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An Australian Abroad: The secret life of the 
brushtail possum (Trichosurus vulpecula) 

 

 

A thesis presented in fulfilment of the requirements for the degree of 

 

Doctor of Philosophy 

in  

Veterinary science 

 

 

at 

Massey University, Manawatū, 

New Zealand 

 

 

Kyle Stephen Richardson 
2016 

 

 

  



II 
 

 

 

 

Dedication 

For Apple Monster 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



III 
 

Abstract  

The “superspreader” hypothesis relates disease transmission to social contacts and 

assumes transmission is driven by the frequency, type and distribution of contacts 

among infected and susceptible individuals. I investigated characteristics of brushtail 

possum (Trichosurus vulpecula) home ranges for six wild free-living subpopulations, 

(four grids were studied; all of them before possum depopulation and two of them after 

possum depopulation) constructing social networks relevant to bovine tuberculosis (TB) 

transmission before and after depopulation. I also experimentally infected possums with 

a novel strain of TB to monitor secondary case infections in relation to these contact 

and other factors, including population density and sex ratio. 

Before depopulation home range estimates showed adult males had larger home ranges 

than female and younger possums. Home range overlap and area of overlap differed 

between subpopulations, and possum sex and age; with adult males having more and 

larger overlaps with other possums. Possums were fitted with proximity-logging collars 

and contacts registered between April and October, 2012. The number of connections 

an individual has with others and the probability of the distribution of contacts it has 

within the population, or node degree and betweenness, also known as the shortest 

distance between individuals, were associated with sex, with males having higher 

values for each. Males also contacted more possums than females. Post-depopulation 

results showed an influx of male possums, higher population density, and smaller home 

range sizes than before depopulation. Possums post-depopulation also lacked an 

apparent ‘routine’ in contact networks, interacting with other possums haphazardly. The 

greater level of contact among adult males, than before depopulation, and their effects 



IV 
 

on recovering populations post-depopulation, was likely the cause of more TB infection 

in adults and males.  

This thesis provides empirical evidence that adult male possums have home range and 

contact network characteristics that are likely to enhance their involvement in the 

transmission and persistence of TB, relative to female and younger possums. 

Observations of experimentally infected individuals showed that infected males 

survived longer than females and that, as a consequence, those males potentially acted 

as a “supershedding” subgroup. I therefore provide evidence that adult male possums 

are the most important drivers of TB transmission and persistence of infection in 

populations, and could be targeted for control measures.     

 

  



V 
 

Acknowledgements 

First I would like to thank the following individuals for their guidance and support, and 

for showing me the joy I could find with a carrier in science. Michelle Anderson, Rick 

Douglass, Bill Good and Amy Kuenzi, you’ve all been an inspiration to me. 

Thank you to my fellow students at the Hopkirk Research Institute in Palmerston North, 

I think we all found help in helping each other. You made my time in New Zealand a 

joy. 

Thank you to the Royal Society of New Zealand Marsden Fund for making this thesis 

possible. I wouldn’t have completed it without the help of Isa Blasco-Costa, Marcus 

Bridge, Sam Brown, Dean Clark, Kev Drew, Nyree Fea, Anja Friedrich, Zoe Grange, 

Steve Hough, Mox, Chris Niebuhr, James Smith, and Cracker. You guys came out and 

worked harder grids under worse conditions than most scientists ever encounter. You all 

have my respect and deepest gratitude.  

I would like to thank Dr. Nicola Nelson, Dr. Weihong Ji and Dr. Lee Skerratt for taking 

the time and putting forth the effort to review this thesis. Your recommendations and 

input are greatly appreciated and have resulted in a better finished product. Thank you. 

I’ve devoted almost four years of my life to this project, but this study had five other 

men just as dedicated and driven to the task at hand as I was. Nigel French, I know I 

wasn’t easy for you to deal with or the best student for scheduling meetings (or just the 

best student in general), but I wasn’t a bore either. I thank you for that. Most of all, you 

gave me three years to witness first-hand what it takes to be a true top tier scientist. You 

definitely set the bar. Chris Jewell, it’s always nice to have a stats wiz on board. You sat 

for hours with me working the data. Thanks for being a part of this project and a valued 



VI 
 

advisor. Bryce Buddle, it feels like every question we set out to investigate during this 

study you already knew the answer to. Lots of people know possums and lots of people 

know disease, but I’d be hard pressed to find anyone who knows more about disease in 

possums than you. You’re a trooper in the bush, a master with a scalpel and a true 

professional to work with. No one offers better counsel or direction. Dan Tompkins, 

you’ve been the most important person in my life these last three years both personally 

and professionally. To say you went above and beyond the expectations as an advisor 

would be an enormous understatement. You offered everything you were able from 

guidance and support to food, drink and a roof over my head. You were the anchor of 

this study and for the team conducting it. I’m proud to call you my advisor and friend. 

Thank you to all of you for the opportunity you’ve given me to learn, and for the 

important roles you’ve each contributed to my live. To the last of the five but by no 

means the least Carlos Rouco, we sure rocked this project didn’t we? Possums, TB, 

earthquakes, wind and rain, no roads, no water, too much water, pigs, the possum pit, 

there was nothing we couldn’t handle. I’m not sure how two guys worked so well for so 

long out there without killing each other. Sure we had some bumps and bruises; there 

was a fair amount of pain and blood loss and one a hospital trip, just walk it off right. 

Along the way you found a way to teach me everything except how to speak Spanish 

and in the end we got the job done, thanks for everything my friend.  

I would also like to thank Scott Carver. You’ve advised me from my undergrad research 

through to the end of my PhD. There isn’t time to mention the countless times you’ve 

supported me. Professionally and personally I hold you in the highest regard, thanks for 

everything. Melanie Laird, you kept me smiling through the hardest times of this thesis. 

You encouraged me, supported me and helped me to push through to the finish. From 

the bottom of my heart, thank you.  



VII 
 

Finally, I would like to thank my family, Gary and Denise Richardson, my sister Claire 

and brother Cody. You’ve loved and supported me all my life. I’m only here now 

because of you. 

  



VIII 
 

Thesis structure and format 

This thesis is presented as a series of seven chapters. Encompassed by a general 

introduction and discussion, five research chapters have been prepared and are 

presented for future publication in peer reviewed journals.  

 

Chapter one 

General introduction and literature review introduces the concepts behind the 

research contained in this thesis by discussion and reviewing current literature of basic 

ecology of brushtail possums and disease ecology associated with the aspects of bovine 

tuberculosis. 

 

Chapter two 

Interacting determinants of brushtail possum (Trichosurus vulpecula) home range 

size and implication for possum population management will be submitted to 

Australian Journal of Ecology 

  

Chapter three 

Home range overlaps in the brushtail possum (Trichosurus vulpecula): 

investigating potential intrinsic and extrinsic determinants will be submitted to 

Australian Journal of Ecology 

 

Chapter four 

Construction of brushtail possum (Trichosurus vulpecula) contact networks to 

inform on bovine tuberculosis transmission between individuals, and its 

persistence in wild populations 

 

  



IX 
 

Chapter five 

Changes in population structure following depopulation; implications for TB 

transmission and persistence 

 

Chapter six 

Relating variation in tuberculosis (TB) transmission in brushtail possums  

(Trichosurus vulpecula) to potential drivers found at the environmental, population 

and individual level 

 

Chapter seven 

General discussion summarises the significant findings of this study. The relevance 

and implications are discussed and future research directions are suggested. 

 

Chapter eight 

Literature cited has been collated at the end of the thesis to reduce repetition. 

Literature is referred to in the format consistent with the format used for the journal 

Ecology. 

 

Chapter nine 

Appendix: Improving animal welfare standards while reducing disease exposure risk 

during euthanasia of trapped brushtail possums (Trichosurus vulpecula), C. Rouco, 

K.S. Richardson, D.M. Tompkins. Published Animal Welfare 2015, Vol 24; pg 235-

239. 

 

 

 

 

 

 



X 
 

Table of Contents 

 

1. General introduction and literature review ……………………………….......................1 

1.1.Study aim ………………………..………………………………………….…...1 

1.2.Study species- the brushtail possums ……………………………………….......5 

1.3.M. bovis and its presence in possums ……………………………………….......6 

1.4.Home range, distribution and behaviour ………………………………………..7 

1.5.Contact networks ……………………………………………………………....10 

1.6.TB transmission in the brushtail possum ………………………………………11 

1.7.Thesis chapter contents ………………………………………………………...12 

2. Interacting determinants of brushtail possum (Trichosurus vulpecula) home range size 

and implication for possum population management ……………………………….…14 

2.1.Introduction ……………………………………………………………………14 

2.2.Methods and materials ………………………………………………………....17 

2.2.1. Study site ……………………………………………………………....17 

2.2.2. Data Collection …………………………………………………...……18 

2.2.3. Population-scale density and mean home range estimates …………….19 

2.2.4. Determinants of individual home range size …………………………..20 

2.3.Results ……………………………………………………………………...….20 

2.3.1. Population-scale density and mean home range estimates …………….20 

2.3.2. Determinants of individual home range size …………………………..24 

2.4.Discussion ………………………………………………………………….…..27 

3. Home range overlaps in the brushtail possum (Trichosurus vulpecula): investigating 

potential intrinsic and extrinsic determinants ………………………………………….29 

3.1.Introduction ……………………………………………………………………29 

3.2.Methods and materials ………………………………………………………....31 

3.2.1. Study site ……………………………………………………………....31 

3.2.2. Data collection ………………………………………………………....32 

3.2.3. Analysis ………………………………………………………………..32 

3.3.Results …………………………………………………………………………33 

3.3.1. Number of overlaps …………………………………………………....33 

3.3.2. Area of overlaps …………………………………………………….....38 

3.4.Discussion ……………………………………………………………………...42 



XI 
 

3.4.1. Implications ………………………………………………………...….44 

4. Construction of brushtail possum (Trichosurus vulpecula) contact networks to in for on 

bovine tuberculosis transmission between individuals, and its persistence in wild 

populations …………………………………………………………………...………..47 

4.1.Introduction ……………………………………………………………………47 

4.2.Methods and materials ………………………………………………………....50 

4.2.1. Data collection ………………………………………………………....50 

4.2.2. Analysis ………………………………………………………………..51 

4.2.2.1. Population-level analysis ……………………………….……...52 

4.2.2.2. Individual-level analysis ………………………………..……...54 

4.2.2.3. Contact-level analysis ……………………………..…………...54 

4.3.Results …………………………………………………………….…………...59 

4.3.1. Population-level summaries of network characteristics ……………….59 

4.3.2. Individual-level analysis ……………………………………………….61 

4.3.3. Contact-level analysis ………………………………………………….65 

4.4.Discussion ……………………………………………………….……………..67 

5. The response of brushtail possum (Trichosurus vulpecula) populations to control, and 

implication for TB transmission and persistence ………………………………...……72 

5.1.Introduction ……………………………………………………….……...……72 

5.2.Methods and materials …………………………………………….…………...74 

5.2.1. Study site ……………………………………………………………....74 

5.2.2. Data collection ………………………………………………………....74 

5.2.3. Analysis ………………………………………………………………..74 

5.2.3.1. Population-level analysis ……………………………………....75 

5.2.3.2. Individual-level analysis ……………………………………….75 

5.2.3.3. Contact-level analysis ………………………………………….75 

5.3.Results ……………………………………………………………….……...…75 

5.3.1. Home range …………………………………………………………....75 

5.3.2. Population-level analysis ……………………………………………....77 

5.3.3. Individual-level analysis ……………………………………………….80 

5.3.4. Contact-level analysis ………………………………………………….84 

5.4.Discussion ………………………………………………………….…………..86 



XII 
 

6. Relating variation in tuberculosis (TB) transmission in brushtail possums (Trichosurus 

vulpecula) to potential drivers found at the environmental, population and individual 

level …………………………………………………………………………..………..93 

6.1.Introduction ………………………………………………………….……...…93 

6.2.Methods and materials ……………………………………………….………...97 

6.2.1. Experimental design ………………………………………………...…98 

6.2.2. Experimental infection methodology …………………………….....…99 

6.3.Analysis ……………………………………………………………….……...101 

6.3.1. Survival rates of challenged possums ………………………………...101 

6.3.2. Population-level drivers of transmission ……………………………..101 

6.3.3. Subgroups-level drivers of transmission ……………………………..101 

6.3.4. Individual-level drivers of transmission …………………………...…102 

6.4.Results ………………………………………………………………….…….102 

6.4.1. Survival rates of challenged possums in season 2 ……………………102 

6.4.2. Population-level drivers of transmission ……………………………..105 

6.4.3. Subgroup-level considerations ……….……………………………....109 

6.4.4. Individual-level drivers …………………………………………...….110 

6.5.Discussion ………………………………………………………………….…111 

7. General discussion …………………………………………………………………....115 

7.1.Possum home range ………………………...……………………….………..116 

7.1.1. Home range overlaps ……………………………………...………….117 

7.2.Possum contact networks …………………………………………………….119 

7.3.Post-depopulation possum dynamics ………………………………………...120 

7.4.TB transmission ……………………………………………………………....122 

7.5.Implications and management ………………………………………………..123 

8. Literature cited ………………………………………………………………………..126 

9. Appendix ……………………………………………………………………………..147 

 

  



XIII 
 

List of tables and figures 

 

Tables  

2-1 ………………………………………………………………………………...……16 

2-2 ……………………………………………………………………………...………22 

2-3 …………………………………………………………………………...…………23 

2-4 ……………………………………………………………………………………...25 

3-1 ………………………………………………………………………...……………34 

3-2 ……………………………………………………………………...………………35 

3-3 …………………………………………………………………...…………………37 

3-4 ………………………………………………………………...……………………40 

4-1 ……………………………………………………………...………………………53 

4-2 …………………………………………………………...…………………………60 

4-3 ………………………………………………………...……………………………62 

4-4 ……………………………………………………...………………………………63 

4-5 …………………………………………………...…………………………………64 

4-6 ………………………………………………...……………………………………65 

5-1 ……………………………………………...………………………………………77 

5-2 …………………………………………...…………………………………………79 

5-3 ………………………………………...……………………………………………80 

5-4 ……………………………………...………………………………………………81 

5-5 …………………………………...…………………………………………………83 

6-1 ………………………………...…………………………………………………..103 

6-2 ……………………………...……………………………………………………..107 

6-3 …………………………...………………………………………………………..110 

Figures  

2-1 ………………………...……………………………………………………………18 

2-2 ……………………………………………………………………………………...26 

3-1 ……………………...………………………………………………………………36 

3-2 …………………...…………………………………………………………………39 

3-3 ………………...……………………………………………………………………41 

3-4 ……………...………………………………………………………………………42 

4-1 …………...…………………………………………………………………………57 

4-2 ………...……………………………………………………………………………58 



XIV 
 

4-3 ……...………………………………………………………………………………63 

4-4 …...…………………………………………………………………………………66 

4-5 ...……………………………………………………………………………………67 

5-1 ………………………………………………...……………………………………85 

5-2 ……………………………………………...………………………………………86 

5-3 …………………………………………...…………………………………………90 

6-1 ………………………………………...……………………………………………92 

6-2 ……………………………………...……………………………………………..104 

6-3 …………………………………...………………………………………………..105 

6-4 ………………………………...…………………………………………………..108 

6-5 ……………………………...……………………………………………………..109