Tree Hollows and Wildlife Conservation in Australia

By Philip Gibbons and David Lindenmayer

More than 300 species of Australian native animals — mammals, birds, reptiles and amphibians — use tree hollows, but there has never been a complete inventory of them. Many of these species are threatened, or are in decline, because of land-use practices such as grazing, timber production and firewood collection.

All forest management agencies in Australia attempt to reduce the impact of logging on hollow-dependent fauna, but the nature of our eucalypt forests presents a considerable challenge. In some cases, tree hollows suitable for vertebrate fauna may take up to 250 years to develop, which makes recruiting and perpetuating this resource very difficult within the typical cycle of human-induced disturbance regimes.

Tree Hollows and Wildlife Conservation in Australia is the first comprehensive account of the hollow-dependent fauna of Australia and introduces a considerable amount of new data on this subject. It not only presents a review and analysis of the literature, but also provides practical approaches for land management.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Apr 5, 2002
• ISBN: 9780643099746

Book preview

TREE HOLLOWS

AND WILDLIFE CONSERVATION

IN AUSTRALIA

The effect of useless veterans. In all classes of virgin forest useless veterans dominate an appreciable percentage of the soil. They should be eliminated as soon as possible and replaced by a useful crop, even coppice for firewood as in the background of the picture. The veterans put on little growth but dominate the forest in their vicinity more than vigorous young mature trees. Soon after they are killed the soil in their vicinity supports a new group of seedlings efficiently.

Our understanding of the importance of old trees in ecosystems has evolved from that illustrated by this photo and accompanying caption which appeared in Growth Habits of the Eucalypts (Jacobs 1955).

TREE HOLLOWS

AND WILDLIFE CONSERVATION

IN AUSTRALIA

PHILIP GIBBONS AND DAVID LINDENMAYER

© CSIRO 2002

All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests.

National Library of Australia Cataloguing-in-Publication entry:

Gibbons, P. (Philip).

Tree hollows and wildlife conservation in Australia.

Bibliography.

Includes index.

ISBN 0 643 06705 1 (paperback).

ISBN 0 643 09003 7 (eBook).

1. Tree cavities—Australia. 2. Forest animals—Australia—Identification.

3. Forest conservation—Australia. I. Lindenmayer, David. II. Title.

577.30994

Available from:

CSIRO PUBLISHING

150 Oxford Street (PO Box 1139)

Collingwood VIC 3066

Australia

Front cover

Greater Glider (Petauroides volans). Photo by Esther Beaton

Back cover

Mountain ash (Eucalyptus regnans). Photo by David Lindenmayer

l. to r.: Major Mitchell Cockatoo (Cacatua leadbeateri). Photo by Esther Beaton; White-throated Treecreeper (Cormobates leucophaea). Photo by Phil Gibbons; Gould’s Long-eared Bat (Nyctophilus gouldi). Photo by Esther Beaton; Lace Monitor (Varanus varius). Photo by Phil Gibbons.

Set in Adobe Sabon, Optima and Futura

Cover design by James Kelly

Typeset by Desktop Concepts P/L, Melbourne

Printed in Australia by Brown Prior Anderson

CONTENTS

Acknowledgements

1    INTRODUCTION

2    THE HOLLOW-USING FAUNA OF AUSTRALIA

Obligate or opportunistic?

Amphibians

Reptiles

Birds

Mammals — bats

Mammals — arboreal and scansorial

Invertebrates

The distribution of hollow-using fauna in Australia

3    THE EVOLUTION OF HOLLOW USE

Factors underpinning the evolution of hollow use

Adaptive traits of hollow-using fauna

4    HOLLOW FORMATION

Decay formation in eucalypts

The different types of hollows in eucalypts

Characteristics of trees associated with hollow formation

The age at which eucalypts form hollows

Variation in numbers of trees with hollows in Australian landscapes

Accelerating hollow development in eucalypts

5    THE INVENTORY OF HOLLOWS AND HOLLOW-BEARING TREES

Identifying trees with hollows from ground-based observations

Counting hollow-bearing trees in the landscape

Estimating hollow-tree densities from basic stand information

Estimating hollow-tree density from aerial photographs or high-resolution satellite imagery

Monitoring

6    THE SELECTION OF HOLLOWS BY FAUNA

Predicting the likelihood that hollows are suitable for occupancy

A generic model for identifying trees suitable for occupancy by hollow-using fauna

Identifying hollows occupied by fauna

Other considerations when selecting hollow-bearing trees for retention

Marking suitable trees

7    HOLLOW NUMBERS AND FAUNA POPULATIONS

The number of hollow-bearing trees used by fauna

Changes to the hollow resource since European settlement

Implications for fauna

Principles for management

From principles to practice

8    PERPETUATING HOLLOWS

Hollow dynamics in unmanaged eucalypt forests and woodlands

Post-European land use practices and the disruption of hollow recruitment

Selecting recruitment trees

Protecting retained trees

9    PEST AND INTRODUCED SPECIES THAT USE HOLLOWS

Exotic species

Native species with expanded ranges or increased population sizes

Management responses to invading species

10  THE ROLE OF NEST BOXES IN RESEARCH AND MANAGEMENT

Nest boxes and research

Nest boxes and field survey

Nest boxes and population recovery

Nest box design

The economics of nest boxes as a management tool

Nest boxes versus natural hollows

11  CONCLUDING REMARKS

The hollow-using fauna of Australia – an incomplete inventory

A depleted hollow resource

Recruitment

Firewood collection

Introduced and pest species

Inventory and monitoring

Institutional impediments

Elements of a sound management regime for hollow-using fauna

Appendix A

Appendix B

Appendix C

References

Index

ACKNOWLEDGEMENTS

Many people gave their time and expertise to help us complete this book. Joern Fischer, Doug Mills, Anne Findlay from Editing Works, Nick Alexander from CSIRO Publishing, and Julian Fox provided editorial comments that greatly improved earlier versions of the manuscript. Photos were kindly provided by Esther Beaton, Andrew Claridge, Jim Trappe, Dave Milledge, David Jacquier, Linda Karssies, Michael Vardon, Cindy Trewin, John Briggs, Mick Tanton and Doug Mills. Hugo Phillipps of Birds Australia gave permission to use the nest box plan. This book benefited from discussions with many colleagues including Ryan Incoll, Mark Fitzgerald, Kirsten Parris, Mick McCarthy, Doug Mills, Simon Barry, Mick Tanton, Henry Nix, Charlie Mackowski, Kevin Wormington, Bill McComb, John Banks, John Briggs, Stephen Ambrose, Adrian Wayne, Ian Abbott, Warwick Bratby, Anthony Overs, Sue Briggs, Julian Seddon, Stuart Doyle, Sandy Gilmour, Chris Tidemann, Denis Saunders, Chris Davey and various members of the Ecological Society of Australia who responded to questions posted on that organisation’s listserver. Susan Rhind, Peter Robertson, Ray Brereton, Adrian Manning, Robert Bender, Julian Ash, Josh Dorrough, Steve Jackson and Matthew Pope kindly provided access to unpublished information. Yvonne Ross, Jerry Alexander, Ian Abbott, Joern Fischer and Julian Fox alerted us to relevant published information. Joern Fischer assisted with the collection of information on the use of hollows by birds and compiled the list of threatened fauna. Doug Mills provided advice on the list of hollow-using bats. Support by the Centre for Resource and Environmental Studies, The Australian National University is much appreciated. Jim Atkinson and Di Stockbridge are thanked for their support of this work. Finally, to Sarah and Karen, who debated our crazy ideas, kept us balanced and continued to support us despite our frequent absences throughout this project.

To Sarah and Karen

and the next cohort

CHAPTER

1

INTRODUCTION

This is a book on tree hollows in the Australian environment and their importance to native fauna. Tree hollows are semi-enclosed cavities that naturally form in many species of trees — predominantly old or dead trees — and are a prominent feature of natural forests and woodlands. Many species of vertebrates and invertebrates use hollows as diurnal or nocturnal shelter sites, for rearing young, for feeding, for thermoregulation, and to facilitate ranging behaviour and dispersal. For many of these species the use of hollows is obligate — no other habitat resource represents a feasible substitute.

We believe that a book on hollows, their use by wildlife and their management is important for several reasons.

First, a large number of Australia’s fauna use hollows. A previous estimate by Ambrose (1982) put the total at approximately 400 species. However, an inventory of hollow-using fauna in Australia has never been assembled before.

Second, a number of the species considered threatened in Australia are hollow-users. Approximately 100 species of vertebrates that potentially use hollows are listed as rare, threatened or near-threatened on state or commonwealth endangered species legislation in Australia (Appendix A).

Third, land managers are obliged to manage the hollow resource sustainably. For example, the loss of hollow-bearing trees has been listed as a threatening process in the Victorian Flora and Fauna Guarantee Act (Garnett and Loyn 1992). All of the Regional Forest Agreements struck for the long-term management of Australia’s forests specify the need for targeted prescriptions for hollow-using fauna (e.g. Anon. 1997b, Anon 1998a).

Fourth, native forest silviculture, firewood collection, rural dieback, grazing and clearing are causing ongoing depletion of the hollow resource (Figure 1.1). For example, remnant woodlands in northern Victoria supported, on average, 17 hollow-bearing trees per hectare (Bennett et al. 1994). However, agricultural land — supporting around two large trees per hectare (Soderquist et al. 1999) — covers 91% of this region (Bennett et al. 1998). Dieback, combined with a general absence of recruitment, is causing an ongoing decline of mature trees in agricultural landscapes (Reid and Landsberg 2000) (Figure 1.2).

Fifth, the period it takes for eucalypts to develop hollows (>120–150 years) (Mackowski 1984, Stoneman et al. 1997, Wormington and Lamb 1999, Gibbons et al. 2000a) presents some challenges for land managers. Hollows can only be perpetuated if existing trees with hollows are retained as well as trees that presently do not contain hollows, but which are likely to do so in the future. Conditions must therefore be created for both the periodic recruitment of trees into a stand and the long-term protection of these trees. Such conditions are presently not met in many Australian landscapes.

Finally, many introduced and pest species in Australia use hollows. Some such as the Common Myna (Acridotheres tristis) and European Honeybee (Apis mellifera), compete with native species for hollows (Pell and Tidemann 1997b, Wood and Wallis 1998b). Some native hollow-using species such as the Galah (Eolophus roseicapillus), Little Corella (Cacatua sanguinea) and Common Brushtail Possum (Trichosurus vulpecula) occur in higher population densities, and/or have expanded their geographical ranges since European settlement. These species compete with other native taxa for hollows and will prey upon, or destroy, the eggs and nestlings of less abundant and widespread hollow-using species (Garnett et al. 1999). Other introduced species such as the Cat (Felis catus) and Black Rat (Rattus rattus) are predators of hollow-using fauna and have been particularly damaging to island populations (Olsen 1996).

The conservation of hollow-using fauna is a prominent land management issue in many other countries. Samuelsson et al. (1994) noted that the paucity of dead wood (including dead hollow-bearing trees) was a critical threatening process for birds in Scandinavian forests. Similarly, Berg et al. (1994) calculated that almost 50% of the Red-listed species in Sweden were dependent on dead hollow-bearing trees or logs. In North America, recovery of the Eastern Bluebird (Sialia sialis) has necessitated the use of nest boxes, such has been the depletion of natural hollows (Hunter 1990). We have drawn on considerable material on hollow-using fauna from overseas, but the majority of the examples we present come from Australia.

The focus of this book is hollows in standing trees — specifically, hollows suitable for vertebrate fauna. Unfortunately there is a dearth of studies on hollow use by invertebrates. We have not explored the important role of hollows in logs on the ground, although we recognise their importance for an array of Australian vertebrates and invertebrates (e.g. McComb and Lindenmayer 1999, MacNally et al. 2000). We also have not examined other roles of hollow-bearing trees for wildlife, such as the importance of large living trees as a source of nectar.

The first part of this book examines the ecology of fauna that use hollows (Chapters 2 & 3) and the process of hollow formation (Chapter 4). In the latter part of the book (Chapters 5–10) we apply relevant information on the process of hollow formation and the ecology of hollow-using fauna in a conservation and management context. We conclude (Chapter 11) with a summary of the key findings.

Figure 1.1 A logging coupe in the Central Highlands of Victoria in which hollow-bearing trees have been almost completely removed. (D. Lindenmayer)

Figure 1.2 Dieback among trees in rural landscapes caused by inundation and/or salinity. (D. Lindenmayer)

CHAPTER

2

THE HOLLOW - USING FAUNA OF AUSTRALIA

The use of tree hollows is prominent among Australian terrestrial vertebrate fauna — approximately 13% of all terrestrial amphibians, 10% of reptiles, 15% of birds and 31% of mammals may at some time use this resource. We estimate that there are 303 native hollow-using species on the continent, or around 15% of all terrestrial vertebrate species, with an additional 10 introduced species that use hollows. There is a paucity of information on hollow use by amphibians and reptiles. For invertebrates the insufficient data we have means we cannot list the taxa that use hollows. We also cannot determine whether all species are obligate hollow-users, or use this resource opportunistically. Indeed, the relationship that some species have with hollows appears to change throughout their distribution, depending on factors like climatic conditions.

Table 2.1 The number of native species by broad taxonomic group that use hollows in Australia (mainland and Tasmania) and the percentage of the total terrestrial vertebrates (endemic and introduced) that they represent.

Our research and assessment of the literature indicates that 303 native vertebrate species, or 15% of all terrestrial vertebrate species on mainland Australia (including Tasmania), use hollows. This list includes 27 amphibians, 79 reptiles, 114 birds and 83 mammals (Table 2.1). An additional 10 introduced species use hollows. These estimates are different from those by other authors (viz. Hall 1981, Ambrose 1982, Saunders et al. 1982) for several reasons:

•   more is known now about the breeding biology and shelter/nesting requirements of Australian wildlife than when previous workers completed their studies;

•   there have been major taxonomic revisions in several groups of vertebrates (e.g. bats) over the past decades and the numbers of species in these assemblages has therefore changed; and,

•   other workers have used different criteria to us.

Obligate or opportunistic?

Our list of hollow-using fauna includes species that are obligate hollow-users and species that may be described as opportunistic hollow-users. It is difficult to determine which species belong in each group. Many hollow-using species have been observed to nest in structures other than hollows. The Sugar Glider (Petaurus breviceps) has been observed denning in piles of timber on the ground (Fleay 1947), under tin sheeting and in thickets of Blackberry (Rubus fruticosus) (Morrison 1978). The Common Ringtail Possum (Pseudocheirus peregrinus) often uses hollows but is also capable of constructing nests or dreys. Bats frequently roost in hollows, but also behind peeling bark, in fence posts and tractor exhausts (Lumsden et al. 1994).

Do such observations indicate these species to be only opportunistic hollow-users? This can only be answered with an understanding of changes to rates of predation and fecundity among individuals using these alternative sites and whether alternative sites remain suitable for use by these species in all seasons and habitats. For example, the Lesser Long-eared Bat (Nyctophilus geoffroyi) can use many different structures as roost sites, but females require substantial tree hollows to establish maternity colonies (Lumsden et al. 1994).

Hollow use appears to be obligatory in certain habitats, but not in others. The Common Ringtail Possum appears to be dependent upon hollows in cold environments, such as Snow Gum (Eucalyptus pauciflora) woodlands (Green and Osborne 1994), and relatively open environments like woodland habitats (Thomson and Owen 1964, Soderquist et al. 1999), but may construct dreys elsewhere (How et al. 1984). Jones et al. (1994) and Inions et al. (1989) found that dreys constructed by the Western Ringtail Possum (Psedocheirus occidentalis) were rare or absent in certain habitats in south-west Western Australia. Recent radiotracking studies of the Western Ringtail Possum have shown that the most commonly used nest sites were dreys in one part of the forest, but standing trees with hollows in another (A. Wayne, personal communication). In another example, the Peregrine Falcon (Falco peregrinus) predominantly used cliff ledges for nesting in some environments (Olsen 1995), but used tree hollows in woodlands dominated by River Red Gum (Eucalyptus camaldulensis) (Pruett-Jones et al. 1981).

We are therefore reluctant to classify species as opportunistic hollow-users only on the basis that they are known to utilise structures other than tree hollows. Thus, our list of hollow-using species includes all taxa either known, or judged likely, to use tree hollows.

Amphibians

There are 27 arboreal or semi-arboreal frog species of the genera Lechriodus, Litoria, Nyctimystes and Cophixalus that may use hollows in Australia (Table 2.2). This is about 13% of all Australian frog species. Ambrose (1982) suggested that 37 species of frogs occurring in Australia use hollows, but did not nominate which taxa. We could confirm hollow use for only eight species but have included others because of their arboreal habits, and therefore the potential for them to utilise this resource. Hollow use by frogs may be difficult to detect because most species are small and little is known of their ecology. Unlike mammals and birds, they often do not leave evidence of hollow occupancy (such as nesting material) and generally do not call from hollows (although we have obtained a number of reports of the Green Tree Frog calling from hollows).

Frogs use hollows for several purposes. Ambrose (1982) noted ‘pans’ or hollows between branches that collected water sometimes contained sheltering or foraging frogs.Tadpoles of Fletcher’s Frog have been recorded in water-filled tree hollows in south-east Queensland (Kitching and Callaghan 1982). Peron’s Tree Frog and the Desert Tree Frog have been observed basking near entrances of hollows and retreating into them when disturbed. It may be that hollows are important to amphibians that occur in warm or dry climates because they provide a suitable microclimate — hollows have a higher relative humidity than ambient conditions (McComb and Noble 1981a).

Reptiles

We estimate that 79 species of reptiles may use hollows in Australia (Table 2.3). This is about 10% of all species. Ambrose (1982) suggested that 148 species of reptiles use hollows in Australia. We have confirmed the use of hollows by 23 species, and expect that the use of hollows by the other species is probable given their arboreal habits. Hollow use by some species of reptiles may be infrequent, and therefore difficult to detect. For example, from observations of 18 Frillneck Lizards over a three-month period spanning three years, only one animal was observed to enter a hollow (Shine and Lambeck 1989).

Table 2.2 Frogs recorded from hollows, and other arboreal or semi-arboreal frogs that may use hollows in Australia (nomenclature follows Barker et al. 1995). § indicates the species is confirmed to use hollows. (Sources: Ambrose 1982, Kitching and Callaghan 1982, Menkhorst 1984b, Barker et al. 1995, Cogger 1996 and personal communications from various members of the Ecological Society of Australia.)

Reptiles use hollows for a number of different reasons. The Brown Tree Snake (Boiga irregularis) may lay its eggs in tree hollows. The Broad-headed Snake is an arboreal species that occupies tree hollows only in late spring and summer (Webb and Shine 1997). At this time of the year, other retreat sites (e.g. cracks between rocks) are too hot for animals to thermo-regulate effectively (Webb and Shine 1998).

As well as using hollows as den or nest sites, a number of reptile species feed on prey found in hollows. The diet of the Reticulated Velvet Gecko, an arboreal species, includes invertebrates that occur within decaying wood (e.g. termites and cockroaches) (How and Kitchener 1983). The diet of the Lace Monitor includes several vertebrate species that nest in tree hollows, such as insectivorous bats (Mansergh and Huxley 1985), the Greater Glider, Sugar Glider and Common Brushtail Possum (Weavers 1983).

Table 2.3 Reptiles in Australia recorded using tree hollows, and reptiles with an arboreal, or semi-arboreal habit which may use this resource (taxonomy follows Cogger 1996). § indicates the species is confirmed to use hollows. (Sources: How and Kitchener 1983, Weavers 1983, Braithwaite et al. 1984, Menkhorst 1984b, Pianka 1986, Mackowski 1987, Shine and Lambeck 1989, CNR 1993, Thompson 1993, Barker et al. 1995, Christian and Bedford 1996, Cogger 1996, Webb and Shine 1997, Thompson et al. 1999, Jackson 2000b.)

Birds

Birds are the largest group of hollow-users in Australia. We estimate that 114 native species of birds use hollows (Table 2.4). The list of hollow-using birds in Australia includes an additional five introduced species: Common Myna, Common Starling, House Sparrow and Tree Sparrow and Mallard. Saunders et al. (1982) suggested that 94 species of birds use hollows in Australia while Ambrose (1982) estimated the total to be 119 species. The reasons for any differences are outlined in the first section of this chapter.

Our figure of 114 native species represents about 15% of all land birds in Australia. This estimate is considerably higher than other regions of the world. For example, approximately 55 species (9% of all species) use hollows in southern Africa and 58 species (10% of all species) use hollows in northern America (Saunders et al. 1982).

Most birds use hollows seasonally, typically for rearing young. Some species also use hollows as diurnal or nocturnal roost sites. Species that roost in hollows when not breeding include the Masked Owl, Sooty Owl, Australian Owlet-nightjar and White-throated Treecreeper.

Some birds take prey from hollows, although we have not included these taxa in the list given in Table 2.4. For example, the Forest Raven (Corvus tasmanicus) has been observed taking a Feathertail Glider (Acrobates pygmaeus) from a hollow (McCulloch and Simpson 1987). The Grey Butcherbird (Cracticus torquatus) was recorded taking nestlings of the Laughing Kookaburra from nest hollows (Hindwood 1947). Krebs (1998) found that Currawongs (Strepera spp.) were major predators on eggs and nestlings of the Crimson Rosella.

Table 2.4 Birds that use tree hollows in Australia (taxonomy follows Marchant and Higgins 1993, Australian Biological Resources Study 1995, Marchant and Higgins 1998, Higgins 1999). The list does not include taxa that feed in hollows but do not otherwise use them (e.g. some species of corvids). (Sources: Blakers et al. 1984, Slater et al. 1986, Mackowski 1987, Garnett and Loyn 1992, Marchant and Higgins 1993, Marchant and