THE ECOLOGY OF THE INTRODUCED RED FOX (VULPES VULPES) IN THE ARID ZONE. by NICOLA JANE MARLOW Thesis submitted for the degree of Doctor of Philosophy, University of New South Wales, Australia January, 1992 UNIVERSilY OF NEW SOU1H WALES Thesis I Project Report Sheet Abstract 350 words maximum: (PLEASE lYPE] The ecological r6le of the introduced European red fox (Vulpes vulpes) was investigated by studying the diet, the home range usage, and the population dynamics of foxes in arid N.W. N.S.W. There has been a coincident decline in the populations of small and medium sized mammals since the introduction of the fox into Australia and this study was initiated to determine the current extent of predation upon native fauna. The dietary composition of foxes was correlated with the field abundances of their prey species and rabbits (Oryctolagus cuniculus) were found to be the most important vertebrate prey species. Dasyurids, ground-dwelling birds, and reptiles, as well as carrion and invertebrates, were all ingested. When the availability of rabbits was low foxes switched their predatory preferences to dasyurids. A rabbit removal experiment revealed that when rabbits and dasyurids were both unavailable to foxes they predominantly ingested ground­ dwelling birds and reptiles. Because foxes are able to increase their density out of all proportion to that of their native prey species by ingesting rabbits when they are numerous, they are able to have a profound detrimental impact upon native species by switching to them when rabbits are scarce. The age structure for the fox population at Fowlers Gap was obtained from shot specimens; the sex ratio was 1:0.92, and the average litter size was 2.33 cubs per vixen. Mean fox density was 0.93 foxes per km2. Home range analyses were undertaken using the Anderson method of home range analysis. Male foxes were found to have slightly larger weekly home-range areas than females but no seasonal or yearly differences in home-range size between the sexes were found. Mean weekly, seasonal and yearly home-range areas were 130, 160 and 518 (ha) respectively. Declaration relating to disposition of project report/thesis I am fully aware of the policy of the University relating to the retention and use of higher degree proj~t reports and theses, namely that the University retains the copies submitted for examination and is free to allow them to be consulted or borrowed. Subject to the provisions of the Copyright Act 1968, the University may issue a project report or thesis in whole or in part, in photostat or microfilm or other copying medium. 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(Signed) -~~- .. · · · · · · · UNIVERSiTY OF N.S.W. 1 5 OCT 1993 LIBRARIES II TABLE OF CONTENTS PAGE LIST OF FIGURES VII LIST OF TABLES IX ABSTRACT XI ACKNOWLEDGEMENTS XII CHAPTER 1: GENERAL INTRODUCTION 1.1 PREAMBLE 1 1. 2 FOX DISTRIBUfiON IN AUSTRALIA 2 1.3 THE IMPACT OF FOXES IN AUSTRALIA 4 1.3.1 Fox predation upon native fauna 4 1.3.2 Status of other Australian vertebrate fauna 14 1.3.3 Other factors that may be responsible for the decline of the mammalian fauna in Australia 15 1.3.3.1 The feral cat (&ill_ catus) 15 1.3.3.2 Changes in fire regime 16 1.3.3.3 Rabbits and other introduced herbivores 16 1.3.3.4 Disease 18 1.4 HOME RANGE AND HABITAT PREFERENCES 18 1.5 GENERAL BIOLOGY 21 1.5.1 Fox diet in other countries 21 1.5.2 World distribution/ taxonomic relationships 22 1.5.3 Other vulpine species 22 1.6 SPECIFIC AIMS OF THIS sruDY 22 CHAPrER 2: GENERAL METHODS 2.1 STUDY AREA 24 2.1.1 General Description 24 2.1.2 Climate 25 2.1.3 The Study Sites 'lJ 2.1.3.1 Warrens 2:} 2.1.3.2 Ram 3) 2.1.3.3 Lambing 3) 2.1.3.4 Mating 31 2.1.3.5 Salt 3 31 Ill 2.1.4 Fauna 31 2.1.4.1 Rabbits 32 2.1.4.2 Dasyurids and rodents 32 2.1.4.3 Macropodids 33 2.1.4.4 Feral cats 33 2.1.4.5 Ground-dwelling birds 33 2.2 CAPrUBE TECHNIQUES 34 2.2.1 The Cannon-Net 34 2.2.2 Snares/Leghold Traps 35 2.2.3 Handling and Collaring Foxes 00 2.3 CENSUS TECHNIQUES 00 2.3.2 Rabbit Abundance Estimations 00 2.3.3 Light Trap 37 2.3.4 Pitfall trapping 37 2.4 STATISTICAL ANALYSES 38 CHAPrER 3: DIET ANALYSES 3.1 INTRODUCTION a:J 3.2 MIITBODS 40 3.2.1 Scat Collection 40 3.2.2 Scat Analysis 40 3.2.3 Field Abundances 42 3.2.4 Analytical Methods 42 3.2.5 Impact of Predation on Native Populations 44 3.3 :RESULTS 44 3.3.1 Overall Dietary Composition 44 3.3.2 Relationships between Species Availability and Dietary Occurrence 45 3.3.3 Yearly, Seasonal and Paddock Interactions 52 3.3.4 Yearly and Seasonal Dietary Interactions 52 3.3 5 Yearly and Paddock Dietary Interactions 52 3.3.6 Seasonal and Paddock Dietary Interactions 54 3.3.7 Impact upon Native Populations 57 3.4 DISCUSSION 58 IV CHAPfER 4: POPULATION PARAMETERS AND DENSITY 4.1 INTRODUCTION 70 4.2 MEI'HODS 73 4.2.1 Ageing Techniques 74 4.2.2 Placental Scars 74 4.2.3 Sex ratios 75 4.2.4 Life tables 75 4.2.5 Probability Density Estimations 76 4.2.6 Changes in Fox Density with Season, Paddock and Year 71 4.2. 7 Relationships with Prey Species Densities 78 4.3 RESULTS 78 4.3.1 Sex ratios 78 4.3.2 Age structure 79 4.3.3 Fecundity 8> 4.3.4 Life Table 81 4.3.5 Overall Fox Density in the Study Area 81 4.3.6 Fox Density Variations between Paddocks 82 4.3. 7 Seasonal Fox Density Variations 83 4.3.8 Effects of other Environmental Variables 83 4.3.8.1 Food availability 83 4.3.8.2 Lunar phase 84 4.4 DISCUSSION 84 CHAPTER 5: HOME RANGE ANALYSES 5.1INTRODUCTION 5.1.1 Basic Concepts 5.1.2 Home-range Studies in other countries 5.1.3 Home-range Studies in Australia 5.1.4 Dispersal 5.2 METHODS 5.2.1 Hand Tracking 5.2.2 STATION TRACKING 5.2.4 Data Handling 5.2.4.1 Creating and editing plotfiles 5.2.4.2 Fourier transform method V 5.2.4.5 Harmonic mean centres ffi 5.2.4.6 Home-range overlap ffi 5.2.4. 7 Estimating dispersal distances 00 5.3RESULTS 00 5.3.1 Home-range Size 00 5.3.1.1 Sex differences 00 5.3.1.2 Seasonal differences 00 5.3.2 Home-range Use 101 5.3.2.1 Resource preferences 101 5.3.2.2 Home-range Fidelity 102 5.3.2.3 Shifts in activity centres 102 5.3.2.4 Home-range Overlap Between Different Individuals 104 5.3.3 Dispersal Distances 107 5.4 DISCUSSION 108 CHAPrER 6: EFFECfS OF RABBIT REMOVAL 6.1 INTRODUCTION 114 6.2 MEI'HODS 115 6.3 RESULTS 117 6.4 DISCUSSION 12A CHAPrER 7: FOX CONTROL MEI110DS 7.1 INTRODUCTION 128 7.2 MEI110DS 100 7.2.1 Preparing and Laying Baits 100 7 .2.2 Shooting 131 7.3 RESULTS 131 7 .3.1 Bait Ingestion Rate 131 7 .3.2 Recolonisation Rate 131 7.4 DISCUSSION 132 VI CHAPI'ER 8: GENERAL DISCUSSION 134 REFERENCES 140 APPENDICES Appendix 1 165 Appendix 2 167 Appendix 3 168 Appendix 4 170 VII J,Tffi' OF FIGURES Figure TITLE PAGE Number 1.1 Distribution and spread of red foxes (Vulpes vulpes) in Australia 3 2.1 Topography of Fowlers Gap Station 2.2 The Study area. 28 2.3 The cannon-net. 35 3.1 Overall dietary composition 45 3.2 Seasonal changes in dietary intake 46 3.3 Comparisons of ingestion rates and field abundances for each dietary category. 47 3.4 Comparison of rabbit ingestion rates among paddocks 51 3.5 Dietary composition in relation to season and year 53 3.6 Rabbit ingestion rate in relation to the intake of other dietary categories 55 3.7 Dietary intake and field abundances for each dietary category for Years 1 and 2 61 3.8 Relative field abundance of rabbit in Warrens and Lambing paddocks 3.9 Dietary intake of rabbits and dasyurids with season 3.10 Seasonal variation in diet in Warrens and Lambing paddocks.