1.4.1. Habitat Use by the Long-Nosed Potoroo 32
University of Wollongong Thesis Collections University of Wollongong Thesis Collection
University of Wollongong Year
Habitat associations of the long-nosed potoroo (potoroos tridactylus) at multiple spatial scales
Melinda A. Norton University of Wollongong
Norton, Melinda A, Habitat associations of the long-nosed potoroo (potoroos tridactylus) at multiple spatial scales, MSc thesis, School of Biological Sciences, University of Wollongong, 2009. http://ro.uow.edu.au/theses/832
This paper is posted at Research Online. http://ro.uow.edu.au/theses/832
HABITAT ASSOCIATIONS OF THE LONG-NOSED POTOROO (Potoroos tridactylus) AT MULTIPLE SPATIAL SCALES
Melinda A. Norton BSc. (Hons) UNSW
A thesis submitted in fulfilment of the requirements for the degree of
Master of Science (Research)
School of Biological Sciences, University of Wollongong March 2009
CERTIFICATE OF ORIGINALITY
I, Melinda A. Norton, declare that this thesis, submitted in accordance with the regulations of the University of Wollongong in fulfilment of the requirements for the degree Master of Science (Research). The work in this thesis is wholly my own unless otherwise references or acknowledged. The document has not been submitted for qualifications at any other academic institution.
Melinda Ann Norton
31 March 2009
ABSTRACT
The long-nosed potoroo (Potorous tridactylus) is a threatened, ground-dwelling marsupial known to have been highly disadvantaged by changes brought about since
European settlement in Australia. Key threats to the species are believed to be fox predation and habitat loss and/or fragmentation. In order to conserve the species, the important habitat elements for the species at both the coarse and fine scale need to be identified and managed appropriately. The aims of this study were to examine the coarse- and fine-scale habitat preferences of the long-nosed potoroo, using a variety of techniques, in two National Park reserves (Barren Grounds Nature Reserve and
Budderoo National Park) in the Southern Highlands of New South Wales in order to inform management. The ecology of the long-nosed potoroo in this region is poorly understood, making this study both timely and critical. Assessments of the morphometrics of the local long-nosed potoroo populations and their relative abundance, in addition to fox predation pressure at these localities, were also undertaken to assist in the conservation of the local potoroo population.
Live-trapping was conducted in autumn and spring, from 2004 to 2008, at 103 trap sites across the two study areas and morphometric data were collected. The local long-nosed potoroos were found to be larger in size than Victorian animals but smaller than north- eastern NSW animals supporting the concept of a cline in body size for the species with weight increasing with latitude on the mainland. Sexual dimorphism was also observed with adult males having larger body weights, head lengths and pes lengths. Between one to two thirds of all males and females at either study area were only captured in a single trapping session, indicative of high levels of transience and/or low levels of survivorship.
i Of the two study areas, Barren Grounds Nature Reserve supported a larger number of individuals and appeared to have a greater degree of home range overlap between individuals, which was considered indicative of a higher quality habitat at this study area. Overall, the two study area populations appear to have increased over the course of the study. The sand plot technique, used in both study areas each Autumn and Spring from 2005 to 2008 as a second technique to monitor potoroo relative abundance, was considered less effective than trapping. This was due to its inability to decipher between individuals with overlapping home ranges in higher density populations and the species’ reduced utilisation of tracks compared to many other species.
A number of habitat attributes were examined at each trap site to allow comparison with trap success ratings as an indication of macrohabitat preferences. In Spring 2007 and Autumn 2008, microhabitat use was also examined at both study areas, using the spool-and-line technique and an assessment of forage diggings. The results indicated that while potoroos were trapped at sites with a wide range of macrohabitat attributes, the species displayed a number of macrohabitat preferences, particularly for greater levels of canopy and shrub cover, for ferns as a dominant ground cover type and for lower levels of floristic diversity in ground cover. Differences in the macrohabitats present at each study area, as well as those preferred at either study area, were also observed. Microhabitat attributes were assessed along the spool paths as well as in the available habitat to allow comparison of observed and expected usage. The spooling results revealed that while most individual potoroos had significant preferences for some microhabitat attributes, no clear trends were evident across all individuals spooled. Comparison of the presence/absence of forage diggings and associated microhabitat attributes at systematic sample points within the available habitat was also undertaken. Potoroos also displayed preferences for foraging in locations with
ii higher shrub cover densities and more open ground cover. Between the two scales of investigation, patterns of habitat preferences differed. The species’ habitat use appears to be influenced by both macro- and micro-scale preferences, highlighting the importance of examining habitat associations at multiple scales.
The relative abundance of foxes fluctuated over the study as indicated by sand plots monitored in both Autumn and Spring from 2005 to 2008 in both study areas. Yet despite the often high fox predation risks, individual potoroos were not all preferentially utilising higher levels of ground cover or habitat complexity. Despite dense vegetative cover being a common attribute in potoroo habitat, my results support the theory that the species requires habitat patchiness, with structural and floristic preferences varying during different activities. This includes the use of relatively open, floristically-diverse patches for foraging activity, providing some level of cover from aerial but not ground predation during foraging. Analysis of fox scats at the same study sites indicated a high prevalence of potoroo remains. Consequently, it was not considered likely that the species is afforded adequate protection against fox predation by its use of habitat.
Future management should aim to perpetuate the diversity of vegetation attributes at each of the study areas while avoiding practices that simplify such habitat. The effective control of foxes in and around potoroo habitat was also considered likely to assist in the conservation of the species
iii ACKNOWLEDGEMENTS
This research was supported by the University of Wollongong and the NSW
Department of Environment and Climate Change (DECC), Parks and Wildlife Division, formerly the NSW National Parks and Wildlife Service. Research was carried out with permission from DECC (Licence no. 10696) and both the DECC and the University of
Wollongong Animal Ethics Committees (AEC No. 031027/02 and AE07/06).
Many thanks go to the DECC Highlands Area Office for supporting this research.
Thanks to Graham Bush and Chris Keyzer, as Area Manager and Acting Area Manager, for supporting my research project. Approximately half of the fieldwork undertaken for this study was carried out while I was in the employ of the NSW Department of
Environment and Climate Change (DECC) which provided funding for the project, and the use of both DECC equipment and some staff assistance.
To the numerous staff across DECC, particularly within the South Coast Region, who assisted with various parts of the fieldwork – thanks for coming along to lend a hand and taking an interest in the project. A big thanks to Ford Kristo, Phil Craven, Ian
Foster, Jacqueline Devereaux, Nick Carlisle and Lisa O’Neill for all your assistance with the trapping and spooling fieldwork. Invaluable assistance was provided by Tony
Moody, Les Mitchell and Sam Demuth on local vegetation identification and an additional thanks to Sam for all your insights into the world of potoroos and for turning up for a chat when least expected. Many volunteers also kindly and ably assisted with this research – thank you to all. A thousand thank yous and more to Alison Prentice and
Juliet Dingle for helping me with so much of the field work, for being great friends, for keeping the laughs coming in the field amongst the rain, drizzle, fog, soggy veg and leeches, for hanging in to the end of some exhausting days and for covering the fort at
iv work while I was off in Masters land. You made it possible for me to get though my masters and have a load of fun along the way.
Valuable advice was received from Dr Andrew Murray and Dr Tony Friend. Another big thank you to Helen George for all her expert advice and assistance with dropped pouch young. Advice and assistance on the mastering of the spool-and-line technique was gratefully received from Dr Tanya Strevens and Luke Collins. My appreciation to
Georgeanna Story of “Scats About”, Majors Creek, New South Wales for providing expert identification of hair in predator scats collected from my study areas.
I am sincerely grateful to my supervisors Associate Professor Kris French and Dr
Andrew Claridge. Thank you Kris for taking on the role of primary supervisor, for always having your door open and for all your advice and assistance on project design, statistical analysis, writing-up and the workings on Wollongong Uni. Also a huge thank you to Andrew for your advice and assistance in getting the whole project started, for showing me how to handle the animals and any hurdles with calm and consideration and for your supervision, encouragement and ideas. Thank you also to Professor Rob
Wheelan for your invaluable advice on research design and thesis structure.
Thank you to my parents, Grainne and Gary, for encouraging me when I decided to take on a Masters and checking in on me along the way. Finally, my love and thanks to the
Shiptons: David for sharing this experience with me, for your encouragement and support, and for the regular welfare checks and cups of tea, and Emma for helping follow spools through the tight spots, dealing so well with the soggies and enjoying potoroos as much as me.
v
vi TABLE OF CONTENTS
ABSTRACT I
ACKNOWLEDGEMENTS IV
1.0. INTRODUCTION 1
1.1. THEORY OF HABITAT USE 1
1.2. TECHNIQUES USED TO EXAMINE THE HABITAT USE OF SMALL AND MEDIUM-SIZED MAMMALS 6
1.2.1. Trapping 7
1.2.2. Direct observations 11
1.2.3. Fluorescent Pigment tracking 13
1.2.4. Radio-tracking 14
1.2.5. Spool-and-line 15
1.2.6. Hair tubes 18
1.2.7. Indirect observations of activity 19
1.3. THE LONG-NOSED POTOROO – A MEDIUM-SIZED GROUND-DWELLING MAMMAL 23
1.3.1. Taxonomy and conservation status 23
1.3.2. Description 24
1.3.3. Reproduction 25
1.3.4. Habits 25
1.3.5. Diet 27
1.3.6. Potential threats 29
1.4. HABITAT ATTRIBUTES AND THEIR USE BY POTOROO SPECIES 31
1.4.1. Habitat use by the Long-nosed potoroo 32
1.4.2. Habitat use by the Long-footed potoroo 40
1.4.3. Habitat use by Gilberts potoroo 42
1.5. AIMS AND RATIONALE FOR THIS STUDY 43
2.0. STUDY AREAS 47
vii 2.1. LOCATION 47
2.2. VEGETATION AND CLIMATE 48
2.3. FAUNA 50
3.0. MORPHOMETRICS AND TRAP SUCCESS OF THE LONG‐NOSED POTOROO AND THE THREAT POSED BY THE LOCAL FOX POPULATION 54
3.1. INTRODUCTION 54
3.2. METHODS 57
3.2.1. Potoroo live trapping 57
3.2.2. Potoroo processing 61
3.2.3. Loss of pouch young 64
3.2.4. Sand plot monitoring 65
3.2.5. 1080 fox baiting 66
3.2.6. Assessing fox diet 66
3.3. RESULTS 67
3.3.1. Potoroo morphometrics 67
3.3.2. Trapping and potoroo occurrence 69
3.3.3. 1080 baiting, fox abundance and diet at the two study areas 73
3.4. DISCUSSION 77
4.0. MACROHABITAT USE BY THE LONG‐NOSED POTOROO 86
4.1. INTRODUCTION 86
4.2. METHODS 88
4.2.1. Potoroo live trapping 88
4.2.2 Trap site macrohabitat attributes 88
4.2.3. Statistical analysis 95
4.3. RESULTS 97
4.3.1. Macrohabitat attributes 98
4.3.2. Macrohabitat complexity scores 103
4.3.3. Trap success ratings in relation to cover 104
viii 4.4. DISCUSSION 106
5.0 MICROHABITAT USE BY THE LONG‐NOSED POTOROO 111
5.1. INTRODUCTION 111
5.2. METHODS 112
5.2.1. Potoroo live trapping for spool-and-line tracking 112
5.2.2. Spool-and-line tracking 113
5.2.3. Microhabitat attributes along spool paths 116
5.2.4. Microhabitat availability 119
5.2.5. Microhabitat foraging preferences 123
5.2.6. Statistical analysis 124
5.3. RESULTS 125
5.4. DISCUSSION 133
6.0. GENERAL DISCUSSION 139
7.0. REFERENCES 147
ix FIGURES Figure 2.1: Location of Barren Grounds Nature Reserve and Budderoo 47 National Park, New South Wales Figure 2.2: Location of Barren Grounds NR and Budderoo NP study areas 48 Figure 2.3: Average daily maximum and minimum temperatures for each 49 month between January 2004 and December 2008. Figure 3.1: Location of trap sites and sand plots within Barren Grounds NR 59 Figure 3.2: Location of trap sites and sand plots within Budderoo NP 60 Figure 3.3: Number of new and recaptured potoroos and trap success per 70 Autumn and Spring seasonal trapping sessions (number of trap nights) at Barren Grounds NR Figure 3.4: Number of new and recaptured potoroos and trap success per 70 Autumn and Spring seasonal trapping sessions (number of trap nights) at Budderoo NP Figure 3.5: Number of individual male and female potoroos captured per 71 seasonal trapping session across the two study areas combined Figure 3.6: Potoroo captures per trap night versus percent of sand plot nights 73 with potoroo tracks over time at Barren Grounds NR Figure 3.7: Potoroo captures per trap night versus percent of sand plot nights 73 with potoroo tracks over time at Budderoo NP Figure 3.8: Percent of sand plot nights with fox tracks at Barren Grounds NR 74 and Budderoo NP over time Figure 3.9: Percent of the ‘definite’ fox scats collected at either study area 76 containing each prey item Figure 4.1: Trap locations and mapped dominant vegetation community 91 within Barren Grounds NR Figure 4.2: Trap locations and mapped dominant vegetation community 92 within Budderoo NP Figure 4.3: Proportions of nil, poor and good trap sites with each dominant 98 vegetation community Figures 4.4 a-e: Proportions of nil, poor and good trap sites with: a) each tree 105 canopy cover percentage group, b) ferns as a dominant ground cover type, c) rushes as a dominant ground cover type, d) heath as a dominant ground cover type, e) 2-3 m touch scores, compared to expected Figure 5.1: Background vegetation sample points and trap sites where 121 spooling was conducted at Barren Grounds NR Figure 5.2: Background vegetation sample points and trap sites where 122 spooling was conducted at Budderoo NP Figure 5.3 a - f: Proportions of ‘dig’ and ‘no dig’ background vegetation 132 sample points with: a) acacia present within a 5m radius, b) each shrub cover percentage group, c) density of ground cover vegetation, d) plant debris (PD) as a dominant ground cover type, e) sedges as a dominant
x ground cover type, f) heath as a dominant ground cover type, compared to expected
TABLES Table 2.1: Five dominant vegetation communities and the number of trap sites 50 within each at the Barren Grounds NR and Budderoo NP study areas Table 3.1: Average body weights and measurements for male and female 68 potoroo captures across both study sites and all seasons Table 3.2: Details of instances where multiple individuals were captured at a 72 single trap site in a single season at either study area. Table 3.3: Percent of ‘definite’ predator scats (fox, dog, cat and quoll) 75 collected from the two study areas containing potoroo remains Table 4.1: Macrohabitat attributes and their relative abundance or floral 94 categories, recorded within a 20 x 20 m quadrat around each cage trap Table 4.2: Scores for the relative abundance categories of a number of 95 microhabitat attributes used to calculate Macrohabitat Complexity Scores 1 and 2 Table 4.3: ANOSIM results for study areas and trap success ratings for each 101 vegetation attribute group analysed. Table 4.4: Chi-square results for Barren Grounds NR and Budderoo NP 102 comparing observed and expected relative abundances of a number of macrohabitat attributes at ‘potoroo’ and ‘nil’ trap sites. Table 4.5: Barren Grounds NR and Budderoo NP results of Analysis of 103 Variance between ‘potoroo’ and ‘nil’ trap site Macrohabitat complexity scores Table 4.6: Analysis of Variance results comparing the Macrohabitat 104 complexity score 1 (MacroHCS1) of each trap site within each dominant vegetation community across both study areas Table 5.1: Microhabitat attributes and their relative abundance categories 118 recorded Table 5.2: Scores for the relative abundance categories of a number of 118 microhabitat attributes used to calculate Microhabitat Complexity Scores Table 5.3: Spooling attempts and successes data at Barren Grounds NR and 126 Budderoo NP (including ratio of males to females from which full spools were achieved) Table 5.4: Potoroo preferences and avoidances of a number of microhabitat 128 features at Barren Grounds NR and Budderoo NP in Spring 2007 and Autumn 2008. Table 5.5: Potoroo microhabitat preferences and avoidances of dominant 129 ground cover types at Barren Grounds NP and Budderoo NP in Spring 2007 and Autumn 2008.
xi Table 5.6: Microhabitat Complexity Scores for individuals spool paths and 131 their available habitat at Barren Grounds NP and Budderoo NP in Spring 2007 and Autumn 2008.
PLATES Plate 2.1 a – f: Long-nosed potoroo habitat within Barren Grounds NR 52 Plate 2.2 a - d: Long-nosed potoroo habitat within Budderoo NP 53 Plates 3.1 a - b: Trap positioning within the local environment 61 Plate 3.2 a - f: Weighing; scanning for a microchip; inserting a microchip: 63 measuring the ear: head; and pes length Plate 3.3 a - b: Setting up sand plots across tracks at each study area 65 Plate 4.1 a – d: Measuring macrohabitat attributes within the study areas 93 Plate 5.1: Attachment point of spool package to potoroo rump 115 Plate 5.2 a - d: Thread paths 116 Plate 5.3: Potoroo forage diggings 123
All photos by M. Norton unless stated
xii 1.0. INTRODUCTION
1.1. THEORY OF HABITAT USE
Patches of habitat used by a species must provide it with the resources it requires to grow, survive and reproduce (Levins 1968, Orians and Wittenberger 1991, Kozakiewicz
1995, Mysterud and Ims 1998). These patches may vary in suitability with critical resources providing lower and upper limits within which a species will thrive
(Kozakiewicz 1995, Begon et al. 1990). Variations in factors such as climate, aspect, slope, altitude and geology result in the availability of different resources and are vital in the determination of a patch as potential habitat (Catling and Burt 1995a). In this thesis, the term ‘habitat’ is used to describe patches of environment with a mix of physical and biotic factors in which a species can live and meet all of its resource requirements (Partridge 1978). It should be noted that habitat can also be used as a term for a ‘vegetation community’, although it is not used in this sense here.
Natural landscapes are heterogeneous and at any scale of resolution can be viewed as mosaics of patches (Wiens 1995). When looking at a patch of environment where the patch is large relative to the movements of an individual, fulfilling all resource requirements of the animal, the environment is termed coarse-grained (Levins 1968,
Morris 1984, Kozakiewicz 1995, Law and Dickman 1998). Alternatively, when patch size is small relative to the movements of an individual and a mosaic of patches is needed to fulfil resource requirements, the environment is termed fine-grained (Levins
1968, Morris 1984, Kozakiewicz 1995, Law and Dickman 1998). An examination of macrohabitat use is an examination of coarse-grained patch use while fine-grained patch use is captured by an examination of meso- or microhabitat use.
1 If a variety of vegetation communities are examined (such as those described by Specht et al. (1974) and Walker and Hopkins (1990)) and a particular species' range is associated with only some communities, the species may have macrohabitat preferences
(Morris 1984). At a finer scale, the species may be using some components within the vegetation community preferentially over others, thus exhibiting microhabitat preferences (Morris 1984). Microhabitat preferences are generally used to describe preferences for patches with particular floristic compositions, vegetation structural formations and/or other attributes such as food resources, soil moisture and dominant species (Dueser and Shugart 1978, Fox and Fox 1981, Claridge and Barry 2000, Vieira et al. 2005, Haythornthwaite 2005). Furthermore, the term meso-habitat has been used by some studies to describe a scale of resolution between the macro and micro scale
(Claridge and Barry 2000, Moura et al. 2005). Meso-scale preferences generally describe the preferential use of areas within the species range with components such as a specific temperature range, rainfall level, geology or position in the landscape.
However, the terms macro-, meso- and microhabitat often describe different scales of resolution between studies. Morris (1987) suggests that the ecological attributes of an organism such as geographical range, home range and daily movements be used to define the species' perception of scale and thus determine the appropriate scales at which to examine habitat selection.
Just as the environment can be termed coarse- or fine-grained, the behaviour of a species has also been termed fine- and coarse-grained. Fine-grained behaviour
(opportunistic) results in the use of resources in proportion to their availability and coarse-grained behaviour (picky) results in the use of some resources preferentially compared to availability (Rosenzweig 1981). However, Morris (1987) suggests that all species are actually likely to be both coarse- and fine-grained in resource and habitat
2 use, choosing some components in proportion to their availability and others preferentially.
When determining preferences by comparing usage and availability data, Johnson
(1980) suggests caution. Conclusions drawn are critically dependent on the array of components the investigator deems available to the individual. In the instance where a vital component is highly abundant within an individual’s home range, the individual may only use a small proportion of what is available. This could lead to the incorrect assessment that the component is being avoided. Furthermore, for species with reduced population densities, it can be difficult to determine habitat preferences. It may not be possible to conclude whether the species is absent from certain habitats because these certain habitats are truly unacceptable or purely because their population density is too low to allow all of their preferred habitats to be filled (Partridge 1978). However, a good understanding of the habitat use of such species, usually of high conservation priority, is obviously of particular importance (Vernes 2003).
The study of a species’ habitat preferences must examine both spatial and temporal scales of habitat use (Morris 1987) since both resource requirements and availability vary across spatial and temporal scales (Partridge 1978, Kozakiewicz 1995). Variations in resource availability and requirements influence the patterns of habitat use observed for different species (Orians and Wittenberger 1991, Stapp 1997). The availability of resources to an individual will vary not only according to quantity but also in relation to predation risks, intra- and inter-specific competition as well as with behavioural differences influenced by season, weather and moon phase (Morris 1987,
Haythornthwaite and Dickman 2000, Kelt et al. 2004). Individuals may make choices regarding their resource use by taking into account the associated costs and benefits
3 (Haythornthwaite 2005) resulting in trade-off situations affecting habitat selection
(Mysterud and Ims 1998).
Competition can exclude animals from preferred habitats, forcing them into less- preferred habitats and resulting in habitat distribution that does not mirror habitat preference (Partridge 1978). For example coexisting desert rodent species were found to differ in their use of foraging microhabitat, with each species shifting its use of foraging microhabitat in response to the removal or addition of competing species
(Price 1978). Furthermore, a patch that provides excellent forage may not provide the quality of cover required by an individual to avoid predation causing a trade-off.
Analysis of trade-off situations may reveal the value of different components of a habitat to a species and how different selective pressures have influenced habitat selection behaviour (Orians and Wittenberger 1991).
The term ‘habitat selection’ has been used in a number of studies where habitat use is assessed (Levins 1968, Braithwaite and Gullan 1978, Johnson 1980, Orians and
Wittenberger 1991, Stapp 1997, Moura et al. 2005). Stapp (1997) suggests that habitat selection can be seen as the translation of individuals' behavioural decisions into local patterns of distribution and abundance. Orians and Wittenberger (1991) suggest that an individual’s habitat selection can be viewed as a hierarchical process starting with selecting the site in which to live, then how it will use different patches within their site, then the search modes it will employ and finally its response to specific objects it encounters.
Johnson (1980) developed a four-step hierarchical process of habitat selection. First- order selection is the selection by the species of its physical or geographic range.
Second-order is the selection of the home range of individuals within the species range.
Third-order is the usage of various habitat components within an individual’s home
4 range such as feeding sites. Finally, Johnson's fourth order is selection within the various habitat components such as the selection of actual food items from those available. The term home range, as used in Johnson’s second-order of selection, was described by Burt (1943) as the area an individual traverses in its normal activities of food gathering, mating and caring for young. This area can, and generally does, overlap with the home ranges of other individuals and its size may be dependent on habitat quality (Burt 1943, Seebeck et al. 1989).
The scale at which habitat selection occurs may be limited for some species that are more restricted in their movement (Stapp 1997, Law and Dickman 1998). The ability of birds and larger mammals to travel long distances enables the selection of specific patches, often some distance apart, to meet specific resource requirements (Orians and
Wittenberger 1991). Coulson (1993) found that individual western grey kangaroos
(Macropus fuliginosus) in Victoria had three to four different macrohabitat types in their home ranges. Within these they were found to favour the open habitat types in the morning and the habitat types with greater cover at midday, moving large distances to balance foraging and thermoregulation requirements. In comparison, species of rock- wallabies, being somewhat smaller in size, use complex rocky habitat to provide refuge from weather and predators. While they still move off some distance from their refuge to forage, they are limited by the amount of distance they can cover in a single night
(Short 1982, Sharp 1999a). Rodent species utilise an even more restricted range of the habitat spectrum compared to larger mammal species (Stapp 1997). The appropriate scales at which to examine habitat selection must be based on the species’ perception of scale (Morris 1987). Certainly, use of inappropriate scales of analysis may result in situations where key factors involved in habitat selection are not detected (Orians and
Wittenberger 1991).
5 As my research examines the habitat associations of the long-nosed potoroo (Potorous tridactylus) at multiple spatial scales, I have reviewed a number of techniques used in previous studies of habitat use by small and medium-sized mammals both in Australia and overseas.
1.2. TECHNIQUES USED TO EXAMINE THE HABITAT USE OF SMALL AND
MEDIUM-SIZED MAMMALS
A number of methods have been used to examine habitat use of terrestrial fauna that vary with size of the species, the type of habitat and the scale/s at which habitat use is being examined. A comparison of survey techniques for ground-dwelling and arboreal mammals was conducted by Catling et al. (1997) comparing trapping (both Elliott and cage traps), spotlighting, pitfalls, hair tubes and sand plots. They concluded that no single method adequately sampled all size classes or groups of mammals. Some methodologies such as observations along transects, scat surveys, aerial surveys and sand plots (Priddel 1988, Coulson 1993, Newsome et al. 1975, Catling and Burt
1995a&b, Sharp 1999b) used in the examination of larger mammal habitat use are not easily utilised for smaller mammals and those preferring dense cover for predator avoidance.
The current thesis examines habitat use by the long-nosed potoroo, the adults of which weigh approximately 1000-1200 g (van Dyck and Strahan 2008). For mammals,
Bourliere (1975) recognised three broad size categories, with small mammals weighing up to 3000 g and large mammals weighing in excess of 5000 g. While the long-nosed potoroo would be classified as a small mammal according to Bourliere (1975), Dickman
(1996a) defines Australian mammals that are between 450 and 5000 g in weight as medium-sized. Therefore in this section I have summarised a variety of techniques
6 employed in the examination of habitat use of small and medium-sized mammal species: wire-mesh cage and Elliott trapping using grid and transect designs, hair tubes, radio-tracking, spool-and-line tracking, fluorescent pigment tracking, sand plots, direct observations and indirect observations of activity. A number of studies have used combinations of these techniques to enable a comparison of the information provided on habitat use by each technique and an examination of habitat use at varying scales of resolution.
1.2.1. Trapping
The use of trapping to examine habitat use involves the setting of traps across a landscape and the comparison of capture success with habitat variables measured either at trap sites or in some pattern across the landscape. Ransome and Sullivan (1997) examined macrohabitat use of two squirrel species in old and second-growth forest in
British Columbia, using mark-recapture techniques across trapping grids. They found that there were no significant differences in the proportion of adults breeding, recruitment or survival rates for either species between the two habitats, despite old growth having significantly higher population sizes of one of the species and significantly larger males of the other species.
By contrast, Jorgensen et al. (1995) focused solely on microhabitat use for rodents in an arroyo (dry desert watercourse) within a desert/montane ecotone in New Mexico. They identified five linearly-distributed microhabitat patches varying in types and levels of cover and trapped using a row of traps in each patch type. Comparing trap results with a number of habitat cover variables measured at each trap, they found that the rodent species did not use the five patch types equally. They avoided the ‘wash’ patch which
7 offered no cover but were twice as likely to be caught in the patches primarily composed of grasses and forbs compared to the patches of primarily dense shrub.
Other studies have used trapping and habitat variables recorded at trap sites to examine a range of both spatial and temporal scales of habitat preference for small mammals
(Dueser and Shugart 1978, Morris 1984 & 1987, Jorgensen and Demarais 1999).
Evidence of small mammal macrohabitat preferences and segregation at the microhabitat scale has been found with microhabitats exploited differing significantly in structure and configuration (Dueser and Shugart 1978). Morris (1984) found evidence of macrohabitat selection across sites and over time and significant differences in microhabitat use within macrohabitats where small mammal species co-occurred.
However, in a similar study, macrohabitat and temporal effects, but not microhabitat, were identified as significant predictors of rodent density (Morris 1987). Jorgensen and
Demarais (1999) also concluded that habitat use in their study was determined by macrohabitat, not the local availability of appropriate microhabitats. They suggest that in unused macrohabitat types there were equivalent microhabitats to those in used macrohabitat types.
Trapping has also been used extensively in Australia to examine small- and medium- sized mammal habitat preferences. The introduced black rat (Rattus rattus) was observed to exhibited clear habitat use patterns in Sydney bushland following an examination of both the macro- and microhabitat use where trap success was compared with a range of macro- and micro-scale habitat attributes examined at each trap site
(Cox et al. 2000). Barnett et al. (1978) found that small mammal species (Rattus fuscipes, R. lutreolus, R. rattus, Antechinus stuartii, Melomys cervinipes and Mus musculus) trapped across a pine plantation/native forest interface in north-eastern NSW displayed some level of microhabitat preference in either plantation or native forest.
8 In Victorian heathland, Braithwaite and Gullan (1978) examined habitat preferences of five small- to medium-sized mammals after grouping trap sites into six floristic and five structural categories. Three small mammals and the short-nosed bandicoot (Isoodon obesulus) all showed significant preferences for some floristic and some structural categories, while their specific preferences varied. Despite some floristic preferences, the swamp rat (Rattus lutreolus) was the only species for which no structural preferences were identified. In a similar study Moro (1991) found habitat preferences for a number of small mammal species for particular heath communities and sub- communities. Despite finding no preferences of the short-nosed bandicoot (Isoodon obesulus) for any particular vegetation type, the species was found to be associated with vertical vegetation diversity.
Taylor (1993) used trapping to examine the habitat use of the Tasmanian bettong
(Bettongia gaimardi) across the species range. Results indicated that the species’ distribution was not associated with any particular vegetation community or understorey type. However, their distribution was associated with areas with an open understorey that had extensive mycorrhizal root development. The diet of bettongs is made up of a significant proportion of hypogeous (underground) fungi (van Dyck and Strahan 2008).
In this study, the highest density of bettongs occurred in sites with infertile soils which are believed to be optimal conditions for underground fungi.
Similarly, habitat preferences in relation to the spatial and temporal heterogeneity of food resources for were examined by Cockburn (1981) in a trapping study of the smoky mouse (Pseudomys fumeus). The species was found to display microhabitat preferences based on the seasonal availability of high quality food and not on structural components. The species switched from a predominantly seed-based diet in summer to a predominantly underground fungus-based diet in winter/early spring.
9 The habitat use of three mammal species was examined by Vernes (2003) in
Queensland tropical wet sclerophyll forest using trapping. The northern brown bandicoot (Isoodon macrourus) showed a preference for Eucalyptus woodlands regardless of its topographic position. At a finer scale the species displayed a preference for sites with dense ground cover, fewer tree stems and more pig diggings.
The northern bettong (Bettongia tropica) showed a preference for ridges over mid-slope and gully habitat irrespective of forest type. At a finer scale, the species showed a preference for Eucalyptus woodlands with sparse ground cover, higher densities of tree stems and fewer pig diggings. These results support the earlier findings of a trapping study of the northern bettong by Laurance (1997) where the species was shown to be strongly associated with some wet and mesic sclerophyll forest/woodland communities compared to rainforest communities and avoided areas with fertile soils and heavy pig damage.
While trapping is a technique used in the majority of habitat use studies, it does have some shortfalls. The attraction of baited traps (offering food and cover from predation) is likely to result in animals being caught in habitats they might otherwise avoid
(Jorgensen et al. 1995). While trapping in the middle of habitat patches may provide reliable data for habitat preferences, trapping along patch edges may result in individuals being lured from neighbouring patches by the baited traps (Cox et al. 2000,
Moura et al. 2005, Vieira et al. 2005). This may be particularly important when examining habitat use at the micro scale where the luring of individuals just a short distance into a baited trap may result in them moving from one microhabitat to another.
Trapping does not provide an indication of the proportions of time spent in different habitats or the animal’s reasons for being there. Jorgensen et al. (1995) suggests that their captures of rodents in microhabitat patches with sparse to absent cover did not
10 represent a preference for these patches but rather just the requirement of individuals to pass through to preferred patches. Thompson (1982) also concluded that trapping data may not provide an accurate assessment of spatial utilisation. The nature of open habitats allow some species to travel through faster and further and thus traps in more open habitat may be more likely to be encountered, regardless of any habitat preferences.
Conclusions drawn from trapping results can also be compromised when dealing with species at very low densities and those that do no readily enter traps, such as planigales and some Sminthopsis (Scotts and Craig 1988, Catling et al. 1997). Trap success may also be influence by the availability of food and/or cover within some habitats compared to what is offered by the traps. Baits must be highly palatable and considered safe enough to access if an animal is to choose it over natural forage.
1.2.2. Direct observations
Direct observation work is obviously limited in its applicability for some species and in some habitats. The use of direct observations is difficult for cryptic species and those where their habitats preclude clear views of individuals. Direct observations along a grid pattern of transects was used by Southwell (1987) to examine habitat preferences of medium- and large-sized Australian macropods. Observations were made during both daylight and evening hours and the locations of observations compared with habitat variables measured along transects. Of seven macropod species present at the study site, only four were observed at sufficiently high levels to allow detailed analysis of their distribution, and only one of these was a medium-sized mammal, the rufous bettong (Aepyprymnus rufescens). The higher numbers of sightings of this species may be related to the mosaic of pasture, grassy woodland and open forest in which they were
11 found. The limited sightings of the other three species were restricted to the interface of pasture and vegetation with a dense tree/ground cover structure. It is therefore unclear whether the low observations of these species were related to low levels of abundance or low visibility in their preferred habitats.
While the use of artificial lighting systems allows the problem of observing nocturnal activity to be overcome, the impact of these systems and the presence of the observer on species behaviour are unclear. Thompson (1982) used both direct observations and trapping to examine microhabitat preferences and habitat partitioning of rodent species in 2 desert habitats in California. As the species studied were nocturnal, small Beta- lights were glued to the heads of individuals allowing direct observation work at night.
Individuals could be viewed at distances of up to 50-75m from the observer and usually became habituated to the observed within a single night. The number of different foraging behaviours and the proportion of time spent in shrub versus open microhabitat were recorded. Thompson’s observational data suggested that the rodent species focused their foraging efforts primarily in shrub and/or avoided open areas. However, his trapping results indicated that some of the species biased their activities toward open areas, and others towards shrubs. Thompson concluded that the microhabitat preferences for foraging in open areas suggested by trapping were overestimates. An examination of the use of trees as nesting and foraging sites by ground-dwelling small mammals (Dickman 1991) also employed direct observations by day or using red or white torchlight or cyalume lights at night.
It is also not possible to examine the movements of many species with large home ranges. Unlike trapping, direct observations requires the observer to be present at the location at the exact same time as the animal and thus generally more time and effort is required to collect sufficient observational data.
12
1.2.3. Fluorescent Pigment tracking
This technique involves the dusting of individuals with a fluorescent pigment and the night tracking of their pigment trails using ultraviolet-light. This technique provides researchers with the ability to collect data on the exact microhabitats used by individuals while avoiding potential biases caused by direct observation or trapping techniques. The variability in the length of pigment trails within and between studies can be viewed as a problem of this technique. The size of the study animal and terrain also limits the applicability. Dense understorey will impact on the observer’s ability to follow the trails and the health and safety of the observer whilst moving about some terrains at night may be an issue. The fluorescent pigment used in this technique and its application must also comply with animal welfare requirements. Despite these limitations it has been used in a number of studies to identify microhabitat use.
Individual northern grasshopper mice (Onychomys leucogaster) were tracked for up to
100 m and microhabitat variables recorded at a random point within each 5m segment of pigment trail, at random points adjacent to the pigment trail and along random transects within the trapping grid (Stapp 1997). Microhabitat preferences for mounds and burrows and little seasonal variation differences were demonstrated. Furthermore, movement characteristics varied with different microhabitats and the species largely selected macrohabitats on the abundance and characteristics of mounds and burrows rather than on broad-scale macrohabitat features.
In the Simpson Desert, Queensland, Haythornthwaite (2005) examined microhabitat use and foraging behaviour of a small marsupial, Sminthopsis youngsoni, using pigment tracking. Microhabitat variables were recorded along pigment trails of 5-128 m in length and along corresponding random transects for comparison of habitat use with
13 overall habitat availability. The species foraged extensively in open microhabitats with females preferring open habitat where spinifex clumps were nearby, compared to males.
Further, there were few differences in seasonal use of microhabitats by the species. In terms of trade-off situations Haythornthwaite (2005) suggests that the benefits of foraging in the open must outweigh the associated perceived predation risk.
Pigment tracking was also used to examine home ranges of southern brown bandicoot in
Western Australia across heath and woodland habitats (Broughton and Dickman 1991).
Pigment trails were observable for up to 750m before pigment granules became too sparse to detect.
1.2.4. Radio-tracking
The use of radio-transmitters allows examination of habitat use, including home range estimates and general movement patterns. Radio-tracking methods include the use of handheld antenna and receiver (tracking by foot), the use of established radio-tracking points or towers, often three or more used simultaneous to allow triangulation, and the use of satellite technology.
In addition to trapping, Cox et al. (2000) examined the macrohabitat use of the black rat using radio-tracking. Radio-tracking fixes of a number individuals were taken hourly between sunset and midnight at four points along trails bordering the study site. This technique provided estimates of the home ranges of tracked individuals, which were plotted and compared with estimates of the proportion of each macrohabitat available to determine macrohabitat use. The species used forest macrohabitat proportionately more than open, heath or scrub.
14 Radio-tracking has also been used to study microhabitat use. Murray and Dickman
(1994) examined microhabitat use of two Australian desert rodents: the Spinifex hopping-mouse (Notomys alexis) and the sandy inland mouse (Pseudomys hermannsburgensis). Individuals were radio-tracked at night and the microhabitat scored. Proportions of each microhabitat used were calculated for both radio and pigment tracking data and showed that the two species used different microhabitats, potentially explaining the differences in seed species observed in their diet.
Radio-tracking does not suffer from the potential bias that trapping suffers because of the reliance on a lure during trapping. It can also give a good indication of the time spent in different habitats. However, the technique can be time consuming, the presence of the observer has the potential to influence natural behaviours and study animals must be captured to both fit and remove the radio-tracking equipment. The technique is also not able to provide the same level of precision as pigment tracking and spool-and-line tracking can provide in regards to fine-grained habitat use.
1.2.5. Spool-and-line
Spool-and-line devices (Miles et al. 1981, Boonstra and Craine 1986) have been used to investigate the patterns of habitat utilisation of many small- and medium-sized mammal species. This technique involves the attachment of a spool of thread in an external casing, using superglue. The end of the thread is tied off to a fixed point and the individual released. The spool unravels from the inside, so as the individual moves through the environment the thread feeds out easily, leaving a pathway of thread. This technique allows for the mapping of pathways and analysis of microhabitat use with a very high degree of accuracy that can not be matched by radio-tracking or live-trapping which rely on periodic fixes (Key and Woods 1996, Moura et al. 2005). This technique
15 is cheap, simple and less invasive than radio-tracking and does not require the recapture of individuals at the end of the study to remove tracking equipment. The animal simply grooms the spool casing off. Furthermore, in contrast to pigment tracking, the tracking of the spool path is best undertaken during daylight hours generally making it an easier and safer technique.
Moura et al. (2005) examined habitat selection of three didelphid marsupials in Brazil using spool-and-line technique and habitat variables recorded at points along the path where a direction change occurred. Microhabitat selection involved a comparison of habitat variables recorded for the direction chosen by an individual with variables recorded at 90, 180 and 270 degrees of the direction change (representing microhabitat that was distinctly selected against). Meso-habitat selection involved a comparison of habitat variables measured along the whole path of an individual and those recorded at each trap site. While it was found that some individuals in each species selected at the microhabitat level, pattern of selection for each species were only detected at the meso- habitat level.
Microhabitat use by the eastern pygmy-possum (Cercartetus nanus) in bushland near
Sydney, NSW was examined by Tulloch and Dickman (2006). For each individual, structural and floristic habitat variables were recorded at 5m intervals along both the spool path and a line of equal length running from the release point in a randomly selected direction (to represent microhabitats available for selection). The species was not found to be clearly associated with any structural component of the microhabitat but was found to have a strong association with microhabitats containing certain plant species providing food sources.
In addition to trapping, the microhabitat use of the black rat using spool-and-line tracking was also undertaken by Cox et al. (2000). A number of habitat attributes were
16 scored at 5 m intervals along both the spool path and a random line and compared. The results supported those obtained from trapping and indicated microhabitat preferences for deep litter cover and dense understorey with numerous vertical stems.
Microhabitat use and movements of two endangered bettong species were examined by
Pizzuto et al. (2007). Habitat variables were recorded along the spool path at five randomly selected points and at each activity point (described as a succession of quick large changes in direction). Habitat variables at an equal number of sampling points were also recorded along a random line for each individual to allow an assessment of whether microhabitats were used in proportion to their availability. The total number of foraging diggings was also recorded along the spool paths and random lines. Both species were found to select components of the available habitat at the microhabitat level. These include canopy cover, sand cover, litter depth and ground vegetation height during movements and canopy cover and ground vegetation cover during foraging.
Some studies have also used spool-and-line techniques to examine particular aspects of habitat use such as predator avoidance, nest site characteristics and home ranges
(Anderson et al. 1988, Briani et al. 2001, Loretto and Vieira 2005). Zollner and Crane
(2003) used spool-and-line tracking to examine whether chipmunks use coarse woody debris to reduce their risk of predation. They calculated the percentage of spool line that travelled along coarse woody debris and found that individuals travelled along coarse woody debris more in habitat with open canopy and thick shrub cover, where they were at greater risk of predation.
This technique can be affected by the premature removal of the spool package during grooming, the loss of a thread path due to extremely thick vegetation or a break in the thread. It doesn’t give an indication of either the time taken for an individual to travel
17 the length of the spool nor whether it travelled continually or stopped to rest/shelter along the way within particular microhabitats. To ensure that the flight response of a spooled individual is reduced, the individual should be left onsite in its capture bag, untied. This allows the individual to leave the bag of its own accord and maximise the amount of spool path laid out during normal activity. The length of the spool is limited by the size of the animal and the spool packages are generally less than 5 % of the weight of the study animal (Anderson et al. 1988, Brock and Kelt 2004, Tulloch and
Dickman 2006).
1.2.6. Hair tubes
Hair tubes are simply sections of PVC piping with double-sided adhesive tape stuck along the inside and a bait to lure species. The hair stuck to the tape can then be identified to species level. Suckling (1978) first used hair tubes to detect small mammal species that were making use of trees within eucalypt forest and woodland areas in south Gippsland, Victoria. The placement of hair tubes at different heights and in different tree species enabled investigation of microhabitat preferences. Hair tube success rates were comparable with the results of simultaneous ground trapping.
Lindenmayer et al. (1994a) used hair tubes to census mammals at 70 sites in the Central
Highlands of Victoria. While 13 species of mammal were detected during the study, only 3 were detected frequently enough to allow a detailed comparison with vegetation structure and composition of hair tube sites. The configuration of the study sites was found to have a major impact on the patterns of microhabitat use of two species of small mammal. Variables such as ground cover and proximity to particular plant species and hollow bearing trees were found to be important for the species. A similar study by
Lindenmayer et al. (1994b) identified the habitat requirements of the mountain brushtail
18 possum (Trichosurus caninus) using hair tubes. The species was found to occur in sites with numerous tree ferns and where specific Acacia species were present.
The ability of hair tubes to detect species depends on both the design of the hair tube and its positioning in the environment (Lindenmayer et al. 1994a, Catling et al. 1997).
The size of the hair tube must be matched with the size of the target species to ensure the contact and capture of hair on the tape. Hair tubes have the advantage of being cheap and much less labour intensive in the field than trapping. They can be left unchecked in the field for long periods of time without any animal welfare issues and are more likely to record species that may otherwise not be detected. However, microscopic identification of hair samples can be time consuming and difficult
(Lindenmayer et al. 1994b). Also, information on the number of times a hair tube was visited, the number of hair tubes visited by the same individual and specific details on the individuals such as age or sex can not be identified (Lindenmayer et al. 1994b).
1.2.7. Indirect observations of activity
Footprints, scats, scratches, forage diggings and predator scat analysis can be used as indirect observations of species presence within habitats (Triggs 1996). However, few of these can be used to give an accurate indication of habitat use due to the paucity of records. Only limited broad-scale habitat use can be examined for prey species using presence in predator scats, as the mobility of predators can result in their scats being some distance from where the prey were consumed.
Catling and Burt (1995b) used tracks left on soil plots to examine the effects of habitat variables on the distribution and abundance of ground-dwelling mammals in south- eastern NSW. A transect was established along the vehicle trail, at each of 13 study areas, with a sample site every 200m. At each sample site vegetation data were
19 collected and medium/large-sized mammals were surveyed using the presence/absence of their tracks in a 1m wide soil plot across the trail. Small mammals were also surveyed at every alternate sample site using an Elliott trap. A habitat complexity score was calculated at each site based on canopy cover, shrub cover, ground vegetation cover, amount of litter, rocks and fallen logs and soil moisture. The study found that small native mammals were positively correlated with habitat complexity while eastern grey kangaroos (Macropus giganteus), common wombats (Vombatus ursinus) and
European rabbits (Oryctolagus cuniculus) were negatively correlated, indicating their preference for forest with an open understorey. A number of medium and large mammals were not detected at sufficient levels to include in analyses. These species may have been at low levels in the study areas or they may have been under-sampled by the soil plot technique.
With a lack of a lure to soil plots, species that move along trails are most likely to be surveyed by this technique and species that rely on thicker understorey may be easily missed. Furthermore, the openness of the surrounding terrain is likely to influence the amount of use of the trails by species that would otherwise prefer moving along trails.
It is obviously also less invasive than trapping and easily undertaken once the observer has learnt to differentiate the tracks of the species present. Although the tracks of more closely related species can be difficult to differentiate. The technique is also weather- dependent, as tracks are easily destroyed by strong winds and wet weather and thus the use of this technique may be prohibitive at some study sites, at least during some seasons. However, despite these shortcomings, a comparison of techniques by Catling et al. (1997) suggests that while Elliot trapping produced the best results for small mammals, soil plots were found to be the best technique to examine habitat use by
20 medium and large mammal species. They suggest it was a lot more labour-efficient and effective than cage trapping.
In addition to footprints, evidence of foraging can also be used to give an indication of habitat use during foraging. Mycophagous species feed on the fruiting bodies
(sporocarps) of hypogeal fungi, which are fungi that fruit underground and are commonly known as “truffles”. In Australia, these fungi are believed to form a mycorrhizal association with myrtaceous plants, particularly Eucalyptus trees, and improve plant growth (Malajczuk et al. 1987). Australian species known to be mycophagous, at least during certain seasons, include potoroos, bettongs, rat-kangaroos, bandicoots, and some rodent and macropod species (Claridge et al. 2007).
Mycophagous species must dig in order to access the sporocarps, and the resulting diggings can be used as evidence of their habitat use during foraging activities (Taylor
1992). However, a habitat type (particularly at the microhabitat scale) should not be labelled as unused by the species based on a lack of diggings. The species may still use this habitat type but for reasons other than foraging. Furthermore, depending on the full diet of the species examined, it may be using this habitat type to forage for other food types that do not require digging.
While the use of digging activity to identify habitat preferences has been used by a number of studies, this technique requires that the observer must be able to differentiate between the diggings of the species present. This is particularly difficult where a number of mycophagous species overlap in range. The diggings of a number of non- mycophagous species in Australian can also cause confusion, including echidna forage diggings and rabbit/hare scratches.
The seasonal distribution of Tasmanian bettong (Bettongia gaimardi) diggings within
25 m² quadrats was examined by Taylor (1992) to assess spatial and temporal habitat
21 use. The quadrats were located across five major vegetation-soil associations within open dry sclerophyll forest communities. These five associations were lateritic gravels, drainage flats, dolerite hills, heath on sand and bracken on sand. Results indicated a preference for foraging activity within sites with sandy soils. The author proposes that this is most likely due to a suggested inverse relationship between hypogeal fungi and soil fertility. While lateritic gravels have lower soil fertility than sandy soils they are also more difficult to dig in. Across all associations the species diggings were highly clumped reflecting the clumped distribution of the sporocarps they were digging for.
The numbers of diggings were also greatest across all associations in late winter, a likely reflection of increased sporocarp production during this period’s heightened soil moisture levels.
In a similar study by Johnson (1994a) Tasmanian bettong diggings were counted and compared with habitat variables within a primary quadrat in their preferred habitat and a number of smaller secondary quadrats set out across all the major vegetation types.
Results indicated that density of diggings were higher in areas dominated by particular eucalypt and acacia species and that digging densities increased directly with the density of mature trees of this eucalypt species. Within their preferred habitat a relationship was detected between diggings and Eucalypt/Acacia stem densities. The author suggests that this was directly related to the density of sporocarps associated with eucalypt/acacia roots. Diggings were also found to be no more likely to occur in bare patches than patches with high densities of ground vegetation.
22 1.3. THE LONG-NOSED POTOROO – A MEDIUM-SIZED GROUND-
DWELLING MAMMAL
1.3.1. Taxonomy and conservation status
The long-nosed potoroo is a member of the rat-kangaroo family (Marsupialia:
Potoroidae), which also includes other potoroo species, bettongs and the Musky rat- kangaroo (Hypsiprymnodon moschatus)(Claridge et al. 2007). There are three extant species of potoroos in Australia: the long-nosed potoroo (Potorous tridactylus), the long-footed potoroo (Potorous longipes) and Gilberts potoroo (Potorous gilberti). All extant species of potoroo are listed as Threatened species. A fourth species, the broad- faced potoroo (Potorous platyops), became extinct in the last century (van Dyck and
Strahan 2008).
The long-nosed potoroo ranges along the eastern sea-board from south-eastern
Queensland to the south-west of Victoria, northern and eastern Tasmania and on some
Bass Strait Islands (Seebeck et al. 1989). The species is split into two sub-species across its range: Potorous tridactylus tridactylus in mainland Australia and Potorous tridactylus apicalis in Tasmania and the Bass Strait Islands. Potorous tridactylus tridactylus is listed as Vulnerable in New South Wales, Queensland and nationally and
Endangered in Victoria. The Cudgen, Cobaki and Tweed Heads West populations of this species in northern NSW (Tweed Local Government Area) have recently been listed as Endangered Populations. Potorous tridactylus apicalis is considered common in Tasmania but rare on the islands (van Dyck and Strahan 2008). The long-footed potoroo is found in a few small areas in Victoria and south-eastern New South Wales and is listed as Endangered in both states and nationally. Gilbert's potoroo was presumed extinct until it was rediscovered in south-western Western Australia in 1994.
It is now listed as Critically Endangered.
23
1.3.2. Description
Long-nosed potoroos (Potorous tridactylus) have brown to grey fur above, with a grey underfur layer, and light grey to cream below, with some individuals also having white tail tips, particularly in the southern part of its range (Amos 1982, van Dyck and Strahan
2008). Their nose is long and tapered with a naked patch of skin extending from the nose onto the snout. This species is slightly smaller than the very similar Long-footed
Potoroo (Potorous longipes), and has a shorter tail and a smaller hind-foot (shorter than its head) (Seebeck and Johnston 1980). They have an average head and body length of about 360 mm and a tail length of 230 mm (Claridge et al. 2007). Across Australia the species weighs between 660 and 1640 g and shows only slight sexual size dimorphism with an average adult male weighing 1180 g and female 1020 g (van Dyck and Strahan
2008). However, it appears that the species’ size may vary across its range. An average weight of 1463 g for males and 1313 g for females was recorded in north-eastern New
South Wales (Mason 1997). However, in Victoria Bennett (1987) recording a maximum weight of only 950 g and an average weight of 789 g for males and 777 g for females and Long (2001) recorded 781 g for males and 689 g for females. In north- western Tasmania, the species was found to be similarly small by Heinsohn (1968) with an average of 850 g for males and 770 g for females, although a much larger average body weight of males (1311 g) was observed by Hughes (1964) in south-eastern
Tasmania. The differences in body weight across northern Tasmanian long-nosed potoroos were found to be correlated with rainfall: the species is smaller in the wetter west and larger in the drier east (Johnston and Sharman 1976).
24 1.3.3. Reproduction
The species’ mating systems are poorly understood due to its secretive behaviour and dense habitat (Long 2001). They produce a single young per litter, have an oestrus cycle of 42 days, a gestation period of 38 days and a pouch life of 126 days (Claridge et al. 2007). Young are weaned at 24 weeks and sexual maturity is considered to be approximately 12 months for both males and females (Hughes 1964, Rose 1989,
Bennett 1987). Females are capable of producing an average of 2.7 young per year
(Bennett 1987). They have a post-partum oestrus and exhibit embryonic diapause
(Hughes 1962). Males are believed to become sexually mature, based on the presence of epididymal sperm, somewhere between 600 to 900 g body weight (Hughes 1964).
While Hughes’ study had a 561 g male with no sperm, a 639 g male and a 901 g male were both found to have only a few, suggesting recent sexual maturity.
There is no particular breeding season but peaks typically between July to September and December to January (Bryant 1989). However, in a study by Bennett (1987) on
Victorian long-nosed potoroos there was no apparent seasonal variation in percentage of adult females with pouch young, but levels were consistently high (most frequently 90
% but ranging from 70 - 100 %).
1.3.4. Habits
Adult long-nosed potoroos can reach an age of seven years in the wild (van Dyck and
Strahan 2008). The species is considered to be solitary, non-territorial and largely nocturnal (Seebeck et al. 1989, van Dyck and Strahan 2008, Long 2001). While Guiler
(1958) suggested that the species was strictly nocturnal, Long (2001) found that just over half of the trapping success for the species occurred during daylight trapping sessions and frequent observations were made at different times of day and under
25 varying climatic conditions. Likewise, Seebeck (unpublished), in Seebeck et al. 1989, recorded over one third of his captures during daylight hours.
The majority of their time during daylight hours is spent in squats (shallow depressions) located under dense vegetative cover (Long 2001). They are not known to construct complex nests (Seebeck et al. 1989). Individuals have been found to have several squat sites within their home range (Kitchener 1973, Long 2001).
Guiler (1958) considered the species to be semi-nomadic, moving during spring, suggesting that home ranges were not occupied as a permanent range throughout the life of an individual. Movements varied seasonally in response to breeding requirements and seasonal distribution of fungi as its main food source (Guiler 1971). A number of temporary home ranges were then adopted during the rest of the year. More recent studies have suggested the use of more defined home ranges.
In southern Tasmania, Kitchener (1973) estimated an average home range of a long- nosed potoroo to be 19.4 ha for males and 5.2 ha for females with considerable overlap between individuals. This differs from the home range estimates of 2.0 ha for males and 1.4 ha for females by Bennett (1987) in Victoria, an estimate based on trapping data. The difference may be attributable to the habitat quality at both sites, with smaller home ranges in better habitat. Using radio-tracking techniques at the same location as
Bennett’s study, Long (2001) found the average home range of adult males to be 4.0 ha and 2.9 ha for females. Male home ranges overlapped with the home ranges of between
1 and 4 females, while a female home range overlapped with 2 - 3 males. Despite range overlap, females were found to associate with only a single male and males with only 1
- 2 females. Bennett (1987) also proposed that individuals have a small nest area which is mostly exclusive and a larger feeding area which overlaps greatly with other individuals.
26 Juveniles (found to be markedly trap-shy during their first few months of independence) are believed to stay within the maternal home range until around sexual maturity. At this time Bennett (1987) proposed that both sexes disperse, which in addition to the species’ small body size, restricted home range, extensive range overlap and continuous breeding, all allow the species to exploit the small and patchy habitats in which they reside. However, Claridge et al. (2007) suggested that in rat-kangaroo species, generally only the males disperse, with the females remaining close to their site of birth.
1.3.5. Diet
Long-nosed potoroos are primarily mycophagous (fungus-feeding) and the majority of fungal material consumed are hypogeal sporocarps (underground fruiting bodies)
(Bennett and Baxter 1989, Claridge et al. 1993b, Tory et al. 1997). Fungal material makes up between 30 and 90 % of their diet with the rest made up of plant tissue, seeds, arthropods and fleshy fruit and flowers (Guiler 1971, Bennett and Baxter 1989, Claridge et al. 1993a and 1993b, Tory et al. 1997). Proportions of fungi in the diet are greatest in autumn and winter and lowest in spring and summer at which time consumption of other food items increase in importance (Bennett and Baxter 1989, Claridge et al.
1993b). The high levels of autumn/winter fungus consumption may be related to increased soil moisture and an increased diversity of species and number of hypogeal sporocarps present during these months (Claridge et al. 1993b and 2000a). Tory et al.
(1997) observed proportions of fungus in the species diet to peak at 90% in winter and drop to a low of 52% in summer. They suggested that these proportions, which are higher than previously reported, were most likely related to the more sensitive techniques employed to assess diet.
27 The proportion of fungus in the diet has also been found to vary according to site disturbance history. Within regrowth forest, while fungus was still their major food group, it formed a significantly smaller component of the diet (33-38%) (Claridge et al.
(1993b). Furthermore, there were less species of fungii per faecal sample in regrowth forest and less species consumed overall compared to multi-aged forest, which may be related to older host plants supporting higher relative proportions of sporocarps.
The occurrence of hypogeous fungi within the environment is strongly concentrated within 2m of adult eucalypt trees (Johnson 1994b) and correlated with the average minimum temperature of the coldest month, the annual mean moisture index, time since fire, average litter depth and number of large fallen trees (Claridge et al. 2000b). While some species were more likely to occur as these variables increased, others were less likely to occur. Bennett (1993) suggested that fungal sporocarps are more often found in more open areas where light can penetrate to the forest floor, leading to his observation that the species utilised more open and floristically-diverse patches within their habitat for foraging activity.
Claridge et al. (2000b) found that there is greater species diversity of fungal species at sites with greater soil fertility and organic matter. Sites on sheltered slopes and gullies had higher fungal diversity than more exposed sites, a likely reflection of soil moisture differences. Also, sites with the highest diversity of eucalypts had the highest fungal diversity and sites with the lowest eucalypt diversity had the lowest fungal diversity.
No significant relationship was found between the diversity of potential understorey plant hosts and fungal diversity suggesting a primary role of eucalypts as host species.
28 1.3.6. Potential threats
Since European settlement, the species has suffered a dramatic reduction in its range and abundance, mainly attributed to associated changes in the landscape (Calaby 1971,
Johnson et al. 1989, Bennett 1993, Taylor 1993, Short 1998, Priddel and Wheeler
2004). With European settlement came the introduction of feral competitors and predators. It also brought habitat loss and fragmentation caused by clearing for agriculture and human settlement, and habitat degradation, with the loss of dense understorey cover, through changed fire regimes and overgrazing by stock. The species also became viewed as agricultural pest and bounties were introduced.
Predation by foxes and habitat loss/change are believed to be key factors that are currently threatening species (Seebeck et al. 1989, Claridge and Barry 2000). However, there is some debate over whether one of these factors can be identified as the primary threat over the other. Across the rat-kangaroo family, Short (1998) suggests that foxes are the primary cause of decline and extinction in New South Wales, more so than the effects of habitat modification. Guiler (1958) suggested that the absence of foxes from
Tasmania undoubtedly advantaged the long-nosed potoroo. Heinsohn (1968) considered fox predation to be the main factor in the decline of long-nosed potoroo populations on the mainland compared to the continuing high populations in Tasmania.
Alternatively, Seebeck (1981) suggested that alteration of habitat was the primary cause of the decline of mainland long-nosed potoroo populations.
Fox scats collected in the Otways Region of Victoria had a very low incidence of long- nosed potoroo remains in them (<1%), despite them being considered one of the three most abundant species in the study area (Seebeck 1978) suggesting that foxes were not a controlling factor of the species. More recent studies have also provided evidence of potoroo remains in fox scats (Schlager 1981, Lunney et al. 1990, Capararo and Beynon
29 1996). The proportion of fox scats containing potoroo remains have varied in these studies but have been as high as 13% (Capararo and Beynon 1996). Predation by wild dogs and dingoes has also been recorded in other studies, however, the proportions of these scats with long-nosed potoroo remains has been very low (Newsome et al. 1983,
Lunney et al. 1990). Claridge (1998) also provided evidence of direct predation by foxes on the species although this was achieved by foxes accessing cage traps containing potoroos via trampled trapping lines through dense understorey. The degree of fox predation on the species in their natural environment remains uncertain.
However, effective fox control resulting in reduced fox activity, has been found to significantly increase abundance of some long-nosed potoroo and other potoroid populations (Murray et al. 2006, Claridge et al. 2007).
It has been suggested that potoroos utilise patches of dense ground cover within their habitat for shelter and avoidance of predators (Bennett 1997). Well defined run-ways through the dense understorey allow potoroos to travel rapidly within the dense cover while maintaining protection from both aerial and ground predators (Bennett 1993).
Short (1998) claims that long-nosed potoroos are ‘protected’ from fox predation by the dense ground cover within their habitat. Certainly, the NSW Fox Threat Abatement
Plan (NPWS 2001) allocated the long-nosed potoroo a low priority rating for the likelihood of population-level impacts by fox predation, compared to a number of other critical weight range threatened species. This was based on the perception that the species was offered significant protection by its use of dense ground cover. However,
Heinsohn (1968) suggested that the efficient hunting skills of the fox would not be impeded by the dense understorey vegetation.
The long-nosed potoroo is also believed to move up to 40m into relatively open patches within their habitat for foraging activity and exploratory activities (Schlager 1981,
30 Bennett 1987 and 1997). This may expose them to much higher predation risk than they face while in the dense understorey component of their habitat. An improved understanding of how the species uses its habitat and the cover it offers is required to shed more light on whether the species is provided adequate protection against fox predation within its habitat.
While mortality within long-nosed potoroo populations following fire is expected, and there is a significant positive relationship between time since fire and potoroo occurrence (Claridge and Barry 2000, Catling et al. 2001), the exclusion of fire from the species’ habitat may prevent the continued development of the habitat mosaics the species requires (Mason 1997). Seebeck (1981) also suggested that the species may survive high-intensity fires, by sheltering in other species’ burrows. The author observed three unharmed potoroos searching for food within hours of such a fire.
However, reduced cover following the fires is likely to increase predation risk, particularly in the highly flammable coastal heath habitats where effective cover is likely to be greatly reduced (Schlager 1981). As the vegetation regenerates post-fire, the species does repopulate. The use of frequent low-intensity prescribed burns may also result in the simplification of habitat attributes and the loss of mosaics with variable floristic and structural diversity (Catling 1991).
1.4. HABITAT ATTRIBUTES AND THEIR USE BY POTOROO SPECIES
In order to conserve potoroo species, a good knowledge and understanding of their use of essential resources and habitats, as well as threats to their ongoing conservation, is required (Bennett 1993, Dickman 1996b, Claridge and Barry 2000, Cox et al. 2000).
Important habitat elements for these species need to be identified and managed appropriately. While species of bettongs have been found to be associated with more
31 open habitats, species of potoroos have been found to be largely associated with very dense cover (Seebeck et al.1989). Therefore, a review of research into the habitat use of extant potoroo species will assist in directing my research approach.
1.4.1. Habitat use by the Long-nosed potoroo
Long-nosed potoroos have been found to inhabit a large variety of vegetation communities across their range including rainforest, dry and wet sclerophyll open- forests, woodland, shrublands and heath vegetation communities and their ecotones
(Heinsohn 1968, Kitchener 1973, Schlager 1981, Seebeck 1981, Seebeck et. al. 1989,
Mason 1997, van Dyck and Strahan 2008). Most populations occur within 50km of the sea and between sea-level and 800m (Seebeck 1981). They are generally restricted to areas with an annual rainfall greater than 760 mm per annum and areas with light and sandy soils, resulting in a patchy distribution across their range (Seebeck 1981, van
Dyck and Strahan 2008). In NSW, the species occurs along parts of the east coast and hinterland (van Dyck and Strahan 2008).
In general, there are two types of environments in which the species is found: coastal sandy wet heaths and inland moist woodland and forest communities along plateau sections and associated slopes and gullies (Schlager 1981). Within the coastal habitat component, the sandy, shallow, nutrient-poor soils support heath communities with a dominant stratum of small trees or large shrubs (Schlager 1981). Within the inland habitat component, the species most commonly occurs in poorly drained areas in a variety of forest, woodland, wet heath and rainforest communities (Schlager 1981,
Seebeck 1981, Bennett 1987). Other site characteristics for the species include an annual rainfall in excess of 760mm and a high canopy, however sparse (Seebeck 1981).
32 Despite the extensive thick ground cover offered by heath communities, treeless heath is not used (Seebeck 1981).
While the species’ habitat preferences at the scale of vegetation communities have been described by a number of studies, their habitat preferences at finer scales of resolution are less understood (Seebeck et al. 1989). In one of the first studies of the species,
Guiler (1958) conducted regular cage trapping over a one year period in Tasmania. He found the species was caught in all three of the habitat types present in the study area
(thick scrub, open woodland and cleared areas), however, he identified definite habitat preferences, with over 60 % of captures being in, or close to, thick scrub. Nonetheless,
40 % of captures were in open scrub or open clearings, a fact that the author suggested was most likely explained by the animals being in transit from one feeding area to another. As he observed very few diggings in open areas, he suggested that the species was unlikely to be targeting the more open areas for feeding. While this study provided early insight into the species habitat use, it still only provides a coarse-scale view and provides no details on the habitat attributes within each of the three habitat classes.
A common feature across all vegetation communities in which the species occurs is the presence of dense vegetative cover (Schlager 1981, Seebeck 1981, Mason 1997). This is suggested to offer concealment from and limited access by predators. The dense cover is provided by either the field vegetation layer (eg. sedges, ferns, heaths) or low shrub layer (eg. Leptospermum, Melaleuca spp.) (Seebeck 1981, Bennett 1987). The species utilises small runways for rapid movement through the dense cover and some studies suggest that the species generally stays within 20 to 40 m of this dense cover during feeding and exploratory activities (Schlager 1981, Bennett 1987).
There is some debate about whether floristic composition or structural components are important in habitat preference. Schlager (1981) proposed that rather than broad-scale
33 floristic descriptions of vegetation communities, the habitat preferences of the long- nosed potoroo were more related to the structural aspects of their microhabitat.
However, this was not found to be the case by Bennett (1993) nor Claridge and Barry
(2000).
In Victoria, Bennett (1993) compared trap success and digging abundance with a number of vegetation structure and floristic attributes. The abundance of diggings at the micro-scale were positively correlated with floristic richness and negatively correlated with total vegetation density under 3 m. Furthermore, trapping data were not strongly correlated with any structural component of the vegetation or any particular floristic composition. At the microhabitat level the understorey at capture sites varied from dense to relatively open. The varying microhabitat preferences suggested by the trapping and digging data highlight the benefits of using multiple techniques to assess habitat use. It is unclear to what extent these differences are due to the ability of trapping to identify habitat use associated with all daily activities, as opposed to just foraging activity. At the fine scale of resolution examined by Bennett (1993), it is highly feasible that the baited traps could lure animals just a few metres into the small habitat patches he was assessing. Therefore, the lack of significant correlations between his habitat attributes and trap success is not surprising.
Claridge and Barry (2000) examined the presence/absence of diggings and a number of meso- and microhabitat attributes at 136 sites across southern NSW and Victoria. This study found no relationship between the presence of potoroo diggings and the density of ground cover at the micro-scale. While this differs to the diggings results of Bennett
(1993), it should be noted that Bennett examined digging abundance, not presence, and examined cover over a greater height spectrum. His examination of cover was also at a finer scale. The use of terms such as microhabitat obviously represents different scales
34 of resolution in different studies and needs to be noted when comparing habitat use studies.
A study by Claridge et al. (1993a) also found varying habitat preferences when using different indicators of potoroo abundance. Potoroo captures, digging presence and digging abundance were compared over space and time with habitat attributes at two study sites (an old growth forest site and a regrowth forest site). The potoroo captures and foraging diggings were found to have different distributions in both space and time.
In old growth forest, both potoroo captures and the presence of forage diggings were more likely in mid-slope sheltered and gully sites while no such relationship was found with digging abundance. In regrowth forest, potoroo captures, digging presence and digging abundance were all fewer in gully sites. While potoroo captures, digging presence and digging abundance were greater in mid-slope sheltered sites, potoroo captures were also high in ridge sheltered sites. Potoroo captures, digging presence and digging abundance did not vary over time with the exception that in old growth forest digging abundance was significantly greater in autumn and winter than late spring and summer.
The differences in foraging activity found by Claridge et al. (1993a) between old growth and regrowth sites is suggested to partially reflect differences in the amounts of hypogeal fungi consumed at either site. They recorded lower levels of fungi consumed at the regrowth site. The authors also suggested that other factors such as differences in site disturbance histories, rainfall, vegetation age and characteristics, and soil features may contribute to the differences in foraging activity observed. Claridge and Barry
(2000) also surveyed the types of hypogeal fungi species present across their 136 sites and found no relationship between the presence of potoroo diggings and the diversity and abundance of hypogeal fungi recorded. However, they did find that the probability
35 of finding potoroo diggings at a site increased with increasing minimum temperature in the coldest month, was highest at sites longest unburnt and decreased with increasing soil fertility. A significant positive relationship between time since fire and potoroo abundance has been found (Catling et al. 2001). Catling (1991) suggested that the frequent use of low-intensity, prescribed fire results in the simplification of habitat attributes and should be avoided. However, the total suppression of fire from the species habitat may also prevent the continued development of the habitat mosaics the species requires (Mason 1997).
It remains unclear whether the diversity and abundance of hypogeal fungi increases, decreases or remains static with time since fire (Johnson 1995, 1997, Claridge and
Barry 2000) and increasing soil fertility (Taylor 1993, Claridge and May 1994, Johnson
1994b, Claridge et al. 2000a). Claridge and Barry (2000) suggested that their observed relationship between digging occurrence and time since fire is probably related to a reduction in the availability of ground cover across the sites (providing nesting material and protection from predators) and not related to availability of hypogeous fungi.
While it is widely accepted that dense vegetation cover is an important aspect of potoroo habitat across the species’ range, both Bennett (1993) and Claridge and Barry
(2000) suggested that dense ground cover may not be so important at finer scales of habitat use. Both authors suggest that at microhabitat scales the species may require habitat patchiness, provided by vegetation mosaics/ecotones (Kitchener 1973, Seebeck
1981, Seebeck et al. 1989, Bennett 1993, Claridge and Barry 2000, Coops and Catling
2002). Bennett (1993) suggests that this habitat patchiness provides individuals, within their relatively small home ranges, access to the different kinds of resources they require. He suggests that potoroos utilise more dense and structurally-complex patches
36 for shelter and avoidance of predators and relatively open and floristically-diverse patches within their habitat for foraging activity.
While the use of digging activity to identify habitat preferences has been used by a number of studies, potoroos and bandicoots can co-occur and their diggings can be difficult to tell apart (Bennett 1993, Broome 1994, Triggs 1996, Claridge and Barry
2000). Bandicoot diggings are generally classified as conical in shape while potoroo diggings are classified as cylindrical and are generally deeper and wider (Triggs 1996).
However, the size, shape and depth of a digging are also influenced by the nature of ground and the species of fungi being sought. Claridge et al. (1993a) found that potoroo diggings varied in depth with time of year and topography and suggests that some of these differences were due to the characteristics of different fungus species fruiting at different depths. Many studies have sought to address this problem by discounting indeterminate diggings (Bennett 1993, Broome 1994, Claridge and Barry
2000) which may result in some level of bias in the results. The use of diggings in combination with other techniques appears to be a safer approach to assessing habitat use.
Other techniques have been also been used to examine long-nosed potoroo habitat preferences with varying success. Mason (1997) used trapping and hair tubes to assess habitat preferences in north-eastern NSW. While trapping results suggested a significant preference for open shrubland, potoroo hair samples were only recorded in
17 of the 228 hair tubes used and revealed no significant habitat preferences. In southern NSW, Broome (1994) found that of 80 hair tubes laid out for potoroo detection, only one returned a positive identification, despite a much greater evidence of potoroo diggings in the habitats surveyed.
37 Capararo and Beynon (1996) surveyed the species in 2 major vegetation communities with dense understorey within Red Rocks Nature Reserve in the Southern Highlands of
NSW. Despite no potoroo captures in cage traps, potoroo hair was found in one hair tube in open woodland/heathland and in six in peppermint open forest. The understorey of the peppermint open forest was considered more variable and likely to contain patches of less dense understorey. However, as with the other hair tube studies, the data were unable to provide an indication of the number of individuals sampled. Obviously caution should be used when drawing conclusions on coarse-grained habitat preferences from studies with unknown sample sizes.
In addition to time since fire, Catling et al. (2001) compared habitat complexity with potoroo abundance based on the presence/absence of their prints on sand plots across 99 forested study sites within Nadgee Nature Reserve in southern NSW. The habitat complexity scores were based on five structural features of the habitat, with the higher the score, the thicker the understorey and more dense the ground and litter cover.
Habitat complexity was found to be significantly related to potoroo abundance estimates. The expected abundance of the species increased slightly with modelled habitat complexity increases and decreased with lower habitat complexity denoting habitat with little ground cover and few understorey shrubs.
It should be noted however, that in the study by Catling et al. (2001) ‘patchiness’ is not one of the structural features used in their habitat complexity calculation. These scores incorporate estimates of canopy, shrub and ground percent cover but not their arrangement. Therefore a number of sites, with varying degrees of ‘patchiness,’ can all have the same habitat complexity score. Due to the potential importance of fine scale habitat patchiness, Claridge and Barry (2000) suggest that future studies categorizing
38 microhabitat suitability of potoroos should attempt to develop a measurement of habitat
'patchiness.'
The spool-and-line technique was also used in a study by Veltheim (2000) to assess some aspects of microhabitat use and foraging patterns of the species in Victoria.
Spooled individuals were left inside their capture bags at the time of release to allow the animals to emerge voluntarily. Out of 30 spool packages attached, 16 were dropped within 35 m of their release point. One spool path was used for each of eight individuals spooled in summer 2000. For each, cover levels across three strata were recorded at 20m intervals along both the spool path and four straight-line random transects starting at the point of release. Soil moisture and both the distance to and size of the nearest eucalypt were recorded at each fresh digging and at random points along each spool path. The first 20 m of their thread paths were excluded from analysis to account for potential flight responses upon exiting their bags.
Veltheim (2000) found that the potoroos used habitat with greater ground cover and lateral shrub cover, but not canopy cover, than what was randomly available to them.
The species were also found to be selecting to forage in patches with higher soil moisture and a greater distance to the nearest Eucalypt than was randomly available to them. However, it should be noted that results were based on 8 individuals in a single season and that while the spool packages contained 265m of thread, the spool paths achieved varied from 94 - 236 m. It is unclear whether the spool packages were dropped at these distances or the thread paths lost or broken. Obviously data missing from individuals due to the loss of spool paths in thick vegetation would bias the results.
Furthermore, in the statistical analysis used by Veltheim (2000), for each cover type she lumped the cover data associated with individual animals and did not separate individual responses. This assumes that the ‘available cover’ data randomly collected
39 for each individual was also ‘available’ to the other individuals examined, despite the study area encompassing three different habitat types.
Veltheim’s study described the data collected at points along the spool path as ‘foraging path’ data. While numerous diggings were observed along all spool paths, it is likely that non-foraging movements are also reflected in the spool path such as interaction with other individuals and travelling between foraging sites. Overall, the study found the spool-and-line technique to be a valuable tool in the identification of finer-grained details of habitat use. However, it only provides limited information on the habitat preferences of the species as it was conducted in a single area, over a single season and used a small number of animals and examined only a handful of habitat attributes, the data for which were lumped.
1.4.2. Habitat use by the Long-footed potoroo
The long-footed potoroo (Potoroos longipes) was first described in Victoria by Seebeck and Johnson (1980). In 1986, the species was found in southern NSW. Due to their recent discovery, cryptic behaviour and limited distribution, few studies into their habitat use have been conducted. Seebeck and Johnson (1980) found the species at two sites: one in regrowth open forest with a sparse understorey and a field layer dominated by wiregrass and bracken and the other in open forest ecotones with a dense understorey and a field vegetation layer of swordsedge, wiregrass, ferns and Senecio spp.
Scotts and Seebeck (1989) examined habitat preferences of the species using trapping success and both floristic and structural variables at each trap site. The species was found to have clear preferences for wet to damp forest types with mixed species over- storeys and avoided dry forest types present on upper slopes and ridges. They also displayed temporal changes in the communities they preferred. In spring and summer
40 they preferred warm-temperate rainforest gullies and adjacent riparian forest while in autumn and winter they favoured damp lowland sclerophyll forest on lower- and mid- slope positions. Some amount of the seasonal variation in habitat preferences may be explained to seasonal variation in the availability of fungal fruiting bodies. The authors found that across all habitats favoured by the species throughout the year a common structural characteristic was the presence of patches of bare ground interspersed with a mosaic pattern of interconnected dense vegetation.
Scotts and Craig (1988) used hair tubes and trapping concurrently to identify the presence of long-footed potoroos at four sites within East Gippsland, Victoria. Despite
5250 trap nights the species was only trapped at one site and at 4 % success rate.
However, the species was detected at three of the four sites with hair samples in 10 of
411 hair tubes. While no conclusions on habitat use of the species were able to be drawn due to such low success rates, the study was able to identify the presence of the species at different sites. Likewise Broome et al. (1997) used extensive trapping, hair tubes and remote cameras in southern NSW in an attempt to identify the distribution and habitat use of the species. While no long-footed potoroos were trapped or photographed, 9 of
13,180 hair tubes did reveal long-footed potoroo hairs. Due to the limited success of the study, no specific habitat use information was available.
Green et al. (1998) used trapping grids and radio-tracking to examine the species’ microhabitat use at two sites in Victoria. Vegetation communities were mapped and grouped into wet, moist or dry habitat classes. Individual captures were allocated to the habitat in which the trap was located. A total of 17 animals over the two sites were radio-tracked. Despite large levels of signal bounce due to the terrain, two bearings were taken every 15 minutes during tracking sessions. The proportions of habitats used were compared with the proportions available for both the radio-tracking and trapping
41 results. Trapping revealed that while most captures were in dry habitat, there were no significant preferences for any of the three habitats when compared to availability.
The results of Green et al. (1998) contrast with the preference for moist and wet habitats noted by Scotts and Seebeck (1989). They suggest that this difference can best be ascribed to the intensive fox baiting that had been conducted since the first study, allowing potoroos to move out from the protection of gullies and denser vegetation into the drier, more open habitats. They also report that the population at this site has almost doubled since the first study which may also be due to fox control. However, the exclusion of fire from the site and general succession of vegetation may also be other plausible reasons for these differences. Radio tracking revealed a similar trend in microhabitat use to trapping but also highlighted variation between individuals.
Based on their study, Green et al. (1998) also suggest that the long-footed potoroo may be territorial and monogamous when at low densities and have a greater degree of overlap when at higher densities. A similarly flexible social biology has been proposed for the southern brown bandicoot (Isoodon obesulus) by Broughton and Dickman
(1991).
1.4.3. Habitat use by Gilberts potoroo
This species has only recently been rediscovered (1994) after it was believed to have gone extinct by 1909. The only known extant wild population comprises of fewer than
20 animals and occurs on Mount Gardiner in Two Peoples Bay Nature Reserve,
Western Australia (Courtenay and Friend 2004). Within this area the species occurs in at least four separate patches of dense shrubland that are situated on valley slopes and have not been burnt for more than 50 years (Courtenay and Friend 2004). These
42 patches of habitat are largely uniform and comprise of a 1.5 - 2 m tall Melaleuca shrub layer (of 70 – 100 % canopy cover) with a dense sedge understorey.
Individuals live in small groups within the patchy habitat as revealed by trapping and radio-tracking work (Friend 2000). Only one detailed study has been conducted on the microhabitat use of the species. Vetten (1996) undertook a spool-and-line study on the
Gilbert’s potoroo in Western Australia, to determine their microhabitat requirements with respect to the density of vegetation and species composition. Spooling was conducted in August 1996 using six animals and 340 m long spools. Each individual was released just prior to sunset at their capture site, but left in their capture bags with the end open to allow the animals to emerge at its leisure. A total of 14 spool paths was achieved, however, these varied in length. For each spool path, the vegetation types and the classes of percentage cover present were recorded, both as a frequency and as a proportion of the total spool path. These data were compared with similar data collected along a series of sixteen transects, each 340 m long. The majority of spools indicated selective behaviour for certain classes of foliage cover and vegetation types but the particular classes and types varied between spools. An analysis of the number of diggings adjacent to the spool paths revealed that the majority were in open or semi- open heathland. Vetten (1996) concluded that the species’ microhabitat use was not clearly associated with any particular floristic group or strongly correlated with any particular density of vegetation cover. Instead, study animals appeared to utilise a range of vegetation ecotones, with varying degrees of cover.
1.5. AIMS AND RATIONALE FOR THIS STUDY
The important habitat elements for the long-nosed potoroo at both the coarse and fine scale need to be identified and managed appropriately in order to help conserve the
43 species. While a number of studies have examined the species macrohabitat use, there is little information available on the species’ microhabitat use and there is some debate about whether floristic composition or structural components are important in the species’ microhabitat preference. The few studies that have examined microhabitat use for this species have been conducted in Victoria where the species appears to be smaller in size than in New South Wales. Differences in body size may result in differences in microhabitat preferences across the species range. Further, in the comprehensive examination of the species’ microhabitat use by Bennett (1993), the use of trapping may have impacted on the results achieved if potoroos were lured into trap site microhabitats by the trap bait.
The aim of my Masters research project was therefore to examine the macro- and microhabitat preferences of the long-nosed potoroo, using a variety of techniques, at a series of sites in the Southern Highlands of New South Wales in order to inform management. The ecology of the long-nosed potoroo in this geographic locality is poorly understood, making this study both timely and critical. An assessment of fox predation pressure and other threats to the species in this locality will also assist in the conservation of the local potoroo population.
The use of trapping for mammal species has been proved very effective in supplying information on the local distribution, abundance and demographics of the species. This technique has also been both popular and reliable in the assessment of a species habitat use when used to assess coarser-grained scales of resolution. For both these reasons, I used cage trapping to provide information on the morphometrics of the local population of the long-nosed potoroo and to provide an indication of its distribution and relative abundance in order to assess the species’ macrohabitat preferences. The use of the soil plot technique, developed by Newsome et al. (1995), provided a second measure of the
44 relative abundance of potoroos, as well as fox relative abundance. The technique was found by Catling et al. (1997) to provide an accurate indication of medium and large mammal abundance compared trapping results and was more labour-efficient and effective. The collection of fox scats during this study also provided an indication of fox diet in the study areas.
In my assessment of potoroo habitat preferences I used the term ‘macrohabitat preferences’ to describe habitat choices at the scale of individuals’ home ranges within the species range. This was assessed by comparing potoroo distribution and relative abundance data (provided by trapping and sand plot techniques) with a number of macrohabitat attributes. The term ‘microhabitat preferences' described habitat choices at the scale of individuals’ movements within their home ranges. To assess microhabitat preferences I used spool-and-line tracking and examination of forage diggings.
Spool-and-line tracking has been utilised in two studies of potoroo habitat use and found to be very effective at identifying finer-scale preferences. The one study employing the technique for the long-nosed potoroo examined a few aspects of the habitat use of Victorian animals (smaller in size) in different vegetation communities and structures to those in my study areas. However, this study afforded only a small insight into the species microhabitat use. Spool paths may be laid out during a range of evening activities and are therefore likely to represent a mix of foraging and non- foraging movements including interaction with other individuals and travelling between foraging sites. Conclusions about habitat preferences drawn from spool paths alone will be influenced by the proportions of these activities conducted while the spool fed out.
The comparison of spool-and-line tracking results and forage digging attributes allows some insight into the species non-foraging habitat preferences. Forage diggings have
45 been used in a number of studies to examine aspects of foraging habitat preferences and when used in combination with other techniques has provided invaluable information.
Specific aims of my research were to:
1. Assess the morphometrics of the local long-nosed potoroo populations;
2. Assess the relative abundance of potoroos at Barren Grounds NR and Budderoo NP;
3. Assess the potential impact of foxes on the local potoroo populations by examining the relative abundance and diets of foxes in both my study areas;
4. Examine the macrohabitat preferences of the local potoroo populations;
5. Examine the microhabitat preferences of the local potoroo populations;
6. On the basis of 1-5 above, provide management recommendations for the long-nosed potoroos in two National Park reserves in the Southern Highlands of New South Wales.
The remainder of this thesis comprises five further chapters. The following chapter
(Chapter 2) describes the study areas, in the Southern Highlands of New South Wales, used in this research in terms of location, vegetation, climate, geology, disturbance history and fauna. Chapter 3 examines the morphometrics and trap success of the long- nosed potoroo in my study areas. Chapter 4 investigates the macrohabitat use by the long-nosed potoroo by comparing cage trapping results and a number of macrohabitat attributes at each trap site. Chapter 5 investigates the microhabitat use by the long- nosed potoroo by comparing a number of microhabitat attributes available in the local habitat with those selected by individuals as indicated using the spool-and-line technique and an assessment of forage diggings. Finally, Chapter 6 presents a general discussion of the findings presented earlier before providing management recommendations to assist in the conservation of these local populations as well as the species in general.
46 2.0. STUDY AREAS
2.1. LOCATION
The study was conducted within Barren Grounds Nature Reserve (hereafter Barren
Grounds NR) and a section within the nearby Budderoo National Park (hereafter
Budderoo NP), approximately 100 km south of Sydney (34˚40”55”S., 150˚43’58”E.)
(Figures 2.1 and 2.2). Barren Grounds NR and Budderoo NP contain distinctive highland, plateau and escarpment landscapes, over 600m above sea level, on an underlying sandstone. Adjacent private land is predominantly used for cattle and sheep raising, dairying and cropping.
Please see print copy for image
Figure 2.1: Location of Barren Grounds Nature Reserve and Budderoo National Park, New South Wales
47
Please see print copy for image
Figure 2.2: Location of Barren Grounds NR and Budderoo NP study areas
2.2. VEGETATION AND CLIMATE
The region receives an average annual rainfall of between 2145 mm and 1250 mm, depending on the specific location (Sydney Catchment Authority weather stations
568128 and 568190). Average daily maximum and minimum temperatures recorded in the township of Robertson, approximately 10-15km north-west of the study areas, are presented in Figure 2.3 for each month, between January 2004 and December 2008. A maximum temperature of 39.1 ˚C and a minimum temperature of -6.3 ˚C were recorded during this time period.
48
Figure 2.3: Average daily maximum and minimum temperatures for each month between January 2004 and December 2008.
Both reserves contain a complex range of vegetation types including cool temperate rainforest, open forests, woodlands, heaths and sedge-lands on the plateau and tall open forests, warm temperate rainforest and subtropical rainforest on the slopes, gullies and ridges below the escarpment (NPWS 1998). The vegetation types in the study areas can be broken down into five dominant vegetation communities (Tindall et al. 2005, Table
2.1). The geology of the reserves is mostly Hawkesbury Sandstone with peaty or sandy soils that are infertile, shallow and frequently waterlogged (NPWS 1998).
From east to west across the plateau sections of the reserves the rainfall and soil moisture decreases and the soil depth increases (NPWS 1998), resulting in the predominance of heath in Barren Grounds NR and diverse woodlands and forests in
Budderoo NP (NPWS 1998). Both study areas had not had any fires or land clearing/logging for over 25 years.
49 Table 2.1: Five dominant vegetation communities and the number of trap sites within each at the Barren Grounds NR and Budderoo NP study areas
Vegetation Study site # trap Description of community community sites Budderoo-Morton Barren Grounds 31 low eucalypt forest with a dense Plateau Forest sclerophyll shrub stratum and open Budderoo NP 20 groundcover dominated by sedges Blue Mountains- Barren Grounds 1 open canopy of tall shrubs and a dense Shoalhaven Budderoo NP 0 groundcover of sedges and forbs Hanging Swamps Coastal Sandstone Barren Grounds 28 open to dense shrub canopy with Plateau Heath emergent mallees and groundcover of Budderoo NP 0 sedges and forbs Escarpment Barren Grounds 3 eucalypt forest with a mesophyll Foothills Wet shrub/small tree stratum and an Budderoo NP 11 Forest understorey of vines and ferns Shoalhaven Barren Grounds 0 eucalypt woodland with an abundant Sandstone Forest Budderoo NP 9 sclerophyll shrub stratum and a groundcover dominated by sedges.
2.3. FAUNA
Barren Grounds NR is rich in fauna, with approximately 165 native bird species, ten of which are listed as Threatened species under the NSW Threatened Species Conservation
Act 1995, and include the ground parrot (Pezoporus wallicus wallicus) and eastern bristlebird (Dasyornis brachypterus). The reserve also contains at least eight species of amphibians (including the threatened heath frog (Litoria littlejohni) and giant burrowing frog (Heleioporus australiacus)), six species of reptiles and 25 species of native mammals, including the threatened spotted-tailed quoll (Dasyurus maculates), long- nosed potoroo (Potorous tridactylus), eastern pygmy-possum (Cercartetus nanus) and eastern bent-wing bat (Minipterus schreibersii oceanensis).
Within Budderoo NP there are also records for at least 14 amphibians (including the threatened heath frog), 13 reptiles, and 70 bird species, again including the ground parrot and eastern bristlebird. Budderoo NP also houses approximately 30 native
50 mammal species including the threatened spotted-tailed quoll, long-nosed potoroo, eastern pygmy-possum and eastern false pipistelle (Falsistrellus tasmaniensis). While
Budderoo NP has been less studied than the highly popular Barren Grounds NR, it may be expected that there could even be more species diversity in Budderoo NP due to its greater diversity of vegetation communities (NPWS 1998).
Examples of potoroo habitat within these reserves are provided in Plates 2.1 and 2.2.
51 a. b. c.
d. e. f.
Plate 2.1 a – f: Long-nosed potoroo habitat within Barren Grounds NR
52 a. b. c.
d.
Plate 2.2 a - d: Long-nosed potoroo habitat within Budderoo NP
53 3.0. MORPHOMETRICS AND TRAP SUCCESS OF THE LONG-
NOSED POTOROO AND THE THREAT POSED BY THE LOCAL
FOX POPULATION
3.1. INTRODUCTION
Rat-kangaroos have been highly disadvantaged by changes in the landscape brought about since European settlement, with the majority of extant species now listed as threatened (Calaby 1971, Bennett 1993, Taylor 1993, Short 1998, Claridge and Barry
2000, Priddel and Wheeler 2004, Claridge et al. 2007). The long-nosed potoroo is no exception. While it is considered relatively common in Tasmania, its distribution is patchy along the eastern sea-board from south-eastern Queensland to the south-west of
Victoria (van Dyck and Strahan 2008). A reduction in its range and abundance has resulted in their current listing as Vulnerable in New South Wales and Queensland and
Endangered in Victoria.
There are two primary factors believed to be currently threatening the species: predation by foxes and inappropriate habitat change (Seebeck et al. 1989, Claridge and Barry
2000). Inappropriate habitat change has been through the loss and fragmentation of some habitat caused by clearing for agriculture and human settlement, and through habitat degradation (with the loss of dense understorey cover) by changed fire regimes and overgrazing by stock. However, the relative effects of these two processes are uncertain. While some authors suggest that foxes are the main cause of the species decline (Guiler 1958, Heinsohn 1968, Short 1998), others suggest that the dense vegetative cover in potoroo habitat offers virtually total concealment from and limited access by introduced predators (Schlager 1981, Seebeck 1981, Mason 1997).
54 The long-nosed potoroo fits within the category of medium-sized (450-5000g) ground- dwelling mammals upon which the impact of fox predation is suggested to be substantial (Dickman 1996a). However, in the NSW Threat Abatement Plan for
Predation by the Red Fox (NPWS 2001) the long-nosed potoroo was listed as a ‘low’ priority threatened species, suggesting the likelihood of fox predation causing population-level impacts on the species was low. This was based on the perception that the species’ gains significant protection from predation by occupying dense understorey. Certainly the proportion of fox scats with potoroo hairs has varied widely at different study areas across the country, from less than one percent to thirteen percent
(Seebeck 1978, Schlager 1981, Lunney et al. 1990, Capararo and Beynon 1996).
However, the impact of fox predation on the species in their environment remains uncertain.
The long-nosed potoroo is a cryptic species that mostly utilises dense vegetative cover
(Seebeck et al. 1989), making direct observational studies of the species difficult.
However, a number of other techniques have been used to study this species across its range, with varying success. Trapping has been the most widely used technique (Guiler
1958, Heinsohn 1968, Kitchener 1973, Bennett 1987 and 1993, Claridge et al. 1993a,
Mason 1997) and allows details to be taken on both the relative abundance of the species as well as specific information on the species such as morphometrics and demographics. Trap success has varied across the species range, with instances of nil trap success despite its known presence in the area (Guiler 1958, Schlager 1981,
Seebeck 1981, Broome 1994, Bennett 1993, Capararo and Beynon 1996, Catling et al.
1997, Mason 1997).
The soil plot technique developed by Newsome et al. (1975) has been used in a few studies (Catling and Burt 1995b, Catling et al. 1997 and 2001, Coops and Catling 2002)
55 to successfully examine the relative abundance of a number of ground-dwelling mammal species. This technique relies on study species travelling on the tracks on which the soil plots are established and being at sufficient levels to avoid under- sampling (Catling and Burt 1995b). Coops and Catling (2002) suggest that the presence/absence on soil plots of potoroo prints represents overall changes in population size, due to the small home range of individuals and thus the likelihood that each plot with prints represents a different individual. The technique was found by Catling et al.
(1997) to provide an accurate indication of medium and large mammal abundance compared with trapping results and was more labour-efficient and effective. The technique has also been found to be highly effective in providing relative abundance information on foxes (Catling and Burt 1995c, Catling et al. 1997, Mahon et al. 1998).
The aims of this chapter were to record the population parameters of local long-nosed potoroos in the Southern Highlands of New South Wales and to monitor changes in their relative abundance in relation to its primary threat in the study areas, the fox. As both study areas are located within National Parks reserves, with no clearing or logging for over 25 years, habitat loss/change was not considered to be a major threat to the local populations. In order to gain knowledge in my study areas of local long-nosed potoroo morphometrics and relative abundance, and fox activity, I used a combination of live-trapping and soil plot techniques. An understanding of abundance changes of the target species in relation to fox predation pressures at both study areas will assist in later examinations of macro- and micro-habitat use, where such pressures may impact on species preferences.
A 1080 fox baiting program has been conducted across Barren Grounds NR since June
2005 as part of local reserve management by the Department of Environment and
Climate Change. Although this baiting program was not part of my masters research,
56 its impact needs to be considered when examining changes in long-nosed potoroo relative abundance.
3.2. METHODS
3.2.1. Potoroo live trapping
Long-nosed potoroos were live-trapped at Barren Grounds NR and Budderoo NP using wire mesh cage traps (200 x 200 x 400 mm, R.E. Sinclair, Melbourne, Australia). Traps were set adjacent to walking tracks and fire trails, with trap sites located approximately
100 m apart (Figures 3.1 and 3.2). The proximity of trap sites between Barrren
Grounds NR and Budderoo NP was between 5.7 and 11 km. At each trap site a single cage trap and two Elliott aluminium box traps (Elliot Scientific Equipment, Upwey,
Victoria, Australia) were set in close proximity, baited with a small amount of peanut butter, rolled oats and honey mix (Plate 3.1 a – b). The Elliott traps were used to reduce the probability of small mammals being cage-trapped at the expense of long-nosed potoroos. Trap site positions were well marked and their grid references recorded, and they were marked off as checked, to ensure all traps were accounted for.
To reduce the effects of rain, wind or hot weather on trapped individuals, all traps were placed in well-sheltered positions under dense vegetation such as coral fern. Where there was insufficient vegetation to fully shade the traps, hessian was draped over the traps to provide shade. The cage traps were also two-thirds covered with thick shade- cloth and the Elliott traps placed in plastic bags and containing a wad of dacron fibre for additional insulation.
An initial trapping session was conducted at Barren Grounds NR in March 2004 using
23 trap sites. Following this session, regular trapping at both areas was conducted twice-yearly in autumn and spring between March 2005 and March 2008. A total of 40
57 trap sites were operated each session at Budderoo NP and between 40 and 45 at Barren
Grounds NR, with the exception of March and October 2007 where 63 trap sites were operated at Barren Grounds NR to cover some additional vegetation communities not previously sampled.
Autumn and spring were considered the best seasons for trapping due to a reduced likelihood of extreme weather conditions. It was planned that trapping would be postponed if a period of unseasonably hot, cold or wet weather conditions, or a high fire threat, were forecast. However, no such weather patterns coincided with the trapping sessions and only a few individual trapping days with high temperatures were experienced.
Trapping was conducted over four consecutive nights for each trapping session. Traps were checked and reset at dawn each morning and the species caught in the Elliotts and cage trap at each trap site were recorded. Traps were rebaited as required. During any days with high temperatures (> 25 ˚C) traps were rechecked early-afternoon and any trap sites with potoroo captures were then closed down until the following morning.
This was to avoid skewing trap results by doubling trapping effort within a 24 hour period.
During each trap checking session any potoroo captured was removed from its cage and placed in a soft cloth capture bag for further processing. All other species were released without further processing. A number of potoroos were re-captured on successive mornings in a session and where this occurred on more than 2 occasions the relevant trap site/s were shut down for the remainder of the trapping session.
Two values for trap success were calculated each season for each trap area: the number of potoroo captures per trap night and the number of potoroo individuals per trap night.
58 Please see print copy for image
Figure 3.1: Location of trap sites and sand plots within Barren Grounds NR
59 Please see print copy for image
Figure 3.2: Location of trap sites and sand plots within Budderoo NP
60 a. b.
Plate 3.1 a - b: Trap positioning within the local environment
3.2.2. Potoroo processing
Handling of captured potoroos was minimised to that necessary to identify, mark, weigh, measure and sex each individual animal (Plate 3.2 a - f). Potoroo weights
(measured using Pesola spring precision scales, medio-line 2500 g) and pes, ear and head lengths (measured using 15 cm ProEarth metric dial stainless steel callipers) were recorded once per season for each individual. Females were also examined for reproductive status and the developmental stage of any pouch young noted. Pouch young were classed as ‘small’ if they were pink and poorly developed, ‘medium’ if they were more developed (eye lids and lashes but ears flat against head) but either pink or light velvety grey fur, and ‘large’ if they were furred and fully developed (eyes open and ears upright). Medium-sized pouch young are estimated to be between approximately 10 and 95 g with large pouch young between 95 and 260 g according to
Bryant (1989).
Potoroos were handled within the confines of the capture bag at all times to prevent undue stress. The identity of each potoroo captured was recorded and the animals were examined for injuries and superficial injuries were treated prior to release. No serious injuries were incurred. All adult and sub-adult individual potoroos were implanted with
61 a Trovan micro-chip between their shoulder blades and an ear tissue sample (2mm biopsy using a biopsy punch) was also taken for future genetic examination.
Hughes (1964) found numerous sperm in Tasmanian long-nosed potoroo males of 908 g or more, a few sperm in two males weighing 639 g and 901 g, and none in any smaller males. The average body weight of adult males in Hughes’ study was approximately
1300 g. Based on this research and the smaller average adult body weight of his
Victorian study animals (800 g), Bennett (1987) regarded his male potoroos as adults when they reached 600 g. Therefore, with an early estimate of an adult male body weight of 1000g in my research, I classed males as sub-adult if they weighed less than
800 g. Females in my research were classed as adults if they had any extended teats, a well-formed pouch, a pouch young present or a history of pouch young present. Female weights included any pouch young they held.
The weights, head lengths, pes lengths and ear lengths of individual adult males and females caught each session were compared using analyses of variance (ANOVA; JMP
Version 5.1). A comparison between the two study areas of the number of potoroo captures/trap night, individual potoroos/trap night and captures per individual were compared using paired t-tests. A comparison was also made between males and females of the number of seasons over which each individual was captured (ANOVA).
62 a. b. c.
d. e. f.
Plate 3.2 a - f: Weighing; scanning for a microchip; inserting a microchip: measuring the ear: head; and pes length. (Photos a – c: F. Kristo, Photo f: A. Prentice)
63 3.2.3. Loss of pouch young
In a small number of instances, female potoroos drop their pouch young either in the cage or in the capture bag (see Claridge et al. 2007). When this occurred the mother and young were left in the capture bag together at the trap site. The bag was placed in a well shaded area with the top of the bag left open for the animals to find their way out of when ready. All traps at the site were closed. The bag was checked in the early evening and again the following morning to ensure the pair had reunited and left the bag.
This technique was altered following 2 unsuccessful reunions in 2007. Subsequently, when a female dropped her pouch young, the young was assisted back in the pouch. On two occasions when first attempts failed, the young was kept in a series of cloth bags in an emergency kit (a large cloth bag with hot water bottle and thermometer) for one hour to allow the mother time to take up her pouch muscles again before trying again.
Unfurred pouch young were held at an air temperature of 32 ˚C and furred pouch young were held at 28 ˚C. During this time the mother was kept in the capture bag in the closed trap in situ.
The mother (with young now back in her pouch) was then placed back in the capture bag in the closed trap in situ for approximately 5 hours, after which time the pair were re-checked to ensure the young was still in the pouch. During these checks the mother was always found to have calmed down and kept the young in her pouch. The pair was then left in the capture bag, in the shade, with the top rolled down to allow the mother to leave when ready. The bag was checked during the evening to ensure they had departed. The initial two attempts to tape up the pouch opening up with ‘Elastoplast’ tape, to ensure the young stayed in the pouch, failed and was found to be an unnecessary additional precautionary measure.
64
3.2.4. Sand plot monitoring
The relative activity of potoroos and foxes was monitored in both Autumn and Spring from 2005 to 2008 in both study areas by recording their distinctive tracks in soil plots.
Sterilised ‘plasterers’ sand was imported to form each soil plot (now termed sand plot) due to the rocky nature of the local track surfaces and to minimise erosion. Sand plots were spaced at 200 – 250 m intervals along tracks within both study areas (Figures 3.1 and 3.2), with a total of 25 used at Barren Grounds NR and 27 at Budderoo NP. Each sand plot was the width of the track and approximately 1 m long to reduce the chance of an animal leaping over the plot and thus leaving no prints (Plate 3.3). Over three consecutive mornings the presence/absence of fox and potoroo tracks on each plot were recorded and then all tracks cleared. Where rain or strong wind made tracks unreadable, the sand plots were re-prepared and tracks recorded as soon as possible until a total of 3 nights of activity were recorded for the season. Each sand plot was in roughly the same position each season. For both potoroos and foxes the percent of plot nights with their tracks was calculated for each session and compared graphically. a. b.
Plate 3.3 a - b: Setting up sand plots across tracks at each study area.
65 3.2.5. 1080 fox baiting
A 1080 fox baiting began across Barren Grounds NR in June 2005 as part of local reserve management by the Department of Environment and Climate Change. Baits were buried in bait stations and check daily, replacing as required. Initially, two-week- long baiting sessions were conducted every three months across 22 bait stations. The first week involved free feeding only (unpoisoned baits). Any bait stations with free- feed takes by spotted-tailed quolls were abandoned for the rest of the baiting session, with 1080 Foxoff baits used in all other stations during the second week. Baiting efforts were increased to a 4 week block every 3 months in May 2006 and the number of bait stations was increased to 27. While the baits were still buried in bait stations, the baiting regime was changed to one visit per week and the continuous use of 1080
Foxoff baits. The cessation of free feeding and continuous use of 1080 Foxoff baits was influenced by the observed lack of consumption of this bait type by quolls in a study by
Kortner et al. (2003). No fox baiting has been conducted in the vicinity of the
Budderoo NP study area.
3.2.6. Assessing fox diet
Predator scats were collected opportunistically from each study area between 2005 and
2008. They were not touched by hand during collection to minimise exposure to any parasites. All scats collected were sent for analysis to a professional hair analyst
(Georgeanna Story, “Scats About”, Majors Creek, New South Wales). Prior to analysis, scats were oven-dried, placed in fine weave nylon bags and washed in a washing machine for approximately 15 minutes (Johnson and Alred 1982). Prey items present within each scat were recorded. The predator species to which the scat belonged were identified with the use of ‘probable’ and ‘possible’ classes where the predator species was uncertain. The percentages of all ‘fox’ and ‘fox (probable)’ scats collected
66 containing each of the prey items were identified. The proportion of all predator scats collected containing long-nosed potoroo were also calculated for both study areas. The proportion of each prey in the fox scats collected were compared graphically.
3.3. RESULTS
3.3.1. Potoroo morphometrics
The weights of individual adult males (1063 g) caught each session were significantly greater than those of the individual adult females (962 g) caught each session, including their pouch young where present (F1, 118 = 16.199, P = <0.0001) (Table 3.1). The range of adult weights was 820 – 1440 g for males and 680 – 1160 g for females. Over the course of this study, approximately 90 % of adult females captured had pouch young.
Within the adult females, there was considerable overlap between average weights with and without different sized pouch young. The average weight of females with ‘small’ or no pouch young was 929 ± 89 g. All male potoroos weighing less than 800 g, and therefore automatically classed as sub-adults, were found to be new individuals (n = 9).
Of these individuals, six were not caught again while the other three were trapped six months on from their initial capture with body weights between 880 and 900 g. Two adult male individuals were also found to drop in body weight to 820 g and 900 g over a minimum six month period. The minimum sub-adult weight was 510 g for males and
420 g for females.
Adult males caught each session were found to have significantly larger head lengths
(F1, 95 = 17.734, P = <0.0001) and pes lengths (F1, 107 = 15.012, P = 0.0002) than those of the adult females caught each session (Table 3.1). There was no significant difference between the ear lengths of adult males and females (F1, 104 = 0.0426, P =
0.837).
67 Table 3.1: Average body weights and measurements for male and female potoroo captures across both study sites and all seasons
Average Females with: Average head Average Average Age 1 1 1 1 Sex Weight ± n Average length ± SD n ear length n pes length n group n SD (g) Weight1 ± SD (g) (mm) ± SD (mm) ± SD (mm) 1020 All 85 87 ± 5 76 36 ± 3 80 78 ± 3 82 ± 183 Sub- 656 Male 9 79 ± 2 8 35 ± 2 5 76 ± 4 5 adult2 ± 104 1063 Adult3 76 88 ± 5 69 36 ± 3 75 79 ± 3 76 ± 139 929 All 52 82 ± 5 33 35 ± 4 38 76 ± 3 40 ± 158 Sub- 664 5 74 ± 5 3 34 ± 3 4 76 ± 4 4 adult2 ± 169 Female no pouch young 977 ± 81 8 962 small4 pouch young 894 ± 80 11 Adult3 44 83 ± 4 28 36 ± 4 31 76 ± 2 33 ± 127 medium5 pouch young 1045 ± 99 10 large6 pouch young 1130 ± 42 2 1excluding values from multiple recaptures of individuals within any one season 2 sub-adult = independent females not yet of breeding age = independent males less than 800 g 3 adult = females known to be of breeding age = males weighing 800 g or more 4 small pouch young = pink and poorly developed 5 medium pouch young = pink or grey velvet fur but developed 6 large pouch young = furred and fully developed
68 3.3.2. Trapping and potoroo occurrence
Numerous mammal species were captured at both study areas in the Elliott and cage traps used in this study: long-nosed potoroos (Potoroos tridactylus), spotted-tailed quolls (Dasyurus maculatus), long-nosed bandicoots (Perameles nasuta), brown antechinus (Antechinus stuartii), dusky antechinus (Antechinus swainsonii), bush rats
(Rattus fuscipes), and swamp rats (Rattus lutreolus). Egernia and Eulamprus lizard species were also captured as well as two eastern bristlebirds (Dasyornis brachypterus).
Of the 63 trap sites at Barren Grounds NR, 28 had potoroo captures at some time during the study. Of the 40 trap sites at Budderoo NP, 20 had potoroo captures. Over the course of the study a total of 44 individual potoroos were caught at Barren Grounds NR out of 162 potoroo captures and 1466 trap nights. At Budderoo NP a total of 23 individual potoroos were caught out of 50 captures and 1104 trap nights.
A significant difference was found between potoroo capture rates at the two study areas
(t6 = 5.642, p = 0.001), with an average of 0.11 ± 0.04 potoroo captures/trap night at
Barren Grounds NR and 0.05 ± 0.05 potoroo captures/trap night at Budderoo NP.
Likewise, the capture rates of individual potoroos at the two study areas also differed (t6
= 2.860, p = 0.014), with an average of 0.07 ± 0.02 individual potoroos/trap night at
Barren Grounds NR and 0.04 ± 0.04 individual potoroos/trap night at Budderoo NP. No significant difference was found between the two study sites in the number of captures per individual (t6 = 1.994, p = 0.0932).
The number of new individuals and recaptures fluctuated at both study areas, as did the total number of individual potoroos captured (Figures 3.3 and 3.4). However, over consecutive spring seasons there was an increase in the total number of individuals captured. Trap success also varied across sites and seasons over the course of the study.
Despite operating additional trap sites in Autumn and Spring 2007, no potoroo captures 69 were achieved at these sites. The average number of new individuals captured each season was 5.5 ± 2.4 at Barren Grounds NR and 3.3 ± 3.7 at Budderoo NP. A number of individuals were caught over multiple seasons, with some being captured up to three years after their original capture. No individual was caught at both study areas.
Figure 3.3: Number of new and recaptured potoroos and trap success per Autumn and Spring seasonal trapping sessions (number of trap nights) at Barren Grounds NR
Figure 3.4: Number of new and recaptured potoroos and trap success per Autumn and Spring seasonal trapping sessions (number of trap nights) at Budderoo NP 70
The overall male to female ratio of potoroo individuals was 1 : 0.76. However, a comparison of the number of male and female potoroo captures each season across the two areas (Figure 3.5) revealed an average male to female ratio of 1 : 0.50. The number of seasons over which each individual male was captured was significantly higher than that for females (F1, 65 = 4.935, P = 0.030), with an average of 2.45 seasons for males and 1.65 for females.
A number of both male and female individuals were not recaptured over the course of the study. At Barren Grounds NR 37.5 % of individual males (average weight 777 ±
192 g) and 55 % of individual females (average weight 881 ± 213 g) were not recaptured in subsequent trapping seasons, while at Budderoo NP these values were 36
% of males (average weight 902 ± 172 g) and 67 % of females (average weight 938 ±
104 g).
Figure 3.5: Number of individual male and female potoroos captured per seasonal trapping session across the two study areas combined
Of all the individual potoroos caught, the majority were caught at multiple trap sites over the course of the study (an average of three and a maximum of six trap sites). 71
Where this occurred, the average distance between the furthest traps in which each individual was caught was found to be 288 ± 177 m. At both study areas, multiple individuals were also caught at a single trap site within a single season. This occurred at more trap sites and more frequently, with more individuals, at Barren Grounds NR than at Budderoo NP (Table 3.2). The majority of instances involved the capture of both male and females and the minority involved only females.
Table 3.2: Details of instances where multiple individuals were captured at a single trap site in a single season at either study area.
% of instances with an overlap maximum number n Study n between in any instance (trap area (instances) male & male/s & female & sites) males females male/s female/s female/s Barren Grounds 16 45 51 % 67% 16 % 2 3 NR Budderoo 6 6 33 % 83 % 0 % 2 1 NP
A comparison of the trends over time in the number of potoroo captures per trap night and the percent of sand plot nights with potoroo tracks (as two indicators of potoroo abundance) are provided for each study area (Figures 3.6 and 3.7). While it appears that both indicators suggest similar changes in potoroo abundance between Autumn 2005 and Autumn 2006, this was not the case beyond Autumn 2006. Rather, different trends in abundance were suggested by the indicators with the peaks in the number of potoroo captures not being matched by peaks in potoroo activity on the sand plots. The sand plot results do however suggest that potoroo abundance was lower at Budderoo NP compared to Barren Grounds, as is suggested by the trap success results.
72
Figure 3.6: Potoroo captures per trap night versus percent of sand plot nights with potoroo tracks over time at Barren Grounds NR
Figure 3.7: Potoroo captures per trap night versus percent of sand plot nights with potoroo tracks over time at Budderoo NP
3.3.3. 1080 baiting, fox abundance and diet at the two study areas
Despite fox baiting beginning in June 2005 no baits were taken until December 2005 when only two baits were removed, both by foxes. Following the Autumn 2006 potoroo trapping session another three bait takes were achieved, one confirmed as a fox
73 take. To date, despite increasing baiting efforts to a 4 week block every 3 months in
May 2006 and an average of 4 bait takes achieved per session, only an average of 2 baits per session are confirmed fox takes. No confirmed dog takes have been recorded to date. The results of the sand pads indicate fluctuating fox activity at both study areas over the course of the study (Figure 3.8). Within Barren Grounds NR, fox levels pre- and post-successful baiting were similar. In this study area incidences of dog tracks on the sand plots were rare (between nil and 5 % of sand plot nights with dog tracks) while cat tracks fluctuated more obviously (between nil and 16 % of sand plot nights). At
Budderoo NP no cat tracks were observed and the percent of sand plot nights with dog tracks ranged from nil to 1.3 %.
Figure 3.8: Percent of sand plot nights with fox tracks at Barren Grounds NR and Budderoo NP over time
Of the 151 predator scats (fox, dog, cat and quoll) collected opportunistically from both study areas between 2005 and 2008, 13.2 % were found to contain long-nosed potoroo remains. Analysis of the scat contents enabled the scats to be identified as a ‘definite’,
‘probable’ or ‘possible’ scat belonging to a particular predator species. No ‘definite’ cat or dog scats were collected from Budderoo NP. 74
Fox scats (‘definite’ scats only) were found to be most likely to contain potoroo (Table
3.3). No ‘definite’ cat or quoll scats were found to contain potoroo remains. Of these fox scats, 15.7 % from Barren Grounds NR and 11.1 % from Budderoo NP contained long-nosed potoroo (Figure 3.9). The main dietary items of foxes at Budderoo NP appear to be macropod species, wombats and invertebrates. These were present in much higher proportions of fox scats than other prey items in this study area. At Barren
Grounds NR macropod and Antechinus species appear to be the main dietary items for foxes, with potoroos the third most common prey item to be present in fox scats.
Wombats and invertebrates were in less than 10 % of fox scats in this study area. The presence of small amounts of fox hair in the fox scats at both study areas is believed to be the result of grooming.
All the ‘definite’ dog scats collected were from Barren Grounds NR and over 35 % of these contained macropod remains. The next five most common prey species, each found in between 10 and 20 % of these scats, were long-nosed potoroos, long-nosed bandicoots, Antechinus sp., Rattus sp., and common ringtail possums (Pseudocheirus peregrines).
Table 3.3: Percent of ‘definite’ predator scats (fox, dog, cat and quoll) collected from the two study areas containing potoroo remains
Predator species # scats collected % containing potoroo remains fox 69 14.5 dog 28 10.7 cat 1 0 quoll 12 0
75
35
30 Barren 25 Grounds N R (51) 20
15 Budderoo 10 NP (18)
5
% of fox scats with each prey species species prey witheach scats fox of % 0 t t a p. te on sp. sp. s sp. sp. p. sp. Ca Fo x a ti tylus s s s bbi c tus nasut od us u ru Ra eta nus t Mus sp. ur ir u Bi r d rtebr da Ra es op a bat us sp. e tri et os m Reptile sp. Veg P h Inv mel Macr doche Vo ous Ant echi Tric or Per a Pseu Pot Prey Items
Figure 3.9: Percent of the ‘definite’ fox scats collected at either study area containing each prey item
76
3.4. DISCUSSION
Both the number of individual potoroos captured and trap success fluctuated over the study at both Barren Grounds NR and Budderoo NP. Overall, comparing spring results, there was an increase at both study areas in the total number of individuals captured and a general increase in the number of new individuals captured. Trap success values also increased each spring at both study areas with the exception of Spring 2007 at Barren
Grounds NR. In this instance a number of additional trap sites were operated to cover some additional vegetation communities not previously sampled. However, no potoroos were caught at these trap sites. If these additional trap sites are excluded to allow a fairer comparison across seasons, then the greater number of individuals captured compared to the previous spring would result in a higher trap success.
Therefore, it can be concluded that potoroo abundance increased each spring over the study in both study areas. It is unclear however, why a corresponding increase each autumn was not observed.
A comparison of trap success between study areas reveals significantly higher trap success at Barren Grounds NR. Regardless of gender, more individuals overlapping at trap sites more frequently at Barren Grounds NR than Budderoo NP, suggesting the home ranges of individuals overlapped more at Barren Grounds NR.
The sand plot technique revealed that foxes were present in both study areas at varying levels. Catling et al. (2001) provided abundance ratings for foxes within the eucalypt forests of eastern New South Wales with a low rating for 5-15 % soil plot nights with fox prints, a medium rating for 15-40 % and a high rating of >40 %. In relation to these abundance ratings, Barren Grounds NR initially recorded a high fox abundance level which then dropped to low prior to any 1080 poisoning. Fox abundance levels then fluctuated between low and medium with ongoing fox baiting efforts. Larger
77 fluctuations in fox abundance levels (between low and high) were observed at Budderoo
NP in the absence of any fox control. These results suggest a limited impact on foxes in
Barren Grounds NR by the 1080 fox baiting program, although fox levels following successful baiting were within the limits of the those recorded prior to any successful baiting.
The increase in potoroo abundance at both study areas each spring, despite no fox control at Budderoo NP, and the higher potoroo trap success observed at Barren
Grounds NR prior to any successful fox control, compared to Budderoo NP, suggests non-fox control related differences between the two study areas. The ability of Barren
Grounds NR to support a larger number of individuals and a greater degree of home range overlap between individuals may be more indicative of higher quality habitat at this study area, a topic examined in later chapters.
Predator scat contents collected during this study were examined to identify whether potoroos formed part of the diet of the predators within the study areas. While it is acknowledged that some proportion of potoroo remains in predator scats was likely to be due to scavenging, direct predation was considered to be the major cause of occurrence. Potoroos were found to be a significant part of the diet of predators in the two study areas and were most commonly found in fox scats, with 14.5 % containing potoroo remains. Obvious differences in the diets of foxes were observed between the two study areas. At Budderoo NP macropod species, wombat and invertebrates were all present in over one third of all fox scats. Potoroos were present in 11 % of fox scats at this study area. At Barren Grounds NR macropod and Antechinus species were the two most common prey species in fox scats, with potoroos in 16 % being the third most common in this study area. The slightly higher proportion of fox scats containing
78 potoroo at Barren Grounds NR compared to Budderoo NP is most likely related to the higher potoroo abundance at this study area.
Although long-nosed potoroo remains were also found in a proportion of dog scats, the sample size was much smaller. It is also unclear whether these were from feral dogs or dingos and whether the potoroos were preyed upon or scavenged. Much lower levels of long-nosed potoroo occurrence in dog/dingo scats have been observed by other authors
(Newsome et al. 1983, Lunney et al. 1990) compared with this study, although the higher levels observed in this study were only from Barren Grounds NR. It is unclear to what extent potoroos are predated by cats. The limited number of cat scats collected is not believed to be indicative of low cat numbers but rather the general habit of cats to bury their scats compared to the other species. Opportunistic sightings of cats within
Barren Grounds NR increased over the course of the study.
While the sand plot technique has been found to provide reliable relative abundance estimates for foxes and canids (Catling et al. 1997, Mahon et al. 1998, Allen et al.
1996), its reliability as an indicator of potoroo abundance is less certain. The use of tracks as movement corridors by canids (May and Norton 1996, Claridge 1998) may make it a more suitable technique for monitoring the relative abundance of fox and canids compared to potoroos.
As indicated by the potoroo trapping results, the sand plot technique also indicated that potoroo relative abundance was higher at Barren Grounds NR than Budderoo NP.
While both techniques also provided similar trends in fluctuating potoroo abundance from Autumn 2005 to 2006, the indicated trends by either technique then varied through to the end of the study. Some of the sand plot sessions had very low to nil potoroo counts, while trap results for these seasons indicated potoroos were at higher levels.
Furthermore, I had other sand pad sessions with relative high potoroo sand pad counts 79 but few potoroos captured. It is unclear why these techniques provided contrasting results after Autumn 2006; however, it is clear that at least the sand plot technique was not able to provide an accurate estimate of potoroo abundance over time.
While Coops and Catling (2002) suggested that sand plot results represent overall changes in population size, it is feasible that this is not always the case. The sand plot technique relies on the study species to move across sand plots on tracks in order to be identified. With the strong association between potoroos and dense vegetative cover
(Seebeck et al. 1989), the species may well be much less inclined to venture out onto tracks, resulting in the under-sampling of this species by this technique. During my study potoroos were only ever observed darting across the tracks, not travelling along them. Their use of cover could also be particularly influenced by the presence of predators nearby, as well as other factors such as moon phase and weather conditions.
With cage traps being positioned off the tracks and in vegetation, their success might be considered less susceptible to influences such as predation threat, than the use of open tracks.
My suggestion that trapping was the more reliable indicator of potoroo relative abundance than sand plots contrast with an assessment of both techniques by Catling et al. (1997). They concluded that soil plots were the best technique to provide relative abundance data of medium- and large- sized mammals, while trapping produced the best results for small mammals. However, they had grouped potoroos with other species into a ‘small macropod’ group making it difficult to identify the effectiveness of the technique specifically for the long-nosed potoroo. They also did not manage to capture any long-nosed potoroos during cage trapping and based their assessments on only one session of soil plots and trapping. This contrasts markedly with my study
80 where I had no difficulties in trapping the species and was able to compare four years of trapping and sand plot data.
It appears that sand plots may be a less effective technique to assess potoroo abundance compared to trapping when they are at greater levels. My study recorded much higher percentages of sand plot nights with potoroo prints compared to those recorded by
Catling et al. (2001). They rated potoroos as scarce to low throughout their study which corresponded with levels of between 0 and 1.5 % of trap nights with potoroos. At
Budderoo NP I recorded levels of between 0 and 5 % (covering the full spectrum of ratings, from 0 to >3, supplied by Catling et al. (2001) for the species). At Barren
Grounds NR my levels of sand plot nights with potoroos were from 6 and 12 %. The distribution of sand plots in my study only allowed for the detection of a potoroo presence at every 200-250 m interval along tracks. However, my cage trapping was spaced at 100-200 m intervals and the trapping results indicated that in parts of my study areas, up to four potoroos overlapped at a single trap site within a single season.
Aside from the considered greater reliability of the trapping results, trapping also enabled the collection of morphometric data on the local potoroo populations. Data collected provided an average body weight of adult male seasonal captures, approximately 270 g larger than the average male weight recorded by Bennett (1987) in
Victoria. Likewise, the average weight of female captures with ‘small’ or no pouch young were approximately 150 g larger than those recorded by Bennett (1987). My study animals were also somewhat smaller than the animals examined by Mason (1997) in north-eastern NSW where adult average weights were 1463 g for males and 1313 g for females. Likewise they were smaller than animals from Gosford (1336 g for males and 1156 g for females) but similar in size to animals from Cobargo, approximately 250 km further south (1095 g for males and 992 g for females) (Johnston and Sharman
81
1976). It should be noted that the body weights I collected were the weights of potoroos captured each season. Therefore the regular re-trapping of some individuals each season may have skewed my results. However, this is not likely to be the reason for the large differences in weights observed by the different studies above.
These results support the notion of a cline in body weight for the species with size increasing with latitude on the mainland. However, it is unclear whether this is related to climatic and/or vegetational variations with altitude. This cline is not consistent with
Bergamm’s rule that body mass increases with latitude and colder climates.
Longitudinal clinal variation in body weight of the Tasmanian sub-species has previously been shown with smaller animals in the wetter north-west and larger animals in the drier north-east (Johnston and Sharman 1976). Although these authors did not find a significant relationship between body weight and latitude on the mainland, they had included some specimens which have since been identified as the long-footed potoroo. They did find a latitudinal cline in muzzle proportions with shorter broader, deeper muzzles in northern animals, despite the inclusion of the long-footed specimens.
Clinal variation in body size has also been observed in a number of other mammal species in Australia, with size decreasing with increasing latitude in the quokka (Setonix brachyurus) (Sinclair 1998) while increasing with increasing latitude in the common brushtail possum (Trichosurus vulpecula), Gould’s wattled bat (Chalinolobus gouldii), the sugar glider and the squirrel glider (Petaurus breviceps and P. norfolcensis)
(Tidemann 1986, Kerle et al. 1991, Quinn et al. 1996). Clinal variation in body size has also been observed in numerous mammals (Koch 1986, Bekele et al. 1993, Tumlison
1993, Sharples et al. 1996, Storz et al. 2001).
A positive relationship has been found between home range and body size (McNab
1963). It has also been suggested that for the long-nosed potoroo, home range size may 82 alter with changing habitat quality (Seebeck et al. 1989, Claridge et al. 2007): with larger home ranges where habitat quality is poorer. This would suggest that potoroo body size also increases as habitat quality decreases, as was found for Potorous tridactylus apicalis in Tasmania by Johnston and Strahan (1976). Larger home ranges were observed by Kitchener (1973) in southern Tasmania in the vicinity of where the relatively larger-sized potoroos were observed by Hughes (1964). Alternatively much smaller home ranges were observed for the relatively smaller potoroos near Naringal, in south-western Victoria, by Bennett (1987) and Long (2001). If, by inference, there is such a relationship between weight, home range size and habitat quality, then the habitat within Barren Grounds NR and Budderoo NP would be considered of medium quality and home range sizes could be expected to be somewhere between those observed by these other studies.
While Bennett (1987) found no sexual dimorphism in Victorian long-nosed potoroos, van Dyck and Strahan (2008) and Seebeck (1981) suggest slight sexual size dimorphism. In my research I found that males were significantly larger than females in terms of body weights, head lengths and pes lengths. Also, in contrast to Bennett
(1987) I found that the number of trapped males always outnumbered females, with a male to female ratio of potoroo individuals of 1:0.76 over the whole study. In addition, male captures occurred twice as frequently as female captures and male individuals were captured over significantly more seasons than female individuals. It is unclear whether these results indicate that males survived longer than females or males were more ‘trappable’ than females. The larger home range of males compared to females
(Bennett 1987) may have also resulted in males having access to more traps and therefore made them more likely to be trapped.
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Male and female home ranges are known to overlap considerably (Bennett 1987,
Claridge et al. 2007). In both my study areas, males were found to regularly overlap at trap sites with females, much more often than with other males. An examination of the home range of the species by Bennett (1987) found a similar result. However, in
Bennett’s female-biased potoroo population, females overlapped at similar levels with males and other females, while in my male-biased study, females rarely overlapped at trap sites with other females.
Bennett (1987) defined individuals that were only captured in a single trapping session as ‘transients’. At both my study areas, just over one third of all males, and over half to two thirds of all females, fitted this description. While Bennett (1987) observed much lower levels (approximately 10 % of either sex) it should be noted that his four day trapping sessions were conducted at approximately six week intervals. My four day trapping sessions were conducted at six monthly intervals. The longer intervals between my trapping sessions may well have been the cause of the higher level of
‘transience’ I observed. At the timescale between my trapping sessions, the low proportions of recaptures over multiple seasons may be related to survivorship as much, if not more so, than transience. No significant difference was found between my two study areas in the levels of recaptures of individuals, suggesting similar levels of transience/survival in both areas.
In this study I assumed that males weighing less than 800 g were sub-adults, based on the mid-weight range of the adult males captured and the studies by Hughes (1964) and
Bennett (1987). This estimate appears to have been fairly well supported by the results.
I found that all nine individuals that fitted this sub-adult weight category were first time captures. Six of these were ‘transients’ while the other three were recaptured six months on and found to be approximately 900g each. With sexual maturity at
84 approximately one year of age (Rose 1989, Bennett 1987), two of the confirmed adult males were found to drop in body condition to between 800 and 900g in successive captures. These results suggest that males are likely to be sexually mature by about 800 to 900 g at the Barren Grounds NR and Budderoo NP study areas. Interestingly, this is greater than the average size of an adult male in Victoria (Bennett 1987, Long 2001). I found that the average weight of all male ‘transients’ in this study was only 777 g, suggesting the majority of the male transients were sub-adults. These may be considered more naïve than adults and thus more susceptible to predation, particularly given the high levels of predation observed during the study.
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4.0. MACROHABITAT USE BY THE LONG-NOSED POTOROO
4.1. INTRODUCTION
At any scale of resolution, natural landscapes can be viewed as mosaics of ‘patches’
(Wiens 1995). When the patch is large relative to the movements of an individual and the individual can fulfil all its resource requirements within it, the environment is termed coarse-grained (Levins 1968, Morris 1984, Kozakiewicz 1995, Law and
Dickman 1998). This contrasts with a fine-grained environment where patch size is small relative to the movements of an individual and a mosaic of patches is used in order to fulfil their resource requirements. The examination of a species use of a coarse-grained patch can be termed macrohabitat use. The use of a certain macrohabitat may be the result of the selection for some microhabitats it contains and vice versa
(Morris 1984).
Morris (1987) suggests that the ecological attributes of an organism such as geographical range, home range and daily movements should be used to determine the appropriate scales at which to examine habitat selection. The geographic range of that species may be associated with certain vegetation communities with other communities within the range being less favoured. At a finer scale, the home range of individuals may be associated with certain components of some vegetation communities.
The long-nosed potoroo (Potorous tridactylus) has undergone both distributional and population-level declines since European human settlement (Claridge et al. 2007) and is listed as a threatened species within New South Wales. In order to conserve the species, the important habitat elements for the species at both the coarse and fine scale need to be identified and managed appropriately. However, caution must be used when identifying the important habitat elements by comparing usage and availability data,
86 particularly for threatened species (Partridge 1978, Johnson 1980). For species with reduced population densities, certain habitats may either be unoccupied because they are truly unacceptable or because the population density of the species is too low to enable all preferred habitats to be filled (Partridge 1978). This may lead to the conservation and management of only part of a threatened species habitat.
The ecology of the long-nosed potoroo in the Southern Highlands of New South Wales is poorly understood. Other studies have found that the long-nosed potoroo occurs in a large variety of vegetation communities, though particularly: coastal sandy wet heathlands and inland moist woodland and forests along plateaus and associated slopes and gullies (Claridge et al. 2007). Coastal sites where the species occurs are typically on sandy, shallow, nutrient-poor soils with a dominant stratum of small trees or large shrubs. Inland sites are mostly found on poorly drained areas in a variety of forest, woodland, wet heath and rainforest vegetation communities (Schlager 1981, Bennett
1987, Seebeck et al. 1989). However, little information is available on the species’ macrohabitat preferences at the scale examined in this Chapter, other than the presence of a dense vegetative cover appears to be a common feature across all of the vegetation communities in which the species occurs (Schlager 1981, Seebeck 1981, van Dyck and
Strahan 2008). This cover is provided by either the ground layer (eg. sedges, ferns, heaths) or shrub layer (Leptospermum, Melaleuca sp) (Seebeck 1981, Bennett 1987).
The aim of this chapter was to examine which dominant vegetation communities were used by potoroos and identify the habitat choices at the scale of individuals’ home ranges in the Southern Highlands. In this chapter, while the species’ association with the dominant vegetation communities was examined, habitat choices at the scale of individuals’ home ranges within the species range were defined as the species’ macrohabitat preferences. Based on previous research of this species, largely in Victoria
87 and Tasmania, it was expected that macrohabitat preferences would include habitat with greater shrub and/or ground cover, with greater habitat complexity scores and in sheltered mid-slope or gully locations (Seebeck et al. 1989, Claridge et al. 1993a,
Catling et al. 2001).
4.2. METHODS
4.2.1. Potoroo live trapping
Long-nosed potoroos were live-trapped at Barren Grounds NR and Budderoo NP in cage traps as per methods outlined in Chapter 3.
The potoroo trapping data was used to examine macrohabitat use at both study areas.
Each trap site was retrospectively identified as either a ‘potoroo’ trap site or a ‘nil’ trap site based on whether a long-nosed potoroo was ever captured at it during any of the trapping sessions. To examine macrohabitat use in more detail, ‘potoroo’ trap sites were arbitrarily split into ‘poor’ sites (where a potoroo was captured between zero and
25 % of the trapping sessions) and ‘good’ sites (where a potoroo was captured in more than 25 % of the trapping sessions).
4.2.2 Trap site macrohabitat attributes
A total of five dominant vegetation communities were present within the Barren
Grounds NR and Budderoo NP study areas: Budderoo-Morton Plateau Forest, Blue
Mountains-Shoalhaven Hanging Swamps, Coastal Sandstone Plateau Heath,
Escarpment Foothills Wet Forest and Shoalhaven Sandstone Forest (Tindall et al. 2005,
Table 2.1). For each of the 103 trap sites, the dominant vegetation community in which the trap site was situated was recorded (Figures 4.1 and 4.2) to compare with the trap sites’ rating as ‘nil’, ‘poor’ or ‘good’.
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A detailed study of the habitat attributes at each trap site within the two study areas was also undertaken between March and May 2007. At each trap site some general site details were recorded as well as some attributes of the vegetation formation and floristics within a 20 x 20 m quadrat (Plate 4.1). These macro-scale attributes are detailed in Table 4.1. The percent ground cover was defined as the percent of the ground cover layer sufficiently dense to obscure a potoroo. Vegetation structure was also measured using a similar technique to that of Bennett (1993). Within the 20 x 20 m quadrat five 2 x 2 m sub-plots were examined. The sub-plots were positioned at the centre of the quadrat and 5 m to the north, south, east and west. Within each sub-plot
10 sample points were located systematically. At each sample point a vertical 16 mm diameter pole was used to record the presence or absence of vegetation touching at 13 height classes. At each trap site, for each height class, the sum of all 50 sample points was calculated and then represented as a touch score (Table 4.1).
Two habitat complexity scores (Catling and Burt 1995b, Catling et al. 2001) were also calculated for each trap site based on the relative abundance scores of a number of the macrohabitat attributes (Table 4.2). The first habitat complexity score was most similar to that used by Catling and Burt (1995b) and Catling et al. (2001), with the use of four of the five habitat attributes used by these authors. A moisture rating was not assessed at each trap site in my research and so was not included in the calculation of this score.
The Macrohabitat Complexity Score 1 (MacroHCS1) was therefore based on the formula:
MacroHCS1 = tree crown cover score + shrub cover score + open ground score +
(leaf litter score + rock score + coarse woody debris score) / 3.
A second habitat complexity score was also assessed to take habitat patchiness into consideration, a characteristic suggested as being of importance in potoroo habitat 89
(Bennett 1993, Claridge and Barry 2000). This score did not take leaf litter/rock/coarse woody debris into consideration as the levels of these attributes were found to be fairly standard across each of my trap sites. Therefore Macrohabitat Complexity Score 2
(MacroHCS2) was based on the:
MacroHCS2 = tree crown cover score + shrub cover score + open ground (in relation to patchiness) score.
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Figure 4.1: Trap locations and mapped dominant vegetation community within Barren Grounds NR
91
Figure 4.2: Trap locations and mapped dominant vegetation community within Budderoo NP
92
a. b.
c. d.
Plate 4.1 a – d: Measuring macrohabitat attributes within the study areas (Photo d: J. Dingle)
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Table 4.1: Macrohabitat attributes and their relative abundance or floral categories, recorded within a 20 x 20 m quadrat around each cage trap Attribute Categories ANOSIM groupings Canopy height < 10 m, 10–30 m OR > 30 m % leaf litter cover 0 %, > 0-5 %, > 5-25 %, > 25-50 %, > 50-75 % OR > 75 %
% rock cover General site % coarse woody debris (> 20 cm diameter) cover information Ground cover patchiness Heterogeneous OR Homogeneous Position in the landscape Gully, Slope OR Flat % tree crown cover 0 %, > 0-20 %, > 20-50 %, > 50-80 % OR > 80 % Site information % shrub cover (> 2 m) % open ground (≤ 2 m) 0-20 %, > 20-50 %, > 50-80 % OR > 80 % Vegetation formation Dominant ground cover vegetation type/s (> 2 m) Fern, Sedge, Tall sedge, Grass, Rush, Shrub, Heath & Mixed Vegetation types Dominant genera (tree canopy layer) Dominant genera (tree) Dominant genera (> 2 m shrub layer) Dominant genera (>2m shrub) Dominant genera (1-2 m vegetation layer) maximum of three genera Dominant genera (1-2m) Dominant genera (0.2-1 m vegetation layer) Dominant genera (0.2-1m) Vegetation floristics Dominant genera (< 0.2 m vegetation layer) Dominant genera (0-0.2m) Estimated # species (tree canopy layer) Estimated # species (> 2 m shrub layer) 1-3 species, 4-6 species, 7-10 species, 11-20 species Number of species Estimated # species (1-2 m vegetation layer) OR > 20 species Estimated # species (0.2-1 m vegetation layer) Estimated # species (< 0.2 m vegetation layer) Touch score (0-0.1 m) Touch score (0.11-0.2 m) Touch score (0.21-0.3 m) Touch score (0.31-0.4 m) Touch score (0.41-0.5 m) Touch score (0.51-0.6 m) 0 % touches, > 0-20 % touches, > 20-40 % touches, > 40–60 Vegetation densities Touch scores Touch score (0.61-0.7 m) % touches, >60–80 % touches OR > 80 % touches Touch score (0.71-0.8 m) Touch score (0.81-0.9 m) Touch score (0.91-1.0 m) Touch score (1.01-1.5 m) Touch score (1.51-2.0 m) Touch score (2.01-3.0 m) 94
Table 4.2: Scores for the relative abundance categories of a number of macrohabitat attributes used to calculate Macrohabitat Complexity Scores 1 and 2
Relative Ground cover Attributes abundance MacroHSC1 MacroHCS2 patchiness categories 0 0 0 % tree crown cover > 0-20 % 1 1 & > 20-50 % 2 2 % shrub > 50-80 % 3 3 cover > 80 % 4 4 heterogeneous 1 > 80 % 1 homogenous 2 homogenous OR > 50-80% 2 3 heterogeneous % open homogenous OR 3 ground > 20-50 % 3 heterogeneous heterogeneous 4 0-20 % 4 homogenous 5 0 % homogenous 5 5 % 0 % 0 leaf litter > 0-5 % 1 cover & > 5-25 % 2 rock cover & > 25-50 % 3 coarse woody debris > 50-75 % 4 cover > 75 % 5
4.2.3. Statistical analysis
A Chi-square contingency test (JMP Version 5.1) was used to compare the success rating of each trap site (‘potoroo’ or ‘nil’) with the dominant vegetation community in which it was located to examine whether trap success was greater in particular vegetation communities.
95
Differences in a number of macrohabitat attributes of potoroo and nil trap sites were compared using analysis of similarity (ANOSIM; PRIMER Version 5). A number of macrohabitat attributes were grouped for analysis (Table 4.1). A Bray-Curtis Similarity
Matrix was developed for each group of macrohabitat attributes except the ‘Site information’ group for which a Normalised Euclidean Distance Matrix was developed, as the group used variables with a range of different units of measurement. Two-way crossed ANOSIMs (a randomised permutation analysis) were run on each matrix using study areas (Barren Grounds NR and Budderoo NP) and trap success ratings (‘potoroo’ or ‘nil’) as the two factors. Where significant global r values were obtained for either factor, a SIMPER analysis was then conducted to identify which attributes were contributing most to the significant results.
For each study area, Chi-square contingency tests (JMP Version 5.1) were then run for each macrohabitat attribute to identify whether the categories for each attribute at ‘nil’ and ‘potoroo’ trap sites were used in similar proportions to those expected. Expected values were based on the null hypothesis that habitat selection occurs randomly and thus the attributes are used in proportion to their availability. Pearson’s p values were used (p
≤ 0.05) except when one fifth or more of the expected categories’ values for any attribute were less than five. Where this occurred a 2-tailed Fisher’s exact test p value was used if provided by JMP and when no such value was provided a p value of ≤ 0.01 was used as significant to account for low sample sizes.
I compared macrohabitat complexity scores for each study area using an analysis of variance (ANOVA; JMP Version 5.1) to identify if the scores were significantly different between ‘potoroo’ and ‘nil’ trap sites. The macrohabitat complexity scores within each of the dominant vegetation communities across both study areas were also compared using ANOVA to assess variation in scores between the different vegetation
96 communities. To examine habitat complexity score variation within the vegetation communities present in both study areas the Macrohabitat complexity score 1
(MacroHCS1) values for trap sites within the Escarpment Foothills Wet Forest and the
Budderoo-Morton Plateau Forest vegetation communities were compared using
ANOVA.
To identify any cover related macrohabitat attributes associated with lower or higher trap success a second set of Chi-square contingency tests (JMP Version 5.1) was run for
‘nil’, ‘poor’ and ‘good’ trap sites across both study areas. Macrohabitat attributes considered to be related to cover were: % canopy cover, % shrub cover, % open ground, ground cover patchiness, dominant ground vegetation type and touch scores. Again expected values were based on the null hypothesis that habitat selection occurs randomly and thus the attributes are used in proportion to their availability. For any attribute where one fifth or more of the expected categories’ values were less than five, a p value of ≤ 0.01 was used as significant to account for low sample sizes.
4.3. RESULTS
Of the total number of trap sites across both study areas, 53 % never yielded potoroo captures in any trapping sessions (‘nil’ sites), while 17 % yielded potoroo captures in less than 25 % of trapping sessions (‘poor’ sites) and 30 % yielded potoroo captures more frequently (‘good’ sites). Both study areas had similar proportions of ‘nil’, ‘poor’ and ‘good’ trap sites. Despite ‘good’ traps being those with potoroo captures in more than 25 % of trapping sessions, the ‘good’ trap sites at Barren Grounds NR actually averaged potoroo captures in 75 % of sessions compared with only 36 % at Budderoo
NP.
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Potoroos were captured in three of the five dominant vegetation communities present at the two study sites. Of these 88 % were in Budderoo-Morton plateau forest community at Barren Grounds NR whilst only 60 % were in this community type in Budderoo NP.
Figure 4.3 also suggests that ‘nil’ trap sites were less likely, and ‘good’ trap sites more likely, to be in the Budderoo-Morton plateau forest community (χ²8 = 20.94, P = 0.007) than expected.
Figure 4.3: Proportions of nil, poor and good trap sites with each dominant vegetation community (≥20% of expected counts were less than 5)
4.3.1. Macrohabitat attributes
Potoroo captures were in all relative abundance categories of canopy cover, shrub cover and ground cover present in the local environment with the exception of 0 % shrub cover. They were also caught in all dominant ground cover vegetation types present with the exception of grasses and heath. The majority of recaptured individual potoroos
(59 %) were caught at multiple trap sites over the study. For each of these individuals the macrohabitat levels of cover and the dominant ground cover vegetation types varied
98 at each of their trap sites, with the exception of 2 individuals at Budderoo NP. These individuals were each only caught at 2 trap sites over the course of the study.
Trap sites at which potoroos were caught were found to have greater levels of canopy cover (mostly Eucalyptus sieberi) and > 2 m shrub cover (mostly Banksia and Hakea spp.) and than ‘nil’ trap sites (Table 4.3). They were also found to have greater vegetation density in the 2-3 m layer and were more likely to have ferns (mostly
Gleichenia spp.) as a dominant ground cover type, than ‘nil’ trap sites. Alternatively, the ‘nil’ trap sites were more likely to have greater numbers of plant species present, and often sedges, within the 0 - 0.2 m vegetation layer, Banksia spp. as a dominant genus in the 0.2 - 1 m layer and Leptospermum spp. as a dominant genus in the > 2 m shrub layer. However, the relatively low Global r values and Dissim/SD ratios for most of the data suggest reasonable variation within ‘potoroo’ and ‘nil’ sites and low explanatory power of these variables.
ANOSIM also revealed significant differences between the two study areas for all macrohabitat attribute groups with the exception of the ‘dominant ground vegetation types’ group (Table 4.3). The trap sites at Budderoo NP had a greater level of canopy cover on average than Barren Grounds NR, a greater number of tree species, and a greater likelihood of having Gleichenia dicarpa as a dominant species between 0 and 1 m, Banksia spp. as a dominant genus in the 1-2 m layer, Hakea spp. as a dominant genus in the > 2.0 m layer, and Eucalyptus piperita as a dominant tree species. Trap sites at Barren Grounds NR had a greater likelihood of having sedges in the 0-0.2 m layer, Banksia spp. as a dominant genus in the 0.2-1 m layer and greater vegetation density in the 0.4-0.5 m and 2-3 m layers.
The observed and expected relative abundances of each macrohabitat attribute at
‘potoroo’ and ‘nil’ sites revealed varied potoroo preferences at the two study areas 99
(Table 4.4). ‘Potoroo’ trap sites were more likely to have particular levels of canopy cover, greater shrub cover and more open ground than expected at Barren Grounds NR while no such preferences were observed at Budderoo NP. Barren Grounds NR
‘potoroo’ trap sites were also more likely to have rushes and less likely to have heath as dominant ground vegetation types than expected. No preferences were observed at
Budderoo NP, although no heath was present at this study area. The majority of dominant genera below 1m were used in proportion to their availability at both study areas, however at Barren Grounds NR, lomandra was found to be preferred while at
Budderoo NP, bracken was preferred and sedges were used in lower proportions than their availability. Banksias (greater than 1 m) were preferred at Barren Grounds NR but selected against at Budderoo NP in the 1-2 m layer. Melaleucas (greater than 2 m) were also preferred at Barren Grounds while at Budderoo NP all shrub species greater than
2m were used in proportion to their availability. Finally, while areas with greater touch scores between 2-3 m were preferred at Barren Grounds NR, at Budderoo NP greater touch scores between 0.7-0.8 m were preferred.
100
Table 4.3: ANOSIM results for study areas and trap success ratings for each vegetation attribute group analysed.
SIMPER dissimilarity Global p Average most contributing % greatest amount of Habitat attribute groups Factor r value dissimilarity variable contribution Dissim/SD the variable at tree canopy cover 29.96 1.14 potoroo sites General site information (% canopy Trap success rating cover, % shrub cover, % ground 0.094 0.001 26.29 > 2 m shrub cover 28.06 1.08 potoroo sites cover, position in the landscape) Study areas 0.115 0.001 26.09 tree canopy cover 34.19 1.23 Budderoo NP ferns 21.85 0.86 potoroo sites Dominant ground vegetation types Trap success rating (heath, sedge, tall sedge, grass, 0.062 0.012 62.6 sedges 19.35 0.86 nil sites fern, rush, shrub and mix) Study areas 0.047 0.06 sedges 18.11 0.98 nil sites Trap success rating 0.04 0.038 71.86 Gleichenia sp. 17.43 0.92 potoroo sites Dominant genus in the 0-0.2m layer sedges 19.19 1.12 Barren Grounds NR Study areas 0.175 0.001 76.00 Gleichenia sp. 17.14 0.91 Budderoo NP Gleichenia sp. 13.91 10.28 potoroo sites Trap success rating 0.051 0.021 73.87 Banksia sp. 13.2 0.91 nil sites Dominant genus in the 0.2-1m layer Gleichenia sp. 13.94 0.92 Budderoo NP Study areas 0.133 0.002 76.01 Banksia sp. 13.21 0.93 Barren Grounds NR Trap success rating 0.032 0.058 Dominant genus in the 1-2m layer Study areas 0.131 0.001 82.04 Banksia sp. 13.27 0.98 Budderoo NP Banksia sp. 16.76 0.89 potoroo sites Dominant shrub genus in the >2m Trap success rating Hakea sp. 16.7 0.92 potoroo sites layer 0.034 0.035 73.66 Leptospermum sp. 16.01 0.89 nil sites Study areas 0.055 0.041 74.23 Hakea sp. 20.38 1.11 Budderoo NP Trap success rating 0.056 0.018 61.93 Eucalyptus seiberi 28.23 0.88 potoroo sites Dominant tree species Study areas 0.295 0.001 69.78 Eucalyptus piperita 32.36 1.41 Budderoo NP Trap success rating 0.08 0.001 25.18 0-0.2 m layer 26.43 1.24 nil sites # species present in each layer Study areas 0.228 0.001 26.37 Tree canopy 28.71 1.59 Budderoo NP Trap success rating 0.055 0.015 27.45 2-3 m layer 10.21 1.24 Potoroo sites 40-50 cm layer 9.76 1.28 Barren Grounds NR Study areas Touch scores 0.134 0.001 28.09 2-3 m layer 9.73 1.23 Barren Grounds NR 101
Table 4.4: Chi-square results for Barren Grounds NR and Budderoo NP comparing observed and expected relative abundances of a number of macrohabitat attributes at ‘potoroo’ and ‘nil’ trap sites. Study Macrohabitat specific 2 df p value ‘nil’ trap sites ‘potoroo’ trap sites area attribute attribute χ
more likely to have no canopy cover more likely to have >0-25 % or >50-80 % canopy % canopy cover 9.48 3 0.0235 cover % shrub cover 15.737 4 0.0034* more likely to have <50 % shrub cover more likely to have >50 % shrub cover % open ground 12.203 3 0.0067* more likely to have ≤20 % open ground more likely to have >20 % open ground
Dominant ground rushes 10.705 1 0.0015** rushes vegetation type is less common rushes vegetation type is more common vegetation type heath 11.859 1 0.0006** heath vegetation type is more common heath vegetation type is less common Barren Grounds Dominant genera in Lomandra is less common in 0.2-1 m Lomandra 8.490 1 0.0054** Lomandra is more common in 0.2-1 m layer NR 0.2-1 m layer layer Dominant genera in Banksia 5.403 1 0.0244** Banksia is less common in 1-2 m layer Banksia is more common in 1-2 m layer 1-2 m layer
Dominant genera in Banksia 9.258 1 0.0036** Banksia is less common in >2 m layer Banksia is more common in >2 m layer >2 m shrub layer Melaleuca 5.308 1 0.0323** Melaleuca is less common in >2 m layer Melaleuca is more common in >2 m layer 2.01-3.0 m more likely to have 0 % of sample points more likely to have >20-40 % or >60 % of Touch score 15.413 4 0.0039* layer with touches sample points with touches Dominant genera in Sedge 10.000 1 0.0033** Sedge is more common in 0-0.2m layer Sedge is less common in 0-0.2m layer 0-0.2 m layer
Dominant genera in Sedge 5.714 1 0.0471** Sedge is more common in 0.2-1m layer Sedge is less common in 0.2-1m layer Budderoo 0.2-1 m layer Bracken 7.059 1 0.0202** Bracken is less common in 0.2-1m layer Bracken is more common in 0.2-1m layer NP Dominant genera in Banksia 5.227 1 0.0484** Banksia is more common in 1-2m layer Banksia is less common in 1-2m layer 1-2 m layer 0.71-0.8 m more likely to have >0-20 % of sample more likely to have >20-60 % of sample points Touch score 12.364 3 0.0062* layer points with touches with touches
*≥20% of expected counts were less than 5 and a p ≤ 0.01 was considered significant **p value from 2 tail Fisher’s exact test 102
4.3.2. Macrohabitat complexity scores
At Barren Grounds NR the two macrohabitat complexity scores were both significantly higher at ‘potoroo’ trap sites than ‘nil’ trap sites while at Budderoo NP there was no significant difference between the ‘potoroo’ and ‘nil’ trap site scores (Table 4.5). The average scores were also lower at Barren Grounds NR than at Budderoo NP. A comparison of Macrohabitat complexity score 1 between the dominant vegetation communities across both study areas also revealed a significant difference in habitat complexity among vegetation community (Table 4.6). A similarly significant result was achieved for Macrohabitat complexity score 2. A significantly higher habitat complexity was observed for Budderoo NP, compared to Barren Grounds NR, for the
Budderoo-Morton Plateau Forest vegetation community using the Macrohabitat complexity score 1 values (F Ratio = 8.266, p = 0.006).
Table 4.5: Barren Grounds NR and Budderoo NP results of Analysis of Variance between ‘potoroo’ and ‘nil’ trap site Macrohabitat complexity scores
Study p Trap site Average score ± Score type F Ratio Area Value type standard deviation ‘potoroo’ 7.7 ± 1.3 Barren MacroHCS1 5.439 0.0230 Grounds ‘nil’ 6.6 ± 2.2 NR ‘potoroo’ 7.6 ± 1.1 (n=61) MacroHCS2 11.589 0.0012 ‘nil’ 6.5 ± 1.6 ‘potoroo’ 9.0 ± 0.9 Budderoo MacroHCS1 0.326 0.572 ‘nil’ 9.1 ± 0.9 NP ‘potoroo’ 8.4 ± 0.8 (n=38) MacroHCS2 0.001 0.978 ‘nil’ 8.4 ± 0.9
103
Table 4.6: Analysis of Variance results comparing the Macrohabitat complexity score 1 (MacroHCS1) of each trap site within each dominant vegetation community across both study areas
Average score F Ratio P value Dominant vegetation community ± standard deviation Budderoo-Morton Plateau Forest 8.1 ± 1.7 Blue Mountains-Shoalhaven Hanging Swamps 5 12.179 <0.0001 Coastal Sandstone Plateau Heath 6.4 ± 1.7 Escarpment Foothills Wet Forest 8.7 ± 1.1 Shoalhaven Sandstone Forest 9.7 ± 0.7
4.3.3. Trap success ratings in relation to cover
The results in Figure 4.4 a – e suggest that the canopy cover was more likely than expected to have between 20 - 50 % canopy cover at ‘poor’ trap sites and 50 - 80 % canopy cover at ‘good’ trap sites, compared to 0 % at ‘nil’ trap sites (χ²6 = 18.37, P =
0.005). There was no heath at any ‘good’ or ‘poor’ trap sites. The dominant ground vegetation types were more likely than expected to be ferns (χ²2 = 7.07, P = 0.03) and/or rushes (χ²2 = 12.17, P = 0.002) at ‘good’ trap sites while the dominant ground vegetation types at ‘poor’ trap sites and ‘nil’ were in similar proportions to what was randomly available. Between 2-3 m ‘poor’ trap sites were more likely to have 20 - 40 % touch scores and ‘good’ trap sites above 40 % touch scores, while ‘nil’ trap sites were more likely to have less than 20 % touch scores than expected (χ²8 = 20.85, P = 0.008). No other significant differences were observed between ‘nil’, ‘poor’ and ‘good’ trap sites for macrohabitat attributes relating to cover.
104 a) b)
X²=18.369, df=6, P=0.0054* X²=7.067, df=2, P=0.0292 c) d)
X²=12.165, df=2, P=0.0023 X²=11.854, df=2, P=0.0027 e)
X²=20.847, df=8, P=0.0076* Figures 4.4 a-e: Proportions of nil, poor and good trap sites with: a) each tree canopy cover percentage group, b) ferns as a dominant ground cover type, c) rushes as a dominant ground cover type, d) heath as a dominant ground cover type, e) 2-3 m touch scores, compared to expected. *≥20 % of expected counts were less than 5 and a p ≤ 0.01 was considered significant. 105
4.4. DISCUSSION
Across the eastern seaboard of Australia and Tasmania, long-nosed potoroos (Potorous tridactylus) occupy a variety of habitats including rainforest, dry and wet sclerophyll open-forests, woodland, shrublands and heath vegetation communities and their ecotones (Claridge et al. 2007). Similarly, in the current study potoroos were recorded in three of the five major vegetation communities present at the Barren Grounds NR and
Budderoo NP study areas: plateau forest, wet forest and plateau heath. A comparison across the vegetation communities present at these sites, of the proportion of trap sites with high potoroo capture rates out of the total number of trap sites present in each vegetation community, revealed a preference for Budderoo-Morton plateau forest vegetation community (Tindall et al. 2005). Successful capture sites were also present in Coastal sandstone plateau heath and Escarpment foothills wet forest vegetation communities; however, no preferential utilisation of these vegetation communities was detected.
At a macrohabitat level, long-nosed potoroos were caught in sites with a broad range of ground cover vegetation densities, types and levels of floristic diversity, as well as canopy and shrub cover levels. However, some of these categories were used in greater proportions than others and in greater proportions than their availability, suggesting preferential utilisation. Despite there being some degree of variability and overlap in the attributes of trap sites with and without captures, potoroos were found to exhibit an overall preference for greater levels of canopy and shrub cover, for ferns as a dominant ground cover type and for lower levels of floristic diversity in ground cover. A comparison of macrohabitat attributes at trap sites with and without potoroos revealed potoroo preferences varied between the two study areas. While at Barren Grounds NR potoroos were found to preferentially utilising a number of both structural and floristic
106 macrohabitat attributes, at Budderoo NP most macrohabitat attributes were used in proportion to their availability with the exception of a few floristic attributes, which varied from those preferred at Barren Grounds NR. Collectively, these results imply that while the species uses a range of macrohabitats within its local environment, it does display macrohabitat preferences although these preferences vary between locations.
To assess whether there were differences in the structurally related macrohabitat attributes at trap sites with low or high trap success regardless of location, data from both study areas were pooled. While a number of significant macrohabitat preferences were observed across all trap sites with regular potoroo captures, there were few significant differences between available habitat and either the sites with few or no potoroos. Trap sites with regular potoroo captures were found to have greater canopy cover and greater structural density in the 2-3 m layer than trap sites with low trap success. Regular potoroo captures were also associated with ferns as a dominant ground vegetation type. As was observed by Seebeck (1981) in coastal Victoria, the species was absent from treeless heath and was more likely to be absent in other areas with no canopy cover.
A common feature across all vegetation communities in which long-nosed potoroos occur is the presence of dense vegetative cover (Seebeck et al. 1989). This cover is provided by either the ground layer or shrub layer (Seebeck 1981, Bennett 1987). The three vegetation communities in which the species was caught during the current study are all described as having dense shrub and/or ground cover strata (Tindall et al. 2005).
Overall the potoroo captures were significantly associated with greater shrub cover but not ground cover. Despite extensive ground cover being present at each of the two study areas its distribution was patchy in nature. In fact, at Barren Grounds NR they were found to be associated with some levels of open ground.
107
Total cover may also be more important to a potoroo than cover at any one particular layer. Therefore habitat complexity scores calculated for each trap site, similar to that used by Catling and Burt (1995b) and Catling et al. (2001), provided a means of assessing cover across the three major layers combined (ground, shrub and canopy) rather than assessing each cover layer separately. In addition to examining the density of vegetative cover across the ground, shrub and canopy layers, the first habitat complexity score calculated (MacroHCS1) also incorporated cover of leaf litter, rocks and fallen logs. The second (MacroHCS2) incorporated the patchiness of the vegetative ground cover layer instead. Both scores provided similar results for either study area.
At Barren Grounds NR trap sites with potoroo captures were significantly more complex at the macrohabitat scale than those trap sites at which no potoroos were captured over the course of the study. However, at Budderoo NP there appears to be no difference in macrohabitat complexity between trap sites with and without potoroo captures. Habitat complexity scores at Budderoo NP were greater than at any site in
Barren Grounds NR suggesting that there may be a lower limit to habitat complexity needed by potoroos.
While Barren Grounds NR and Budderoo NP had similar proportions of ‘nil’, ‘poor’ and ‘good’ trap sites, potoroo occurrence was much greater at Barren Grounds NR. The
‘good’ trap sites at Barren Grounds NR yielded a much higher proportion of trapping sessions with potoroo captures than Budderoo NP. However, despite its higher trap success, Barren Grounds NR had lower ‘macrohabitat complexity’ than Budderoo NP.
The different complexity scores between the two study areas may be attributable to varying ‘habitat complexities’ both within and between the dominant vegetation communities present at each study area. Certainly a significantly greater canopy cover was observed at Budderoo NP than Barren Grounds NR which would increase habitat
108 complexity scores. Further, the avoidance of low heath present only in the Barren
Grounds NR study area, with its lack of tall shrub and tree cover, would have had some influence on the lower average complexity at Barren Grounds NR and the observed preference for higher complexity levels.
The higher trap success in the study area with the lower ‘habitat complexity’ conflicts with the findings of Catling et al. (2001) where the expected abundance of potoroos was reported to increase as ‘habitat complexity’ increased. Further, within Barren Grounds, potoroos were caught at trap sites with significantly higher ‘habitat complexity’. While
Catling et al. (2001) also showed a decrease in abundance with lower habitat complexity scores, it may be that there is an upper limit to ‘habitat complexity’ at which point the suitability of habitat for potoroos also decreases. The dominant vegetation community with the highest average score, Shoalhaven sandstone forest, had nil potoroo trap success. Alternatively, the most preferred dominant vegetation community,
Budderoo-Morton plateau forest, only had a mid-range average macrohabitat complexity score. It may be that the habitat at Budderoo NP was too ‘complex’ for the species to thrive.
The use of the term ‘habitat complexity’ can be considered misleading when considering favourable potoroo habitat in terms of a habitat complexity score. The more dense the layers of cover the more complex the habitat is considered. However, both Bennett (1993) and Claridge and Barry (2000) suggest that habitat patchiness may actually be more important for the species. In the present study potoroos were captured in all canopy cover, shrub cover and ground cover macrohabitat categories except 0 % shrub cover. This variation between trap sites with potoroos was suggested by the relatively low Global r values and Dissim/SD ratios. Further, numerous individuals were each captured at a number of trap sites with varying levels of cover. These results
109 suggest that, to some extent, the potoroos may have been utilising habitat patchiness at the scale at which I assessed macrohabitat. However, the potential importance of habitat patchiness is not taken into account in the habitat complexity assessment used by
Catling and Burt (1995b) and Catling et al. (2001) and was only a very minor part of my Macrohabitat complexity score 2. Consideration of habitat patchiness as an essential part of potoroo habitat would make the term habitat complexity imply more about varying levels of cover than maximised cover.
While half the traps at both study areas were in the moderately ‘complex’ plateau forest vegetation community, a much higher proportion of all potoroo captures at Barren
Grounds NR were in this vegetation community compared to Budderoo NP. It is unclear whether this difference was solely due to the significantly lower ‘habitat complexity’ observed at Barren Grounds NR. Certainly the rainfall and soil moisture is higher and the soil shallower at Barren Grounds NR (NPWS 1998), perhaps resulting in a number of differences within the plateau forest communities.
As a threatened and declining species, long-nosed potoroos may be absent from certain macrohabitats because these habitats are truly unacceptable or because their population density is too low to allow all of their preferred habitats to be filled (Partridge 1978). In an examination of habitat use, this may lead to some macrohabitat preferences not being identified or being underrepresented. In this study, long-nosed potoroos were found to be absent from some trap sites with macrohabitats matching those at trap sites with potoroos. This may suggest that habitat availability is not the limiting factor for this species; rather that other factors determine the habitation or otherwise of locations.
However, the patterns of potoroo habitat use and preferences at the macrohabitat level may also be directly influenced by the microhabitat features available to them within each macrohabitat.
110
5.0 MICROHABITAT USE BY THE LONG-NOSED POTOROO
5.1. INTRODUCTION
While Chapter 4 examined the coarse-scale habitat preferences of the threatened long- nosed potoroo, an understanding of its fine-scale habitat preferences is also required to assist with the conservation and management of the species. At a finer scale, the species may use some components within a macrohabitat preferentially over others.
Preferences for some of these microhabitats may be the sole reason for the use of the macrohabitat they are within (Morris 1984). The aim of this Chapter was to examine the microhabitat preferences of the long-nosed potoroo at a series of sites in the
Southern Highlands of New South Wales. In this study, microhabitat preferences were defined as habitat choices at the scale of individuals’ movements within their home ranges and were assessed principally using spool-and-line tracking and an examination of forage-diggings.
Long-nosed potoroos are primarily mycophagous (fungus-feeding) and the majority of fungal materials consumed are hypogeous or underground-fruiting in origin (Bennett and Baxter 1989; Claridge et al. 1993b; Tory et al. 1997). Fungal material makes up between approximately 30 and 90% of their diet depending on the season (Guiler 1971;
Bennett and Baxter 1989; Claridge et al. 1993a and 1993b; Tory et al. 1997). Evidence of their cylindrical foraging diggings to access fungal material can be used to give an indication of habitat use during foraging (Taylor 1992). However, a habitat type
(particularly at the microhabitat scale) should not be labelled as unused by the species based on a lack of diggings. The species may still use this habitat type for reasons other than foraging. Further, depending on the full diet of the species examined, it may be
111 using this habitat type to forage for other food types that do not require digging-up or at different times of year.
A handful of other studies have examined the microhabitat use of the species, however, the scale at which these studies were conducted and the techniques used have varied significantly, make direct comparisons of findings difficult. This may have been partially responsible for the ongoing debate as to whether the species’ microhabitat preferences are more related to the floristics of a site or its structural components
(Schlager 1981, Bennett 1993, Claridge and Barry 2000).
5.2. METHODS
5.2.1. Potoroo live trapping for spool-and-line tracking
Long-nosed potoroos were live-trapped at Barren Grounds NR and Budderoo NP in cage traps set approximately 100 m apart, adjacent to walking tracks and fire trails. At each trap site a single cage trap and two Elliott aluminium box traps were set in close proximity, baited with a small amount of peanut butter, rolled oats and honey. The
Elliott traps were used to reduce the probability of small mammals (primarily
Antechinus stuartii and Rattus fuscipes) being cage-trapped at the expense of long- nosed potoroos.
Some of the potoroos used for spooling came from the regular spring 2007 and autumn
2008 trapping sessions conducted for the examination of macrohabitat use for the species (see previous chapter). However, additional targeted trapping sessions were conducted where extra potoroo spooling was necessary. Due to the high trap success observed in some sections of the regular trapping area at Barren Grounds NR, all spooling work was limited to two patches within this reserve. At Budderoo NP, lower
112 trap success across the reserve resulted in a much larger proportion of the regular trapping area being targeted for spooling.
Traps were checked approximately 2 hours after dusk and the identity of each potoroo captured was recorded. All other species were released without further processing.
Where spooling was being conducted as part of regular trapping sessions, sites without potoroo captures were left open after the evening check and then checked as part of regular trapping the following morning. Alternatively, where spooling was not conducted as part of targeted trapping sessions, the traps were generally closed down after the evening check and reset mid-afternoon the following day. In some instances where trapping success was low, traps were left open after the evening check and checked again at dawn the following day. Males and females with no pouch young were then held during the day for spooling that evening. These animals had their spools attached at sunset and were left on site in their capture bags to leave when they chose.
Adult females with large pouch young were not used in the spool-and-line work to avoid undue stress on these individuals. Further, each individual was only spooled once during each field session.
5.2.2. Spool-and-line tracking
A three-day trial spooling session was undertaken in July 2007 at Barren Grounds NR to assess the feasibility of using this method in potoroo habitat, the appropriate length of spool to use, the best attachment methods and some of the relevant habitat attributes to be used in the present study. For this pilot six potoroos were spooled. Each spool package (3.5 g) consisted of a 12 mm x 32 mm cocoon bobbin (Danfield Limited,
Lancashire, England) containing approximately 140 m of 2-ply nylon thread, in a black heat shrink plastic casing. The package was attached to a section of fur clipped close to
113 the skin on the animal’s rump, approximately 2 cm above its tail base, using cyanoactrylate (‘Super Glue’) (Plate 5.1). The spool package was positioned so that the thread fed out from the base, to minimise the chance of the animal getting caught up in its thread as it left it’s thread path behind (Plate 5.2). The free end of the thread was tied off to the trap and the animal left at the point of capture, in a capture bag, with the bag rolled down to expose the animals back. This allowed the animal to leave the bag when ready, in an attempt to reduce the flight response of the animal and maximise the amount of spool path fed out during ‘normal’ activity. All traps at the trap site were closed to avoid re-trapping the spooled individual after it left its capture bag.
Based on the results of the spooling trial a number of decisions were made on how to approach the broader spooling program. It was decided to continue using 140m spools due to the time taken to follow each spool, particularly in dense vegetation. For future spooling each bobbin was dyed in a 50:50 mixture of pink herbicide marker and water to increase visibility of the thread. Also, the fur on each potoroo’s rump was clipped much closer to the skin to reduce the chance of packages being dropped/groomed off prematurely. It was also decided that the distance along each spool path to the first fresh diggings and/or a series of large direction changes would be noted as an indication of flight distances (Vernes and Haydon 2001). All other aspects of the spooling technique used in the trial remained unchanged.
Spooling proper was conducted at both study areas in September/October 2007 and
March/April 2008. All spooling was conducted after sunset, when potoroos were thought to be most active, and spool paths were assessed the following day. To limit confusion between the spool paths of different individuals, spooling at any two neighbouring traps within one night was avoided
114 Once an individual’s spool path had fed out it was left with the heat shrink casing attached to its rump, which was expected to be groomed off some time thereafter.
Where these individuals were captured the following night, the only evidence of their spooling experience was a small bald patch where the glue had stuck the package to their shortly cropped fur.
Plate 5.1: Attachment point of spool package to potoroo rump (Photo: A. Prentice)
115 a. b.
c. d.
Plate 5.2 a - d: Thread paths
5.2.3. Microhabitat attributes along spool paths
The occurrence and relative abundance of a number of microhabitat attributes (Table
5.1) were examined at 5 m intervals paced out along the course of each spool path. The majority of these habitat attributes were also examined at the macrohabitat scale
(chapter 4). Average scores for each microhabitat attribute were then calculated for the entire spool length by aggregating the values at each point and dividing by the number of sample points at which measurements were taken.
As the 5 m intervals between sample points along each spool path were only paced out, the total number of sample points per completed spool varied between 27 and 35. It is also possible that there was some variation in the manufactured thread length of each bobbin. An individual spool event took 1.5 to 3 hours to read depending on the
116 thickness and structure of the ground vegetation. As it was followed, the thread of each thread path was wound up and upon completion it was removed from site.
In some instances, the spool path was not able to be read to the end. This was due either to the spool package being removed by the study animal prematurely, the thread snapping with no sign of the rest of the thread or the spool path being lost due to the density/structure of ground vegetation or presence of impenetrable vegetation. Unless a minimum of 25 sample points were able to be recorded, these spools were not considered ‘full’ spools and were not used in subsequent analysis. A minimum target was set of five ‘full spools’ from five individual potoroos per study area per season.
A habitat complexity score was also calculated for each spool sample point based on the relative abundance of a number of the microhabitat attributes examined at each sample point (Table 5.2). The calculation of the habitat complexity score used was largely the same as that for one of the two scores examined at the macrohabitat level
(MacroHCS2). Therefore the score (MicroHCS) was based on the following formula:
MicroHCS = tree crown cover score + shrub cover score + ground cover (in
relation to patchiness) score.
For each spool a MicroHCS was calculated for each sample point and then a number of sample points were randomly selected for statistical analysis (26 for Barren Grounds
NR spools and 27 for Budderoo NP spools).
117 Table 5.1: Microhabitat attributes and their relative abundance categories recorded Attribute Relative abundance categories Details % tree crown cover1 0 %, > 0-20 %, > 20-50 %, > 50-80 % & > 80 % % shrub cover (> 2 m)1 0 %, > 0-20 %, > 20-50 %, > 50-80 % & > 80 % Within a 5m radius Woody plant genus present2 Eucalyptus, Acacia, Melaleuca, Callistemon, Leptospermum, Baeckea, Hakea, and Banksia of sample point Dominant shrub genus2 Ground cover1 Open (0-25 %), Mid (> 25-75 %) & Closed (> 75 %) Average ground cover height1 <0.5 m, 0.5-1 m, > 1-2 m Within a 2m radius Ground cover patchiness1 heterogeneous or homogenous of sample point Dominant ground vegetation type (> 2 m)1 Fern, Sedge, Tall sedge, Grass, Rush, Shrub, Heath, Mixed & Suspended plant debris Dominant ground cover genus (< 2 m)2 Within a 1m radius Fresh or old forage-diggings1 Presence/absence of sample point Position in the landscape2 Gully, Slope & Flat 1 Examined at both spool sample points and microhabitat availability sample points 2 Examined at microhabitat availability sample points only, to identify foraging microhabitat preferences
Table 5.2: Scores for the relative abundance categories of a number of microhabitat attributes used to calculate Microhabitat Complexity Scores Attribute Relative abundance categories Ground cover patchiness Score 0 0 % tree crown cover > 0-20 % 1 & > 20-50 % 2 % shrub cover > 50-80 % 3 > 80 % 4 homogenous 1 0-25 % (Open) heterogeneous 2 homogenous 3 % ground cover > 25-75 % (Mid) heterogeneous 3 homogenous 4 > 75 % (Closed) heterogeneous 5
118 5.2.4. Microhabitat availability
The relative availability of microhabitat attributes was also recorded across the area in which spooling was conducted to determine whether potoroos selected certain attributes over others. This was done by scoring the same microhabitat attributes (Table 5.1) in a grid at a number of sample points based around trap sites within the spooling area.
Sample points were set along transects paced in off either side of the track, with the first sample point being 5 m in from the edge and each subsequent sample point being 25,
50, 75 and 100 m further along. Figures 5.1 and 5.2 identify the trap sites at which spooling was conducted and the layout of the microhabitat availability sample points at both study areas.
At Barren Grounds NR transects ran in an east/west direction and were approximately
50 m apart. At Budderoo NP transects ran in a north/south direction and were approximately 100 m apart. Due to a lower level of trap success at this site, a much larger area was targeted for spooling to ensure an adequate sample size. It was due to the size of the area sampled that a greater distance was set between transects at
Budderoo NP.
The ‘full spool’ data collected for each individual were compared with the microhabitat availability data collected from transects passing within 100 m of the trap site where the individual was caught. Therefore, in the 200 x 200 m grid around most spooling trap sites, there were 50 microhabitat availability sample points assessed for comparison at
Barren Grounds NR and 30 at Budderoo NP. Microhabitat availability was only scored once during this study as the vegetation would not change significantly during the spooling works. Scores for each category of microhabitat attribute at each set of sample points were similarly summed and then divided by the number of sample points used.
119 The Microhabitat Complexity Score (MicroHCS) was again calculated for each microhabitat availability sample point based on the relative abundance of a number of the microhabitat attributes examined at each sample point (Table 5.2). Out of each set of microhabitat availability sample points (relating to each spool) a number of sample points were randomly selected for statistical analysis (26 for Barren Grounds NR spools and 27 for Budderoo NP spools).
120 Please see print copy for image
Figure 5.1: Background vegetation sample points and trap sites where spooling was conducted at Barren Grounds NR
121 Please see print copy for image
Figure 5.2: Background vegetation sample points and trap sites where spooling was conducted at Budderoo NP
122
5.2.5. Microhabitat foraging preferences
During the assessment of microhabitat availability, some additional microhabitat attributes were examined at each sample point to assist in the identification of microhabitat foraging preferences. The sample points were split into those with and those without forage-diggings (Plate 5.3) present at the time of data collection (Summer
2008). To identify microhabitat preferences specifically during foraging activities, a comparison was made between dig and non-dig sample points for all microhabitat attributes (Table 5.1). While the use of digging activity to identify habitat preferences has been used by a number of studies, potoroos and bandicoots can co-occur and their diggings can be difficult to tell apart (Claridge and Barry 2000). In this study, only three individual long-nosed bandicoots (Perameles nasuta) were ever caught at the two study sites and so, as there were much higher numbers of potoroos captured, it was assumed that all diggings were from potoroos. a. b.
Plate 5.3: Potoroo forage diggings
123 5.2.6. Statistical analysis
For the assessment of microhabitat preferences, data from only one ‘full’ spool was used per individual per season. For each individual, goodness-of-fit tests were used to compare spooling data proportions for each microhabitat attribute (observed values) with the relevant set of microhabitat availability data proportions (expected values). A p value of ≤ 0.01 was used for any habitat attribute where more than one fifth of the expected categories values were less than five to account for low sample sizes.
For each study area, for each spooling season, a comparison was made of the sets of
Microhabitat Complexity Scores of the randomly selected spool sample points and corresponding microhabitat availability sample points (2 factor nested ANOVA; JMP
Version 5.1). Where a significant difference was observed a t-test was used for each individual to compare its sets of randomly selected spool and microhabitat availability sample points.
During spooling, despite some individuals displaying a flight response after leaving the capture bag, data from all sample points were used in the analysis. Habitat use during any flight response was considered to be an acceptable part of their overall habitat use during their nightly activity.
For the assessment of foraging microhabitat preferences, Chi-square contingency tests were used to compare microhabitat attributes at dig and non-dig sites at the two study areas. These were used to identify whether their categories were used in similar proportions to those expected based on chance. Expected values were based on the null hypothesis that habitat selection occurs randomly and thus the attributes are used in proportion to their availability. Pearson’s p values were used (p ≤ 0.05) except when one fifth or more of the expected categories’ values for any attribute were less than five.
Where this occurred a 2-tailed fisher’s exact test p value was used if provided by JMP
124 and when no such value was provided a p value of ≤ 0.01 was used as significant to account for low sample sizes.
To assess microhabitat complexity in relation to forage diggings a comparison of the
MicroHCS at dig and non-dig sites was made for the two study areas (ANOVA).
5.3. RESULTS
Between five and seven full spools were achieved per study area per season (Table 5.3).
A small number of spooling attempts failed due to spool packages being dropped and spool paths being lost in thick vegetation. All trap sites at Barren Grounds NR at which full spools were achieved were classed as ‘good’ trap sites according to the definition used in Chapter 4. ‘Good’ trap sites were those at which a potoroo was captured in more than 25 % of the trapping sessions, while ‘poor’ trap sites were those at which a potoroo was captured between zero and 25 % of the trapping sessions. At Budderoo NP three of the ten trap sites at which full spools were achieved were classed as ‘poor’ sites.
In any one season, the majority of full spools achieved were at different trap sites.
While at Budderoo NP all the individuals from whom full spools were achieved in each season were all different, at Barren Grounds NR the majority of full spools in both seasons were obtained from the same individuals.
In thick ground vegetation, the spool paths generally passed through small runways, not much taller than the height of a potoroo. A few spool paths crossed tracks in either study area although none travelled along the tracks. No spool paths were followed to squats, suggesting that all spooled individuals continued their evening activities after the spool package was exhausted. The use of coarse woody debris along spool paths was fairly low, with logs generally crossed rather than travelled along. However, in two
125 instances at Budderoo NP hollow logs were travelled through, providing cover in otherwise quite open habitat patches.
Table 5.3: Spooling attempts and successes data at Barren Grounds NR and Budderoo NP (including ratio of males to females from which full spools were achieved)
Trap area Barren Grounds NR Budderoo NP Spring Autumn Spring Autumn Season 2007 2008 2007 2008 No. spooling attempts 10 10 7 6 No. full spools achieved 7 (5M:2F) 8 (6M:2F) 5 (5M) 5 (3M:2F) No. spool packages dropped 1 1 1 1 No. spool paths lost in thick vegetation 2 1 1 0 No. full spools with fresh diggings 6 8 5 4 No. trap sites at which full spools achieved 6 6 5 5 No. trap sites with full spools classified as 6 6 3 4 ‘good’ sites No. of trap sites with full spools in Spring 2007 that also yielded full spools in 5 2 Autumn 2008 Percent of individuals with full spools in Spring 2007 that also yielded full spools in 71% 0 % Autumn 2008
The majority of potoroo spooling sample points had between 0 to 50 % canopy cover and shrub cover at the microhabitat level. The ground cover densities and distributions varied while the average ground cover height was generally between 0 and 1 m. Of the most common dominant ground vegetation types, ferns were at 50 % of sample points, suspended plant debris at 45 % and sedges at 27 %.
A comparison of the proportions of microhabitat attributes available with those utilised by potoroos during spooling revealed that the majority of potoroos showed significant preferences for certain categories of cover densities, distributions and heights (Table
5.4). However, the specific categories selected varied widely between individuals across study areas and seasons. While some individuals preferred high densities of cover,
126 others displayed significant preferences for low cover densities. Individuals displaying no significant preferences for any particular microhabitat attribute were always in the minority of animals spooled.
Microhabitat preferences for particular dominant ground cover types again varied widely between individuals, study areas and seasons. Overall, potoroos were found to use fern and heath microhabitats less than or in similar proportions to their availability
(Table 5.5), although heath was never a large component of the available habitat where potoroos occurred. Shrub, rush and mixed microhabitats were generally either used in similar proportions to their availability or preferred. Grasses were used in similar proportions to their availability, while the use of sedges, tall sedges and suspended plant debris varied widely.
127 Table 5.4: Potoroo preferences and avoidances of a number of microhabitat features at Barren Grounds NR and Budderoo NP in Spring 2007 and Autumn 2008.
Barren Grounds NR Budderoo NP Categories Spring 2007 Autumn 2008 Spring 2007 Autumn 2008 Microhabitat within each proportion of individuals proportion of individuals proportion of individuals proportion of individuals features microhabitat (n=7) (n=8) (n=5) (n=5) feature Prefer* Avoid* Neither Prefer* Avoid* Neither Prefer* Avoid* Neither Prefer* Avoid* Neither 0 0.57 0.88 0.20 0.20 0.40 >0-20 0.43 0.14 0.50 0.80 0.60 % canopy cover >20-50 0.57 0.14 0.00 0.63 0.13 0.80 0.00 0.60 0.40 >50-80 0.20 >80 0 0.13 >0-20 0.29 0.13 0.25 0.80 0.20 0.60 % Shrub cover >20-50 0.14 0.29 0.29 0.38 0.13 0.13 0.80 0.20 0.60 0.20 0.00 >50-80 0.29 0.13 0.25 0.20 0.20 0.20 >80 open 0.43 0.14 0.13 0.25 0.60 0.20 0.20 Ground cover mid 0.14 0.14 0.75 0.13 0.60 0.00 0.40 0.40 closed 0.43 0.13 0.63 0.20 0.40 0.20 0 0.29 0.20 Ground cover >0-0.5m 0.29 0.29 0.75 0.40 0.20 0.20 0.29 0.13 0.20 0.20 height >0.5-1m 0.14 0.29 0.50 0.20 0.60 0.20 >1-2m 0.14 0.14 0.50 0.40 Ground cover homogenous 0.14 0.80 0.20 0.14 0.13 0.00 0.20 Patchiness heterogeneous 0.71 0.88 0.20 0.60
* Significant: either P<0.05 with <1/5th of expected values of <5 OR P<0.01 with >1/5th of expected values of <5.
128 Table 5.5: Potoroo microhabitat preferences and avoidances of dominant ground cover types at Barren Grounds NP and Budderoo NP in Spring 2007 and Autumn 2008. Barren Grounds NR Budderoo NP Spring 2007 (n=7) Autumn 2008 (n=8) Spring 2007 (n=5) Autumn 2008 (n=5) Dominant proportion of individuals # sites proportion of individuals # sites proportion of individuals # sites proportion of individuals # sites ground Neither present* Neither present* Neither present* Neither present* cover type Prefer Avoid Prefer Avoid Prefer Avoid Prefer Avoid fern 0.00 0.43 0.57 7 0.00 0.25 0.75 8 0.00 0.60 0.40 5 0.00 0.40 0.60 5 sedge 0.14 0.29 0.57 7 0.00 0.50 0.50 8 0.20 0.40 0.40 5 0.40 0.00 0.60 5 tall sedge 0.00 0.86 0.14 7 0.13 0.38 0.50 8 0.00 0.00 1.00 4 0.20 0.00 0.80 5 rush 0.14 0.00 0.86 7 0.63 0.00 0.38 8 0.00 0.33 0.67 3 0.00 0.00 1.00 2 grass 0.00 0.00 1.00 4 0.00 0.00 1.00 5 0.00 0.00 1.00 2 0.00 0.00 1.00 1 shrub 0.14 0.00 0.86 7 0.25 0.00 0.75 8 0.20 0.00 0.80 5 0.20 0.00 0.80 5 heath 0.00 0.33 0.67 3 0.00 0.50 0.50 4 0.00 0.00 0.00 0 0.00 0.00 0.00 0 mix 0.50 0.00 0.50 4 0.20 0.00 0.80 5 0.20 0.00 0.80 5 0.00 0.00 1.00 4 plant debris 0.17 0.33 0.50 6 0.88 0.00 0.13 8 0.00 1.00 0.00 5 0.40 0.20 0.40 5 *# sites present = the number of spooling sites some proportion of which was made up of the dominant ground cover type
129 The Microhabitat Complexity Scores were found to be significantly different between individuals and between their sample point types (spool versus microhabitat availability) for Budderoo NP in both Spring 2007 and Autumn 2008 and for Barren
Grounds NR in Autumn 2008 (Table 5.6). However, in Spring 2007 at Barren Grounds
NR there was a significant difference between individuals but no significant difference between their sample point types. Individual potoroos were found to vary in their preferences for microhabitats with more or less complexity than was available to them.
Potoroo forage-diggings were found to occur in all categories of tree, shrub and ground cover present in the landscapes of both study areas. In relation to foraging microhabitat preferences (Figure 5.3 a-n), sample points with diggings were more likely to be in > 50
% shrub cover and less likely to be in > 0 - 20 % shrub cover (χ²3 = 11.42, P = 0.0097) than expected. Sample points with forage-diggings were also more likely than expected to be in open ground cover (χ²2 = 8.90, P = 0.0117), and have sedges (χ²1 = 11.25, P =
0.0009) and suspended plant debris (χ²1 = 6.09, P = 0.0145) as dominant ground cover types, and less likely than expected to have heath as a dominant ground cover type (χ²1
= 5.97, P = 0.0158) and Acacias present within a 5 m radius (χ²1 = 6.95, P = 0.0112).
130 Table 5.6: Microhabitat Complexity Scores for individuals spool paths and their available habitat at Barren Grounds NP and Budderoo NP in Spring 2007 and Autumn 2008.
greater f f Season Source p value Individual p value MicroHCS Study ratio ratio Area for: Individual Spring 4.79 0.0001 Sample 2007 3.77 0.053 point type 6963116 30.97 <0.0001 spool data 695FA58 5.78 0.020 spool data Barren Grounds 627ED26 0.12 0.734 NR Individual Autumn 6.17 <0.0001 63DD5EF 3.34 0.074 Sample 2008 12.68 0.0004 6434C38 0.05 0.817 point type 66DDE5E 12.02 0.001 spool data 6591E83 1.07 0.307 627EF10 2.92 0.094 availability 66DC8D8 5.62 0.022 data Individual 6965AOD 4.58 0.037 spool data Spring 17.69 <0.0001 Sample 2007 94.74 <0.0001 66DE54F 22.58 <0.0001 spool data point type 6584C30 0.98 0.327 6964BAC 70.17 <0.0001 spool data Budderoo NP 6584C75 29.89 <0.0001 availability data 6965675 33.72 <0.0001 availability Individual data 38.90 <0.0001 Autumn availability Sample 66E2517 5.54 0.022 2008 37.72 <0.0001 data point type 6593CE8 25.39 <0.0001 availability data 66DFE9E 11.58 0.001 availability data
131 a) b)
X²=5.966, df=1, P=0.0112** X²=11.418.421, df=3, P=0.0097* c) d)
X²=8.896, df=2, P=0.0117 X²=11.252, df=1, P=0.0145** e) f)
X²=11.252, df=1, P=0.0009** X²=5.966, df=1, P=0.0158**
Figure 5.3 a - f: Proportions of ‘dig’ and ‘no dig’ background vegetation sample points with: a) acacia present within a 5m radius, b) each shrub cover percentage group, c) density of ground cover vegetation, d) plant debris (PD) as a dominant ground cover type, e) sedges as a dominant ground cover type, f) heath as a dominant ground cover type, compared to expected. *≥ 20% of expected counts were less than 5 and a p ≤ 0.01 was considered significant **p value from 2 tail Fisher’s exact test
132
5.4. DISCUSSION
An examination of habitat preferences at the microhabitat scale found that the majority of potoroos in each of the study areas preferentially utilised some microhabitat components available to them during evening activities. However, specific patterns of microhabitat use varied between individuals, sites and seasons, revealing different preferences for different cover densities, distributions, heights and types. For cover density, distribution and height, only a minority of individuals displayed no preferences by using the microhabitat features in proportion to their availability. However, for the majority of ground cover vegetation types, no preference was displayed by the majority of individuals.
‘Habitat complexity’ preferences at the microhabitat scale were also found to vary between individuals, study areas and seasons. The majority of individual potoroos at
Budderoo NP were found to have significant microhabitat complexity preferences, however the levels of complexity preferred varied between individuals and seasons.
Alternatively, at Barren Grounds NR the majority of individuals displayed no microhabitat complexity preferences in either season.
A similar lack of microhabitat preferences for the species was observed by Bennett
(1993) in south-western Victoria, using live-capture data. There, capture rates of the species were not strongly correlated with any structural component of the vegetation or any particular floristic composition within a 4 x 4 m quadrat at each trap site. A spool- and-line study on the closely related Gilbert’s Potoroo (Potorous gilbertii) in Western
Australia by Vetten (1996) also found that microhabitat use of this species was also not clearly associated with any particular floristic group or strongly correlated with any
133 particular density of vegetation cover. The study animals appeared to utilise a range of vegetation ecotones.
A similar study on the long-nosed potoroo in Victoria also used the spool-and-line technique and also found individual variation in the levels of cover used during their evening activities (Veltheim 2000). On average, they used greater ground cover and lateral shrub cover, but not canopy cover, than was available to them. However, for each stratum Veltheim (2000) only used the average percent cover used per spool and the average percent cover available for statistical analysis and thus variation in cover usage within the evening’s activities could not be assessed. Further, in her statistical analysis of this data, for each cover type she lumped the cover data associated with individual animals and did not separate individual responses. This assumes that the
‘available cover’ data randomly collected for each individual was also ‘available’ to the other individuals examined, despite the study area encompassing three different habitat types.
Home range estimates for long-nosed potoroos in Victoria are between 2.0 and 4.0 ha for males and 1.4 and 2.9 ha for females (Bennett 1987, Long 2001). However, no studies have examined the home range of the species in New South Wales where the animals appear to be larger in size than in Victoria. Therefore the use of 140 m long spools in my research was expected to only provide a representation of the area used by a potoroo in the local habitat. Certainly, longer spool lengths may have clarified the non-significant trends displayed by some of the individuals’ spool paths. Further, the use of more ‘good’ trap sites at Budderoo NP for spooling may have also clarified some of the results.
The loss of one spool path out of thirteen spool attempts at Budderoo NP and three of twenty spool attempts at Barren Grounds NR due to thick ground vegetation was not
134 thought to have impact on the trends observed in microhabitat preferences due to ground cover density. Specifically, it would not have changed the overall result that the majority of potoroos displayed significant preferences for certain levels of ground cover at the microhabitat scale and that these levels differed between individuals and over time, and covered the full range of ground cover levels available.
Both the study by Bennett (1993) and my own results revealed that at the microhabitat level the understorey at capture sites varied from dense to relatively open. Despite dense vegetative cover, provided by either the ground or shrub layer (Seebeck 1981, Bennett
1987), being a common attribute in potoroo habitat, both Bennett (1993) and Claridge and Barry (2000) suggest that at the microhabitat level the species may actually require habitat patchiness. This patchiness is provided by vegetation mosaics and ecotones.
Bennett (1993) suggests that this habitat patchiness provides individuals, within their relatively small home ranges, with access to the different kinds of resources they require: dense, structurally-complex patches for shelter and predator avoidance and relatively open, floristically-diverse patches for foraging activity.
If microhabitat preferences for structural and floristic diversity vary during different activities as suggested by Bennett (1993) due to the utilisation of habitat patchiness, then the ability to draw meaningful conclusions on microhabitat preferences from spool and line data will be reduced. This is because spool paths may be laid out during a range of evening activities. They are likely to represent a mix of foraging and non- foraging movements including interaction with other individuals, travelling between foraging sites and sheltering. Therefore, conclusions about microhabitat preferences drawn from a spool path will be influenced by the proportions of these activities conducted while the spool fed out. Nearly all spool paths in this study had indications
135 of fresh foraging activities at points along them. However, it is not known what proportions of the spool paths were laid out during non-foraging activities.
To examine habitat-use specifically during foraging, a comparison of the microhabitat characteristics of locations with and without potoroo diggings was undertaken. These results revealed that potoroos foraged in all levels of tree, shrub and ground cover present in the landscape but displayed preferences for locations with higher shrub cover densities and more open ground cover, generally with sedges and plant debris. While no significant difference in habitat complexity was found between dig and non-dig sites, it should be noted that sites with varying arrangements of cover across the canopy, shrub and ground levels can have similar complexity scores.
Examining the abundance of long-nosed potoroo diggings in south-western Victoria,
Bennett (1993) also found that diggings were negatively correlated with total vegetation density under 3 m. He suggested that the fungal food resources of potoroos may be more abundant and accessible where there is more open ground vegetation and light penetration. Bennett (1993) also found a positive correlation between digging abundance and floristic richness. In contrast, Claridge and Barry (2000) found no relationship between the occurrence of potoroo diggings and the density of ground cover (0.5 - 2 m) in their study across southern NSW and Victoria. However, they examined occurrence of forage-diggings at a larger scale (50 x 20 m plots), examined a narrower stratum of ground cover vegetation, used a different technique to estimate vegetation density and examined digging occurrence rather than abundance.
In Tasmania, Johnson (1994) found that the fruiting-bodies of hypogeous fungi were more likely to be found within a 2 m radius of adult eucalypt trees, implying that forage-diggings of mycophagous (fungus-feeding) marsupials should also be more likely to be found at such micro-sites. In the present study, forage-diggings of long-
136 nosed potoroos were not significantly related to the closeness of eucalypt trees, nor any other woody tree or shrub taxa likely to play host to fungal food resources. This result is most likely attributable to root systems of plant hosts being more evenly distributed across each of my study areas, unlike the study of Johnson (1994) in an open woodland system.
Proportions of fungi in the diet of the long-nosed potoroo are greatest in autumn and winter and lowest in spring and summer at which time consumption of other food items increase in importance (Bennett and Baxter 1989; Claridge et al. 1993b). The high levels of autumn/winter fungus consumption may be related to increased soil moisture and an increased diversity of species and number of hypogeous fruiting bodies present during these months (Claridge et al. 1993b and 2000). Tory et al. (1997) observed proportions of fungi to peak at 90 % in winter and drop to a low of 52 % in summer.
With the presence/absence of forage-diggings only being examined in summer in the present study, a lack of significant correlation of forage-diggings with a number of habitat attributes previously found to be important to the species in other studies may be due to the reduced importance of fungi in the diet. However, Claridge et al. (1993a) found that within a similarly multi-aged forest potoroo site in Victoria, while the abundance of diggings varied over time, the probability of occurrence of diggings did not.
Claridge et al. (1993a) found that microhabitat preferences indicated by the presence of forage diggings varied somewhat compared to those indicated by their trapping results.
In the current study, a similar difference was found between the forage digging and spooling results. This difference is mostly attributed to the variety of activities that can be undertaken during evening spooling compared to the specific foraging microhabitat preferences indicated by the presence of forage diggings. With a preference for more
137 closed shrub and open ground cover during foraging, the varying ground cover density and habitat complexity preferences displayed during spooling may be related to individual preferences during non-foraging activities. While the habitat complexity score of a dense, structurally complex patch (suggested by Bennett (1993) to be used for sheltering), is likely to be higher than for a relatively open, floristically diverse patch
(used for foraging activities), the cover and complexity used during other non-foraging activities may also vary significantly.
138 6.0. GENERAL DISCUSSION
Long-nosed potoroos within the Barren Grounds NR and Budderoo NP of the Southern highlands of New South Wales were found to be larger in size than Victorian animals
(Bennett 1987) but somewhat smaller than north-eastern NSW animals (Johnston and
Sharman 1976, Mason 1997). This supports the concept of a cline in body size for the species with weight increasing with latitude on the mainland. Clinal variation in body size was also observed for the Tasmanian sub-species with smaller animals in the wetter north-west and larger animals in the drier north-east (Johnston and Sharman 1976).
Sexual dimorphism was also observed with adult males having larger body weights, head lengths and pes lengths than females. Males and females were found to often overlap at trap sites, with male/male overlap less frequent and female/female overlap fairly rare.
Despite a female biased long-nosed potoroo population observed by Bennett (1987) in
Victoria, over the course of this study male individuals captured outnumbered female individuals (1 : 0.76). They were also captured twice as often, and across more seasons, than females suggesting that either males survived longer or were less likely to shy away from successive trapping events than females. At both study areas, just over one third of all males, and nearly two thirds of all females, were only captured in a single trapping session. It was unclear whether this was related to transience or survivorship within the populations.
In contrast with Catling et al. (1997), the use of the soil plot technique to accurately represent overall changes in potoroo population size was considered less appropriate than trapping due to its inability to decipher between overlapping individuals in higher density populations and the potoroos reduced utilisation of tracks compared to other
139 species. The cage trapping results revealed that Barren Grounds NR supported a larger number of individuals than Budderoo NP and appeared to have a greater degree of home range overlap between individuals, which was considered indicative of a higher quality habitat at this study area.
Across its range, the species occupies a variety of habitats including rainforest, dry and wet sclerophyll open-forests, woodland, shrublands and heath vegetation communities and their ecotones (Claridge et al. 2007). These habitats generally provide dense vegetative cover at either the ground layer or shrub layer (Seebeck 1981, Bennett 1987).
In the current study the species was found to prefer plateau forest, but was also present in wet forest and plateau heath vegetation communities, all of which had patches of dense shrub and/or ground cover strata interspersed with more open patches.
At a macrohabitat level, potoroos were caught across a broad range of cover levels, types and floristic diversities, with a preference noted for greater levels of canopy and shrub cover, ferns as a dominant ground cover type and lower levels of ground cover floristic diversity. Greater canopy cover, 2-3 m shrub density and fern ground covers were also found to be more common at more successful potoroo trap sites while less popular trap sites were generally fairly similar to trap sites at which potoroos were absent over the study. Macrohabitat preferences were also found to vary between the two study areas with a number of structural and floristic macrohabitat attributes preferred at Barren Grounds NR while only a few different floristic macrohabitat attributes were preferred at Budderoo NP.
The absence of potoroos from some trap sites with macrohabitats matching those favoured by the species suggests that macrohabitat limitation is not important for this threatened species. It may be that their population density is too low to allow all
140 preferred habitats to be filled. However, there may also be microhabitat differences within these patches influencing their macrohabitat preferences
To examine whether total cover was important to a potoroo (rather than cover in any one particular layer) Macrohabitat complexity scores were calculated for each trap site.
These scores revealed a lower ‘macrohabitat complexity’ at Barren Grounds NR than
Budderoo NP, most likely attributable to varying ‘habitat complexities’ both within and between the dominant vegetation communities present at each study area. Barren
Grounds NR potoroos also appeared to prefer sites with higher habitat complexity, while no complexity preferences were observed at Budderoo NP. These results, and the higher trap success observed at Barren Grounds NR, suggest there may be an upper limit to ‘habitat complexity’ at which point the suitability of habitat for potoroos actually decreases. This is also supported by a comparison of the average complexity of each dominant vegetation communities present in both study areas, where the most preferred community had only mid-range complexity.
At the microhabitat level, individuals displayed preferences during their evening activities for particular cover densities, distributions, heights and types, as well as microhabitat complexity; however, these preferences varied between individuals, study areas and seasons. No one microhabitat attribute was found to be preferred by all individuals.
Interestingly, patterns differed at the two scales of investigation. Some habitat attributes were important at the macrohabitat scale, but did not appear as important at the microhabitat scale, and visa versa. Ferns were a preferred ground cover type at the macrohabitat level, while at the microhabitat level potoroos either displayed no preference for ferns, or used them in lesser proportion than their availability. Rushes were also a preferred ground cover at the macrohabitat level, but at the microhabitat
141 level they were only preferred by the majority of potoroos at one study area during one season. Again, while greater levels of tree canopy cover was identified as a preferred macrohabitat attribute, preferences varied at the microhabitat scale. A number of individual potoroos also displayed microhabitat preferences for habitat attributes not preferred at the macro-scale. Likewise, ‘habitat complexity’ preferences also varied between scales. At Barren Grounds NR greater macrohabitat complexity was preferred but they generally used most of the microhabitat complexity levels available. At
Budderoo NP potoroos had no macrohabitat complexity preferences but the majority displayed particular preferences for or against microhabitat complexity. Overall, these results suggest that the species’ habitat use is influenced by both macro- and micro- scale preferences and highlight the importance of examining habitat associations at multiple scales.
Dense vegetative cover is another habitat attribute which appears to be more important at coarser scales of habitat use. Despite dense vegetative cover being an important aspect of potoroo habitat across the species’ range, both Bennett (1993) and Claridge and Barry (2000) suggest that at the microhabitat level the species may actually require habitat patchiness. They suggest that microhabitat preferences for structural and floristic diversity vary during different activities and these preferences are achieved through the utilisation of habitat patchiness provided by vegetation mosaics and ecotones. Bennett (1993) suggests that they require dense, structurally-complex patches for shelter and predator avoidance and relatively open, floristically-diverse patches for foraging activity. My results provide further evidence of the species utilisation of habitat patchiness. While the dominant vegetation communities in which the species was captured had dense shrub and/or ground cover, individual microhabitat preferences varied from dense to fairly open understorey, indicating that habitat patchiness was
142 present and utilised in my study areas. Further, my examination of microhabitat preferences specifically during foraging revealed preferences for locations with higher shrub cover densities and more open ground cover. This type of microhabitat is expected to provide floristic diversity and some level of aerial cover during foraging but not cover from ground predation.
The species association with dense vegetative cover is suggested by a number of authors to offer them virtually total concealment from, and limited access by, introduced predators (Schlager 1981, Seebeck 1981, Mason 1997). However, depending on the density and distribution of cover at ground level this dense vegetative cover does not necessarily offer the species’ significant protection from ground predation. In this study not all potoroos were preferentially utilising either macrohabitats or microhabitats with mid- to high-levels of ground cover. Further, foraging microhabitat preferences reveals the importance of patches of more open ground cover. The high proportion of predator scats, particularly fox scats, with potoroos remains collected from the study areas suggests that the species may face a greater predation risk than would be expected based purely on the presence of dense ground cover in their habitat. Certainly the species does not appear to be afforded adequate protection by its use of habitat from fox predation. Potoroos were found to be a major part of the diet of predators in the two study areas, particularly foxes.
This research has a number of implications for the conservation management of long- nosed potoroos, particularly within these local reserves. Management of habitat for the species across its range should aim to perpetuate a mosaic of habitat types with variable floristic and structural diversity at both the macro and micro-scale. Activities that result in the simplification of habitat attributes, particularly the frequent use of prescribed fire
(Catling 1991, Claridge and Barry 2000), should be avoided. Claridge and Barry (2000)
143 found that the species were more likely to be found in habitats unburnt for more than 20 years. However, the total suppression of fire from the species habitat will also prevent the continued development of the habitat mosaics the species requires (Mason 1997).
While occasional high-intensity wildfires encourage dense understory growth in the long term, frequent low-intensity fires lead to the elimination of dense understorey and increased predation risks.
While mortality following fire is expected, Seebeck (1981) suggests that individuals may survive high intensity fires, by sheltering in other species’ burrows. The author observed three unharmed potoroos searching for food within hours of such a fire. Three closely related bettong species have also been observed to survive a fire event, although survival thereafter appears to be highly impacted by introduced predators (Claridge et al. 2007). Long-nosed potoroo populations in south-east and western Victoria were found to recover from intense fire events (Claridge et al. 2007).
With the two study areas used being situated within National Park reserves the local potoroo populations have been afforded protection from the impacts of clearing and logging for over 20 years, in fact over 50 years at Barren Grounds Nature Reserve. The absence of any fire in these study areas over the past 25 years is also likely to have assisted in the local populations reaching the high levels of abundance observed in this study. The two study area populations appear to have largely increased over the course of the study. Further, a trapping survey for the species in 1990, in a section of Barren
Grounds NR that has returned the highest trap success during my study, resulted in no potoroo captures (Baker and Clarke 1991). This was 8 years after the last fire event in the area.
It is apparent that even in the good quality potoroo habitat offered at both study areas the species is facing serious predation pressures, much higher than those considered
144 likely by other authors given their association with dense vegetative cover. Foxes were found to be the primary predation threat to the local potoroo populations. Therefore the effective control of foxes in and around any potoroo habitat is considered likely to assist in the conservation of the species. Effective fox control, resulting in reduced fox activity, has been found to significantly increase abundance of some long-nosed potoroo and other potoroid populations (Murray et al. 2006, Claridge et al. 2007).
At Barren Grounds NR efforts should be made to increase the effectiveness of the current baiting program, perhaps using a variety of bait types and scent lures, and increasing the area baited to provide a greater buffer to the potoroo population. Fox baiting should also be considered across Budderoo NP and shooting and/or trapping could be used as additional control efforts at both study areas.
The proportion of dog scats with potoroo remains, although lower than fox and quoll scats, was also concerning. Studies examining the levels of predation by wild dog/dingo predation on potoroos provide mixed results. Lunney et al. (1990) and
Newsome et al. (1983) observed low levels of wild dog/dingo predation on the long- nosed potoroo but they were found to be a significant predator of the long-footed potoroo (Scotts and Seebeck 1989).
Consideration should be given as to whether to conduct targeted dog control in Barren
Grounds NR. It is also unclear to what extent potoroos may face predation by the increasing number of cats within the study areas and whether they should be controlled for the protection of the potoroos. Certainly the control of any introduced predators would be essential following disturbances such as fire where the sudden loss of dense vegetative cover would leave them significantly more exposed to predation risks.
145 Surveying for the species, using any one of a range of techniques including trapping, sand plots and remote cameras, should also be conducted elsewhere in the NSW
Southern Highlands to reveal the extent of the species range in this region. This information is essential in order to inform management of the local potoroo populations.
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