Phd Thesis Only Ever Has the Name of One Person Claiming Authorship, but No Phd Is Ever the Work of Just One Person

Human disturbance affects the ecology and population dynamics of the tammar wallaby, Macropus eugenii, on Garden Island, Western Australia

Brian K Chambers BSc. (Hons.)

This thesis is presented for the degree of Doctor of Philosophy of The University of Western Australia 2009

Abstract

Understanding the effect that the disturbance of habitat by humans has on the population dynamics and ecology of wild animals is critical for the management of these populations. By understanding the demographic effects of disturbance the ways in which a population can be managed to increase or decrease its rate of change in size also become apparent. This thesis describes the effect that human disturbance, through the establishment of a large naval base, has had on the population dynamics and ecology of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia.

The disturbance of the environment on the HMAS Stirling Naval Base included the establishment of large areas of irrigated and fertilised couch grass (Cynodon dactylon) that increased and made virtually constant the amount of food available to the tammars in that area. In addition, traffic associated with the naval base resulted in large numbers of tammar wallabies being killed by vehicles. The effects of these disturbances were determined by comparing population dynamics, through vital rates of survival and fecundity and population growth rates, and spatial ecology, through the size of the animals‟ home ranges, in three areas of Garden Island. The three areas were the naval base (highly disturbed), southern bushland (adjacent to the naval base) and the northern bushland (undisturbed).

The tammars on the naval base were in better body condition than those living in the two bushland areas of the island. Males had mean adjusted weights of 4.95 kg (upper and lower s.e. 0.041) on the base and 4.81 kg (upper s.e. 0.055, lower s.e. 0.054) in the northern bushland, compared with 4.63 kg (upper and lower s.e. 0.049; P<0.001) in the southern bushland. Females on the naval base had a mean adjusted body weight of 3.870.038 kg compared with 3.70.10.044 and 3.660.042 kg for the southern and northern bushland (P=0.004). Birth rates were similar in all areas and approached 90% (P=0.201). Weaning rates on the naval base in 2005 and 2006 were 94 and 93% and were not significantly different to the birth rates (P>0.05), while in the southern and northern bushland they were dramatically lower in 2005 at 55 and 27% and 2006 at 65 and 56% respectively (P<0.01). In 2007 the weaning rate was 71% on the naval base, which was significantly lower than the birth rate of 86% (P<0.05), while in the southern

i and northern bushland the weaning rates were not significantly different to the birth rates (P>0.05). These results indicate that when lactating females are placed under physiological stress they are unable to continue lactation, resulting in the death of their pouch young. Habitat modification on the naval base may have allowed the females to cope better with adverse environmental conditions and to be more successful at raising their young.

Over the three years of the study, the population on the naval base had a mean asymptotic rate of change in size () of 1.020.083 (s.e.) per year, which was higher than the population in the southern bushland at 0.920.065 per year and in the northern bushland at 0.930.100 per year. When the impact of road-kills was removed,  increased to 1.150.101 per year on the naval base and 0.960.076 per year in the southern bushland. Fecundity transitions, defined as the product of the rates of birth and pouch-young survival, and adult survival rates were lower in the bushland areas compared with the naval base in two of the three years, which were the main reasons for the lower  estimates.

There were no significant differences in the size of the tammars‟ home ranges between areas with modified or unmodified habitats or between the sexes (P>0.05). In summer the mean size of the home ranges was 3.90.66 ha, which was larger than winter when home ranges were 3.20.54 ha, but this difference failed to reach significance (P=0.058). These results indicate that the modification of the tammars‟ habitat has probably not caused significant changes in the size of the animals‟ home ranges. The size of the home ranges of tammar wallabies is likely to be determined by a complex interaction of many factors, and habitat modification alone has not been sufficient to cause substantial changes.

The results presented in this thesis demonstrate that the disturbance caused by the establishment of the naval base on Garden Island has altered the population dynamics of the tammars wallabies, through increasing in the amount of food available to the tammars and through high numbers of road-kills. These results also demonstrate how gaining detailed knowledge of population dynamics can have direct application to managing the impact of disturbance on populations of wild animals.

ii Contents

Abstract ...... i

Acknowledgements ...... vii

1. General Introduction ...... 1

1.1 Population dynamics ...... 1 1.2 Spatial ecology ...... 2 1.3 Tammar wallabies on Garden Island ...... 2 1.4 Structure of the thesis ...... 5 1.5 Publications ...... 6 1.6 Declaration...... 7

2. Habitat modification affects reproduction in the tammar wallaby (Macropus eugenii) on Garden Island, Western Australia...... 9

2.1 Abstract ...... 10 2.2 Introduction ...... 11 2.3 Materials and Methods ...... 13 2.3.1 Experimental design ...... 13 2.3.2 Study areas ...... 13 2.3.3 Trapping...... 15 2.3.4 Data analysis ...... 16 2.4 Results ...... 18 2.4.1 Body condition ...... 18 2.4.2 Birth and weaning rates ...... 20 2.4.3 Birth schedules ...... 21 2.4.4 Sex of pouch young ...... 23 2.5 Discussion ...... 23

3. Habitat modification and road-kills alter the population dynamics of the tammar wallaby, Macropus eugenii, on Garden Island, Western Australia ...... 29

3.1 Abstract ...... 30 3.2 Introduction ...... 31 3.3 Materials and Methods ...... 33 3.3.1 Experimental design ...... 33

iii 3.3.2 Study areas ...... 33 3.3.3 Mark-recapture study ...... 34 3.3.4 Road-kills ...... 35 3.3.5 Weather and climate data ...... 35 3.3.6 Data analysis ...... 36 3.4 Results ...... 40 3.4.1 Survival and fecundity ...... 40 3.4.2  - The rate of change in size ...... 43 3.4.3 Stable age distributions ...... 44 3.4.4 Perturbation analysis ...... 45 3.4.5 Projections of population size ...... 46 3.5 Discussion ...... 49 3.5.1 Habitat modification ...... 49 3.5.2 Rainfall ...... 50 3.5.3 Road-kills ...... 51 3.5.4 Perturbation analysis ...... 52 3.5.5 Projections of population size ...... 52 3.5.6 Conclusions ...... 53

4. Does habitat modification affect the size of the home ranges of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia? ...... 55

4.1 Abstract ...... 56 4.2 Introduction ...... 57 4.3 Materials and Methods ...... 59 4.3.1 Experimental design ...... 59 4.3.2 Study area ...... 59 4.3.3 Radio tracking ...... 60 4.3.4 Data analysis ...... 62 4.4 Results ...... 63 4.5 Discussion ...... 66

5. Speed limit, verge width and day length are the major factors correlated with the number of road-kills of tammars (Macropus eugenii) on Garden Island, Western Australia...... 69

5.1 Abstract ...... 70 5.2 Introduction ...... 71 5.3 Materials and Methods ...... 73 5.3.1 Experimental design ...... 73 5.3.2 Study area ...... 73

iv 5.3.3 Road-kills...... 74 5.3.4 Spatial variables ...... 75 5.3.5 Temporal variables ...... 76 5.3.6 Data analysis ...... 77 5.4 Results ...... 77 5.4.1 Spatial variables ...... 78 5.4.2 Temporal variables ...... 79 5.5 Discussion ...... 79 5.5.1 Management implications ...... 82

6. General Discussion ...... 85

6.1 Habitat modification ...... 85 6.2 Road-kills...... 88 6.3 The overall effect of disturbance ...... 89 6.4 Future research ...... 90 6.5 Conclusions ...... 91

7. Management recommendations ...... 93

8. References ...... 96

Acknowledgements

The title page of a PhD thesis only ever has the name of one person claiming authorship, but no PhD is ever the work of just one person. There are always many people who each contribute something slightly different to the finished product. This thesis is no different and there are many people that deserve my heartfelt thanks.

To my supervisors Roberta Bencini and Robert Black, my thanks for your assistance with every part of my research work, from planning, to fieldwork, to data analysis and writing. I know without a doubt that I would not have been able to complete this work without you both. Roberta, thank you for your never-ending enthusiasm and ability to find funding from just about anywhere. Bob, thankyou for your meticulous attention to detail and for your patience with my general lack of ability with statistics. Having had the chapters of my thesis reviewed and checked by you gives me a great deal of confidence in their quality.

I would also like to thank the following people who selflessly volunteered to give up sleep to help me with fieldwork: Roberta Bencini Claire Foster Christine Kistner Sally Taylor Dianne Mayberry Rob Creasy Peter Turner Andrew McMillan Travis Murray Chantelle Jackson Ireck Malecki Amy Denholm Penny Hawken Aprille Chadwick Kristine Vesterdorf Morris Prinsloo Scott Carver Harriett Mills Carolina Vinoles Kristin Hunt Daniel Malecki Bob Black Felicity Donaldson Bindhu Holavanahalli Megan Chadwick Cheryl Hetherington Karen Riley Felicia Pereoglou Tara Nababan Danielle Oliver Samantha Blair Sara Peet Lori Kroiss Nicole Willers Melissa Pressman Kaitlyn Height Jessica Cairnes Rachelle Kearney Peter Langlands Vanessa Jackson Donna Sampey Stephanie Robinson Rachael Glasgow Rhiannon Chambers Joshua Quirk Julie Quirk Nicholas Lim Sharron Perks Kylie Robert Paolo Segre I thoroughly enjoyed my fieldwork on Garden Island, and each of these people helped to make that possible.

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I would also like to extend my thanks to Roberta Bencini and Craig MacFarlane for allowing me to use their holiday house in Shoalwater while I was doing fieldwork. Without a comfortable bed to sleep in, I don‟t think I would have survived most of my fieldtrips.

Working on and around the HMAS Stirling naval base required a large amount of support to deal with security arrangements, access to study areas and buildings to work in. Without the help of Joanne Wann, Trevor Smith, Luke Bouwman, Vanessa Jackson, Jackie Nichols, Donna Sampey this research would have been impossible. Trevor, I hope I didn‟t annoy you too much with the mess I continually made in your office. Luke, thanks for not eating all of my TimTams and thank you also for all of the cups of coffee.

I would also like to extend my thanks to Luke Bouwman, Trevor Smith, and the grounds and gardens, and security staff of HMAS Stirling for collecting all of the road- killed tammars for me. Studying road-kills was always going to be a rather unpleasant proposition, but their willingness to get their hands dirty so that I could gather very much needed data was greatly appreciated.

Field based ecological work such as this requires a large amount of money to pay the bills. The Department of Defence and the School of Animal Biology at the University of Western Australia contributed considerable funds for which I am extremely thankful.

The process of writing a thesis like this is not an easy one for me, as I find myself driven slightly mad spending day after day in front of a computer. Distractions were therefore a necessity so that I could avoid the decent into complete madness. I am therefore very grateful for all of the discussions over coffee with Kylie, Scott, Roberta, Harriet and Lotti.

I would also like to thank my family and friends for all of their support throughout my studies. I would like to let you all know that I am going to get a real job now and start paying taxes like the rest of you. You never know, I might even pay off my enormous HECS debt one day.

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Finally, I would like to thank Rhiannon for refusing to let me quit this PhD business and for continually reminding me that having someone to love ensures that there is a lot more to your life than research, wallabies and trying to write a thesis.

1. General Introduction Understanding the changes that occur in populations of wild animals when humans disturb their environment is imperative if we are to manage these changes and reduce the impact of our actions. If disturbance of animals‟ habitat causes changes to extrinsic factors such as predation, food supply or a reduced effect of adverse weather conditions and this results in reduced mortality or increased fecundity of animals, then the rate of change in the size of the population will increase. Conversely, if the disturbance causes changes in factors that increase mortality or reduce fecundity then the rate of change in the size of the population will be reduced (Krebs 2002). Disturbance often results in changes to several extrinsic factors so that the total effect on the population in question may be positive or negative depending on the magnitude of the different effects. This thesis describes such a situation on Garden Island, Western Australia where the construction of a large naval base has resulted in the disturbance of the habitat of a population of tammar wallabies or tammars (Macropus eugenii).

1.1 Population dynamics It can be argued that the population growth rate, or the rate of change in size, is the key unifying variable that links the different aspects of population ecology through its role in forecasting future changes in the size and density of populations (Sibly and Hone 2002). The rate of change in the size of populations is also of central importance in the management of both rare and abundant species of wildlife. The management of abundant species, in particular populations that are deemed to be over-abundant, is focused on reducing the rate of change in the size of the population, to maintain the size and/or density of the population below some predetermined point. The management of populations of rare and/or threatened species is also focused on the rate of change in the size of the population and attempting to increase it, so that the population under management can reach a size where its future is not governed by the fate of individuals, but by the law of averages (Caughley 1994).

The necessity of identifying and alleviating the causes of low or negative population growth rates, or threatening processes, is the cornerstone of successful management of threatened populations (Caughley and Gunn 1996). However, the same general

1 approach can be taken to the management of populations where over-abundance is considered a problem. By identifying and treating the causes of high rates of change in the size of a population, i.e. the cause of high abundance, the size and/or density of the population can be maintained within desired limits. In order to achieve this it is therefore necessary to work within the mechanistic paradigm of population dynamics in order to determine the causes of the high or low rates of change in the size of populations (Krebs 1995, 2002). The mechanistic paradigm tries to answer the question of how do extrinsic factors, such as food supply, predation and weather, and intrinsic factors, such as genetics and physiology, alter the rate of change in the size of populations. However, these mechanisms do not affect the rate of change in the size of a population directly; rather, they act by affecting the vital rates of birth and death. Therefore we also need to consider demography in our analysis of populations to understand fully the mechanisms by which the rate of change in the size of a population is determined (Caswell 2001, Caswell and Fujiwara 2004). The analysis of mechanisms and demography also has direct application to management, as the rates of birth and death can be manipulated even if the root cause of the change in those rates cannot.

1.2 Spatial ecology The extent to which animals move around their environment is usually described by the size and/or shape of their home range, defined as the area over which an animal moves in order to perform its normal activities (Burt 1943). The home range of animals can change significantly as a result of the disturbance of their environment by humans, especially when the disturbance changes the availability of resources or the productivity of the environment (Harrison 1997, Grinder and Krausman 2001, Pearson et al. 2005, Viggers and Hearn 2005, Courtois et al. 2007). The nature of these changes has important ramifications for management, especially where the home ranges of animals include reserve and non-reserve areas, or where the home ranges of animals bring them into conflict with humans.

1.3 Tammar wallabies on Garden Island Garden Island lies approximately five km off the Western Australian coast and hosts the HMAS Stirling Naval Base, which has resulted in approximately 25% of the island being cleared and developed for naval facilities. The remaining undeveloped area of the

2 island is managed as a nature reserve, with limited public access by boat during daylight hours. The limited development on the island presented an opportunity to contrast the ecology and dynamics of populations of tammar wallabies in different areas of the island, with and without the effects of human disturbance. Extrinsic factors such as rainfall, temperature and day length, and intrinsic factors such as genetics and physiology of the tammars were consistent between the disturbed and undisturbed areas of the island, which gave me the opportunity to compare the effect of habitat disturbance on the tammars‟ ecology and population dynamics. The study of the tammars‟ population dynamics also covered three years with three distinct levels of rainfall and winter temperatures, which allowed for the comparison of the effects of the disturbance a under these differing conditions. The tammar wallaby was the only native mammal species present on the island (the introduced house mouse, Mus musculus, was the only other mammal present), which also allowed for the simpler task of describing the dynamics of the populations, without the effects of interspecific competition or predation.

The effect of the disturbance of the environment on Garden Island was considered in terms of population dynamics, through analysis of the vital rates of survival and fecundity and population growth rates (Chapters 2 and 3), and spatial ecology through analysis of the size of the animals‟ home ranges (Chapter 4). The effect of the disturbance was then determined by comparing three areas with different levels of disturbance. These areas were the naval base, which was highly disturbed, the southern bushland adjacent to the base, which was potentially influenced by its proximity to the base, and the northern bushland, which was virtually undisturbed. Detailed descriptions of the study areas are given in Chapters 2, 3 and 4.

The disturbance of the environment on the HMAS Stirling Naval Base had two major components that I felt would impact on the ecology and population dynamics of the tammar wallabies. Firstly, the establishment of large areas of irrigated and fertilised couch grass (Cynodon dactylon) on the ovals, road verges and building surrounds on the naval base had resulted in an increased and constant amount of food being available to the tammars in that area. Secondly, large numbers of tammars were killed by vehicles on the naval base. The increased amount and consistent supply of food available to the tammars on the naval base from the irrigated lawns was expected to result in them being

3 in better condition compared with the animals in the bushland areas of the island. This was then expected to result in higher rates of survival and in them being more successful at rearing their young, especially in years of low rainfall when the amount of food available in the bushland areas would be reduced. The increased rates of survival and weaning on the naval base were expected to result in higher rates of change in size for the population of tammars in that area compared with the populations of tammars in the bushland areas of the island.

The road-kills on the naval base were also expected to affect significantly the dynamics of the population of tammars on the naval base. Between 1994 and 2004, 289±20 (s.e.) tammars were killed each year by vehicles, out of a population estimated at 2172 (95% C.I. 1733 to 2396) individuals (Bradshaw 1988). These road-kills were expected to reduce significantly the rates of survival of tammars on the naval base and also lead to a reduction in the rate of change in the size of the population.

The increased supply of food on the naval base was also expected to result in the tammars in that area having smaller home ranges that those in the bushland areas of the island, as they would not need to move as far to find adequate food. The tammars in the bushland areas were also expected to have significantly larger home ranges in summer and autumn, when food availability is low, compared with winter and spring, when it is high.

Having multiple sites representing the different levels of human disturbance would have been beneficial in this study to provide spatial replication, but unfortunately this was not possible. The naval base study area is the only area on Garden Island where the habitat modification has included the introduction of irrigated lawns, which did not allow for replication of this ‟disturbed‟ site. Replication of the southern bushland, or adjacent to disturbed, and the northern bushland, or undisturbed site, was also not possible as smaller areas of naval infrastructure are found across the island, which would have resulted in some form of habitat modification in all potential replicate sites.

1.4 Structure of the thesis This thesis is presented as a series of stand-alone papers that document how human disturbance, in the form of the presence of the HMAS Stirling Naval Base, has affected the ecology and population dynamics of the tammar wallabies on Garden Island.

Chapter 2 addresses the effect of the increased supply of food on the naval base on the individual animals by analysing their condition. It also shows how this change in condition affected the reproduction and ability of the tammars to raise their young successfully under different environmental conditions.

Chapter 3 considers the effect of the disturbance on the rates of survival and fecundity transitions, defined as the product of birth and weaning rates, and the rates of change in the size of the three populations in different years. Chapter 3 also deals with the effect of the road-kills by comparing rates of survival and rates of change in the size of the base and southern bushland populations with and without the effect of road-kill mortality.

Chapter 4 addresses how the disturbance of the tammars‟ habitat has changed their spatial ecology by comparing the size of the animals‟ home ranges among the three study areas. Chapters 3 and 4 also address how the population of tammars in the southern bushland was affected by its proximity to the naval base. This is achieved by comparing the rate of change in the size of the southern and northern bushland population under the same weather conditions with and without the effect of road-kills in the southern bushland (Chapter 3). Chapter 4 also analyses the home ranges of animals in the southern bushland that lived near the naval base in order to determine if the extra food supply on the naval base affected their spatial ecology.

The results presented in Chapter 3 demonstrate that the rate of road-kills observed in this study was likely to cause a decline in the tammar population on the base and in the southern bushland. Therefore there was a need to reduce the number of tammars being killed by vehicles. Chapter 5 deals with the spatial and temporal factors that were correlated with the numbers of tammars killed on the roads of the island and is intended as a basis for the development of strategies to reduce the number of animals killed by vehicles.

A series of management recommendations are also presented in Chapter 7 as a demonstration of how the type of information gathered in this thesis can be used to inform management decisions to ensure the long-term persistence of populations of wild animals.

The study site descriptions are repeated in each of the chapters, because they are written as stand alone papers. The chapters in this thesis were written as multi-authored papers, and therefore plural rather than singular pronouns are used. The authorship of the chapters is as follows: Chapters 2, 3 and 4 – Brian Chambers and Roberta Bencini Chapter 5 – Brian Chambers, Rebecca Dawson, Joanne Wann and Roberta Bencini To avoid repetition, the references for all chapters are presented as a single list in Chapter 8.

1.5 Publications At the time of submission Chapter 5 has been peer-reviewed and accepted for publication in the book „Macropods: the Biology of Kangaroos, Wallabies and Rat Kangaroos‟ arising from the Australian Mammal Society Symposium, „Macropods, Genome to GIS,‟ held in July 2006. This will be published in 2009 by Surrey Beatty and Sons.

The following conference presentations used data contained in this thesis: Chambers B.K. and Bencini R. (2007). Human disturbance significantly alters the population dynamics of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia. Proceedings of the 20th scientific meeting of the Australasian Wildlife Management Society, Canberra 2-5 December 2007.

Chambers B.K. and Bencini R. (2006). The impact of human disturbance on the population dynamics and ecology of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia. Proceedings of the symposium "Macropods in the 21st century: genome to GIS”. Melbourne, 6-7 July 2006.

Chambers B.K., Dawson R., Wann J. and Bencini R. (2006). Using GIS to determine factors affecting road kills of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia. Proceedings of the symposium "Macropods in the 21st century: genome to GIS”. Melbourne, 6-7 July 2006.

1.6 Declaration All experimental work, data analysis and interpretation presented in this thesis are the work of the candidate except for the retrieval of GIS data in Chapter 5, which was done by Rebecca Dawson. Joanne Wann is also included as a co-author of Chapter 5 as she provided us with the GIS data used in the study and extensive support in accessing the naval base to gather data. Roberta Bencini and Robert Black provided supervision, assistance with experimental design and data analysis and extensive comments on drafts of the chapters. All co-authors have granted permission for these papers to be included in this thesis.

The use of animals was authorised by The University of Western Australia‟s Animal Ethics Committee (Approval RA/3/100/376) and by the Western Australian Department of Environment and Conservation (License SF004951).

All photographs used in this thesis were taken by Brian Chambers

Signed:

Brian Chambers Roberta Bencini Candidate Coordinating Supervisor

2. Habitat modification affects reproduction in the tammar wallaby (Macropus eugenii) on Garden Island, Western Australia

2.1 Abstract We compared the body condition and birth and weaning rates of tammar wallabies (Macropus eugenii) at three sites with differing levels of human disturbance and habitat modification on Garden Island, Western Australia, between May 2005 and November 2007. Due to the presence of irrigated and fertilised lawns that provide year-round high quality food, we expected that the animals in the modified habitat on the HMAS Stirling naval base would be in better condition than those in an area of adjacent bushland and an area of undisturbed bushland, hence referred to as the southern and northern bushland areas. We also expected that in years of low rainfall there would be high mortality of pouch young in the undisturbed habitats due to low food availability.

Tammars on the naval base were in better condition than those living in two bushland areas of the island. Males had mean adjusted weights of 4.95 kg (upper and lower s.e. 0.041) on the base and 4.81 kg (upper s.e. 0.055, lower s.e. 0.054) in the northern bushland, which were significantly higher than those in the southern bushland at 4.63 kg (upper and lower s.e. 0.049; P<0.001). Females on the naval base were in significantly better condition than those in the two bushland areas with a mean adjusted body weight of 3.870.038 kg compared with 3.70.10.044 and 3.660.042 kg for the southern and northern bushland (P=0.004). Birth rates were similar in all areas and were close to the 90% rate that we expected (P=0.201). Weaning rates on the naval base in 2005 and 2006 were 94 and 93% and were not significantly different to the birth rates (P>0.05), while in the southern and northern bushland the weaning rates were dramatically lower in 2005 at 27 and 55% and 2006 at 56 and 65% respectively (P<0.01). In 2007 the weaning rate was 71% on the naval base, which was significantly lower than the birth rate of 86%, while in the southern and northern bushland the weaning rates were 86 and 83%, and were not significantly different to the birth rates of 91 and 96% (P>0.05). When lactating females are placed under physiological stress, they appear to be unable to continue lactation, resulting in the death of their pouch young. Habitat modification resulted in the females being in better condition and this may have allowed them to cope better with adverse conditions and to be more successful at raising their young to weaning.

2.2 Introduction The disturbance of natural habitat by humans can result in changes in the ecology and reproduction of wild animals that directly affect the rate of change in size and therefore the fate of that population (Sibly and Hone 2002). Understanding these changes in ecology and reproduction is therefore important to manage populations that have been affected by our actions (Krebs 1995). One way in which human disturbance can affect populations of animals is through changes to the availability of food, which can then, in turn, affect the condition of animals and rates of reproduction and survival. In many species of large herbivores, rates of adult survival are relatively constant, but recruitment tends to be much more variable (Choquenot 1991, Gaillard et al. 1998). In Field C ode Changed macropods, Australia‟s largest native herbivores, variation in rates of survival and F orm atted: F on t: I talic recruitment have been shown to be linked with body condition, which is determined by the availability of food (Shepherd 1987). We investigated the effect that habitat Field C ode Changed modification had on body condition, reproductive success and pouch young survival in a population of tammar wallabies (Macropus eugenii), where their habitat had been modified by the clearing of native vegetation and the introduction of large areas of irrigated grasses.

The numbers and geographic range of the tammar wallaby have declined dramatically on the Australian mainland since European settlement as a result of habitat loss and predation by the European red fox (Vulpes vulpes, Kinnear et al. 2002) but it has continued to persist on predator-free, offshore islands. On Kangaroo Island, South Australia, the clearing of large areas of the island for agriculture, and the lack of mammalian predators has resulted in the number of tammars increasing to the point where they are considered a pest and are culled in their thousands (Wright and Stott 1999). On Garden Island, Western Australia, habitat modification that has occurred from the development of the HMAS Stirling Naval base provided us with the opportunity to investigate if the modification of the tammars‟ habitat had resulted in changes to their ecology and reproduction.

The development of the naval base, which began in the early 1970s, has resulted in the clearing of ~25% of the island and the construction of buildings, roads, sports ovals and other recreational facilities. The sports ovals, recreational areas and many of the road verges on the naval base were planted with couch grass (Cynodon dactylon) and were

11 irrigated and fertilised. The introduction of these lawns reduced the seasonal variation in food supply on the naval base and the tammars there obtained 85% of their diet from these lawns (McMillan 2006). By contrast, the tammars in the bushland areas of the island relied mainly on permanently green shrub, Acacia rostellifera, and winter perennials, Asparagus asparagoides, Trachyandra divaricata, Asphodelus fistulosus and Austrostipa flavescens, for their food (Bell et al. 1987, McMillan 2006). The amount of food available varied with season and therefore the condition of the tammars in the bushland areas of the island also fluctuated seasonally: animals reached their lowest condition in late autumn/early winter before improving in condition as winter rains stimulated plant growth (Bradshaw 1988). The body condition indices used to draw these conclusions were based on the ratio of body weight to the length of the tibia (Bakker and Main 1980). This is not a statistically valid method to correct weight for body size, as it relies on the incorrect assumption that an isometric relationship exists between body weight and body size, in this case represented by the length of the tibia (Packard and Boardman 1999). Despite this problem, we expected that using a more appropriate statistical method we would still find seasonal changes similar to those reported by Bradshaw (1988). We also expected that the tammars on the naval base would not experience the same changes in body condition as those in the bushland areas and that they would be in better condition, especially in autumn/early winter, due to the increased amount food available from the irrigated lawns.

Tammar wallabies on Kangaroo Island, South Australia had high birth rates (~90%) and similarly high weaning rates unless seasonal conditions were particularly harsh (Inns 1980). On Garden Island birth rates were as high, but weaning rates were considerably lower (Bradshaw 1988). Bradshaw (1988) combined the data from five years of trapping to produce these estimates; therefore determining the effect of seasonal conditions in different years was not possible. Researchers of other macropod species suggested that the growth of pouch young is an all-or-none phenomenon and that under severe drought conditions many pouch young do not survive (Sadleir 1963, Sharman et al. 1964, Newsome 1965). We therefore expected that 90% of female tammars would give birth in both the disturbed and undisturbed areas of the island but that weaning rates would be lower than birth rates in the undisturbed areas in years with low rainfall.

2.3 Materials and Methods 2.3.1 Experimental design We tested our hypotheses by trapping tammar wallabies in three different areas of Garden Island between April 2005 and November 2007. We collected data on the condition of the animals, the sex and age of pouch young and the proportion of females that gave birth and those that successfully weaned their young each year.

2.3.2 Study areas Garden Island is located approximately five km off the West Australian coast approximately 35 km south west of the city of Perth (115o40‟E, 32o16‟S). The long- term mean annual rainfall is 757 mm with the majority of this rainfall (~80%) falling between May and September (Australian Bureau of Meteorology). The tammar wallaby is the only native mammal present on the island and the only other mammal present is the introduced house mouse (Mus musculus, Brooker 1992).

The study was conducted in three areas of Garden Island with different levels of human disturbance. The „base‟ was significantly disturbed with much of the native vegetation replaced by buildings, roads and irrigated lawns and roads, footpaths and car parks artificially lit at night (Figure 2.1). The „northern bushland‟ was at the far northern end of the island approximately 5.6 km from the base and the disturbance here was minimal, with native vegetation covering the whole area except for a single vehicle track and a 30 m wide, cleared firebreak at the southern end (Figure 2.1). There was no naval activity in this area and the only public access was by boat during daylight, with the majority of visitors confining their activities to the beaches (T. Smith pers. comm.). The „southern bushland‟ was directly adjacent to the naval base and had vegetation cover similar to that of the northern bushland (Figure 2.1). It was separated from the base area by a three-metre high chain link fence, but was potentially influenced by its close proximity to the base as the animals could move to and from the base through gaps under the fence.

13 infrastructure are found across the island, which would have resulted in some form of habitat modification in all potential replicate sites for the bushland areas (Figure 2.1).

Figure 2.1. Location of Garden Island, Western Australia (115o40‟E, 32o16‟S) and the three study sites, base, southern bushland and northern bushland, characterised by different levels of human disturbance. Shaded areas represent areas of naval infrastructure where significant habitat modification had occurred.

Annual rainfall over the three years of the study varied greatly: 2005 was a very wet year with 849 mm of rain; 2006 was very dry with 456 mm and 2007 was intermediate with 655 mm of rainfall. The distribution of this rainfall also varied greatly with 53% (448 mm) of the annual rainfall in 2005 occurring in May and June, compared with 13% (61 mm) and 22% (147 mm) falling in the same months in 2006 and 2007 respectively (Figure 2.2). The mean minimum monthly temperatures over winter (June-August) also varied considerably over the three years as 2005 and 2006 were more than 1 oC lower at

11.30.33 oC and 11.10.65 oC respectively, compared with 2007 at 12.30.21 oC (mean±s.e., Figure 2.2).

Figure 2.2. Total monthly rainfall and minimum () and maximum () mean monthly temperatures for Garden Island for the years 2005 to 2007 (Australian Bureau of Meteorology). * = Trapping event.

2.3.3 Trapping Tammars were captured in the three study areas 11 times between April 2005 and November 2007 using “Thomas” soft-wall traps made from shade cloth stretched over a steel frame (450x450x800 mm, Sheffield Wire Works, Welshpool, Western Australia). Traps were baited with a mixture of rolled lupins, rolled oats and sunflower seeds flavoured with molasses (Kangaroo Muesli, Thompson & Redwood Produce Supplies, Upper Swan, Western Australia). Trapping was done in April, July, September and November 2005, February, May, August and November 2006 and February, June and

November 2007. Thirty traps were set in each of the three study areas in a grid of approximately 200 m. In the southern and northern bushland trapping was done for three nights in each trapping session and traps were checked twice each night. On the naval base traps were initially set for three nights and were checked three times each night. Traps were checked more frequently in this area as we found that the tammars were present at higher densities and took less time to enter the traps. After the first four trapping sessions some male tammars on the naval base became „trap happy‟ and excluded other animals from the traps. To overcome this problem we split the trapping area into two halves and doubled the number of trap sites. The two halves were thereafter trapped separately for two nights in each trapping session.

The first time animals were captured they were sedated using a mixture of ketamine (10 mg/kg; Ketamil, Troy Laboratories Pty Ltd, Smithfield, New South Wales) and xylazine (1.25 mg/kg; Xylazil, Troy Laboratories Pty Ltd, Smithfield, New South Wales) given intramuscularly. They were then aged by molar eruption according to Inns (1982) and were given a numbered, metal ear-tag in each ear. We recorded the sex, weight, length of the long pes and ear tag numbers of all tammars captured. For females, the presence, sex and pes length of a pouch young or the presence of an elongated teat was recorded. All animals were released at their site of capture.

2.3.4 Data analysis Body condition of the tammars at the three study sites was compared by Analysis of Covariance (ANCOVA). Body weight was the dependent variable and long pes length was used as the covariate to adjust all weights to a mean pes length (144.3 mm for males and 135.0 mm for females), therefore removing the effect of skeletal size on body weight. The mean adjusted body weight was then used as a measure of the condition of the animals. Study area and trapping session were the independent variables and all two and three way interactions were included in the analysis. The body weights of males were log transformed, as the untransformed data did not conform to the assumption of homogeneous slopes as assessed by the interactions between study area, trapping session and pes length. Data from individual animals were only used once in the analysis to ensure independence and data from animals less than one year old were excluded. Generally, data from animals were included at the trapping session when they were first captured. However, when some trapping sessions had low numbers of

16 animals captured for the first time, randomly selected recaptured animals were included at that trapping session and removed from the data when they were first captured. This procedure meant that the minimum sample size for each trapping session was seven individuals and that no individual was included twice. The ANCOVA models were reduced by removing the interactions between pes length, study area and trapping session where possible according to Hendrix et al. (1982). For both male and females, the models were reduced by removing the pes length x study area, pes length x trapping session and pes length x study area x trapping session interactions. Significant effects of individual factors were further analysed using a Tukey‟s HSD. The least square mean weights of the males and their standard errors were back transformed from log(weight) to weight.

Birth rates were estimated as the highest proportion of females that were captured with a pouch young or an elongated teat at any time during each breeding season (February to November). The presence of an elongated teat was taken as evidence that the animal had recently weaned a pouch young and weaning rates were calculated based on the proportion of females that had an elongated teat in November of each year. Birth rates were compared with an expected rate of 90% using a goodness-of-fit G-test and weaning rates were compared with birth rates using a contingency G-test, both with William‟s correction for continuity (Sokal and Rolf 1995). Birth rates of one-year-old females were calculated based on all females of this age captured with a pouch young between May and September or an elongated teat in November. The birth rates of this age class were then compared among the three study areas using a 2x3 contingency table (Sokal and Rolf 1995). The sex ratios of pouch young in the three study areas were calculated based on all individual pouch young recorded over each breeding season. These ratios were then compared with an assumed 1:1 sex ratio using a goodness-of-fit G-test with William‟s correction for continuity.

Birth schedules were calculated for the population in each of the three study areas by combining the data from all pouch young captured over the three years of the study. The ages of the pouch young were determined from ageing tables based on pes length (Poole et al. 1991) and their estimated age was then subtracted from the date of capture to give an estimated birth date. The schedules were divided into fortnightly intervals starting from the summer solstice (December 22nd) and the schedules for the different

study areas were then compared using Kolmogorov-Smirnov two-sample tests (Sokal and Rolf 1995).

We caught 836 male and 419 female tammars over the course of the study, of which 16 females were less than one year old. The distribution of these animals between the three study areas is shown in Table 2.1.

Table 2.1. The total number of male and female tammar wallabies captured in the three study areas on Garden Island between May 2005 and November 2007. Males Females Total Study Area Individuals Recaptures Individuals Recaptures Individuals Captures Base 377 857 169 115 546 1518 Southern Bushland 234 596 117 142 351 1089 Northern Bushland 225 638 133 199 358 1195 Total 836 2091 419 456 1255 3802

2.4 Results 2.4.1 Body condition The males on the base and in the northern bushland had mean adjusted weights of 4.95 kg (upper and lower s.e. 0.041) and 4.81 kg (upper s.e. 0.055, lower s.e. 0.054) over the entire study period, which was greater than those in the southern bushland at 4.63 kg (upper and lower s.e. 0.049, ANCOVA, df=2,774, F=6.62, P<0.001). The males in all study areas were in significantly better condition in late spring (November 2005 and 2006) compared with late autumn/early winter (May 2006 and June 2005 and 2007; df=10,774, F=12.38, P<0.001; Figure 2.3). There was also a significant fall in the condition of the males between November 2005 and February 2006 (P<0.05). The males in all three study areas had similar changes in condition as there was no significant season by study area interaction (df=20,774, F=1.27, P=0.190; Figure 2.3).

Figure 2.3. Mean body weight ±s.e., adjusted to a mean pes length of 144.3 mm by ANCOVA, of male tammar wallabies captured in the base (●), southern bushland (■) and northern bushland (▲) study areas on Garden Island between May 2005 and November 2007.

The females on the naval base were in significantly better condition than those in the two bushland areas with a mean adjusted body weight of 3.870.038 kg compared with 3.70.10.044 and 3.660.042 kg for the southern and northern bushland areas (ANCOVA, df=2,369, F=7.90, P=0.004). The differences between trapping sessions were close to reaching significance (df=10,369, F=1.74, P=0.071) mostly due to a large fall in condition between April and September 2005 (Figure 2.4). This reduction was due to the condition of the females in the southern bushland area falling by 806 g from a mean adjusted weight of 4.160.160 kg in April 2005 to 3.350.160 kg in September 2005. Over the same period, the mean adjusted weight of the females in the northern bushland and the base fell by 23 and 101 g respectively (Figure 2.4). The changes in condition were similar between the three sites as the interaction between study area and trapping session was not significant (df=20,369, F=1.27, P=0.199, Figure 2.4).

Figure 2.4. Mean body weight, adjusted to a mean pes length of 135.0 mm by ANCOVA, of female tammar wallabies captured in the base (●), southern bushland (■) and northern bushland (▲) study areas on Garden Island between May 2005 and November 2007.

2.4.2 Birth and weaning rates The birth rates for all three study areas in all years were not significantly different from the 90% rate that we expected (df=1, maximum G=1.637, P=0.201; Table 2.2). The weaning rates were significantly lower than the birth rates in the southern and northern bushland areas in 2005 and 2006 (df=1 minimum G=9.53, P<0.01, Table 2.2), but they were not significantly different in 2007 (df=1 maximum G=1.68, P>0.05, Table 2.2). On the base the weaning rate was significantly lower than the birth rate in 2007 only (df=1, G=9.342, P=0.002, Table 2.2).

Birth rates for one-year-old females were significantly higher on the base, at 50% (n=26) and the southern bushland, at 60% (n=15), compared with 15% in the northern bushland (n=20, df=2, 2=8.67, P=0.013). Of the one-year old females that were known to have given birth the smallest animal weighed 1800 g.

Table 2.2. Birth and weaning rates for tammar wallabies in the three study areas on Garden Island over the 2005, 2006 and 2007 breeding seasons. *=weaning rate significantly lower than birth rate (P<0.01). Birth Weaning Year Study Area Rate (%) n Rate (%) n Base 94 17 94 17 2005 Southern Bushland* 100 8 55 11 Northern Bushland* 75 8 27 26 Base 93 30 93 27 2006 Southern Bushland* 96 28 65 17 Northern Bushland* 87 30 56 30 Base* 86 29 71 46 2007 Southern Bushland 91 35 86 28 Northern Bushland 96 42 83 23

2.4.3 Birth schedules The births in all three study areas had a peak in late January, but the births on the naval base also had a second, smaller peak between the 13th and 27th of April (Figure 2.5). The distribution of births was significantly different on the base compared with both the southern and northern bushland (Kolmogorov-Smirnov two-sample test; southern - D=0.275, P<0.05, northern - D=0.215, P<0.05, Figure 2.5), but there was no significant difference between the two bushland areas (D=0.060, P>0.05). The median birth date of all pouch young from the naval base was February 20th, which was later than the st rd northern and southern bushland at February 1 and 3 .

Figure 2.5. Birth schedules for tammar wallabies on the (a) base (n=92), and in (b) southern bushland (n=118) and (c) northern bushland (n=116) study areas of Garden Island, Western Australia. Data pooled from 2005, 2006 and 2007 breeding seasons.

2.4.4 Sex of pouch young The proportion of male pouch young varied from 43 to 64%, but the sex ratios were not different from parity in any of the three breeding seasons or in any of the study areas (P>0.05, Table 2.3). The overall proportion of male pouch young captured in each of the three study areas was between 51 and 54% and was also not significantly different from parity (base: df=1, G=0.64, P=0.425, southern bushland: df=1, G=0.77, P=0.381, northern bushland: df=1, G=0.04. P=0.843, Table 2.3).

Table 2.3. Percentage of male tammar wallaby pouch young recorded in the three study areas on Garden Island in the 2005, 2006 and 2007 breeding seasons. Southern Northern Base Bushland Bushland Total Year % Male n % Male n % Male n % Male n 2005 64 28 57 28 61 23 61 79 2006 43 40 62 37 43 46 49 123 2007 59 32 45 40 54 33 52 105 Total 54 100 54 105 51 102 53 307

2.5 Discussion Our results supported the hypothesis that tammars on the naval base would be in better condition than those in the southern bushland. The females on the base were also in better condition than those in the northern bushland, but the males were not. The changes in the condition of the tammars between seasons were similar to those reported by Bradshaw (1988) with the tammars losing condition over late summer and autumn to reach a low point in early winter before increasing to a peak in late spring. The seasonal changes in condition were more pronounced in males than females. This was likely a result of males being primarily influenced by seasonal changes in food availability, where the condition of the females would also be influenced by the demands of lactation. This would reduce the ability of females to quickly improve their body condition in late winter and early spring when the demands of lactation are the highest (Green et al. 1980).

The large decline in the condition of the females in the southern bushland between April and September 2005 may have been the result of the very wet and cold winter months. Over the same period the condition of the females on the base was virtually unchanged as was the condition of those in the northern bushland. While the females in the

23 northern bushland did not change in condition over the winter of 2005, their condition was similar to that of tammars living in the southern bushland by September of that year. Similar changes in the condition of the females in the bushland areas were found between February and September 2006, which was probably the result of low plant growth due to low rainfall. Over the same periods the condition of the females on the naval base either improved or fell only slightly. This shows that the increased food supply on the naval base allowed the females there to maintain good body condition over late autumn and winter, when the animals in the bushland could not.

Birth rates were not significantly different from the 90% that we expected in the each of the three breeding seasons, regardless of the seasonal conditions. However, the weaning rates were significantly lower than the birth rates in the bushland in 2005 and 2006, but not in 2007. 2005 was a very wet year, which should have increased plant growth and therefore food availability, but the combination of high rainfall and low temperatures may have placed the tammars under physiological stress resulting in some females being unable to continue lactating and therefore losing their pouch young. The females in the northern bushland were in poor condition coming into winter and the condition of those in the southern bushland fell considerably over winter, which shows that they were having difficulty coping with the conditions. In 2006, very low rainfall would have resulted in less plant growth and therefore less food for the tammars in the bushland areas of the island. The combination of the lack of food and low temperatures is probably the reason for the lower weaning rates in 2006 as some females would not have been able to cope with the demands of lactation and would have lost their pouch young as a result. In 2007, birth and weaning rates were not significantly different, which was probably due to the rainfall being closer to the long term mean and winter temperatures being higher, which would have resulted in greater plant growth and the females being able to cope better with the demands of lactation. The condition data support this assertion as the female tammars in the bushland did not lose condition over the 2007 winter, but they did in 2005 and 2006. These results suggest that the tammar wallabies on Garden Island are adapted to breed most successfully in the conditions that occur most frequently on the island, i.e. those close to the long term climatic mean.

In 2005 and 2006, the weaning rates were significantly higher on the naval base compared with those in the bushland areas. This suggests that the habitat modification

24 on the naval base gave the females in that area a better chance of coping with the adverse conditions. We suggest that the increased supply of food on the naval base allowed the females there to cope better with the demands of lactation under the difficult conditions. The condition data support this assertion, as the females on the naval base were in better condition than those in the bushland at the end of winter in both of these years. In 2007, the weaning rates in the bushland areas were higher than on the naval base, which suggests that the extra food on the naval base is an advantage only in very wet, or very dry years.

The lower weaning rates on the naval base in 2007 may be due to pouch young dying after being ejected by their mothers. Female macropods are known to eject their pouch young when pursued (Ealey 1963, Low 1978) and some female tammars are therefore likely to eject pouch young as the result of stressful encounters with people or predators. No mammalian predators have established populations on Garden Island and domestic animals are not permitted; however, some naval personnel reported seeing a fox near the base in May 2007 (L. Bouwman pers. comm.). This sighting was not confirmed, but if a fox was present this may account for some loss of pouch young and therefore the lower weaning rate in 2007.

The proportion of one-year-old females that gave birth was significantly higher on the naval base and in the southern bushland than in the northern bushland. This may be a result of the increased food supply on the base allowing the females in that area to grow faster and to enter puberty sooner than those in the northern bushland. The newly weaned females from the southern bushland may also have been accessing some of the lawns on the naval base, resulting in growth rates similar to females resident in that area (Chapter 4). As tammar wallabies must reach a minimum weight of approximately 1500 g before they go through puberty (Williams et al. 1998) a greater supply of food would result in more females reaching this weight within the first few months after weaning and therefore breeding as one year olds. Lesser food availability over summer in the northern bushland may have resulted in the females in that area taking longer to reach this minimum weight, resulting in fewer one-year-old females breeding. While this could not be tested in this study as very few newly weaned females were caught between November and February, it is consistent with the results of Newsome (1965), who found that female red kangaroos reached sexual maturity on average 6.241.26

(std. dev.) months later in drought years compared with non drought years. A similar pattern has also been found in water voles, Arvicola terrestris, where increased forage availability resulted in a animals reaching sexual maturity at an earlier age (Moorhouse et al. 2008)

The distribution of birth dates of pouch young was significantly different on the naval base and the median birth date was 17 to 19 days later compared with the bushland areas. This may be a result of artificial lighting on the base affecting the reactivation of delayed blastocysts. Tammars reactivate delayed blastocysts as a response to the shortening day length after the summer solstice (Sadlier and Tyndale-Biscoe 1977, Hinds and den Ottolander 1983). It is therefore possible that artificial lighting on the naval base may affect the tammars‟ ability to detect the reducing day length, thereby delaying the reactivation of blastocysts and resulting in a more protracted period of births compared with the bushland areas.

The proportion of male pouch young varied between 43% on the base and in the northern bushland in 2006 and 64% on the naval base in 2005. These changes in the sex ratios of offspring may be related to changes in the condition of females at the time of conception (Sunnucks and Taylor 1997, Cameron 2004). Since the tammar wallaby has 12 months of embryonic diapause, the only comparison possible between condition at conception and sex of offspring from our data is for those young conceived in early 2006 and born in 2007. Between November 2005 and February 2006 the condition of the females on the base and in the northern bushland improved or remained constant whilst over the same period the condition of those in the southern bushland fell. The offspring conceived in early 2006 and born in 2007 were 59% and 54% male in the base and northern bushland and 45% male in the southern bushland. This trend is in the direction predicted by the Trivers-Willard hypothesis that females in better condition will preferentially give birth to the sex with the greatest variation in reproductive success, i.e. males in polygynous species (Trivers and Willard 1973).

The results from our study clearly demonstrate that habitat modification associated with the HMAS Stirling naval base has significantly altered some aspects of the reproduction of the population of tammar wallabies. The modification of the tammars‟ habitat on the naval base has resulted in greater success at rearing pouch young under adverse

26 conditions and greater variation in birth dates compared with the bushland areas of the island. These results also suggest that the potential for increase in the size of the population of tammars is greater on the naval base compared with the bushland areas of the island.

Our results also suggest that increased reproductive success is likely to be a major contributing factor to the increase in size of other macropod populations that have occurred because of the clearing of land and the establishment of pastures for agriculture (Pople and Grigg 1999). Methods that reduce reproductive success, such as surgical sterilisation, immunocontraception and hormonal control, may therefore be useful tools to manage these populations.

3. Habitat modification and road-kills alter the population dynamics of the tammar wallaby, Macropus eugenii, on Garden Island, Western Australia

3.1 Abstract The establishment of the HMAS Stirling naval base on Garden Island, Western Australia in the 1970s included the replacement of large areas of native vegetation with fertilised and irrigated couch grass (Cynodon dactylon) lawns and the construction of a causeway to allow vehicle access, resulting in a large numbers of road-kills of tammar wallabies (Macropus eugenii). We tested the hypothesis that the extra supply of food would increase the rate of change in size of the tammar wallaby population () by increasing fecundity transitions (defined as the product of birth and weaning rates) and rates of survival of young-adult and adult animals. We also expected that the large numbers of road-kills would reduce the  of the population on the naval base. Over the three years of the study, the population on the naval base had a mean asymptotic rate of change in size () of 1.020.083 (s.e.) per year which was higher than the population in the adjacent bushland at 0.920.065 per year and the undisturbed bushland at 0.930.100 per year. When the impact of road-kills was removed,  increased to 1.150.101 per year on the naval base and 0.960.076 per year in the bushland adjacent to the naval base. Fecundity transitions and adult survival rates were lower in the bushland areas compared with the naval base in two of the three years, which were the main reasons for the lower  estimates. Elasticity analysis suggests that management strategies aimed at altering the rate of change in the size of the tammar populations should focus on changing the rates of adult survival and the fecundity transitions as these had the greatest impact on .

3.2 Introduction Macropods in Australia have experienced a wide range of responses to human disturbance. Some species, such as the crescent nailtail wallaby (Onychogalea lunata) and central hare-wallaby (Lagorchestes asomatus), have been driven to extinction and others, such as the bridled nailtail wallaby (Onychogalea fraenata) and black-footed rock-wallaby (Petrogale lateralis), have dramatically reduced in numbers and geographic range (Johnson et al. 1989). Others, such as the red (Macropus rufus) and western and eastern grey kangaroos (Macropus fuliginosus and Macropus giganteus), have greatly increased in numbers and are now culled in their millions because they are considered pests or exploitable resources (Pople and Grigg 1999). The tammar wallaby (Macropus eugenii) has been able to take advantage of the modification of its habitat, but only in the absence of introduced predators (Wright and Stott 1999, Kinnear et al. 2002). On Kangaroo Island, South Australia, the replacement of native bushland with pastures and agricultural crops resulted in a dramatic increase in the size of the tammar population to the point where approximately 30-40,000 were culled by land-holders each year (Wright and Stott 1999). In contrast to this, the species went extinct on the South Australian mainland, and on the Western Australian mainland it was reduced to a small number of isolated populations due to habitat loss and fragmentation, and predation by the European red fox (Vulpes vulpes, Taylor and Cooper 1999, Kinnear et al. 2002).

On Garden Island, Western Australia, an existing population of tammar wallabies persisted in good numbers, possibly due to the absence of feral predators (Bradshaw 1988). The island also hosts the HMAS Stirling Naval Base, which was established in the 1970s and covers approximately 25% of the island. Part of the development of the naval base included the replacement of large areas of native vegetation with irrigated and fertilised couch grass (Cynodon dactylon) lawns and sporting ovals. These provided the animals in the developed areas with an abundant supply of food all year round. Dietary studies confirmed that the tammars in these developed areas rely on the lawns for ~85 % of their diet (McMillan 2006). Given that population growth rates increase in proportion to the amount of food available per individual (Sibly and Hone 2002), we expected that the rate of change in the size of the tammar population in this modified habitat would be higher than for the populations in the bushland areas of the island.

In unmodified habitat and in the absence of mammalian predators, rainfall has a major impact on the survival of adult tammar wallabies and on the rate of change in the size of their populations (Inns 1980). In years of low rainfall, reduced growth of plants resulted in reduced rate of survival of adult tammars on Kangaroo Island, while the survival of juveniles was also reduced, but not as much (Inns 1980). Similar patterns of reduced survival and lower rates of increase during drought have been found in bridled nailtail wallabies (Fisher et al. 2000, Fisher et al. 2001), and in red, western and eastern grey kangaroos (Caughley et al. 1979, Caughley et al. 1984, Bayliss 1985b, a, Caughley et al. 1985, Cairns and Grigg 1993). In contrast to the tammar wallabies on the naval base on Garden Island, those in the undisturbed bushland ate the permanently green shrub Acacia rostellifera and the non-native winter perennials Asparagus asparagoides, Trachyandra divaricata and Asphodelus fistulosus, and the native winter perennial Austrostipa flavescens (Bell et al. 1987, McMillan 2006). The growth of these plants and therefore the amount of food available to these animals varies with rainfall. We therefore expected that tammar wallaby populations in the undeveloped areas of Garden Island would have significantly lower rates of change in size in years with below average rainfall because of lower survival rates of adults and juveniles.

In addition to the modification of the tammars‟ habitat on Garden Island, the movement of large numbers of vehicles resulted in many tammars being killed on the island‟s roads. Between 1994 and 2004 289±20 (s.e.) tammar wallabies were killed by vehicles each year out of a population, estimated at 2172 individuals from spotlight counts, (95% C.I. 1733, 2396, Bradshaw 1988). On the main area of the naval base alone the rate of road-kills between 2000 and 2004 was 3.50.31 deaths/km/month (means.e.) which is the highest rate recorded in Australia (Chambers et al. 2008). Road-kills can affect the rate of change and the dynamics of a population, especially if the rate of deaths is greater than the population can sustain (Jones 2000) or when the road-kills are biased towards some part of the population (Coulson 1997, Gibbs and Shriver 2002, Steen and Gibbs 2004, Aresco 2005, Gibbs and Steen 2005, Steen et al. 2006). Given that the majority of these road deaths occurred in the southern part of the island where the naval facilities are located we expected to find that the high rate of road-kills would reduce the rate of change in size of the tammar populations in that area.

3.3 Materials and Methods 3.3.1 Experimental design To test our hypotheses we conducted a mark-recapture study in three different areas of Garden Island with three different levels of disturbance. We then estimated rates of survival, with and without road-kills, and fecundity transitions and modelled the changes in the size of the populations in the different areas using stage-based matrix modelling.

3.3.2 Study areas Three study areas with three different levels of human disturbance were selected on Garden Island. The „base‟ was directly and significantly disturbed with approximately 40% of the native vegetation cleared and replaced with buildings, roads and irrigated lawns (Figure 3.1). The „southern bushland‟ was directly adjacent to the naval base and was indirectly disturbed as the animals could move to and from the base through gaps under the fence (Figure 3.1). The „northern bushland‟ was at the far northern end of the island approximately 5.6 km from the base and southern bushland (Figure 3.1). The disturbance in this area was minimal: the native vegetation was all present except for a single vehicle track and a 30 m wide firebreak that was cleared at the southern end of the area. There was no naval activity and the only public access was by boat during daylight, with the majority of visitors confining their activities to the beaches (T. Smith pers. comm.).

Having multiple sites representing the different levels of human disturbance would have been beneficial in this study to provide spatial replication, but unfortunately this was not possible. The naval base study area is the only area on Garden Island where the habitat modification has included the introduction of irrigated lawns and smaller areas of naval infrastructure are found across the island, which would have resulted in some form of habitat modification in all potential replicate sites for the bushland areas (Figure 2.1).

Figure 3.1 Location of Garden Island, Western Australia (115o40‟E, 32o16‟S) and the three study sites, base, southern bushland and northern bushland. Shaded areas represent areas of naval infrastructure where significant habitat modification had occurred.

3.3.3 Mark-recapture study The mark recapture study was conducted from April 2005 to November 2007. Animals were trapped 11 times over the study period in April, July, September and November 2005, February, May, August and November 2006 and February, June and November 2007. Tammars were caught using „Thomas‟ soft-wall traps made from shade cloth stretched over a steel frame (450x450x800 mm, Sheffield Wire Works, Welshpool, Western Australia). Traps were baited with a mixture of rolled lupins, rolled oats and sunflower seeds, flavoured with molasses (Kangaroo Muesli, Thompson & Redwood Produce Supplies, Upper Swan, Western Australia). Thirty traps were set over each of the three study areas in a grid at intervals of approximately 200 m. In the southern and

34 northern bushland trapping was done for three nights in each trapping period and traps were checked twice each night. On the naval base traps were initially set for three nights and were checked three times each night. Traps were checked more frequently on the base as the tammars were present at higher densities and took less time to enter the traps. After the first four trapping sessions some of the male tammars on the base became „trap happy‟ and excluded other animals from the traps. To overcome this problem we split the trapping area into two halves and doubled the number of trap sites. The two halves were thereafter trapped separately for two nights in each trapping session.

The first time animals were captured they were sedated using a mixture of 10 mg/kg of Ketamine (Ketamil, Troy Laboratories, Smithfield, New South Wales) and 1.25 mg/kg Xylazine (Xylazil, Troy Laboratories, Smithfield, New South Wales) given intramuscularly. Tammars were individually identified using numbered metal ear-tags, which were recorded for each capture along with the animal‟s sex, weight and pes length. For females, the presence and sex of a pouch young or the presence of an elongated teat was recorded. They were then aged by molar eruption according to Inns (1982) and were given an ear-tag in each ear. They were then held for two to three hours to allow them to recover from the sedation before being released at the site of capture.

3.3.4 Road-kills All tammars killed by vehicles from May 2005 to November 2007 were collected by the security and gardening staff on the island and stored frozen so that animals with tags could be identified and recorded. Collection usually took place within two hours of death and up to a maximum of 12 hours. The date and location of each road-kill was also recorded.

3.3.5 Weather and climate data Monthly weather data were obtained from the Western Australian Bureau of Meteorology from an automated weather station located at the southern end of Garden Island. Long-term climatic data for the Kwinana BP Refinery (approximately six km to the east of Garden Island on the mainland) were also used to compare the weather for the three years of the study with the long-term climate.

Annual rainfall over the three years of the study varied greatly: 2005 was a very wet year with 849 mm of rain; 2006 was very dry with 456 mm; and 2007 was intermediate with 655 mm of rainfall. The distribution of this rainfall also varied greatly with 53% (448 mm) of the annual rainfall in 2005 occurring in May and June, compared with 13% (61 mm) and 22% (147 mm) falling in the same months in 2006 and 2007 respectively (Figure 3.2).

Figure 3.2 Monthly rainfall for Garden Island for the years 2005 to 2007 (Australian Bureau of Meteorology). * = Trapping event.

3.3.6 Data analysis Capture histories for all animals were used to estimate age-specific survival rates using a multi-strata mark-recapture model in Program MARK (Gary C. White, Department of Fishery and Wildlife, Colorado State University). An initial model was defined with two sexes and three strata: young-adults (one year old), adults (two-five years old) and old adults (>five years old). All transition probabilities between the strata were fixed to zero except for those between the November and February trapping sessions because the majority of tammars are born between late January and early February (Chapter 2). Starting with the full model of two sexes and three strata and full variation in survival and capture probabilities, a number of reduced models were then tested. This was done by removing sex differences and by reducing the number of strata by combining the adult and old adult stages. The models were compared using corrected Akaike‟s Information Criterion (AICc) values and the model with the lowest AICc value was chosen as the best fit for the data (Anderson et al. 1994).

The population on the base and in southern bushland were affected by road-kills and therefore separate estimates of natural and road-kill mortality were required. To do this, the two sex, three strata model described previously was extended to include a fourth „road-kill‟ stratum (Schaub and Pradel 2004). The road-kill data were incorporated into the capture histories by including road-killed animals as a recapture in the road-kill stratum at the trapping session following their death. The recovery and reporting rates for road-kills were both 100% and therefore the estimates of transition rates into this stratum were the probability of an animal in one of the „live‟ strata being killed by a vehicle. The capture probability for this stratum was set to one to account for the 100% recovery and reporting rates and the survival probability was set to zero to make it an absorbing stratum. Model selection was then done in the same way as previously described.

The most parsimonious model for all study areas had no sex differences and two live strata (young-adult and adult), represented by the life cycle graphs shown in Figure 3.3.

Figure 3.3 Single sex life cycle diagrams for the populations of the tammar wallaby in the three study areas on Garden Island. YA = young-adult (1yr old), A = adult (≥2yrs old), RK=road-kill. Px = P(animal in stratum x and time t survives to time t+1), Px-RK = P(animal in stratum x at time t is killed by a vehicle by time t+1) . Fx = weaning rate (P0) x proportion of female pouch young (mx). Time step is one year.

The life cycles were converted to a 2x2 Lefkovitch matrix that was used to estimate finite population growth rates (). The annual survival rates were calculated by multiplying the survival estimates for the intervals between trapping events. Standard errors for the survival estimates were calculated using the „Delta method‟ and the corresponding 95% confidence intervals were calculated on the logit scale before being back transformed to probabilities (Cooch and White 1997). A year was classified as starting in February and ending in January, when the majority of females give birth (Smith and Hinds 1995). The survival estimates for the 2005 and 2007 years were extrapolated from the estimates available: April 2005 to February 2006 and February to June 2007. The estimates for the June to November 2007 interval could not be used as the survival probability for the final interval and the recapture probability at the final capture occasion are confounded (Cooch and White 1997). For the populations on the base and in the southern bushland rates of survival, including the effect of road-kills, were calculated by the formula Px(total)=Px(1-Px-RK), where Px = P(animal in stratum „x‟ alive at time „t‟ survives to time „t+1‟) and Px-RK = P(animal in stratum „x‟ is killed by a vehicle between time „t‟ and time „t+1‟). When the effect of road-kills was removed, animals killed by vehicles were assumed to have survived and then have the same survival rates as the rest of the population.

The fecundity transitions were calculated as Fx=mxP0 where mx = number of female offspring per female and P0=first year survival. Tammar wallaby young are weaned at 10 months of age (Smith and Hinds 1995) and because the survival rates of newly weaned animals could not be determined due to low numbers of captures, weaning rates were used as an estimate of P0. All P0 values must therefore be viewed as overestimates because they assume 100% survival from weaning to one year of age. 95% confidence intervals were calculated for the fecundity transitions by bootstrapping using the Poptools add-in for Microsft Excel (Greg Hood, CSIRO Wildlife and Ecology, Canberra) with 2000 replicate resampling routines for each estimate. A birth-pulse model was used because tammar wallabies are seasonal breeders.

Finite rates of increase () were estimated by projecting the model into the future with unchanging vital rates, until a stable age distribution was reached. The rates of change in the size of the populations on the base and in the southern bushland were calculated

38 with and without the effect of road-kills. To estimate levels of demographic stochasticity, which occur from random variation in rates of survival and fecundity transitions, 95% confidence intervals for the projected growth rates were calculated by bootstrapping using a resampling routine in the Poptools add-in. Two lists of codes representing the transitions made by animals in the populations were created based on the survival and fecundity estimates and were then resampled with replacement to generate a new list of codes. Survival and fecundity rates were then calculated from the resampled list of codes and a resampled  was calculated. This procedure was repeated 2000 times and 95% confidence intervals were calculated from these 2000 estimates.

Estimates of , rates of survival and fecundity transitions were compared among study areas and among years and two estimates were considered significantly different if neither fell within the 95% confidence interval of the other. Elasticity values were used to predict the reduction in  from road-kills and these predictions were then compared with the actual reduction observed from the models with and without road-kills. Stable age distributions and elasticity values were calculated using the Poptools add-in for Microsoft Excel. Variance stabilized sensitivities (VSS) were also calculated as they prevent some of the misleading results that can arise from elasticity analysis (Link and Doherty 2002). The mean stable age distributions for the three study areas were compared with the age distribution from the females captured using a contingency Chi2 test.

Temporal stochasticity, to account for random variation in environmental conditions over time, was estimated based on the procedure and BASIC computer program „SIM_VAR‟ described by Ebert (1999, Chapter 10). We modified the program to project the size of the population for 100 years with 100 replications. In the bushland areas the simulation used a 20% probability of the high (2005) and low rainfall (2006) years occurring and a 60% chance of a medium rainfall year (2007) occurring and the matrices from the corresponding years were then used in the projection. The projection for the base population did not weight the probability of the three years occurring differently, because the survival and fecundity rates on the naval base were not dependent on rainfall like those in the bushland populations. The mean and 95% confidence intervals calculated from these 100 replicates were used to project the growth of the populations over 100 years. The projection of changes in the size of the

population did not account for density dependent changes in survival or reproductive success, or for immigration. They are therefore not realistic predictors of population size, but should be viewed as predictors of general trends that are likely to occur.

In total 836 male and 419 female tammar wallabies were caught and tagged in the study. The distribution of these animals between the different study areas is shown in Table 3.1. Five-hundred and forty-five tammars were killed by vehicles, 80 of which were animals captured on the naval base and 20 were animals captured in the southern bushland.

Table 3.1 Total number of male and female tammars captured in the three study areas on Garden Island between May 2005 and November 2007. Males Females Total Study Area Individuals Recaptures Individuals Recaptures Individuals Captures Base 377 857 169 115 546 1518 Southern Bushland 234 596 117 142 351 1089 Northern Bushland 225 638 133 199 358 1195 Total 836 2091 419 456 1255 3802

3.4 Results 3.4.1 Survival and fecundity

Adult survival rates (PA) were significantly higher in the base population in all three years when compared with the two bushland areas, when the effect of the road-kills was ignored, but the rates of adult survival in the two bushland areas did not differ

significantly in any of the three years (Table 3.2). Young-adult survival rates (PYA) were higher on the naval base compared with the bushland areas in all three years, but these differences were only significant when compared with the northern bushland in 2005 and the southern bushland in 2006 (Table 3.2).

The probability of young-adult animals surviving to become adults on the naval base was reduced by road-kills in 2005 and 2006, but not in 2007, with a mean reduction of 0.14±0.087 per year (s.e) over the three years of the study (Table 3.2). Road-kills also reduced significantly the survival rate of adult animals on the naval base in all three years by a mean of 0.12±0.012 per year (Table 3.2). In the southern bushland the probability of young-adult animals surviving was reduced by road-kills by 0.09 per year

40 in 2007, while road-kills reduced the survival of adults by 0.08 per year in 2006 and 0.04 per year in 2007 (Table 3.2).

Adult fecundity transitions (FA) on the base were higher compared with both of the bushland areas in 2005 and 2006, but in 2007 the fecundity transitions were higher in the bushland areas (Table 3.2). The fecundity transitions of young-adults (FYA) were lower in the northern bushland compared with the base in all years, but these differences were significant only in 2005 and 2006. The fecundity transitions of young-adult animals in the southern bushland were also lower compared with the base in 2005 and 2006, but these differences were not significant (Table 3.2).

1 2 3 4 Table 3.2 Annual survival estimates (Px) and fecundity transitions (Fx) for young-adult (one 5 year old) and adult (>one year old) tammar wallabies in the three study areas on 6 Garden Island for the years 2005 to 2007. Road-kills refers to the inclusion (+), 7 or exclusion (-) of road-kill mortality from the estimates of survival rates. *- 8 Values could not be calculated due to very low numbers of recaptures, the rate 9 from 2006 was used instead. 10 Year (% long-term Road- Annual Survival Fecundity Transitions mean rainfall) Study Area kills PYA 95% C.I. PA 95% C.I. FYA 95 % C.I. FA 95 % C.I. 2005 Northern bushland 0.49 0.406, 0.570 0.68 0.650, 0.702 0.02 0.000, 0.120 0.11 0.055, 0.167 Southern bushland + 0.69 0.611, 0.755 0.65 0.590, 0.700 0.14 0.000, 0.333 0.24 0.150, 0.333 (121%) - 0.69 0.611, 0.755 0.66 0.615, 0.698 Base + 0.48 0.291, 0.676 0.80 0.758, 0.840 0.17 0.042, 0.333 0.34 0.252, 0.430 - 0.78 0.676, 0.860 0.92 0.911, 0.933 2006 Northern bushland 0.64 0.473, 0.779 0.70 0.680, 0.725 0.05 0.000, 0.150 0.32 0.286, 0.470 Southern bushland + 0.50 0.415, 0.592 0.64 0.641, 0.649 0.15 0.000, 0.333 0.25 0.159, 0.341 (60%) - 0.50 0.415, 0.592 0.72 0.698, 0.734 Base + 0.81 0.695. 0.888 0.69 0.621, 0.757 0.27 0.111, 0.452 0.53 0.440, 0.632 - 0.93 0.869, 0.962 0.83 0.816, 0.842 2007 Northern bushland * 0.69 0.665, 0.720 0.06 0.000, 0.143 0.38 0.290, 0.470 Southern bushland + 0.58 0.577, 0.580 0.68 0.664, 0.696 0.28 0.067, 0.500 0.47 0.368, 0.582 (87%) - 0.67 0.669, 0.671 0.72 0.709, 0.737 Base + 0.51 0.351, 0.672 0.66 0.639, 0.673 0.21 0.064, 0.370 0.29 0.205, 0.375 - 0.51 0.351, 0.672 0.76 0.747, 0.775

3.4.2  - The rate of change in size The finite rate of change in the size of the population () on the naval base (without road-kills) was 1.184 in 2005, and 1.304 in 2006, which was higher than the two bushland areas. However, in 2007 the rate of change in size (without road-kills) was significantly higher in both bushland areas (Table 3.3). The finite rate of change in the size of the population in the northern bushland was significantly lower than the southern bushland (without road-kills) in 2005, but there was no significant difference between the  of the populations in the two areas in 2006 and 2007 (Table 3.3).

The  of the population in the northern bushland was the lowest at 0.747 in the wet year (2005), highest at 1.094 in the medium rainfall year (2007) and intermediate at 0.934 in the dry year (2006) and all of these differences were significant (Table 3.3). In the southern bushland  (without road-kills) was not significantly different between 2005 and 2006, but was significantly higher in 2007 compared with the other years (Table 3.3).

The 95% confidence intervals for  of the populations in both bushland areas in 2005 and 2006 and the northern bushland in 2007 did not include 1.0 indicating that under these conditions the populations are highly likely to change in size. The  for the population in the southern bushland in 2007 (without road-kills) included 1.0 and the population may therefore remain stable or even decrease in size given the observed survival rates and fecundity transitions (Table 3.3).

Road-kills reduced significantly the rate of change in the size of the population of tammars on the naval base by 16% in 2005, 10% in 2006 and 8% in 2007 (Table 3.3). The  calculated for the base population in 2005, with road-kills, and 2007, without road-kills, both had confidence intervals that included 1.0 and it is therefore possible that the size of these populations may remain constant or increase slightly under the conditions observed in those years. In all other cases the calculated  for the base population was significantly above or below 1.0 (Table 3.3).

Road-kills also reduced the rate of change in the size of the southern bushland population by 1% in 2005, 6% in 2006 and 6% in 2007, but these differences were not

43 significant (Table 3.3). The  estimates for the population in the southern bushland in 2005 and 2006, both with and without road-kills, were significantly lower than 1.0 and this population is therefore highly likely to reduce in size under the conditions observed in those two years (Table 3.3). Under the conditions seen in 2007 this population was projected to increase in size (without road-kills; =1.108), but the 95% confidence interval for  included 1.0 and the population may therefore remain stable or decline slightly given the vital rates calculated for that year (Table 3.3).

Table 3.3 Finite rates of change () and their corresponding 95% confidence intervals for the populations of tammar wallabies in the three study areas on Garden Island for the years 2005 to 2007. Base and southern bushland estimates are shown with (+) and without (-) the impact of road-kills. Year Road  95% Confidence (% long-term rainfall) Study Area -kills (year-1) Interval 2005 Northern Bushland 0.747 0.695, 0.797 Southern Bushland + 0.870 0.782, 0.961 (121%) - 0.878 0.790, 0.971 Base + 0.998 0.937, 1.072 - 1.184 1.122, 1.251

2006 Northern Bushland 0.934 0.872, 0.989 Southern Bushland + 0.828 0.742, 0.915 (60%) - 0.885 0.804, 0.966 Base + 1.168 1.082, 1.249 - 1.304 1.238, 1.400

2007 Northern Bushland 1.094 1.033, 1.143 Southern Bushland + 1.041 0.928, 1.151 (87%) - 1.108 0.996, 1.210 Base + 0.880 0.805, 0.952 - 0.959 0.894, 1.029

3.4.3 Stable age distributions The mean stable age distributions projected for the populations in the southern bushland and the base had a significantly higher proportion of young-adult animals compared with the age distributions calculated from the animals captured (df=1, minimum 2=12.36, P<0.001, Table 3.4). The stable age distribution predicted for the population in the northern bushland was not significantly different from that observed from the captured animals (df=1, 2=2.31, P=0.129, Table 3.4).

Table 3.4. Stable age distributions predicted from singe sex stage based matrix models of tammar wallaby populations in the three study areas on Garden Island from 2005 to 2007 and the age distribution calculated from the captured animals. Base and southern bushland age distributions include the effects of road- kills. Age Dist. - Study Stable Age Distribution - Predicted Observed Area Age Class 2005 2006 2007 Mean s.e Prop. n Northern Young Adult 0.13 0.26 0.27 0.22 0.047 0.17 22 Bushland Adult 0.87 0.74 0.73 0.78 0.047 0.83 111 Southern Young Adult 0.25 0.27 0.38 0.30 0.040 0.14 16 Bushland Adult 0.75 0.73 0.62 0.70 0.040 0.86 101 Young Adult 0.29 0.37 0.30 0.32 0.025 0.17 33 Base Adult 0.71 0.63 0.70 0.68 0.025 0.83 136

3.4.4 Perturbation analysis The parameter in the life cycle with the largest variance stabilised sensitivity (VSS) estimate over the three years of the study was the survival of adult animals (PA), but in the population on the base (without the impact of road-kills) the fecundity transition of adults (FA) had the same mean VSS (Table 3.5). In all study areas  was least responsive to changes in the fecundity transitions of young adults (FYA; Table 3.5).

The elasticities (Table 3.5) predicted that the road-kills would reduce the  of the tammar population on the naval base by 15%, 11% and 8% in 2005, 2006 and 2007 and in the southern bushland the  was predicted to be reduce by 1%, 7% and 6% over the three years. These values were all within 1% of the actual changes in  that were calculated from the matrix models (Table 3.3).

Table 3.5 Elasticity and variance stabilised sensitivity (VSS) values for the parameters in the projection matrices for the populations of tammar wallabies in the three study areas on Garden Island between 2005 and 2007. Elasticity VSS Study Area Parameter Mean s.e Mean s.e

Northern Bushland PYA 0.15 0.034 0.12 0.018 PA 0.69 0.071 0.41 0.090 FYA 0.01 0.002 0.03 0.010 FA 0.15 0.031 0.25 0.018

Southern Bushland PYA 0.20 0.024 0.15 0.010 Road-kills excluded PA 0.56 0.062 0.37 0.047 FYA 0.05 0.016 0.10 0.016 FA 0.20 0.024 0.29 0.030

Southern Bushland PYA 0.20 0.018 0.17 0.018 Road-kills included PA 0.54 0.051 0.39 0.046 FYA 0.05 0.017 0.11 0.016 FA 0.20 0.023 0.30 0.030

Base PYA 0.21 0.032 0.11 0.027 Road-kills excluded PA 0.53 0.077 0.24 0.055 FYA 0.06 0.013 0.09 0.012 FA 0.21 0.032 0.24 0.006

Base PYA 0.20 0.034 0.16 0.016 Road-kills included PA 0.54 0.081 0.33 0.043 FYA 0.06 0.014 0.10 0.017 FA 0.20 0.034 0.26 0.022

3.4.5 Projections of population size The projection of the population of tammars in the northern bushland indicated a decline to 0.64 times its current size (95% C.I. 0.012 to 3.70) after 100 years (Figure 3.4). The 95% confidence interval included a relative population size of 1.0 and it is therefore likely that the size of the population would not change in size significantly.

Figure 3.4. Projection of the relative size of the population of tammar wallabies (log scaled) in the northern bushland on Garden Island over 100 years. Solid line - mean predicted relative population size. Dashed lines - upper and lower 95% confidence intervals.

The population in the southern bushland was predicted to decrease to 0.04 times its current size over the 100-year simulation (95% C.I. 0.003, 0.117; Figure 3.5). The 95% confidence interval for this prediction did not include 1.0 and a decline in the size of the population is therefore very strongly predicted. If the effect of road-kills was removed, the population was predicted to increase to 5.0 times its current size (95% C.I. 0.46, 19.62; Figure 3.5). The large 95% confidence intervals indicates that it is possible that the size of the population may not change significantly, but the trend strongly predicts that the size of the population will increase without the controlling effect of road-kills.

Figure 3.5 Projection of the relative size of the population of tammar wallabies (log scales) in the southern bushland on Garden Island with (top) and without (bottom) road-kills over 100 years. Solid line - mean predicted relative population size. Dashed lines - upper and lower 95% confidence intervals. Note that the y axes have different scales.

When the effect of road-kills was included the population on the naval base was predicted to decline slowly to 0.33 times its current size over the 100-year simulation (95% C.I. 0.032, 1.168; Figure 3.6). The 95% confidence interval of this prediction includes 1.0, but given that it is close to the 95% limit, a decline in the size of the population is likely. Without the effect of road-kills the population was predicted to increase very rapidly to 5.83x104 times its current size (95% C.I. 3974, 2.55x105; Figure 3.6). This population size is clearly unrealistic, but the model demonstrates that without road-kills the base population has the potential to greatly increase in size.

Figure 3.6 Projection of the relative size of the population of tammar wallabies (log scaled) on the naval base on Garden Island with (top) and without (bottom) road-kill mortality over 100 years. Solid line - mean predicted relative population size. Dashed lines - upper and lower 95% confidence intervals. Note that y axes have different scales.

3.5 Discussion 3.5.1 Habitat modification The projected  without road-kill mortality for the population of tammars on the naval base was significantly higher than the two bushland areas in the very wet (2005) and very dry (2006) years, which partially supported our hypothesis. In 2007 the  of the population on the naval base was significantly lower compared with the bushland areas as a result of a lower rate of survival of young-adults and lower adult fecundity transitions. The rate of survival of adults was significantly higher on the base compared

49 with the bushland areas in all three years, which we suggest was the result of the increased supply of food provided by the irrigated and fertilised lawns. In high rainfall years, the increased food supply on the base may allow the tammars to be in better condition coming into the wet winter months, which would give them a better chance of surviving and raising their pouch young through the cold and wet conditions that negatively affect the animals in the bushland areas. Inns (1980) found that the onset of winter was a period of high mortality for tammars on Kangaroo Island, particularly if the autumn months were very dry and the onset of winter was cold and wet. The impact of a dry autumn on the condition of the tammars would be greatly reduced on the naval base due to the extra food available from the irrigated lawns (Chapter 2), which would probably lead to lower mortality at the start of winter.

3.5.2 Rainfall The s projected for the populations in the two bushland areas were significantly lower in both the high and low rainfall year compared with the year with a medium amount of rainfall, which did not support our hypothesis. We expected that higher rainfall would favour the growth of the tammar populations, but the results suggest that the conditions that most favour the growth of the populations are those close to the long-term climatic mean. The significant differences in the s were primarily the result of lower fecundity transitions in 2005 and 2006, as the rates of survival of adults in the bushland areas did not differ significantly over the three years of the study. The consistent rate of survival of adult animals among years disagrees with the pattern found for tammars on Kangaroo Island, South Australia, where the survival of adults was reduced significantly in years of low rainfall, but the survival of young adults was not affected as strongly (Inns 1980). The survival of young-adult tammars in the bushland areas varied significantly among years, but the pattern of changes was not consistent. In the northern bushland survival of young-adults was lower in the wet year compared with the dry year, but unfortunately the rate of survival could not be estimated for the medium rainfall year. In the southern bushland the survival rate was significantly lower in the dry year, compared with both the years with medium and high rainfall. Due to these conflicting results it is difficult to predict if or how the survival of young adult animals is affected by rainfall, and more data are needed to answer this question. Our results demonstrate that differences in the rate of change in the size of the tammar populations in all areas of

Garden Island were primarily the result of changes in fecundity transitions and rates of survival of young-adults, rather than changes in the rate of survival of adults.

The impact of low rainfall on the rate of change in the size of the populations in the bushland areas was similar to that reported for tammars on Kangaroo Island, which had reductions of up to 35% in the size of their population in years of drought (Inns 1980). The rate of change in the size of populations of red and grey kangaroos in western New South Wales was also reduced in drought years and reached a peak at annual rainfalls approximately 50 to 100 ml above average, but then began to be reduced again at higher levels of rainfall (Caughley et al. 1984). Fisher et al. (2001) found that a population of bridled nailtail wallabies (Onychogalea fraenata) was reduced in size by 9.5% per year during a drought, compared with an increase of 37.5% per year after the drought. The rate of change in the size of the populations of tammar wallabies on Garden Island is affected similarly, but the negative effect of high rainfall seems to be greater than that of low rainfall.

3.5.3 Road-kills The number of animals killed by vehicles affected significantly the rate change in the size of the tammar population on the naval base, which supported our hypothesis. Road mortality also affected the rate of change in the size of the population in the southern bushland, but this did not result in significant changes to . The biggest impact of the road-kills on the naval base population was on the rate of survival of young adult animals, which was reduced by up to 0.30 per year. However, this impact varied greatly between years with no effect in 2007. This may be the result of the estimate for 2007 being an extrapolation from the February to June interval. The majority of tammars were killed by vehicles between May and August (Walker 2002, Chambers et al. 2008) and the survival of animals in this age class may therefore have been reduced by road- kills after the June trapping session. The impact of road-kills on the survival of adults was more consistent and varied between reductions of 0.10 and 0.14. These results suggest that vehicles pose a greater risk to young-adult animals, possibly due to them being naïve and reacting in a way that puts them at risk of being run-over.

The stable age distributions predicted for the populations of tammars in the southern bushland and on the base had significantly higher proportions of young adults than was

51 observed from the captured animals. This is most likely due to the use of weaning rates to estimate first year survival in the models. This assumed that there was 100% survival of animals in the two months from weaning to one year of age. Inns (1980) found that up to 40% of newly weaned tammars died before the following autumn. The first year survival (P0) and therefore the fecundity transitions were probably over-estimates, which would result in an over-estimation the proportion of young-adults in the stable age distributions. The mean stable age distribution predicted for the population in the northern bushland was similar to the observed distribution, which indicates that this population was at, or quite close to it‟s predicted stable age distribution.

3.5.4 Perturbation analysis Changes in adult survival were predicted to have the largest impact on , which is typical of species where adult life-spans are long compared with the time taken to reach maturity (Goodman 1981, Brault and Caswell 1993). Management strategies aimed at changing the  of these populations of tammars should therefore target the apparent rate of survival of adults, either through translocation or culling, but the survival of young adults should not be ignored due to its high variability (Caswell 1997). Adult fecundity should also be considered as it can be manipulated by surgical sterilisation or hormonal control (Cooper and Herbert 2001) and in some cases the adult fecundity transitions had VSS values that were very similar to those of the survival of adults. The changes in  due to road-kills predicted by the elasticities were also very similar to the changes calculated from the matrix models, even when the vital rates were changed by as much as 38% (PYA on the base in 2005). This indicates that the elasticity values for the matrices can be used to predict confidently the effect of management strategies that increase or decrease rates of survival.

3.5.5 Projections of population size The projections of the populations of tammars on the naval base and in the southern bushland demonstrate that the rates of road-kills observed between 2005 and 2007 would result in a long-term decline in the size of the population of tammars. The population in the southern bushland was predicted to be the worst affected despite having smaller reductions in the rates of survival due to road-kills. Without the impact of road-kills the population of tammars in the southern bushland was projected to increase in size, while the population in the northern bushland was not. This suggests

52 that the population in the southern bushland may have been benefiting from its proximity to the naval base. This is most likely due to animals gaining food from the lawns on the naval base as tammars from the southern bushland, tracked by radio telemetry, moved regularly on to the naval base, presumably to feed (Chapter 4). Some individual tammars were also caught in both of the areas, but none of these movements appeared to be permanent. These results indicate that to maintain the size of the population of tammars on the island the rate of road-kills needs to be reduced from the levels seen in this study, but this needs to be carefully managed, as without the impact of road-kills, both of these populations were predicted to increase to sizes that would be difficult to manage.

3.5.6 Conclusions We have demonstrated that modification of habitat has altered significantly the population dynamics of the tammar wallabies on Garden Island by increasing both survival rates and fecundity transitions. The difference between the vital rates in the disturbed and undisturbed areas of the island is particularly large in years with very high or very low rainfall. This could result in higher rates of change in the size of the population on the naval base in years where the conditions were unfavourable for the populations in the bushland areas of the island. The increase in the size of the tammar populations on the naval base and in the bushland adjacent to the base was being controlled by road-kills, as this form of mortality significantly reduced the survival rates of both young-adult and adult tammars.

The results of the projection of the size of the populations of tammars on the base and in the southern bushland demonstrate that the rate of road-kills needs to be reduced below the levels seen from 2005 to 2007 to avoid the size of these populations declining significantly. If the fence between the southern bushland and the naval base was improved so that the tammars in the bushland could not access the base, the dynamics of the population in southern bushland would then probably become similar to those of the population in the northern bushland. Without the effects of the road-kills and access to the additional food sources on the naval base, the size of the population in the southern bushland would probably be regulated by environmental stochasticity, similarly to that of the northern bushland. The problem of road-kills on the naval base could then be managed without impacting on the population in the southern bushland.

The population growth projections also show that attempts to reduce the number of tammars killed by vehicles on the naval base need to be carefully managed as this population has the potential to grow in size very rapidly without the controlling influence of road-kills.

Our results also suggest that large increases in the size of other populations of macropods are likely to be the result of increases in both survival and fecundity. Therefore, management strategies that combine measures to reduce both of these vital rates are likely to be successful at controlling the rate of increase in the size of these populations. If management strategies focus on controlling the rate of change in the size of populations, rather than reducing their size only when they become over- abundant, then the implications of populations growing beyond the carrying capacity of their environments, such as starvation and the over-grazing of preferred plant species, may be avoided.

4. Does habitat modification affect the size of the home ranges of tammar wallabies (Macropus eugenii) on Garden Island, Western Australia?

4.1 Abstract When disturbance and the habitat of animals results in changes to the availability of resources this can result in changes in the size of their home ranges. Nineteen tammar wallabies (Macropus eugenii) were tracked by radio telemetry on Garden Island, Western Australia, to test the hypothesis that animals would have smaller home ranges in a modified habitat, where irrigated and fertilised lawns have been introduced, than in bushland areas of the island. However, there were no significant differences in the size of the tammars‟ home ranges between areas with modified or unmodified habitats (P=0.706). In summer the mean size of the home ranges was 3.90.66 ha, which was larger than winter when home ranges were 3.20.54 ha, but this difference failed to reach significance (P=0.058). There was also no significant difference between the size of the home ranges of male and female tammars (P=0.127), despite significant sexual dimorphism in body mass. These results indicate that the modification of the tammars‟ habitat has probably not been sufficient to cause significant differences in the size of the animals‟ home ranges. The size of the home range of tammar wallabies is likely to be determined by a complex interaction of many factors, and habitat modification alone is not sufficient to cause substantial changes.

4.2 Introduction Home range is the area over which an animal moves in order to perform its normal activities, including finding food, mating, caring for young and avoiding predators (Burt 1943, Harris et al. 1990). Interspecific variation in the size of home range has been explained by factors such as body weight, diet, trophic status (i.e. carnivore, herbivore or omnivore), climate, risk of predation and mating systems (Harestad and Bunnell 1979, Damuth 1981, Gosling 1986, Gompper and Gittleman 1991, Mysterud et al. 2001). Body weight is generally believed to have the single largest effect on the size of home range as energy requirements increase directly with increasing body weight. This theory has strong support from studies in eutherian mammals, but in macropods climate has been reported to influence home range size more strongly than body weight (Fisher and Owens 2000).

Intraspecific variation in home range size is influenced by other factors such as sex, breeding behaviour, and seasonal changes in food availability (Croft 1989, Gompper and Gittleman 1991, Fisher and Owens 2000). Sexual dimorphism in the home range size of macropods has a strong association with use of space by females and mating strategies rather than sexual dimorphism in body size (Johnson 1987, Fisher and Owens 2000). In macropod species with promiscuous mating, where females are social and have extensive overlap of home ranges, sexual dimorphism in the size of home ranges is lower in comparison with species with solitary females (Croft 1989, Evans 1996). As female tammar wallabies are known to be social grazers (Christensen 1977, Inns 1980), we did not expect to find significant sexual dimorphism in the size of their home ranges.

Seasonal variation in the size of home ranges has also been found to be significant in some macropod species and this has generally been related to rainfall and its effect on food availability. Female red-necked wallabies (Macropus rufogriseus) in northern New South Wales had larger home ranges at the time of year when rainfall and plant growth was at its lowest (Johnson 1987). Viggers and Hearn (2005) found that the home ranges of eastern grey kangaroos (Macropus giganteus) were significantly larger in autumn and winter than in spring and summer, which also corresponded to changes in the quantity of pasture available. Agile wallabies (Macropus agilis) had larger home ranges during the tropical dry season than in the wet season, which were attributed to the lower quality and quantity of food resources in the dry season (Stirrat 2003). This

57 was supported by a dietary study in which Stirrat (2002) found that M. agilis ate grass and forbs in the wet season, but also ate browse, leaf litter, fruits, flowers and roots during the dry season when grasses and forbs were less abundant. Similar dietary changes from grazing to browsing were found in bridled nailtail wallabies (Onychogalea fraenata), but this did not correspond to a significant change in the size of their home range (Evans 1996, Evans and Jarman 1999).

On Kangaroo Island, South Australia, there was no significant difference in the size of the home ranges of males and female tammar wallabies, but for all animals the size of the home range in summer (December to March) was significantly larger than in winter (May to November). In summer, animals spent a greater proportion of time in areas of dense bushland than in cleared grassland, which was associated with the tammars gaining a greater proportion of their food from browsing, thus requiring them to range further to find sufficient food (Inns 1980). Bell et al. (1987) and McMillan et al. (2009) found that tammar wallabies in undisturbed bushland on Garden Island ate the permanently green shrub Acacia rostellifera and the non-native winter perennials Asparagus asparagoides, Trachyandra divaricata and Asphodelus fistulosus, and the native winter perennial Austrostipa flavescens. In contrast to the tammars in the bushland, ~85% of the diet of the tammars in the areas of the island developed for the HMAS Stirling naval base was introduced couch grass (Cynodon dactylon), which covers approximately 30% of the land area of the naval base (McMillan et al. 2009). In the bushland, the availability of the tammars‟ main food sources is higher in winter than in summer, due to the growth of winter perennials. We therefore expected that the tammars in these areas would need to expand the size of their home ranges to find adequate food in summer compared with winter. On the naval base the majority of the areas of introduced Cynodon dactylon are irrigated and fertilised and therefore the quantity and quality of the food available to animals in this area is high, concentrated and unvarying with season when compared with the food available in the bushland areas. Animals in more productive environments are expected to have smaller home ranges than animals in less productive environments (Harestad and Bunnell 1979) and we therefore expected that the tammars on the naval base would have smaller home ranges than those in the bushland areas. We also expected that the lower variation in food availability on the naval base between seasons, because of irrigation and fertilisation of lawns and ovals, would result in the tammars in that area having less

58 seasonal variation in the size of their home ranges than those in the bushland areas of the island.

Observations during a previous study suggested that the food on the base is so important to tammars that some travel nightly from adjacent areas of natural bushland presumably to feed on the lawns of the base (Walker 2002). Therefore, we expected that animals living on the bushland adjacent to the naval base would have larger home ranges than those in the bushland away from the naval base if they travelled nightly to the base to forage.

4.3 Materials and Methods 4.3.1 Experimental design To test these hypotheses, we captured 24 tammar wallabies (four males and four females in each of three areas of the island) and fitted them with radio transmitters to determine their home ranges. Home range data from 19 animals were analysed, as five animals either died or had radio transmitters that failed and therefore did not produce estimates of the size of their home ranges in both summer and winter.

4.3.2 Study area Garden Island is located approximately five km off the West Australian coast approximately 35 km south west of the city of Perth (115o40‟E, 32o16‟S). The long- term mean annual rainfall is 757 mm with the majority of this rainfall (~80%) falling between May and September (Australian Bureau of Meteorology). The tammar wallaby is the only native mammal present on the island and the only other mammal species present is the introduced house mouse (Mus musculus, Brooker 1992).

The study was conducted in three areas of Garden Island with different levels of human disturbance (Figure 4.1). The „base‟ area was directly and significantly disturbed with much of the native vegetation cleared and replaced with buildings, roads and irrigated lawns. The „southern bushland‟ was directly adjacent to the naval base and had similar vegetation cover to the northern bushland. It was separated from the base by a three- metre high chain link fence, but was potentially influenced by its close proximity to the base as animals in the area could move to and from the base through gaps under the fence. The „northern bushland‟ was at the far northern end of the island approximately

5.6 km from the base and the disturbance here was minimal, with native vegetation covering the whole area except for a single vehicle track and a 30 m wide, cleared firebreak at the southern end of the area. There was no naval activity in this area and the only public access was by boat during daylight, with the majority of visitors confining their activities to the beaches (T. Smith pers. comm.).

Figure 4.1. Location of Garden Island, Western Australia (115o40‟E, 32o16‟S) and the three study sites, base, southern bushland and northern bushland. Shaded areas represent areas of naval infrastructure where significant habitat modification had occurred.

4.3.3 Radio tracking Twenty four tammar wallabies, four males and four females in each of the three areas, were fitted with two stage radio transmitters with 15 cm whip antennae on nylon collars (Titley Electronics, Ballina, New South Wales, Australia). Twelve animals were

60 collared in September 2005 and were tracked until August 2006. A further 12 tammars were then collared in November 2006 and tracked until October 2007. The animals were captured using „Thomas‟ soft-wall traps made from shade cloth stretched over a steel frame (450x450x800 mm, Sheffield Wire Works, Welshpool, Western Australia). Traps were baited with a mixture of rolled lupins, rolled oats and sunflower seeds, flavoured with molasses (Kangaroo Muesli, Thompson & Redwood Produce Supplies, Upper Swan, Western Australia). Each animal was weighed and aged by visually determining the stage of molar eruption (Inns, 1982) when the collars were fitted and all collared animals were at least two years of age and sexually mature. As the behaviour of animals can be significantly affected for some time after being fitted with collars (Woolnough et al. 1998), the animals were given at least two weeks to become accustomed to their collars and were then presumed to have resumed normal behaviour when the first fixes were taken.

Fixes were taken by triangulation using a handheld, three-element Yagi antenna and battery operated radio receiver (Biotelemetry RX5). A single operator took bearings from at least three positions with no more than three minutes between the recording of consecutive bearings. The locations used to take bearings were recorded using a GPS receiver (Garmin GPS60). Tracking was done for three or four days every month with four fixes taken each day. Fixes were defined as day (0800-1600), dusk (1600-2000, taken within one hour of sunset) and night (2000-0400) and one day, one dusk and two night fixes were taken in a 24 hour period. To attempt to avoid autocorrelation of consecutive fixes at least three hours were left between fixes. When the animals could be seen their position was noted and then recorded later using a GPS receiver.

The computer programme Locate II (V. O. Nams, Pacer Computer Software, Nova Scotia, Canada) was used to calculate the position of the animals from the recorded bearings. Seasons were defined as summer (December to April) and winter (May to November) and home ranges were calculated for each animal where more than 20 locations were available. Home ranges were calculated using the kernel density estimator (KDE) and minimum convex polygon (MCP) methods in Ranges VI (Anatrack Ltd, Institute of Terrestrial Ecology, Wareham, England). The KDE method was chosen as it produces the most realistic estimates of home range size and shape when appropriate sample sizes and smoothing parameters are used (Hayward et al.

2004, Martin et al. 2007, Wauters et al. 2007). The smoothing parameter for the KDE was chosen by applying the mean ratio of hlscv/href, for all home ranges as a multiplier for href (hence referred to as hadj: (Wauters et al. 2007). hlscv is the smoothing parameter calculated by least squares cross validation and href is the reference smoothing parameter, This method was chosen as Wauters et al. (2007) found that using the hadj smoothing parameter reduced over-estimation of home range size when less than 70 locations were used to estimate home ranges less than 30 ha. The hadj smoothing parameter calculated for use in our analysis was 0.562. The mean number of fixes used to estimate home ranges was 531.3 (se) with a minimum of 27 and incremental area analysis was used to ensure that an asymptote had been reached within the number of fixes used. Home ranges were also calculated using the MCP method to allow comparison with the results of Inns (1980), who used this method to estimate the size of the home ranges of tammar wallabies on Kangaroo Island. MCP home ranges were calculated as 100% home range areas, as this was the same method employed by Inns (1980).

4.3.4 Data analysis The data on the size of home ranges were analysed using a repeated measures analysis of variance (ANOVA) with sex and study area as between subjects factors, season as a within subjects factor and 95% KDE home range size as the dependent variable (JMP 7.0, SAS Institute Inc.). The data were inspected prior to analysis for normality and homogeneity of variances as assumed in ANOVA. The magnitude of the main effects of the fixed factors was calculated according to Halderson and Glasnapp (1972). The power of the analysis to detect a 50% difference in the size of home ranges was also calculated using the PASS 2008 computer programme (NCSS, Kaysville, Utah).

The size of the home ranges of the tammars from the southern bushland that included areas of the naval base as part of their home range were compared with those of animals of the same sex from the northern bushland using a one-tailed Student‟s t-test. Linear regression was used to determine if a significant relationship existed between body weight and home range size in either of the two seasons studied.

The home ranges estimated using the MCP method were compared with those published by Inns (1980), who reported the complete data set collected for tammar wallabies on

Kangaroo Island, using a one tailed Student‟s T-test. The home range estimate for one female was removed from the data published by Inns (1980) as it was calculated from only 10 locations, which we felt was not sufficient to estimate adequately the size of its home range.

Means are presented with their standard errors. Effects were considered to be significant when their level of probability was 5% or less.

4.4 Results There was no significant difference between the sizes of the tammars‟ home ranges in the three study areas or between the sexes (Tables 4.1 and 4.2). The mean size of the tammars‟ home ranges in summer was 3.90.66 ha, which was larger than in winter at 3.20.54 ha, but this difference failed to reach significance (P=0.058, Table 4.2). There were also no significant interactions between any of the independent variables (Table 4.2).

Although female animals used in the analysis weighed only 3.90.17 kg (n=9) and males weighed 6.10.43 kg (n=10), the regression between home range and body weight was not significant in either season (summer - r2=0.087, df=17, P=0.218; winter - r2=0.120, df=17, P=0.146).

Table 4.1. The mean size of the 95% KDE home ranges of male and female tammar wallabies in summer (December to April) and winter (May to November) in three different study areas on Garden Island, Western Australia. Home Range (ha) Study Area Sex n Summer se Winter se Female 3 2.5 0.83 1.9 1.13 Base Male 4 4.1 0.87 3.9 0.49

Southern Female 2 3.8 1.42 2.5 1.14 Bushland Male 3 5.4 1.23 3.9 0.19

Northern Female 4 3.0 0.33 3.5 0.91 Bushland Male 3 4.8 2.01 2.9 1.57

Table 4.2. Repeated measures ANOVA results and statistical power for the comparison of the size of the home range of tammar wallabies on Garden Island. *-Magnitude of effect could not be calculated and was therefore set to 0. Between subjects residual MS=5.47. Within subjects residual MS=1.46. Statistical power calculated to detect a 50% difference in home range size. Magnitude of Statistical Source of Variation df F P Effect (%) Power Between Subjects Sex 1,13 2.65 0.127 6.51 0.620 Study Area 2,13 0.36 0.706 0.00* 0.541 Sex x Study Area 2,13 0.22 0.806 0.541 Within Subjects Season 1,13 4.32 0.058 3.29 0.975 Season x Sex 1,13 0.85 0.372 0.975 Season x Study Area 2,13 0.55 0.592 0.956 Season x Sex x Study Area 2,13 1.35 0.294

All three males collared in the southern bushland had home ranges that included parts of the base and one male tammar from the base regularly moved into the southern bushland (Figure 4.2). The mean size of these animals‟ home ranges was 5.50.61 (n=4) ha in summer and 3.80.12 ha in winter. This was not significantly different to the size of the home ranges of males from the northern bushland in summer (t-test, df=5, t=0.34, P=0.374) or winter (df=5, t=0.60, P=0.30). A fourth male in the southern bushland did not move onto the naval base at any time during summer but this animal was not included in the analysis because we only had an estimate of its summer home range. The two females from the southern bushland did not move into the base study area at any time (Figure 4.2). The mean size of their home ranges was 3.81.00 ha in summer and 2.50.81 ha in winter. This was also not significantly different to the size of the home ranges of females in the northern bushland in summer (t-test, df=4, t=0.68, P=0.266) or winter (df=4, t=0.56, P=0.299). A third female from the southern bushland that provided home range data for only one season also moved onto the naval base regularly during summer.

Figure 4.2. Home range plots (95% kernel density estimators) of six tammar wallabies from Garden Island. a) and b) - home ranges of three male tammars from the southern bushland area whose home ranges included the base. c) and d) - home ranges of one male from the base whose home range included the southern bushland and two females from the southern bushland that did not use the base. (Grey shaded areas = bushland, white areas = cleared areas, hatched = buildings. The fence denotes the boundary between the southern bushland and the base. Numbers represent home ranges of different individuals).

The mean size of home ranges estimated for tammars on Garden Island using the MCP method was considerably smaller than that of tammars on Kangaroo Island for both sexes and in both seasons (t-test, P<0.05, Table 4.3).

Table 4.3. Mean size of minimum convex polygon (MCP) home ranges estimated for tammar wallabies on Kangaroo Island (Inns, 1980) and on Garden Island (this study). *=Means significantly different at P<0.05. Kangaroo Island Garden Island Home Home Sex Season range (ha) se n range (ha) se n Summer* 47.0 2.55 7 9.3 1.60 10 Male Winter* 25.0 3.86 5 6.5 0.83 10 Summer* 42.6 9.31 5 7.6 1.23 9 Female Winter* 16.4 3.13 4 6.6 0.83 9

4.5 Discussion The results did not support our expectation that the animals on the base would have significantly smaller home ranges than those in the bushland areas of Garden Island. Our hypothesis was based on the assumption that food availability would have a large effect on the size of the tammars‟ home ranges and that this effect would override that of other factors, as reported in other studies (Inns 1980, Johnson 1987, Stirrat 2003, Viggers and Hearn 2005). Our results suggest that factors other than the availability of food may have had a significant impact on the size of the home range of the tammars, which was in agreement with the findings of Evans (1996) for bridled nailtail wallabies. These factors may have included the availability of shelter and its proximity to grazing areas, disruption of the tammars‟ grazing by people and vehicles, or aggressive interactions between unrelated individuals (Blumstein et al. 2002a). The non- significant result in this case may also represent a type II error as the power of the analysis to detect differences was low due to the small sample sizes used. For this reason it is not possible to conclude confidently that the disturbance of the tammars‟ habitat has not changed the size of the animals home ranges.

The home ranges of the tammars on Garden Island tended to be larger in summer and autumn than in winter and spring, but this failed to reach significance. While the tammars had mean home range sizes that were almost significantly different between the two seasons, this accounted for only 3.3 % of the total variation in the size of the animals‟ home ranges. This result was consistent with our expectation that the tammars would expand their home ranges in summer and autumn in order to find food, but the effect was not as strong as we anticipated. This may be due to the animals altering their

66 diets in summer to consume more Asphodelus fistulosus than in winter, which is widespread in the bushland on Garden Island (Moredoundt 1983, Bell et al. 1987).

We expected that the tammars on the naval base would have significantly less seasonal variation in the size of their home ranges than those in the bushland areas. This was not found to be the case even though the power of the analysis to detect this effect was high. This result suggests once again that factors other than the availability of food may strongly affect that amount of seasonal variation in the size of these animals‟ home ranges.

There was no significant difference between the size of the home ranges of males and females; however, sex did account for 6.5% of the variation explained by the ANOVA, approximately twice the variation explained by season. The variation explained by sex is not related to sexual dimorphism in body weight, as no significant relationship was found between body weight and the size of the animals‟ home ranges. The lack of significant sexual dimorphism in the size of the animals‟ home ranges, despite sexual dimorphism in body size, is consistent with the hypothesis that in macropod species where females are social there is no significant sexual dimorphism in the size of home ranges (Croft 1989).

Contrary to our expectation, there was no significant difference between the size of the home range of animals from the southern bushland that moved onto the naval base and those that were resident in the northern bushland. This shows that the animals in the southern bushland did not have larger home ranges in order to access the base. The reason for this may be that these animals would have made use of these areas regardless of modification of the habitat on the naval base or that these animals may have shifted their home ranges to be closer to the naval base, thus resulting in no significant difference in the size of their home ranges.

The significant difference between the size of the tammars‟ home ranges on Garden Island and Kangaroo Island is most likely the result of the difference in the climate of the two islands and the body weight of tammars and follows the pattern predicted by Fisher and Owens (2000) and Harestad and Bunnell (1979). Kangaroo Island has a mean annual rainfall of 484 mm, which is considerably lower than that of Garden Island

67 at 759 mm (Australian Bureau of Meteorology). Inns (1980) did not provide the body weights of the animals for which home range size was assessed, but the adult body weight of tammar wallabies from Kangaroo Island is approximately 5.5 kg for females and 7.5 kg for males (Smith and Hinds 1995). This is considerably heavier than the tammars used in this study, which had mean body weights 3.90.17 kg (n=9) for females and 6.10.43 kg (n=10) for males. The findings of Fisher and Owens (2000) imply that this would result in the tammars on Garden Island having significantly smaller home ranges, which was what we found. The confinement of the tammar population to Garden Island may also be a factor in producing smaller home ranges and this influence could be investigated by comparing the home ranges of tammars on Garden Island with those of tammars on the Western Australian mainland and on other islands.

Our results indicate that differences in the tammars‟ habitat caused by human disturbance have probably not resulted in significant differences in the size of their home ranges. A suite of different factors are likely to affect the size of the home ranges of tammar wallabies and changes to their habitat in this instance have not been sufficient to cause significant changes in the size of their home ranges.

5. Speed limit, verge width and day length are the major factors correlated with the number of road-kills of tammars (Macropus eugenii) on Garden Island, Western Australia.

5.1 Abstract Approximately 300 tammar wallabies (Macropus eugenii) are killed on the roads of Garden Island every year, which corresponds to approximately 14-18% of the estimated population size. All of these road-kills are a result of the large volume of traffic associated the HMAS Stirling naval base. We investigate the relationship between the number of road-kills and verge width, fences, speed limit, roadside lighting and type of vegetation adjoining the road by subdividing the roads on the naval base into sections of approximately 500 m and fitting a generalized linear model to the data from each section. A GIS held by the Royal Australian Navy was used to obtain data on roadside fences and type of vegetation and to map numbers of road-kills to identify the frequency of road-kills in each section. The impacts of day length, rainfall and the number of personnel in port on the number of animals killed were also determined by linear regression and analysis of covariance. Day length, verge width and speed limit were significantly correlated with the frequency of road-kills. Day length was negatively correlated with the number of road-kills (P<0.001), while increased verge width was correlated with increased road-kills and speed limits of 50 km/h resulted in significantly fewer road-kills per section than speed limits of 60 or 80 km/h (P<0.001). Our results suggest that reducing speed limits, especially between dusk and dawn, reducing the width of verges may be useful strategies to reduce the number of animals killed by vehicles. The effect of day length also shows that concentrating mitigation methods in the winter months would be likely to result in the greatest reduction in the number of animals killed by vehicles.

5.2 Introduction Road mortality has the potential to be a serious threatening process for populations of wild animals especially where the rate of deaths exceeds the population‟s recruitment rate (Jones 2000). Even when the number of animals killed by vehicles is not large enough to cause a decline in the size of the population, road-kills can alter sex ratios and age structures within a population if animals of a particular sex or age are killed more frequently (Hauer et al. 2000, Steen and Gibbs 2004, Steen et al. 2006). On Garden Island, Western Australia, approximately 300 tammar wallabies (Macropus eugenii) are killed each year by vehicles associated with the HMAS Stirling naval base (Walker 2002). As there are approximately 2200 tammars on the island (Bradshaw 1988), this number of deaths equates to 14-18% of the total population each year.

This paper describes the use of a geographical information system (GIS) to gather data on the relationship between high numbers of road-kills and environmental variables. In the past GIS has been used to study habitat selection by wildlife (Stoms et al. 1993), or to predict the distribution of wildlife in the landscape based on habitat structure variables (e.g. Austin et al. 1996, Lahm et al. 1998, Carrascal et al. 2002). More recently GIS has been used to predict the distribution of wildlife in relation to environmental threats such as pollution (e.g. Chow et al. 2005), and habitat modification (Figala et al. 2001) including road construction (Treweek and Veitch 1996). Despite the fact that road mortality is now recognised as a threat for wildlife (Forman and Alexander 1998) to date few studies have used GIS to examine the factors associated with road-kills (Ramp et al. 2005, 2006).

This study aimed to find spatial and temporal variables that were correlated with the number of tammar wallabies killed on different roads and at different times of the year in order to inform decisions on possible mitigation methods. We specifically focused on day length, number of personnel in port, roadside fencing, width of the road verges, roadside lighting, type of roadside vegetation and speed limit.

We expected that day length would be negatively correlated with the number of road- kills, as shorter days are associated with personnel starting and finishing work closer to dawn and dusk when tammars come out to graze. The number of personnel in port was expected to be positively correlated with the number of road-kills, as more personnel in

71 port should result in greater traffic volumes on the naval base and increased traffic volumes have been shown to result in more animals being killed on roads (Ramp et al. 2006).

Roadside fencing has been shown to increase or decrease the number of animals killed by vehicles, depending on the extent to which the fences exclude animals from the road (Romin and Bissonette 1996, Putman 1997, Jaeger and Fahrig 2004). Fences that completely exclude animals from the road obviously result in much fewer animals being killed by vehicles, but when fences act as a barrier to startled animals exiting the road verge, they can increase the number of road-kills by causing the animals to cross the road in an attempt to escape. On Garden Island roadside fencing does not completely exclude animals from the road verge, but may act as a barrier to animals trying to escape from oncoming cars and we therefore expected that roadside fencing would be positively correlated with the numbers of road-kills.

Verge width was expected to be positively correlated with the number of animals killed on the roads as plants on the road verges of the naval base are a major food source for the tammars (McMillan 2006). Lee et al. (2004) and Ramp et al. (2006) found that more macropods were killed by vehicles when there was more food available on the road verges. Wider verges provide more grass for the tammars to graze, and this should bring more animals to the roadside (Brooker 1992). We expected that the greater number of animals at the roadside would result in more animals crossing the road, and therefore in more animals being killed by vehicles.

Tammars have been shown to associate increased levels of nocturnal lighting with safety by reducing the amount of time invested in vigilance activities (Beiebouw and Blumstein 2003). They have also been shown to recognise potential predators by sight rather than by sound or smell (Blumstein et al. 2000, Blumstein et al. 2002b). As the roads on the HMAS Stirling naval base were lit either on one or both sides we expected that the tammars grazing on road verges that were lit on both sides would see and respond to vehicles by moving away from the road sooner than animals grazing on road verges that were less well lit thereby resulting in fewer road-kills.

The type of vegetation near the roadside was also expected to have an impact on the number of tammars killed by vehicles as tammars have been shown to devote more time to vigilance behaviour the further they are from cover (Blumstein et al. 1999). We therefore expected that tammars grazing on verges that did not have nearby dense vegetation would be more flighty and therefore more likely to attempt to cross the road when a vehicle approached, therefore leading to more road-kills.

Vehicle speed has been shown on many occasions to be positively correlated with the deaths on animals on roads as higher speeds reduce the amount of time that a driver has to react to the presence of an animal and avoid a collision (Jones 2000, Ramp et al. 2006). We therefore expected that road sections with higher speed limits would have higher numbers of road-kills than those with lower speed limits.

5.3 Materials and Methods 5.3.1 Experimental design To test these hypotheses we subdivided the roads on the HMAS Stirling naval base on Garden Island into 500 m sections and used a GIS to identify the frequency of road kills and the factors that might affect the frequency of road kills for each section. We then used a generalized linear model to test the effects of the individual factors on the frequency of road kills.

5.3.2 Study area Garden Island is located approximately 35 km south west of the Western Australian city of Perth and approximately five km west of the mainland (Figure 5.1). The island hosts Australia‟s largest naval base HMAS Stirling, which was built during the 1970s. As part of the construction of the naval base a causeway was built from Point Peron on the mainland to the southern end of the island to allow access to vehicles on Defence Department related business. The infrastructure of the HMAS Stirling Naval Base is primarily in the southern part of the island and this was also where the majority of the tammars, approximately 200-250 per year, were killed by vehicles. This area was the focus of our study, as the movement of traffic north of this area was limited to security patrols and traffic volumes were therefore significantly lower than in the study area.

Figure 5.1. Location of Garden Island, Western Australia (115o40‟E, 32o16‟S) and the study area covering the main area of the HMAS Stirling Naval Base.

5.3.3 Road-kills Between January 2000 and December 2004 the gardening, security staff and ranger recorded the date and location of every tammar killed by vehicles on the island. All of the roads on the main area of the HMAS Stirling Naval base were divided into 12 sections of approximately 500 metres each (Figure 5.2) and these were entered into ArcGIS (ESRI, New York) as a new shapefile. The road-kill data were then added to each of these segments along with the explanatory variables. 500 m was chosen as the length of the road sections because the data for the 500 m sections were present in the GIS database from a previous study (Walker 2002). The single road north of this area was not studied, as access is restricted between 1800 and 0600. Due to the restricted access, this road also has much less traffic than the roads on the main area of the naval base.

Figure 5.2. Road sections used in the analysis of road kill frequencies on Garden Island Western Australia.

5.3.4 Spatial variables Fences Data on the presence or absence of fences was obtained from the GIS database held by the Australian Navy and managed by Sinclair Knight Merz (Perth, Western Australia). These fence data in the GIS were used to obtain a table containing the presence of fences and the length of each road segment that was fenced. A road was considered fenced if the open road verge ended in a fence within 10 m of the road. Based on this classification the road sections were classed as being unfenced (0) fenced on one side (1) or fenced on both sides (2). For the purposes of the analysis, fencing was considered as a categorical variable.

Roadside vegetation Data on roadside vegetation were obtained from the GIS database and classified according to the presence or absence of Melaleuca lanceolata-Acacia rostellifera low forest or Melaleuca huegelii scrub (Brooker 1992). To do this, 25 m buffers were created either side of the road segments and these were then clipped with the vegetation data (resolution: 10 m) to determine which vegetation types occurred within the buffers. Where this vegetation was not found within 25 m of the road the area consisted of irrigated lawn, buildings or car parks and these areas were classified as disturbed. These three vegetation types were treated as separate categories in the analysis.

Verge width Verge width (m) was measured for each road section at approximately 100, 250 and 400m along the section. The verge width was measured on both sides and the mean of all six measurements was used in the analysis.

Roadside lighting The presence of roadside lighting was also recorded from a survey of the roads, as these data were not present in the GIS database. All roads had lighting of some form and were therefore classified as being lit on either one (1) or both sides (2).

Speed The location of changes in speed limits was recorded from a survey of the roads on the island. There were three speed zones, being 50, 60 and 80 km/h and each road section had the same speed limit for the entire length. These three speed limits were treated as categorical variables in the analysis.

5.3.5 Temporal variables Day length Day length, measured in hours, was calculated from sunrise and sunset times obtained from Geoscience Australia for the study period. The day length for the 15th day of each month was used as the measure of day length in the analysis. Day length was chosen, rather than hours to work closing or opening, as animals were run over in both the evenings and early mornings.

Personnel in port The number of visiting personnel was calculated from records of ship movements obtained from the Fremantle Port Authority. The number of personnel on each ship was obtained from publicly available information on each naval vessel and this was multiplied by the number of days each month that a ship was in port to give the number of personnel in port each month. The number of personnel in port each day was then averaged for the entire month and this value was used in the analysis.

5.3.6 Data analysis The effects of the spatial variables on the number of animals killed were analysed using a generalized linear model assuming a normal distribution and identity link function. The 500m road section was the experimental unit and total number of animals killed between January 2000 and December 2004 per road section was used as the dependent variable. The data on total road-kills were inspected visually prior to analysis to ensure that they were normally distributed. The model was initially constructed with the total number of road-kills per road section as the dependent variable and all of the independent spatial variables included. Models with all combinations of the independent variables were then tested and the most parsimonious model was chosen based on Akaike‟s Information Criterion (AIC) values.

The effects of the temporal variables of day length, rainfall and number of personnel in port were analysed by linear regression to determine if they were correlated with the number of animals killed. As rainfall and day length are also correlated with each other their effect was determined using analysis of covariance (ANCOVA). The mean rainfall for each month of the year was calculated over the 5 years of the study and the rainfall for each individual month was then classified as above or below average. The number of road kills over all road sections was then analysed against rainfall (high or low) with day length as a covariate.

5.4 Results Dates and locations were recorded for 1258 road-kills at a rate of 3.50.31 deaths/km/month (meanse). The rate of road-kills over the entire study area varied between 0 deaths/km/month in December 2002 to 10.17 deaths/km/month in June 2003.

Over the five-year study period the largest numbers of animals were killed between March and August (Figure 5.3).

30 \

Road-kills 20

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Figure 5.3. The mean (s.e.) number of tammars (Macropus eugenii) killed by vehicles on the HMAS Stirling naval base each month between January 2000 and December 2004 (n=5).

5.4.1 Spatial variables The most parsimonious model included only verge width and speed, without any interaction, as fencing, roadside vegetation and lighting were not significant predictors of the number of road-kills. Verge width was positively correlated with the number of animals killed and more animals were killed in 60 km/h speed zones than in 80 or 50 km/h zones (Table 5.1).

Table 5.1. The coefficients, and probability values of the spatial variables that were significant in predicting the numbers of tammars killed on roads on Garden Island. Variable Coefficient df 2 P Verge width (m) 6.98 1 3.03 0.081 Speed limit 2 8.85 0.012 50 km/h -44.63 60 km/h 37.45 80 km/h -7.18

5.4.2 Temporal variables Rainfall and day length were significantly correlated with the number of animals killed (rainfall: r2=0.44, P<0.001, day length: r2=0.70, P<0.001), while the number of personnel in port was not correlated significantly with the number of road-kills (r2=0.004, P=0.683). When rainfall was considered with day length as a covariate there was no significant effect of rainfall on road-kills (df=1,56, F=1.05, P=0.311), but day length was highly significant with an additional 8.4 deaths per month for each one-hour reduction in day length (df=1,56, F=130.78, P<0.001).

5.5 Discussion Day length was negatively correlated with the number of animals killed by vehicles, which supported our hypothesis. Whilst day length was correlated with rainfall, the ANCOVA results demonstrated that rainfall did not have a significant effect on the number of animals killed. This is most likely the result of shorter days in winter resulting in more people arriving and leaving work before sunrise and after sunset.

Significantly fewer animals were killed on roads with a speed limit of 50 km/h when compared with 60 or 80 km/h. This supported our hypothesis that higher speed limits would be associated with more road-kills and agrees with previous studies showing that vehicle speed is one of the most important causative factors in animal-vehicle collisions (Jones 2000, Ramp et al. 2006). However, the lack of difference between 60 km/h and 80km/h zones was unexpected. When the road-kills hotspots were overlayed with the speed limit zones using the GIS maps it became clear that the a large number of the tammars were killed on the road where the speed limit changed from 80 km/h to 60 km/h (Figure 5.4). Reports from the ranger on the island suggest that many people do not reduce their speed to comply with the 60 km/h speed limit and this may be the cause for this unexpected result (T. Smith pers. comm.). Using actual mean vehicle speed rather than posted speed limits would probably have been a better predictor of the number of animals killed, but unfortunately, it was not possible to measure the actual speed of vehicles.

Figure 5.4. Comparison of posted speed limits and the mean number of tammars killed by vehicles per month on Garden Island, Western Australia, from January 2000 and December 2004.

The width of the road verge was also positively correlated with the number of animals killed by vehicles, which supported our hypothesis. We expected that wider verges would attract more animals to feed and that this would result in a greater number of animals killed by vehicles (Brooker 1992). Wider verges may also be related to different behaviours in the tammars as they have been observed to dedicate more time to vigilance activities as they graze further from cover (Blumstein et al. 1999). The width of verges may therefore affect the behaviour of the animals in relation to vehicles so it would be worthwhile observing the behaviour of animals on road verges when vehicles approach.

The hypothesis that roadside fencing would increase the number of animals killed by vehicles was not supported, as fencing was not a significant predictor of the number of road-kills. This result suggests that the roadside fences on Garden Island do not act as a barrier to animals trying to leave the road verge in response to approaching vehicles. We have observed that many tammars exit the road verge by running parallel to the roadside fences until they come to a hole in the fence. This behaviour may be the

80 reason why fences were not significantly correlated with the number of animals killed by vehicles.

The number of personnel in port was also not related to increased numbers of tammars killed by vehicles, which did not support our hypothesis. We expected that an increase in the number of personnel in port would increase traffic on the island, but we were unable to gather data on traffic volumes. It may be that the increased number of personnel in port did not increase traffic volumes, or that traffic volumes were only increased during the day, when road-kills usually do not occur because the tammars are not active. It would have been advantageous to the have access to traffic volume data and this is something that any future work should attempt to address.

Our hypotheses about the effect of roadside lighting and roadside vegetation were also not supported, as these variables were not significant predictors or road-kills. The lack of a significant relationship between lighting and road-kills may be due to the fact that all of the roads on the naval base were lit to some degree. Our model only distinguished between lighting on one side or both sides of the road and this may not actually produce the differences in vigilance behaviour that were reported in previous studies (Beiebouw and Blumstein 2003). The hypothesis that fewer road-kills would occur on roads with dense vegetation on the road verge was also not supported. This may have been a result of the highly disturbed nature of the environment on the naval base. We expected that the tammars would seek refuge in dense vegetation when vehicles approached, but it is also possible that the tammars on the naval base perceive buildings or other man-made objects as potential shelter in the same way that we expected them to perceive dense vegetation. If this was the case then this may explain the lack of correlation between the type of vegetation and road-kills.

The road-kill frequencies observed in this study were exceptionally high with a mean rate of 3.50.31 deaths/km/month, whereas rates of 1.2 deaths/km/month are normally regarded as high (Ramp et al. 2005). This extremely high frequency of road-kills has the potential to impact seriously on the tammar population on the island, which was estimated at 2172 individuals (95% C.I. 1733, 2396, Bradshaw 1988).

We were successful in finding correlations between three factors and the number of animals killed by vehicles, but there are undoubtedly other factors that contribute to the chances of animals being killed. The volume of traffic, actual vehicle speed and the number of animals grazing on road verges have been found to be significant factors in contributing to road mortality and would likely account for some of the variation in the number of road-kills (Lee et al. 2004, Ramp et al. 2006). Unfortunately, we did not have access to these data for the study period, but any future work should attempt to account for these variables.

5.5.1 Management implications The results of our analysis have shown that speed, verge width and day length were correlated with the number of road-kills and mitigation methods should therefore focus on these three factors. Significantly more tammars were killed on roads where the speed limit was greater than 50 km/h and therefore reducing the speed limit to 50 km/h for all roads on the island, especially between dusk and dawn, is strongly recommended. The use of traffic calming devices, such as speed bumps, is impractical on Garden Island, as emergency vehicles require unhindered access to all areas of the naval base. Therefore the introduction and enforcement of a lower speed limit is the most practical way to attempt to reduce the number of deaths that may be caused by vehicle speed. Enforcement of these reduced speed limits would be particularly important as previous studies have found that, without enforcement, reduced speed limits do not result in lower actual vehicle speeds (Pojar et al. 1975, Dique et al. 2003).

Verge width was positively correlated with the number of animals killed by vehicles, but the exact reasons for this relationship are unclear. Further work should be done to determine how verge width might influence the aggregation of tammars, their behaviour and the influence of these on the chances of animals being run over. If the presence of more animals on wider road verges is the main reason for this correlation then reducing the width of road verges, or removing grasses from the verges would likely reduce the number of animals being killed by vehicles.

While there is obviously nothing that can be done to change day length, the results suggest that targeting management strategies to the months of March to August would have the greatest impact on reducing the number of animals killed. At this time of year

82 the majority of female tammars are carrying pouch young (Chapter 2) and therefore reducing the number of animal-vehicle collisions at this time of year would also reduce the number of pouch young that are killed or need to be taken into care. Limiting the amount of non-essential traffic between dusk and dawn should reduce the number of tammars being killed, and educating drivers, so that they are more aware of the problem of road-kills, may also be useful in reducing the number of animals being killed.

6. General Discussion

The mechanistic paradigm of population dynamics outlined by Krebs (2002) asks the question of how do extrinsic and intrinsic factors alter the rate of change in the size of populations through their effect on the rates of birth, death and movement. In this thesis I have provided some answers to this question in relation to the effect that human disturbance on Garden Island, Western Australia, has had on the resident population of tammar wallabies through modification of the animals‟ habitat and artificial mortality from road-kills.

Despite being unable to replicate the three different levels of disturbance in this study, for reasons described in Chapters 1 to 3, the results obtained showed significant differences in the population dynamics of the different populations of tammar wallabies associated with the modification of the their habitat and the road-kills on the naval base. The shared history of the populations of tammar wallabies in the three study areas, prior to the construction of HMAS Stirling in the 1970s, also controlled for the potential confounding effects of genetic and physiological differences, which may have otherwise affected the results (Krebs 2002). I am therefore confident that the results presented in this thesis provide a clear and valuable insight into the effect of disturbance by humans on the population dynamics and ecology of the tammar wallaby.

6.1 Habitat modification The impact of the habitat modification on the naval base was determined by comparing the effect of extrinsic factors such as rainfall and temperature on the condition of the tammars and on the rates of survival, birth and weaning in modified and unmodified habitats. The results of this study strongly supported the hypothesis that the habitat modification on the naval base would significantly alter the dynamics of the population of tammars. The tammars on the naval base were in better condition than their counterparts in the bushland areas of the island (Chapter 2) and in the years with high or low rainfall (2005 and 2006) this resulted in significantly higher rates of survival of animals of all ages and higher fecundity transitions on the naval base (Table 6.1). The higher fecundity transitions on the naval base were the result of reduced mortality of pouch young, rather than higher birth rates (Chapter 2). These results suggest that the

habitat modification on the naval base was buffering the effects of the weather conditions in those years, allowing more females to raise their young successfully and for a greater proportion of young-adult and adult animals to survive to the following year (Chapter 3). I strongly suggest that the reason for the higher rate of survival and weaning was the better condition of the animals that would have been caused by the increased supply of food on the naval base.

In 2007, when the annual rainfall was closer to the long-term mean and winter temperatures were higher, the fecundity transitions and the rate of survival of young adults were higher in the bushland areas compared with the naval base, while the rate of survival of adults was still higher on the naval base (Table 6.1). The higher fecundity transitions in the bushland areas could be ascribed to the lower mortality of pouch young (Chapter 2). The lower fecundity transitions on the naval base were the result of higher pouch young mortality compared with the previous two years. The reason for the higher mortality of pouch young is not clear, but it may be related to the presence of a fox that was sighted near the base as discussed in Chapter 3.

Table 6.1 Rates of survival and fecundity transitions of tammar wallabies in the three study areas on Garden Island in relation to annual rainfall and mean winter minimum temperatures between 2005 and 2007. The survival rate of young-adults in the northern bushland could not be estimated accurately in 2007. Rainfall (mm) 456 655 849 Winter Min. Temp. (oC) 11.10.65 12.30.21 11.30.33 Year 2006 2007 2005 South. North. South. North. South. North. Base Bush. Bush. Base Bush. Bush. Base Bush. Bush. Survival Young- 0.93 0.50 0.64 0.51 0.67 0.78 0.69 0.49 Adult Adult 0.83 0.72 0.70 0.76 0.72 0.69 0.92 0.66 0.68

Fecundity Young- 0.27 0.15 0.05 0.21 0.28 0.06 0.17 0.14 0.02 Transition Adult Adult 0.53 0.25 0.32 0.29 0.47 0.38 0.34 0.24 0.11

When the habitat of tammar wallabies is disturbed in the way that it has been on Garden Island, and the amount of available food is increased, the effect of high and low rainfall and lower winter temperatures is greatly reduced. The increased supply of food from the lawns on the naval base, particularly over summer and autumn, resulted in the tammars there being in better body condition, which presumably allowed them to cope

86 better with the weather conditions over winter. This resulted in the population on the base having higher rates of survival and lower mortality of pouch young in these years. While other aspects of the human disturbance on the naval base such as buildings, roads and lighting cannot be discounted as having an effect, the relationship between food availability, the condition of the animals and rates of survival and fecundity transitions were similar to those observed for other macropods (Bayliss 1985b, Fisher et al. 2001) and eutherian mammals (Choquenot 1991, Gaillard et al. 1998).

The combined effect of changes to the rates of survival and fecundity transitions from the habitat modification on the naval base is apparent in the differences in the projected growth rates () for the different populations. In the years with high or low rainfall (2005 and 2006) and lower minimum temperatures over winter the population on the naval base had a projected rate of change in size that was significantly higher than both of the bushland areas (Table 6.2). In 2007 when the rainfall was closer to the long-term mean and minimum temperatures in winter were higher the projected s for the populations in the bushland areas were higher than those of the population on the naval base (Table 6.2). These results demonstrate that the modification of the tammars habitat was a benefit to the animals in 2005 and 2006, but not in 2007.

Table 6.2 Projected asymptotic rates of change in the size (year-1) of the populations of tammar wallabies in the three study areas of Garden Island in relation to annual rainfall and winter minimum temperatures between 2005 and 2007. Rainfall (mm) 456 655 849 Winter Min. Temp. (oC) 11.10.65 12.30.21 11.30.33 Year 2006 2007 2005 Base 1.184 0.959 1.304 Southern Bushland 0.878 1.108 1.168 Northern Bushland 0.747 1.094 0.934

The answer to the question of how extrinsic factors affect the rate of change in the size of tammar wallaby populations therefore seems to be that for populations living in undisturbed habitat high or low annual rainfall in combination with low winter temperatures reduce the rate of change in size through increased mortality of pouch young (Chapter 3). Nearly all females give birth in late summer and then if conditions in early to mid winter are particularly unfavourable many are probably unable to maintain lactation and their young die as a result (Chapter 2). Without the demands of

87 lactation, the females that lose their pouch young are then probably able to survive and go on to breed again the following year. This results in a constant rate of adult survival and considerable variation in weaning rates between years. This strategy also improves the chances of breeding females surviving years with unfavourable conditions and allows them to go on to attempt breeding again in the following year. This results in the population being able to increase in size quickly when conditions are favourable and to recover relatively quickly from the loss of animals in years with unfavourable conditions. This pattern is similar to that found for other similar sized macropods (Fisher et al. 2001) and large ungulates (Gaillard et al. 1998).

6.2 Road-kills The high numbers of road-kills on the naval base reduced significantly the rate of survival of adult animals in each of the three years of the study (Chapter 3). They also reduced the rate of survival of young-adult animals, but this effect varied greatly over the three years (Chapter3). This resulted in the projected asymptotic rate of change in size of the population on the naval base being significantly lower when road-kill mortality was included for each of the three years (Chapter 3). The high rates of road- kills were also likely to be maintaining the size of the tammar population below the carrying capacity of the naval base area. The projected rate of change in size of the population () in 2006 was 1.304 (r=0.265) per year, which is likely to be close to this population‟s intrinsic growth rate. The intrinsic growth rate occurs when a population is free from density dependent constraints and the rates of survival and fecundity are not limited, i.e. the population is far below the carrying capacity of its environment (Caughley and Sinclair 1994). If the road-kills on the naval base were to cease completely, the population in that area would increase in size quite rapidly and it would reach, or even overshoot, the carrying capacity of the area. It would then likely be controlled by density dependent reductions in survival and fecundity transitions and/or emigration.

The size of the tammars‟ home ranges on the naval base is also likely to contribute to the large numbers of road-kills, as the number of times an animal crosses roads in any given night is likely to be strongly correlated with the size of that animal‟s home range. Roads that separate feeding areas, such as the ovals, and areas of bushland that are used

88 as refuges also had high numbers of road-kills, as animals were likely to try and return to the shelter of the bushland when startled by vehicles (Chapters 4 and 5).

6.3 The overall effect of disturbance The effect of human disturbance on the dynamics of the population of tammar wallabies can be summarised by the rates of change in size of the different populations (). The comparison the s of the populations in the bushland areas with the population on the base demonstrates that the negative effect of the road-kills on the base was outweighed by the positive effect of the increased food supply in the very wet and very dry years (2005 and 2006), as the rate of change in size was significantly greater on the base (Chapter 3). In the year with a medium amount of rainfall (2007) the negative effect of the road-kills outweighed the positive effect of the increased food supply, as the rate of change in size was significantly lower on the naval base, but this result may have been confounded by the possible presence of a fox near the naval base in mid 2007 (Chapter 3).

The comparison of the projected rates of change in the size of the populations of tammars in the southern and northern bushland also suggests that the southern bushland population was affected by its proximity to the naval base. The rate of change in the size of the population in the southern bushland area (without the impact of road-kills) was higher than that of the population in the northern bushland in 2005 and 2007, but it was significantly lower in 2006. The population projections, including temporal stochasticity, also demonstrated that, in the long term, there would be an advantage to the population in the southern bushland compared with that in the northern bushland (Chapter 3). The study of the tammars‟ spatial ecology (Chapter 4) demonstrated that some of the tammars in the southern bushland area were regularly moving onto the base, presumably to feed on the lawns. The additional food supply available to these animals and the likely effects on their condition and rates of survival and weaning success is therefore likely to be the reason for the increased projected rate of change in the size of the population.

By comparing the rates of change in size () we can summarise the changes that have occurred in rates of survival and fecundity transitions to determine if there is an overall positive or negative effect of the disturbance on these populations of tammars. The

89 results presented in Chapter 3 demonstrate that over the long-term the human disturbance on Garden Island is likely to reduce the size of the populations of tammar wallabies and therefore measures are needed to reduce this impact.

By gathering data on the demographic effects of the human disturbance on the tammar wallabies, the ways in which the populations can be managed become clear. There is a need to reduce the rate at which tammars were killed by vehicles, especially in the case of the population in the southern bushland area (Chapter 3) and some of the factors that may be manipulated to achieve this are shown in Chapter 5. However, the results of the longer-term population projections also show that reducing the mortality from road-kills needs to be carefully managed to avoid the rate of change in the size of these populations increasing dramatically, which could result in them increasing past the carrying capacity of those areas (Chapter 3). The results presented in Chapters 2 and 3 demonstrate that the cause of these high rates of change in size were the increased rates of survival of adults and higher fecundity transitions and both of these vital rates should therefore be targeted in management. Rates of survival could be manipulated by culling or translocation of animals off the island and fecundity transitions could be manipulated by fertility control (Cooper and Herbert 2001). Fertility control by hormonal contraception would be preferable to surgical sterilisation as the reduction in fecundity could be varied each year and animals are not stopped from breeding permanently, which would limit the loss of genetic variation (Cooper and Larsen 2006). Limiting the rate of loss of genetic variation is particularly important in this population as they are already significantly inbred (Eldridge et al. 2004). The proportion of females that would need to be stopped from breeding to maintain a constant population size, i.e., =1.0, could also be accurately predicted using stage-based population models similar to those used in this study.

6.4 Future research The results presented in this thesis were limited to three years of study, but a longer- term study would be required to investigate further the relationship between environmental stochasticity and the population dynamics of the tammar wallabies. This is especially true of the relationship between young-adult survival and rainfall and winter temperatures for which the two bushland areas gave conflicting results (Chapter 3). A long-term study of the dynamics of the populations of tammars is therefore

90 warranted and is strongly recommended. By gathering more data on the rates of survival and weaning success in years with different levels of rainfall and different winter temperatures the relationships that exist between environmental conditions and the vital rates could be determined. This form of study would also allow for the monitoring of the populations of tammars in the different parts of the island to assess the success of management strategies aimed at reducing the impact of the presence of the naval base.

The effect of artificial lighting on the timing of births on the naval base should also be studied as it may have wider implications for the management of wildlife in urban areas. A study on captive tammars to determine if the level of artificial lighting on the naval base is sufficient to disrupt their production of melatonin would demonstrate if the lighting on the base is the cause of the increased variation in birth dates observed in the animals living in this area (Chapter 2). This may have important ramifications for the management of captive colonies of animals that show strong seasonality in their breeding. This would be especially important to institutions involved in captive breeding programmes such as zoos that are generally found in urban areas where light pollution can be significant. This would also be the first documented case of light- pollution affecting the reproduction of a population of mammals by affecting the signalling of changing day length (Longcore and Rich 2004).

6.5 Conclusions The results presented in this thesis demonstrate how disturbance of the habitat of animals can cause significant changes to the vital rates of birth and death and, in turn, the rate of change in the size of the population. Disturbance also affected these populations in unexpected ways, such as the alteration of birth schedules that may be the result of artificial lighting on the naval base. The results also demonstrate that care needs to be taken in the management of the effects of human disturbance, as the desire to manage a perceived problem, in this case road-kills, may result in other problems arising in the future, such as the possibility of an over-abundant population.

By improving our understanding of the mechanisms that affect the rate of change in the size of populations, then the future size of those populations can be predicted more accurately. This should then allow managers to manipulate the rate of change in size to

91 stop populations either becoming too numerous, in the case of abundant species, or reducing in size, in the case of rare species. By changing from a reactive to proactive style of wildlife management the problems associated with over-abundant populations, as well as those of small populations, could potentially be avoided. This style of management requires a more thorough understanding of the dynamics of populations and therefore a greater need for scientists and managers to work together to guide management decisions.

7. Management recommendations

Base on the results presented in this thesis the following management strategies are recommended to reduce the impact of the disturbance caused by the HMAS Stirling Naval Base and to ensure the long-term persistence of the population of tammar wallabies on Garden Island.

1. The perimeter fence of the naval base should be improved to include buried skirting to stop tammars from the adjacent bushland accessing the naval base. The results of this study have shown that the road-kills on the naval base are reducing the rate of survival of tammars in the southern bushland area and this is predicted to have a serious effect on the long-term viability of that population (Chapter 3). By improving the fence the deaths of animals from this area should stop and the populations in the bushland adjacent to the base should be regulated by annual variation in rainfall in a similar way to the population in the northern bushland (Chapter 3).

2. All non-essential traffic outside of the main area of the naval base between dusk and dawn should be stopped where possible. The populations of tammars in the bushland area of the island were predicted to be affected negatively by even small numbers of road-kills and therefore traffic in these areas between dusk and dawn, when the tammars are active, should be reduced, or stopped where possible (Chapter 3). To achieve this I recommend the restriction of recreational access to the armaments wharf to daylight hours and a review of the security patrols through the bushland north of the armaments wharf, as both of these forms of access result in the deaths of tammars.

3. An island-wide 50km/h speed limit should be introduced between dusk and dawn. Speed limits above 50km/h were positively correlated with the number of tammars killed on the roads of Garden Island (Chapter 5) and therefore reducing the speed limit should result in fewer animals being killed. This reduced speed

limit should be introduced along with an campaign to educate people working on the island to the need to slow down to reduce the number of animals being killed. The speeds of vehicles should also be monitored to ensure that people are reducing their speed between dusk and dawn.

4. The width of the grassed road verges should be reduced where possible. The width of verges was correlated with the number of tammars killed by vehicles (Chapter 5), presumably because the number of tammars present is also correlated with the width of the verge (Brooker 1992). Therefore reducing the width, or the amount of grass on these verges should result in fewer tammars grazing and therefore fewer being killed by vehicles.

5. The population of tammars should be monitored annually by trapping to assess changes in the numbers and the health of the animals on the island. The data collected in this study have shown that there is considerable year-to- year variation in the weaning rates and the survival of young-adult tammars in different areas of the island (Chapters 2 and 3). By trapping in November each year in the three areas used in this study the weaning rates could be estimated and rates of survival could be calculated using mark-recapture techniques. This monitoring will therefore be able to detect changes in these rates and any change in the size of the populations of tammars in different parts of the island could also be assessed. Annual monitoring will also allow for the assessment of the effect of the other management strategies on the rate of change in the size of the populations in different areas of the island.

If these recommendations are implemented and annual monitoring demonstrates that the population of tammars on the naval base is increasing in size then measures may need to be taken to maintain the population at a relatively constant size. This could be done by reducing the tammars‟ access to the lawns on the naval base by improving the fences around the ovals to exclude the tammars from those areas or by reducing the area of irrigated lawn on the road verges. Alternatively the rates of fecundity could be reduced by hormonal sterilisation, and translocation of animals could be used to reduce the rates of adult survival. These translocations could be to sites on the mainland, if this was

94 permitted, or these animals may be wanted by research institutions to supplement their captive colonies.

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