Relationships between feral goats (Capra hircus) exotic disease transmission

Relationships between feral goats (Capra hircus) and domestic sheep (Ovis aries) with reference to exotic disease transmission. Peter J.S. Fleming, B...
6 downloads 0 Views 159KB Size
Relationships between feral goats (Capra hircus) and domestic sheep (Ovis aries) with reference to exotic disease transmission.

Peter J.S. Fleming, B Sc (hons), M Res Sc Applied Ecology Research Group University of Canberra

A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, University of Canberra, June 2004

© 2004 Peter J.S. Fleming

ii

UNIVERSITY OF CANBERRA

Certificate of Authorship of Thesis Except where clearly acknowledged in footnotes, quotations and the bibliography, I certify that I am the sole author of the thesis submitted today entitled: Relationships between feral goats (Capra hircus) and domestic sheep (Ovis aries) with reference to exotic disease transmission I further certify that to the best of my knowledge the thesis contains no material previously published or written by another person except where due reference is made in the text of the thesis. The material in the thesis has not been the basis of an award of any other degree or diploma except where due reference is made in the text of the thesis. The thesis complies with University requirements for a thesis as set out in: http://www.canberra.edu.au/secretariat/goldbook/forms/thesisrqmt.pdf .......................................................................... Signature of Candidate .......................................................................... Signature of Chair of the Supervisory Panel Date: ..................................................

iii

Table of Contents Table of Tables............................................................................................x Table of Figures ........................................................................................ xv Acknowledgements ..................................................................................xx Abstract ...................................................................................................xxii 1.

Introduction.........................................................................................1 1.1

General introduction ................................................................................1

1.2

Animal diseases exotic to Australia .........................................................2

1.3

Foot and mouth disease (FMD) ...............................................................5

1.3.1 Foot and mouth disease virus (FMDV) ................................................6 1.3.2 Epidemiological process of FMD .........................................................8 1.3.3 FMD in sheep and goats....................................................................10 1.4

Ecology and behaviour of feral goats.....................................................12

1.4.1 Description of feral goats ...................................................................12 1.4.2 Distribution of feral goats in Australia.................................................14 1.4.3 General ecology of feral goats in Australia ........................................14 1.4.4 Endemic and exotic diseases of goats...............................................15 1.5

Ecology and behaviour of sheep ...........................................................16

1.5.1 Description of merino sheep ..............................................................16 1.5.2 Distribution of sheep in Australia .......................................................18 1.5.3 Endemic and exotic diseases of sheep..............................................19 1.6

Sympatry in ungulates...........................................................................19

1.6.1 Resource partitioning and resource selection ....................................19 1.6.2 Sympatric ungulates and disease transmission .................................20 1.7

Disease models.....................................................................................21

1.7.1 Transmission of disease ....................................................................21 1.7.2 Compartmental models of disease dynamics.....................................25

iv

1.8

2.

Aims of the study...................................................................................27

General Description of the Study Site.............................................29 2.1

Location ................................................................................................29

2.2

Landscape and soils..............................................................................34

2.3

Climate..................................................................................................35

2.3.1 Rainfall ..............................................................................................35 2.3.2 Temperature......................................................................................37 2.3.3 Relative humidity and solar radiation .................................................37 2.4

Vegetation .............................................................................................40

2.5

Fauna....................................................................................................43

2.5.1 Native fauna ......................................................................................43 2.5.2 Terrestrial introduced fauna...............................................................43

3.

General Methods...............................................................................45 3.1

Introduction ...........................................................................................45

3.2

Capture and handling of feral goats.......................................................46

3.3

Age classes and sex ratios....................................................................47

3.4

Field observations .................................................................................50

3.4.1 Definitions of different groups of feral goats and sheep .....................50 3.4.2 Field observations of feral goats ........................................................54 3.4.3 Field observations of merino sheep ...................................................59 3.4.4 Quantification of groups of feral goats ...............................................59 3.4.5 Quantification of groups of merino sheep ..........................................60 3.5

4.

Statistical issues....................................................................................61

Biological parameters of feral goats and merino sheep ...............64 4.1

Introduction ...........................................................................................64

4.2

Population dynamics .............................................................................65

4.2.1 Feral goat and merino sheep population dynamics............................68

v

4.2.2 Rates of increase, birth and death rates of feral goats.......................69 4.2.3 Rates of increase, birth and death rates of merino sheep ..................74 4.3

Methods ................................................................................................75

4.3.1 Methods for estimating feral goat abundance ....................................75 4.3.2 Methods for determining rates of increase.........................................84 4.3.3 Method for determining sheep abundance.........................................85 4.3.4 Methods for estimating population additions, survival and mortality...85 4.4

Results ..................................................................................................89

4.4.1 Aerial surveys of feral goat population density...................................89 4.4.2 Capture, mark and recapture estimates of feral goat herd density .....90 4.4.3 Capture, mark and resight estimates of seasonal feral goat population and herd density........................................................................................92 4.4.4 Mob sizes of feral goats.....................................................................95 4.4.5 Fecundity and birth rates of feral goats..............................................95 4.4.6 Survival and death rates....................................................................97 4.4.7 Sex ratio, age structure and morphometrics of captured goats ........100 4.4.8 Sheep demographic parameters......................................................103 4.4.9 Parameter estimates for FMD models .............................................104 4.5

5.

Discussion...........................................................................................106

Home range size and resource selection of feral goats and merino sheep ...............................................................................................110 5.1

Introduction .........................................................................................110

5.1.1 Home ranges of feral goats .............................................................112 5.1.2 Resource selection and geographical information systems (GIS) ....114 5.1.3 Home range use and resource selection by feral goats and merino sheep ......................................................................................................116 5.1.4 Home range and disease transmission............................................119

vi

5.2

Methods ..............................................................................................120

5.2.1 Home range estimation ...................................................................120 5.2.2 Resource selection by feral goats....................................................122 5.2.3 Home ranges and resource selection by sheep ...............................128 5.3

Results ................................................................................................129

5.3.1 Home ranges of feral goats .............................................................129 5.3.2 Resource selection functions for feral goats ....................................131 5.4

Discussion...........................................................................................137

5.4.1 Home range size of feral goats........................................................137 5.4.2 Habitat preferences of feral goats....................................................138

6.

Contact within and between herds of feral goats and flocks of sheep ...............................................................................................140

6.1

Introduction .........................................................................................140

6.1.1 Quantification of contacts ................................................................144 6.1.2 Appropriate scale for measuring contacts........................................146 6.1.3 Models of contacts...........................................................................147 6.1.4 Social behaviour and contacts within herd and flocks ......................149 6.2

Methods for determining contact rates.................................................150

6.2.1 Contact rates within herds of feral goats and within flocks of merino sheep ......................................................................................................150 6.2.2 Contact model components for use in GIS-disease models.............155 6.2.3 Migration: contacts between herds of feral goats and flocks of merino sheep ......................................................................................................156 6.3

Results ................................................................................................158

6.3.1 Contact rates within herds of feral goats..........................................158 6.3.2 Emigration and immigration of feral goats and merino sheep ..........167 6.3.3 Contact parameters for use in FMD models.....................................171

vii

6.4

7.

Discussion...........................................................................................171

Models of FMDV transmission in feral goats and merino sheep 176 7.1

Introduction .........................................................................................176

7.1.1 FMD scenario ..................................................................................177 7.2

Methods ..............................................................................................179

7.2.1 Model structure................................................................................179 7.2.2 Forces of infection ...........................................................................182 7.2.3 Temporal modelling of FMDV transmission .....................................184 7.2.4 Parameter estimates .......................................................................186 7.2.5 Temporal models of FMDV transmission in populations ..................188 7.2.6 Spatial modelling of FMDV transmission in subgroups ....................190 7.3

Results: Temporal models of FMD in feral goats and merino sheep....191

7.3.1 Temporal model of FMDV transmission between goats...................191 7.3.2 Temporal model of FMDV transmission between sheep ..................195 7.3.3 Models of FMDV transmission between species..............................197 7.3.4 Models with culling of feral goats .....................................................199 7.3.5 Effects of reintroductions of vaccinated or clean sheep ...................200 7.3.6 Summary of results of temporal models...........................................201 7.4

Results: Two-species spatial model of FMD ........................................204

7.4.1 Model predictions ............................................................................204 7.4.2 Model-estimated parameters ...........................................................206 7.5

8.

Discussion...........................................................................................207

Conclusions and discussion .........................................................209 8.1

Biological parameters of feral goats.....................................................209

8.2

Home range and habitat preferences of feral goats .............................210

8.3

Contact rates and movements of feral goats. ......................................212

8.4

FMDV transmission model predictions ................................................213

viii

8.5

A scenario of an FMD emergency and strategies for control ...............215

8.5.3 Scenario for FMD in feral goats in tablelands environments in eastern Australia ..................................................................................................215 8.5.4 Strategies for controlling FMD in tablelands environments in eastern Australia ..................................................................................................216 8.6

The potential role of other ungulates in FMD epidemiology in

Australia.....................................................................................................218

9.

References ......................................................................................220

Appendix I ...............................................................................................276 Appendix II ..............................................................................................282

ix

Table of Tables Table 1.1

Transmissible diseases of ungulates listed by Office International

des Epizooties (OIE) in List A (see text), and their status in Australia (Geering et al. 1995, OIE 2002a, 2002c)...........................................................3 Table 1.2 1989).

A classification of the ungulates found in Australia (after Groves ...........................................................................................................4

Table 2.1 Districts within the study site near Coolah Tops, and the areas and number of paddocks included in each district..................................................33 Table 2.2

Mean number of days with relative humidity (at maximum daily

temperatures) above 60% and maximum daily temperatures below 27°C at Turee Vale, Coolah from autumn 1997 to summer 2000.. ...............................38 Table 2.3

Classification of vegetation types near Coolah NSW (modified

from Specht 1970 and Beadle 1981)...............................................................42 Table 3.1

Age classes of feral goats determined by dentition on the lower

mandible (after Habermehl 1961 in Parkes 1993, Holst & Denney 1980, and Mahood 1985).................................................................................................49 Table 3.2

Scores used to assess the body condition of captured feral goats

(after May et al. 1995). ....................................................................................50 Table 3.3

An example of the calculation of typical group size using four

groups of animals from each of two hypothetical populations (after Jarman 1974).

.........................................................................................................61

x

Table 4.1

Measured parameters required for deterministic models of FMDV

transmission in and between herds of goats and flocks of sheep (after Pech & Hone 1988, Anderson & May 1992 and McCallum 2000). ...........................65 Table 4.2

Densities of feral goats reported for different environments in

Australia. (Standard errors in brackets.)..........................................................71 Table 4.3 goats. Table 4.4

Annual instantaneous rates of increase from other studies of feral .........................................................................................................72 Fecundity and kid mortality rates from studies of feral and

domestic goats................................................................................................73 Table 4.5

Notation for parameters and statistics used for capture-mark-

recapture models (after Seber 1982, Pollock et al. 1990 and Kendall et al. 1995 with Ai added).........................................................................................76 Table 4.6

Aerial survey estimates of seasonal mean density (km-2) and

abundance of a population of feral goats at Turee Vale. CV = coefficient of variation. .........................................................................................................90 Table 4.7

Capture, mark and recapture estimates of abundance (N) and

density (D) of 3 herds of feral goats at Turee Vale. .........................................92 Table 4.8

Seasonal densities of feral goats at Turee Vale estimated with the

survival-modified robust estimator...................................................................93 Table 4.9

The typical, mean, median and modal mob sizes of feral goats

observed in the field at Turee Vale from February 1997 to January 2001 (n = 3,495 mobs).................................................................................................95

xi

Table 4.10 Candidate models for survival and resighting probability of radiocollared feral goats at Turee Vale, Coolah. .....................................................98 ^

Table 4.11 Survival probability ( φ ) and resighting probabilities (p) of radiocollared adult feral goats in the Turee Vale population estimated using model { φ. , p i } during seasons where no goat mustering was undertaken. ......99 Table 4.12 Annual survival probabilities for the unharvested sample (collared) and the harvested sample (tagged) for the Turee Vale feral goat population.100 Table 4.13 The sexes of sub-adult and adult feral goats captured at the study site from Summer 1996 to Summer 2000......................................................100 Table 4.14 Proportions of captured and tagged feral goats at Turee Vale in age classes determined by eruption of incisors. ............................................103 Table 4.15 Parameter estimates of feral goats for use in FMD models.............105 Table 4.16 Parameter estimates of merino sheep for use in FMD models........105 Table 5.1

Mean, median, minimum and maximum home range estimates

(km2), using 95% kernel estimator, of male (n = 116) and female (n = 241) feral goats at Turee Vale, Coolah..................................................................130 Table 5.2

Models with Poisson and normal error distributions of habitat

preference by mobs of feral goats at Turee Vale, Coolah..............................134 Table 5.3

Coefficients ( ) for resource selection functions (with Poisson

errors) of habitat preferences of mobs of feral goats at Turee Vale, Coolah..135

xii

Table 6.1

Fixed (behavioural and animal attributes) and random (landscape

and seasonal) effects included in initial mixed models of within herd contact rates of feral goats and between goats and sheep. .......................................155 Table 6.2

The duration of contacts between individual feral goats and other

animals (standard errors in brackets, n= number of contacts). ......................158 Table 6.3

Attributes of focal goats and neighbours included in mixed models

of contact rates between feral goats within herds..........................................160 Table 6.4

Coefficients of parameters retained in the model of goat to goat

contact rates. ................................................................................................162 Table 6.5

Attributes of focal sheep and neighbours included in mixed models

of contact rates between sheep within flocks. ..............................................163 Table 6.6

Coefficients of parameters retained in the model of sheep to

sheep contact rates.......................................................................................164 Table 6.7

Attributes of focal goats and neighbours included in mixed models

of contact rates between feral goats and sheep within herds and flocks.. .....165 Table 6.8

Coefficients of parameters retained in the model for goat to sheep

contact rates.. ...............................................................................................166 Table 6.9

Contact rates between flocks of sheep (flock-flock day-1) derived

from the number of changes in flock structure or abundance and the husbandry practice responsible for flock changes at Turee Vale, Coolah......170 Table 6.10 Summary of per capita and per herd contact parameters for use in the models in Chapter 7 ................................................................................171

xiii

Table 7.1

Parameters estimated in temporal and spatial models of FMDV

transmission in and between herds of goats and flocks of sheep (after Pech & Hone 1988, Anderson & May 1992, McCallum 2000 and Begon et al. 2002) Table 7.2

.......................................................................................................182 Dynamic force of infection parameters for diseases affecting goats

and sheep. ....................................................................................................184 Table 7.3

The probability of successful contact, , the daily per capita death

rate from FMD, , and the latent, infectious and immune periods for FMD in sheep and goats (after McVicar & Sutmoller 1972, Mishra & Ghei 1983). .....187 Table 7.4

Summary of results of temporal models of FMDV transmission in

feral goats and merino sheep, and the starting parameters used. .................201 Table 7.5

Contact rates and herd and flock parameters developed in the

spatial model, disease introduced to a flock of sheep in Sid eagle district. ....206

xiv

Table of Figures Figure 1.1

A compartmental model of the epidemiology of a directly

transmitted disease in a homogeneously mixed population of animals at equilibrium (after Anderson & May 1992 and McLeod et al. 2000). .................27 Figure 2.1

The distribution of feral goats in 2002 in New South Wales (West

& Saunders 2003), the major river systems in NSW are represented by the red polygon (high feral goat density) and the pink polygons (medium feral goat density). Figure 2.2

..........................................................................................30

District locations at the study site near Coolah in central eastern

NSW: districts encompassed separate herds of feral goats (Table 2.1). .........32 Figure 2.3

Average monthly rainfall at Turee Vale, Coolah (n=55 years prior

to and including 2001, data from C. Martin, Sherwood Coolah).......................36 Figure 2.4

Quarterly rainfall registered during January 1997 to October 2001

for Turee Vale Coolah (solid bars), compared with quarterly averages (line) (n=55 years, data from C. Martin, Sherwood Coolah). ....................................36 Figure 2.5

Maximum (upper line) and minimum temperatures for Turee Vale,

Coolah for January 1997 to February 2001 (standard errors omitted for clarity) Figure 2.6

. ........................................................................................................39 Relative humidity at maximum temperature (%, thin line) and

predicted daily radiation (MJm-2, bold line) for Turee Vale, Coolah for January 1997 to February 2001 (after The Data Drill 2000). ...........................39 Figure 3.1 1980).

Representation of group sizes used in this thesis (after Caughley .........................................................................................................52

xv

Figure 3.2

Representation of nearest neighbour distances from randomly

selected animals, in this case the fourth goat from the left (marked ) and the fourth sheep from the left (marked ). .......................................................58 Figure 4.1

Seasonal mean fecundity (kids parturient female-1) of the Turee

Vale population of feral goats..........................................................................96 Figure 4.2

The seasonal reproductive rates of a population of feral goats

observed in the field at Turee Vale, Coolah.....................................................97 Figure 4.3

The relationship between liveweight (kg) and girth diameter (mm)

for female goats (n= 87). ...............................................................................102 Figure 4.4

The relationship between liveweight (kg) and girth diameter (mm)

for male goats (n= 70)...................................................................................102 Figure 5.1

The relationship between mean annual rainfall (mm) and the

aggregate home range size of female feral goats in Australasia.. .................131 Figure 5.2

The number of GIS-generated grid cells, encapsulated in the

100% outer MCP of goat locations, in which mobs of feral goats were observed (f) on one to 21 occasions. ............................................................132 Figure 5.3

Preferred habitats of feral goats predicted with a resource

selection function of aspect, slope, elevation and vegetation type (grey scale points, darker points are more preferred, lighter points are less preferred, palest grey =no data).. ..................................................................136 Figure 6.1

Some theoretical functions of contact rate in response to animal

density. .......................................................................................................149

xvi

Figure 6.2

The daily contact rates (goat-goat contact day-1) of feral goats at

different observed mob sizes (n= 738 mobs) on Turee Vale, Coolah. ...........161 Figure 6.3

A single, straggler wether tries to join a mob of male feral goats

and is kept at a distance of 1.5–3m by repeated agonistic physical contacts.167 Figure 6.4

The frequency of movement between herds of tagged feral goats

with >10 locations (n= 421 goats). ................................................................168 Figure 6.5

The number of districts in which tagged feral goats with >10

locations (n= 421 goats) were observed........................................................169 Figure 7.1

A general compartmental model of disease transmission at

equilibrium within and between two species (after McLeod et al. 2000).. ......185 Figure 7.2

Modelled projection of feral goat population at Turee Vale in the

absence of disease, hunting or harvesting.. ..................................................192 Figure 7.3

Modelled projection of FMD in a population of feral goats in the

absence of sheep..........................................................................................192 Figure 7.4

Trajectory of the force of infection ( G) of FMD in a population of

feral goats in the absence of merino sheep, projected beyond 1 year. ..........193 Figure 7.5

Sensitivity of the maximum force of infection (upper line) in model

3 and time since infection for the model to reach

max

to the probability of

successful contact ( )....................................................................................194 Figure 7.6

Sensitivity of the maximum force of infection (upper line) in model

3 and time since infection for the model to reach

max

to contact rate.. ..........194

xvii

Figure 7.7

Modelled projection of a population of merino sheep in the

absence of disease.. .....................................................................................195 Figure 7.8

Modelled projection of FMD in a population of merino sheep in the

absence of feral goats...................................................................................196 Figure 7.9

Trajectory of force of infection ( S) of FMD in a population of

merino sheep in the absence of feral goats, projected beyond two breeding pulses. . ......................................................................................................196 Figure 7.10 Predicted population trajectory for FMD in a population of feral goats when merino sheep were present........................................................197 Figure 7.11 Predicted population trajectory for FMD in a population of merino sheep when feral goats were present............................................................198 Figure 7.12 Trajectories of forces of infection ( G,

S,

GS

) of FMD in a

sympatric population of merino sheep and feral goats, projected past two breeding pulses of sheep. ................................................................198 Figure 7.13 Predicted trajectory of FMD in a population of 3,820 goats culled to 8% of initial density 30 days after introduction of FMDV. ...........................199 Figure 7.14 Predicted trajectory of the force of infection ( G) of FMD in a herd of 306 goats culled to 8% of initial density 30 days after introduction of FMDV.

.......................................................................................................200

Figure 7.15 Trajectory of forces of infection ( G,

S,

GS

) when healthy or

vaccinated sheep are reintroduced into a population of feral goats reduced by culling to 8% of initial numbers.. ...............................................................201

xviii

Figure 7.16 Example of the trajectory of forces of infection ( G,

S,

GS

) for a

spatial model of FMDV transmission in a population of sheep and of feral goats.

. ......................................................................................................204

Figure 7.17 Map of projected FMD spread in a population of feral goats (blue shades, lighter points = lower prevalence of infection within 1 ha cell points) and a population of merino sheep (purple shades, lighter points = lower prevalence of infection within 1 ha cell points) at the study site.....................205

xix

Acknowledgements My objective in undertaking this project was to learn about the application of models to the dynamics of diseases and animal populations. Many people have helped me in this objective. My primary supervisor, Jim Hone, encouraged me in my studies and provided many opportunities to further my understanding of disease dynamics and modelling. Peter Holst was my supervisor from the Department of Agriculture, provided interest in the project, reassurance when needed and freely shared his great knowledge of goat and sheep production. I am indebted to both men. The willing collaboration of the land owners in the vicinity of Coolah Tops was vital. Ant and Barbara Martin, Chris and Georgie Martin, Kevin Cluff, Kevin Andrew, Ian Sutton, Don, Doug and Richard Arnott all trusted me and my team to shut the gates. My special thanks to Mike and Kerry Martin on whose beautiful property, “Turee Vale”, the project was centred. I am so grateful for their good-natured cooperation and tolerance of the steady flow of students, volunteers and departmental people all over their land, the late night discussions over coffee about goats, sheep breeding and wool, and the many little things that made it a pleasure to do the project there. I was lucky enough to be helped by some of my friends and colleagues at the Vertebrate Pest Research Unit at Orange, including; Brian Lukins, Peter West, Glen Walker, Sharelle Hart, Suzy Balogh, Mani Berghout, Richard Mason, Michelle Walter and Barry Kay. Greg Jones and Matthew Gentle started as students and became valued colleagues and essential parts of the “Turee Vale” furniture. My thanks to them all and to Glen Saunders for his free allocation of VPRU time to my sometimes-demanding schedule. Gavin Melville and Remy Van de Ven were very helpful in providing biometrical advice and Peter Worsley and Ian McGowen provided assistance with digital elevation models. Many others assisted in the project and I appreciate their help. In particular; Ken England of NSW National Parks & Wildlife Service, Mal Leeson and Robert Snellgrove of Mudgee-Merriwa and Merriwa Rural Lands Protection Boards, Jim Longworth, Ryan Breen, Josh Moore, Jamie Gorry, Melanie Chatfield, Peter Irish, Lucy Reilly, Dan Huie, Craig Faulkner, Steve Locke, Nick Byrne, Cath Anderson

xx

and Australian Trust for Conservation Volunteers, Mudgee Coop, Mudgee Abattoir and Matt Hollingdale and Mark Rogers of Commercial Helicopters P/L. There were also students from University of New England and University of Canberra who spent time at the Coolah site gaining experience as part of their degrees. Chad Martin provided the rainfall records for “Sherwood” and “Turee Vale”. I thank them all. An endeavour of this size is expensive and I am grateful for to the Wildlife & Exotic Disease Preparedness Program, the National Feral Animal Control Program of the Natural Heritage Trust, NSW Agriculture and the Applied Ecology Research Group of the University of Canberra for the necessary financial assistance and resources to undertake the project. There are two members of the VPRU who I must thank especially. Steve McLeod and I spent many hours discussing the construction of disease models and he very kindly undertook the programming of the models in Visual Basic. I could not have completed the project without Steve’s help and great generosity. John Tracey and I embarked on the Coolah project together in autumn 1997 and have continued to discuss feral goats and the project ever since. He has been the proverbial “tower of strength” and helped in all aspects of the project: together we have shared a journey and I am thankful of his friendship. Acknowledgements of families never do justice to their contribution. Lynne, Hugh and Alistair are my life and I am sorry that I was away so much doing the feral stuff. “Thanks for everything”.

xxi

Abstract Merino sheep are the most numerous domestic livestock in Australia and feral goats are wide-spread and locally abundant in many of the regions where sheep are grazed. Foot and mouth disease (FMD) is a disease of ungulates that causes severe economic hardship to countries where outbreaks occur or where it has become endemic. In India, Africa, Greece and recently the United Kingdom and Eire, sheep and goats have been implicated in the spread and maintenance of FMD. In Australia, there are contingency plans (AUSVETPLANS) for dealing with an outbreak of FMD. Included in those plans are strategies for control of the disease in feral ungulates including feral pigs and feral goats. Modelling has provided assistance in developing strategies to combat outbreaks in feral pigs and for controlling outbreaks in domestic livestock. No models have been constructed to aid decisions about controlling FMD in feral goats where they co-occur with merino sheep. In Australia, the greatest densities of free-ranging feral goats and domestic livestock occur in the high rainfall zone (> 500 mm mean annual rainfall) along the eastern tablelands and adjacent slopes of the Great Dividing Range. Previous studies of feral goat biology, population dynamics and behaviour in Australia have concentrated on arid and semi-arid zones or on islands. Interactions between free ranging feral goats and merino sheep have not previously been studied in the high rainfall zone. My study investigated the ecological and behavioural characteristics of feral goats and their interactions with sympatric merino sheep at a high rainfall site in central eastern New South Wales. The population dynamics, biological and behavioural parameters of feral goats and sheep were then used to model FMD in such an environment. Deterministic temporal models and a new spatial stochastic model

xxii

were used. Of particular interest were the rates of contact within and between subgroups of feral goats (termed herds and mobs), within and between subgroups of merino sheep (termed flocks and mobs), and between subgroups of the two species. Feral goats at the study site were found to be numerous (mean density = 34.94 goats km-2, from aerial surveys), in good condition, fecund and had high adult survival and low annual adult mortality (survival= 0.81–1.00) in the absence of harvesting and hunting. They had an observed instantaneous rate of increase of 0.112 per year. Annual rate of increase was similar to other sites in Australia without sustained harvesting pressure. Home ranges were small for both males (3.754 km2, s.e. = 0.232, n = 116 goats) and females (2.369 km2, s.e. = 0.088, n = 241 goats). From this and other Australasian studies, an inverse power function was found to be an excellent descriptor of the relationship between mean annual rainfall and female home range size. A resource selection function was fitted in a geographic information system to observational data of feral goats. The habitat selection of feral goats included a preference for wooded vegetation on eastern and north eastern aspects at higher elevations. The resource selection function was also used to set the probabilities of occurrence of feral goats in 1 ha areas of the landscape and these probabilities were used to generate heterogeneity in a spatial model of foot and mouth disease virus (FMDV) transmission. Daily per capita contact rates were estimated from observed contacts in the field where a contact between individuals was recognised when one approached within 1 body length ( 1m) of another. The contacts between feral goats within herds were frequent and occurred at a rate of 6.96 (s.e. = 1.27) goat–goat contacts day-1. Sheep to sheep contacts were slightly less frequent (4.22 sheep–sheep contacts

xxiii

day-1, s.e. = 0.65) but both estimates were most likely negatively biased because of observer errors in estimating the number of individual animals coming in contact with observation subject (focal) animals. Contacts between herds of feral goats were not common and those between adjacent populations were fewer than 1 per year. In sheep, flock to flock contact was largely governed by husbandry practices and occurred at a mean daily rate of 0.0014 flock–flock contacts. Contacts between sheep and feral goats were less frequent but nonetheless common (2.82 goat–sheep contacts day-1, s.e. = 0.40). In feral goats the size of the mob in which focal goats were observed was found to be the most important factor in determining contact rates between individuals and a counter-intuitive inverse relationship was identified. Contacts were heterogeneous and density was not an important determinant of contact rates implying that, because of the uniformly high densities at the site, saturation had occurred. The temporal models of FMDV transmission showed that the rate of contact within and between species was such that FMD was predicted to spread rapidly throughout an infected herd or flock. Control strategies of intense culling of feral goats at the population level were predicted to allow the disease to persist at low prevalence, with a small peak corresponding to the annual lambing pulse in sheep. However, the same level of control (>90% reduction) at the herd level was predicted to eliminate FMD and allow the safe reintroduction of sheep. Extreme control that left very small groups (

Suggest Documents