4.2.2 Impact on perennial
vegetation
Feral goats may affect perennial vegetation
by eating established plants and by preventing
regeneration of seedlings. Browsing by goats
can kill established plants by defoliation,
especially those less than about two metres
tall, or by debarking their trunks. Regeneration
processes may be affected indirectly when
feral goats reduce the ability of plants to
produce seeds and directly when goats eat
young plants. The results of ungulate browsing
can be sudden and catastrophic if both adult
and young plants are killed, with the degree
of catastrophe depending on the dominance
or importance of the affected species within
the ecosystem. Alternatively, effects can be
delayed if only young plants are killed, but
are eventually catastrophic when the adult
plants die from whatever cause.
‘Feral goats cause long-term
changes to the perennial
vegetation upon which
livestock depend during
droughts.’
Perennial plants in Australia range from
highly palatable (Harrington 1986) to totally
unpalatable and toxic (Aplin 1971).
However, goats are particularly prevalent
in habitats with perennial shrubs and trees,
many of which are palatable and most are
ultimately eaten by goats if they are hungry
enough. The overall impact of feral goats in
Australian perennial shrublands is not clear,
perhaps because goats have not been
present over sufficiently large areas for long
enough and in sufficiently high densities for
their effects to be more obvious, and
because their impacts are confounded with
those of other herbivores,
28
Managing Vertebrate Pests: Feral Goats
A general fail-safe management response
is to assume that even very low densities of
feral goats will be sufficient to inhibit nearly
all regeneration of the most palatable shrub
species. However, in an
exclosure
study in
the Flinders Ranges, rabbits rather than goats
and euros
(Macropus
robustus)
appeared to
determine regeneration success in mulga
(Acacia
aneura)
because they killed nearly
all the seedlings before they were large
enough to be of interest to the other
herbivores. It was also clear that other factors
outside the experimental control were
involved, and that mortality in adult trees
occurred in the absence of goats
(Henzell
1991). The lesson here is that management
of only one herbivore, in this case the goat,
would fail to protect mulga.
4.2.3
Impact on grasses and herbs
Theoretically, ungulates grazing
grass-
land/herbaceous
ecosystems where they have
more-or-less permanent access to all of the
plants should result in feedback mechanisms
that drive the plant-herbivore biomasses
towards dynamic equilibria (May 1975). In
semi-and grasslands in Australia, the stability
of these equilibria depends on erratic rainfall.
Goats could potentially have a more
immediate effect on grasses and forbs than
on shrubs and trees because they are more
accessible and because they are generally
more palatable, containing fewer secondary
compounds than do shrubs or trees. For
example, goats that were short of food in a
study near Cobar (New South Wales) ate
every herb but did not significantly affect
most shrub species (Harrington 1982a). But
in many other habitats the preference of
goats for palatable browse results in their
having a larger effect on shrubs and trees.
4.2.4
Impact on woody weeds
One apparent consequence of
130
years of
grazing by introduced animals on the semi-
arid areas in
Australia
has been the proliferation
of unpalatable shrubs or woody weeds. It has
been suggested, at least for western New South
Wales and south-western Queensland, that
these weeds have increased partly because of
reduced competition from the sheep and
cattle-
browsed grasses and perennial forbs, and
partly because of the reduction of regular fires
both by active suppression and by reduction
of grassland fuel which killed shrub seedlings
(Moore 1969 Harrington et al. 1973; Harrington
et al. 1984). However, the underlying causes
of woody weed encroachment elsewhere in
Australia are not well understood.
‘Goats have been used as an
alternative to fire or chemicals
to control palatable woody
weed species.
Goats eat many of these woody weeds,
and domestic goats have been used as an
alternative to fire or chemicals to control at
least the more palatable species among
native weeds. For example, a stocking rate
of one goat per hectare for three years killed
90% of the hopbush
(Dodonaea
viscosa)
in
a 800 hectare site near Cobar (Torpy et al.
1992). Goats are also used to control such
introduced weeds as blackberries and briar
(Allan
et al. 1993). It is necessary to manage
goats at densities higher than they would
naturally attain to make them effective
against weeds. This requires effective
fencing and stock management.
4.2.5
Goats contribution to total
grazing pressure
The proportion of total grazing pressure that
can be attributed to feral goats can be
assessed either by estimating the proportion
of net annual above-ground productivity
(NAAP) of the vegetation they eat, or by
estimating their proportion of total
large-
herbivore carrying capacity.
Proportion of net annual above-
ground
productivity
(NAAP]
An estimate of the proportional contribution
of feral goats to total NAAP can be made
based on the following assumptions:
z the density of goats is taken as two per
square kilometre (the average density in
Bureau of Resource Sciences/Australian Nature Conservation Agency
29
all states in the early 1990s
-
Table
l),
and
five per square kilometre (an estimate of
densities in more preferred habitats).
the average annual dry matter intake for a
goat of 33 kilograms is 365 kilograms
(Devendra and Burns 1983).
the NAAP is for areas with 240 millimetres
of annual rainfall (assumed to equal annual
evapotranspiration
(AE))
is calculated using
the equation provided by Rosenzweig
(1968) as:
log,,
NAAP
=
-
(1.66)
NAAP
=
195.5 tonnes per
Therefore, goats at densities of two per
square kilometre or five per square
kilometre annually consume 0.73 or 1.83
tonnes of dry matter per square kilometre
respectively, or 0.37% or 0.93% of the total
NAAP, respectively. To put this in
perspective, average densities of rabbits
annually consume 10 tonnes per square
kilometre
(Newsome
1993).
The NAAP includes unpalatable
vegetation, woody tissue not normally eaten
by mammalian herbivores, and inaccessible
parts of plants, although canopy leaves
might become available when they fall to
the ground. Much of the NAAP is consumed
by invertebrates, small vertebrates, and
decomposers (Phillipson 1973).
Proportion of total carrying capacity
Rangelands with 240 millimetres of rainfall
can on average support at least 20 goat-sized
herbivores per square kilometre (Section
7.2.1). Therefore, at the two average densities
modelled
above, feral goats would consume
between 10% and 25% of the food eaten by
the suite of large herbivores present.
In some places goats can reach higher
densities; 27 and 40 goats per square
kilometre have been recorded in the
Olary
Hills and Flinders Ranges, respectively, of
South Australia (Best 1992; Henzell 1983). In
these cases they are the dominant large
herbivore and their impact on preferred food
plants is severe.
4.2.6
Impact on native fauna
The native fauna of Australia has been
profoundly affected by the introduction of
exotic biota (Wilson et al. 1992a). The
intruders have effected these changes by
altering the habitat, by direct competition
for resources, by predation, or by varying
combinations of these. In many cases where
an ecosystem or individual species has
declined it is often difficult to determine
which is the proximal ecological cause
(predation or competition) and thus which
culprit species should be managed.
Feral goats affect terrestrial native fauna
primarily by direct competition for resources
such as food, water, and shelter, and by
contributing to changes in ecosystems.
Usually, these impacts are viewed as
undesirable because they reduce the
biodiversity of ecosystems (Reeves 1992).
Goat dung can be deposited around
waterholes and springs to a depth of several
centimetres. Dung, together with the bodies
of goats that fall into the water and
decompose, are likely to eutrophicate the
water and to have a major effect on freshwater
biota. These effects have not been studied
(see Section 8.8.2).
‘Feral goats compete with
native fauna for resources
such as food, water and
shelter, and contribute to
changes in ecosystems.’
Goats
eat many of the same plants as native
herbivores, and although goats are rarely the
dominant introduced herbivore, this
competition must affect some native
populations, particularly those depending on
goat-favoured species of plants. Goats can
also reduce the amount of water available to
native animals; aggressively exclude some
species (G.
Norbury,
APB, Western Australia,
pers.
comm.
1993); and can cause the water
levels in rock holes to be so lowered as to
exclude other animals or cause animals to fall
in, drown, and pollute the supply. Goats may
also compete with native animals for shelter,
particularly in rock caves. Goats eat some
30
Managing Vertebrate Pests: Feral Goats
invertebrates such as gall-forming and scale
insects, but whether deliberately or
incidentally is unknown.
None of these potential impacts on native
animals are quantified, and the effect at
population levels is unknown and often subtle
or misleading, For example, it is presumed
that feral goats adversely affect yellow-footed
rock-wallabies
(Petrogale
xanthopus)
(Dawson and Ellis
1979;
Sheppard
1990).
There is some circumstantial evidence that
this may be so. For example, it has been
claimed that rock-wallaby numbers recovered
after the
1983
drought in Gap Range (New
South Wales) where goats had been culled,
but concurrently failed to recover at the
nearby Coturaundee Range, where goats were
not culled and therefore increased to very
high densities (Lim et al.
1992).
There are,
however, clearly other factors at work that
may be more critical
(Henzell
199Ob).
Feral
goats have been implicated in the decline of
brush-tailed rock-wallabies
(Petrogale
pencillata) in South Australia (Short and
Milkovits
1990).
Goats have more indirect impact on native
animals because of their effects on native
vegetation and soil, The changes to the native
vegetation harm some native animals, but
benefit a few others, that feed on goat dung,
such as termites and decomposers.
4.2.7
Impact on continental and
oceanic islands
Continental islands, those that were once
part of the mainland, are important as
reservoirs for species that cannot survive in
the face of threats on the mainland. For
example, eight species of small Australian
Feral goats are thought to compete with yellow-foot rock-wallabies
for
food
and
shelter.
Source: Unknown
Bureau of Resource
Sciences/Australian
Nature Conservation Agency
31
mammals survive only on islands (Burbidge
1989). These islands are also important
scientifically because they represent
ecosystems that have varying degrees of
human modification. For example, the only
evidence of Aboriginal use of some Western
Australian islands predates their separation
from the mainland (Abbott 1980). Feral goats
still occur on several continental islands,
and their eradication should be considered.
Priority islands for goat eradication should
be those with particular conservation values
at risk, or those required as baseline or
representative ecosystems.
‘Feral goats still occur on
several continental islands
and their eradication should
be considered.’
Feral goats now occur on only one
Australian oceanic island, Lord Howe Island,
which is a World Heritage Site (Pickard
1976).
Lord Howe Island had no terrestrial
mammals other than bats until people
arrived followed by feral goats, feral pigs,
feral cats, house mice and ship rats in the
late eighteenth century. Feral goats, house
mice and ship rats remain and are subject
to control
(D.
Hiscox, Lord Howe Island
Board, New South Wales,
pers. comm.
1995).
4.3
Resource value and
commercial use
About one million feral goats were mustered
and killed in abattoirs in
1991-92
and a further
40 000 were shot in the field by hunters for
game meat. About
95%
of these goats were
exported as 11 413 tonnes of carcasses
(Toseland 1992). In addition, about 100 000
feral goats are exported live each year to
Muslim countries, although this figure has
been as high as 250 000
(Ramsay
1994).
Ramsay
estimated the total value of exported
goats and goat products was about $29 million
in 1991-92, although this figure includes a
few goats from domesti