Gliding mammals of the world

There are more than 60 species of gliding mammals including the flying squirrels from Asia, Europe and North America, the scaly-tailed flying squirrels from central Africa and the glidin

Gliding Mammals

of the World

Stephen Jackson Illustrated by

Peter Schouten

The world’s gliding mammals are an extraordinary group of animals that have the ability to glide from tree to tree with

seemingly effortless grace There are more than 60 species of gliding mammals including the flying squirrels from Asia, Europe and North America, the scaly-tailed flying squirrels from central Africa and the gliding possums of Australia and New Guinea But the most spectacular of all are the colugos – or so called flying lemurs – that occur throughout South-East Asia and the Philippines

Animals that glide from tree to tree descend at an angle of less than 45 degrees to the horizontal, while those that parachute descend at an angle greater than 45 degrees Gliding is achieved by deflecting air flowing past well-developed gliding membranes, or patagia, which form an effective airfoil that allows the animal to travel the greatest possible horizontal distance with the least loss in height The flying squirrels and scaly-tailed flying squirrels even have special cartilaginous spurs that extend either from the wrist or elbow, respectively, to help support the gliding membrane

Gliding Mammals of the World provides, for the first time, a synthesis of all that is known about the biology of these

intriguing mammals It includes a brief description of each species, together with a distribution map and a beautiful full-colour painting An introduction outlines the origins and biogeography of each group of gliding mammals and examines the incredible adaptations that allow them to launch themselves and glide from tree to tree

About the author

Stephen Jackson is a behavioural and environmental ecologist who has studied Australian mammals in the wild and in

captivity over the last 20 years He has worked in a number of different roles including field ecologist, zookeeper, curator, government regulator, part-time lecturer and wildlife consultant He has published numerous scientific articles and four books

as a result of his research, with several other books nearing completion One of his books, Australian Mammals: Biology and Captive Management, was awarded the prestigious Whitley Medal for the best natural history book from the Royal Zoological

Society of New South Wales

About the artist

Peter Schouten is an acclaimed wildlife artist who has a passion for all things feathered, furred and scaled – from both present

and past He delights in painting creatures that either cannot be or have not been photographed, due to extinction or rarity He aims to draw attention to the unfortunate plight of many of these creatures and to emphasise the need for urgent conservation

He recently completed work on Feathered Dinosaurs: The Origin of Birds – a collection of images which challenges all of our

preconceived notions of those truly colossal animals of the past – the dinosaurs His spectacular paintings are keenly collected and have been widely exhibited at major galleries and museums around the world

Gliding Mammals

of the

World

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Gliding Mammals

© 2012 Text: Stephen Jackson; Illustrations: Peter Schouten.

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:

Jackson, Stephen

Gliding mammals of the world / by Stephen Jackson ;

illustrated by Peter Schouten

Web site: www.publish.csiro.au

Front cover: Squirrel Glider

Front flap: Feathertail Glider

Back flap: Red-cheeked Flying Squirrel

Back cover: Whiskered Flying Squirrel

Original artworks are available from www.studioschouten.com.au

Set in Perpetua 11.5/14

Cover design by Alicia Freile, Tango Media

Text design by James Kelly

Typeset by Oryx Publishing Pty Ltd

Printed in China by 1010 Printing International Ltd

CSIRO PUBLISHING publishes and distributes scientific, technical and health science books, magazines and journals from

Australia to a worldwide audience and conducts these activities autonomously from the research activities of the wealth Scientific and Industrial Research Organisation (CSIRO) The views expressed in this publication are those of the

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owner shall not be liable for technical or other errors or omissions contained herein The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information

Original print edition:

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Appendix 2: Gliding mammal localities 182

Appendix 3: IUCN Red List Categories 189

vi Gliding Mammals of the World

This book explores the origins, distribution and biology of the world’s gliding mammals It aims to reveal – for the first time – the extraordinary beauty, behaviour, ecology and origins of a wonderfully diverse and intriguing group of mammals that are united, not by their evolutionary history, but by their ability to glide Many of the 65 species of gliding mammals discussed here are only poorly known – even the most basic information on the biology and distribution of many species has not been adequately recorded I hope, therefore, that this book will stimulate further research and conservation of these spectacular animals Because the most significant aspect that links this group of animals together is gliding, I have included in the introductory chapter a detailed examinantion of the adaptations and behaviour associated with gliding It looks at the behaviour

of these animals during the preparation, aerial descent and landing phases of a glide, and includes a comparison of the gliding efficiency of the different groups.

In writing this book, exhaustive efforts were made to find every available published reference on the world’s gliding mammals, although not every reference was used This included extensive internet searches and visits to libraries at the Australian Museum (Sydney, Australia), the National Museum of Natural History (Smithsonian Institution, Washington DC, USA), the Natural History Museum (London, England) and the Naturalis Museum (Leiden, Netherlands) The vernacular and scientific names used here follow a major revision of the taxonomy of all gliding mammals which was undertaken by myself and Dr Richard Thorington (Smithsonian Institution, Washington DC) and published as ‘Gliding Mammals: Taxonomy of Living and Extinct Species’ in

Smithsonian Contributions to Zoology (2012) The designation of many subspecies

as species within the giant flying squirrels of the genus Petaurista remains to be

confirmed, and there is an urgent need to review their validity

A colour painting by the internationally renowned artist Peter Schouten accompanies the account of each species, revealing its distinctive features and the wonderful diversity in size, colour and shape of the various gliding mammals For a number of species the paintings are the first ever depictions in any form This fact also highlights the urgent need for further field research on these often little understood mammals The paintings used in this publication were derived from numerous photos of live specimens (where available) as well as museum specimens which the artist and author took of every species (and most subspecies) of gliding mammal from the museums mentioned above and the American Museum of Natural History (New York, USA) The photos included views of the upper and lower surfaces of the whole skins as well as close up views of the front and side of the head.

Some of the distribution maps in the species accounts were collated by adding maps from the regional or country level so that the entire distribution for each species

is shown on the one map Where subspecies are recognised within a species, the maps endeavour where possible to include the approximate distribution of each

Preface

Preface

subspecies There may be some inaccuracies in the sources of the maps and the scale used; however, they are based on the best available information at this time The measurements provided for each species offer an important aid in identification and were derived from information associated with museum specimens and the available literature in books and other published information The measurements given are as follows:

HB the length of the head and body from the tip of the snout to the cloaca

(or anus) along the ventral surface;

TL the length of the tail from the cloaca or anus to the last bone in the

tail tip;

HF the length of the hind foot from the heel to the base of the claw of the

longest toe;

M the body mass; this provides a good indicator of general size and assists

in broadly categorising the different groups of gliding mammals.

The appendices include a list of the gliding mammals found at specific locations around the world The aim of this list is to allow those interested to find out which species are located within their area, be they a tourist wishing to see these species or a scientist wishing to undertake further research It also helps

to highlight the regions that are gliding mammal ‘hot spots’ and therefore should be given particular priority for the conservation of their habitat There is also a glossary that explains some of the technical terms used and an appendix that details the more technical aspects of gliding for those who might want to explore the mechanics of gliding in greater detail.

Owing to the breadth of information used and the difficulty with which this information has been obtained, an extensive reference list has been included which has been the source of information used in this book I hope that this will serve to stimulate further research into this group of often poorly studied animals Every effort has been made to ensure the accuracy of the information used within this book by making exhaustive reference to both published and unpublished literature Readers are encouraged to make use of the primary literature by referring to the references at the end of this book Given the still unstable nature of the taxonomy for some species and the lack of information available for a number of species there are no doubt errors within the text that will be revealed in due course It is also recognised that some errors from the literature may have been continued

One of the motivations for writing this book was to highlight the need for further research to expand the knowledge of these mammals and also to highlight inconsistencies in the literature I encourage future researchers to look at species or groups across their distribution, rather than to one country, wherever possible in order to give a broader perspective and hopefully resolve some of the issues

Dr Stephen Jackson

February 2012

viii Gliding Mammals of the World

This work would not have been possible without significant assistance from a number of people First, I am truly grateful to Peter Schouten for coming on board with this project and the enthusiasm and dedication he has shown in creating the most extraordinary paintings and drawings My sincere thanks go to Richard Thorington, who provided abundant advice on flying squirrels and assisted me greatly before, during and after my visits

to the National Museum of Natural History (Smithsonian Institution) in Washington DC Thanks to James Whatton who organised x-rays of scaly- tailed flying squirrel forearms and answered my queries Thanks also to the curators of the different museums for assisting me during my visits

to take photos of the gliding mammal skins, from which the paintings of each species were completed These included Richard Thorington, Linda Gordon and Kris Helgen (Smithsonian Institution, Washington DC), Eileen Westwig (American Museum of Natural History, New York), Roberto Miguez (Natural History Museum, London) and Hein van Grouw (Nationaal

Natuurhistorisch Museum, Naturalis Museum, Leiden)

Colin Groves from the Australian National University in Canberra supported the concept of this project from the beginning and assisted greatly in providing references and shedding light on various aspects of the taxonomy of fossil and extant gliding mammals Momchil Atanassov provided significant information on the citations of fossil gliding mammals and Christopher Beard answered various questions on the taxonomy of fossil dermopterans Many thanks to Joanne Burden, Peter Stevens, Ian Renard, and Richard and Caroline Travers for translating several important manuscripts Thanks also to Yoshinari Kawamura and Tatsuo Oshida who provided a number of references that were difficult to obtain Eric Sargis provided important information and support during the writing of this text with respect to the Dermoptera Many thanks to Davide Molone for providing accommodation and useful discussions during one of my visits to the Natural History Museum in London Thanks also to Paul Andrew and Dion Hobcroft for helping with photos and information on several species Many thanks also to Anthea Gentry who provided valuable information on the history of the Arrow-tailed Flying Squirrel.

John Scheibe is gratefully acknowledged for providing valuable footage of flying squirrels, several important references and valuable advice Motokazu Ando also provided numerous references on the different species of Japanese flying squirrels and unpublished information, which has been gratefully received Important information on the scaly-tailed flying squirrels was provided by Michael Hoffman, which is much appreciated Ken Aplin provided important information on the taxonomy of the Feathertail Glider and the Greater Glider Various colleagues also read over chapters or sections

of this book depending on their areas of expertise, which has greatly helped the accuracy of this book These colleagues include: Ken Aplin, Douglas

Acknowledgements

Acknowledgements

Boyer, Greg Byrnes, Anthea Gentry, Ross Goldingay, Kris Helgen, Graeme Huxley, Norman Lim, Tatsuo Oshida, Richard Rowe, John Scheibe, Anja Schunke, Richard Thorington and Peter Zahler.

Several libraries and their associated staff were very helpful in bringing the enormous literature that this project required together These include Carol Gokce, Paul Cooper, Eliza Walsh, Kirsten Marshall, John Rose and Emma Solway from the Natural History Museum in London, who provided many

of the references and assisted me during my first visit to the library Nicola Gamba, Paul Cooper, Lisa Di Tommaso, Samantha Gare, Nadja Noel, Kamila Reekie, John Rose and Angela Thresher assisted me during my second visit

to the Natural History Museum Thanks also to Therese Nouaille-Degorce and Evelyne Bremond-Hoslet from the Bibliothèque Centrale du Museum National d’Histoire Naturelle in Paris for providing a number of valuable references Great thanks also to the staff at the libraries of the National Museum of Natural History (Smithsonian Institution, Washington DC) including Martha Rosen, Leslie Overstreet, Daria Wingreen-Mason and Kirstin van der Veen, who helped me enormously in finding and copying references for this project Thanks also to the staff of the National Museum

of Natural History Naturalis in Leiden, including Tom Gilissen, Marianne van der Wal and Agnes Bavelaar for all their help Many thanks also to the Australian Museum and staff including Fiona Simpson, Anina Hainsworth, Fran Smith and Leone Lemmer Thanks also to Rose Bollen and Leonie Cash from the Museum Victoria library for their help in providing access to some historical images.

My gratitude is also extended to Nick Alexander and CSIRO Publishing for their great support of this project Finally a sincere thank you to Kerstin, Olivia and James for all their encouragement and entertainment during the writing of this book.

This book is dedicated to my mother, Dorothy ‘Jill’ Jackson, who passed away before this book was finished, and my father who both encouraged this project from the beginning and continue to inspire

Gliding Mammals of the World

Pseudocheiridae

DERMOPTERA

Cynocephalidae

RODENTIA

Sciuridae, Pteromyini

List of species

List of species

Petaurista albiventer White-bellied Giant Flying Squirrel 112

Petaurista alborufus Red and White Giant Flying Squirrel 114

Anomaluridae

Anomalurops beecrofti Beecroft’s Scaly-tailed Flying Squirrel 168

Anomalurus derbianus Lord Derby’s Scaly-tailed Flying Squirrel 170

Anomalurus pusillus Dwarf Scaly-tailed Flying Squirrel 174

Idiurus macrotis Long-eared Scaly-tailed Flying Squirrel 176

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Intr

2 Gliding Mammals of the World

The world of gliding

The world’s gliding mammals are a diverse group of animals that have the

unusual ability to glide from tree to tree with seemingly little effort They do

this by launching from the upper branches or trunk of a tree and spreading

out their specially adapted gliding membranes, which stretch from the sides

of their body between their fore and hind limbs This allows them to glide

silently through the night air for a considerable distance – some species are

able to glide for more than 100 metres During these glides they can twist and

turn around obstacles to make a safe landing on a target tree without the need

to come to the ground.

There are currently 65 recognised species of gliding mammals from six different

families There are three families of gliding marsupials that live in Australia,

New Guinea and surrounding islands These families include the Feathertail

Glider (Family Acrobatidae), the gliding possums of the genus Petaurus (Family

Petauridae), and the Greater Glider (Family Pseudocheiridae) However, by far

the greatest diversity of gliding mammals occurs in the Order Rodentia, where

they are represented by the flying squirrels belonging to the Family Sciuridae

and the unrelated scaly-tailed flying squirrels of the Family Anomaluridae The

Sciuridae includes all the tree and ground squirrels with some 51 genera and

278 species in total Of these, the flying squirrels comprise 15 genera and 49

species, and are found throughout Asia, Europe and North America The family

of scaly-tailed flying squirrels that live in central and western Africa has seven

species, although one species does not glide Gliding reaches its most spectacular

and efficient in the two species of colugos, also known as flying lemurs, of the

Order Dermoptera, which occur throughout South-East Asia.

Animals that glide between trees descend at an angle less than 45° to the horizontal,

while those that parachute descend at an angle greater than 45° Gliding is achieved

by deflecting air flowing past a well-developed gliding membrane, or patagium,

on each side of the body These membranes convert the animal’s body into an

effective airfoil, allowing it to travel the greatest possible horizontal distance with

the minimum loss of height The flying squirrels and scaly-tailed flying squirrels

even have special cartilaginous spurs that extend either from the wrist, or elbow

respectively, to help support their gliding membranes

In addition to mammals and birds, gliding has evolved independently as a form

of locomotion in several groups of arboreal and even aquatic vertebrates

These include flying fish of the Family Exocoetidae (from which we get the

name Exocet missile), which have either two enlarged pectoral fins or even four

enlarged fins (both pectoral and pelvic) to act as wings These modifications

allow them to make glides of over 60 metres above the water to escape from

predators and potentially save energy

The flying snakes of the genus Chrysopelea (and possibly the genus Dendrelaphis)

of the Family Colubridae have developed a form of gliding by flattening and

broadening their body like a ribbon through the use of hinged ventral scales,

and by drawing in the belly so that it forms a concave surface when they leap

out of trees.

Flying geckos of the genus Ptychozoon, fringed geckos of the genus Luperosaurus,

and house geckos of the genus Cosymbotus (Family Gekkonidae) jump from tree

The Japanese Flying Squirrel weighs about

200 grams and is capable of gliding up to

100 metres.

Introduction 3

Non-mammal vertebrates that have evolved

the ability to glide include (from the top)

the flying lizard (Draco), the flying gecko

(Ptychozoon), the flying snake (Chrysopelea),

the flying fish (Exocoetidae) and the flying frog

(Rhacophorus).

to tree aided by webbed feet, flaps or folds of skin along the lateral body wall, and dorso-ventrally flattened tails that increase their horizontal surface area Among the reptiles, however, the development of gliding reaches its pinnacle

within the gliding lizards of the genus Draco (Family Agamidae) The ribs of these

species are greatly elongated to create a large gliding surface, which folds against the sides of the body when not in use When these lizards jump from a tree, they spread their ribs to stretch out the gliding membrane and can make glides of over 30 metres.

A variety species of frogs from three families are known to parachute or potentially glide These include various species of flying frogs from the genus

Rhacophorus and some of the whipping frogs of the genus Polypedates (Family

Rhacophoridae) from South-East Asia Several species of South American frogs

of the Family Hylidae have extensive webbing including the Gliding Leaf Frog

(Agalychnis spurrelli), limbed Treefrog (Hyla miliaria) and Rabb’s limbed Treefrog (Ecnomiohyla rabborum) and may also have the ability to glide

Fringe-Various other frogs are known or thought to undertake controlled aerial descent

including Hyperolius castaneus (Family Hyperoliidae) that occurs in tropical and

subtropical forests of central Africa The most developed frogs typically possess enlarged toes that have well developed webbing between them, with some species from the old world even having flaps of skin on the forelimbs and hind limbs to help trap air during descent While the frogs with the most highly developed webbing may be able to truly glide, most species are more accurately described as parachuters Nonetheless, the aerial control of these frogs is often

so well developed that they can even make banked 180° turns.

Gliding adaptations

The two things (which may be related) that link every species of gliding mammal together are their nocturnal behaviour and their ability to glide Despite the diversity of their origins, the different groups of gliding mammals show a remarkable degree of convergence in relation to their gliding adaptations and behaviour But how do these animals undertake this extraordinary method of locomotion and how far can they glide?

The patagia, or gliding membranes, of mammals consists of skin with two layers bound together tightly by connective tissue with muscles and nerves between There are four types of patagia: the propatagium, the digipatagium (or dactylopatagium), the plagiopatagium and the uropatagium.

The propatagium (or neck membrane) attaches on each side of the neck and along the anterior edge of the forelimbs of the glider This patagium is most developed in the colugos and little developed or absent in other gliding mammals The digipatagia are found only in the two species of colugos and consist of membranes between each of the five digits on both the front and the hind feet The plagiopatagium (or flank membrane) is the primary gliding membrane and is found in all species of gliding mammals It extends between the forelimbs and hind limbs, and is under good muscular control When the glider is climbing, resting or sleeping the plagiopatagium remains mostly hidden in the fur of the glider’s flanks The exception to this can be found in the colugos, whose movements are somewhat inhibited by their overly developed

Gliding Mammals of the World

4

flank membranes The uropatagium (or tail membrane) extends between the

posterior surface of the hind legs and the tail Only the larger gliding mammals

which weigh more than approximately 1 kilogram have these tail membranes

The uropatagium can range from completely enclosing the tail in the colugos,

to including the proximal third of the tail in the large flying squirrels, to being

absent or rudimentary in the smaller gliding mammals Despite the variation in

patagium design, its surface area in relation to body mass remains remarkably

consistent with body size, regardless of the taxonomic group considered.

In the gliding possums of the genus Petaurus, the plagiopatagium extends from

the joint of the second and third bones in its fifth digit of the front paw to the

metatarsal region in the ankle of the foot A similar arrangement is found in the

plagiopatagium of the flying squirrels, although they possess a thin cartilaginous

spur (called a styliform cartilage) that extends from the pisiform bone in the

wrist The extended cartilage increases the size of the patagium, stiffens and

supports it and helps unfold its lateral leading edge When not gliding, the

cartilage is folded back and held against the forearm.

The scaly-tailed flying squirrels, which are unrelated to other flying squirrels,

have an unciform cartilage that originates from the olecranon process of the

ulna in the forearm (near the elbow) and helps support the leading edge of the

plagiopatagium, effectively increasing the size of the patagium The development

of a styliform or unciform cartilage has allowed these species to evolve a wider

membrane, independent of the length of the bones of the forelimbs.

The Greater Glider is unique among marsupial gliders because it has a very

small accessory cartilaginous spur that extends from the olecranon process near

the elbow Its olecranon is also greatly elongated, extending considerably past

The outline of the patagia and tail shapes of all genera of gliding mammals Top row: Acrobates pygmaeus, Petaurus breviceps, Petauroides volans, Aeretes

melanopterus, Aeromys tephromelas, Belomys pearsoni, Biswamoyopterus biswasi, Euglaucomys fimbriatus Middle row: Galeopterus variegatus, Cynocephalus volans, Eupetaurus sp., Glaucomys sabrinus, Hylopetes nigripes, Iomys horsfieldi, Petaurillus emiliae Bottom row: Idiurus zenkeri, Anomalurops beecrofti, Anomalurus pelii, Petaurista leucogenys, Petinomys genibarbis, Pteromys volans, Pteromyscus pulverulentus, Trogopterus xanthipes.

The cartilaginous spurs of gliding mammals form ‘winglets’, rather like those of an aircraft, which redirect the forces of induced drag laterally at the wing-tip and allow greater flying efficiency.

Introduction 5

its elbow joint The animal glides by holding its paws under its chin so that its elbows extend out to the sides at right angles to the rest of its body, thus helping

to increase the surface area of the plagiopatagium.

The curved styliform cartilage of the flying squirrels, unciform cartilage of the scaly-tailed flying squirrels, and inflected wrists of the petaurids and colugos form ‘winglets’ at the end of their forelimbs There is remarkable similarity in the front appearance of the different groups of mammals as each group has independently come to the same evolutionary conclusion that winglets provide

a valuable aeronautic advantage Many birds, as well as modern aircraft, use these winglets to increase the efficiency and stability of their flight

So how do these winglets work? They increase the effective width of the patagium and play an important role in the control and manoeuvrability of the glider The near-vertical bending back of the winglet reduces turbulence at the leading edge of the patagium by redirecting the airflow from a downward directional force to a more lateral direction This reduces the ‘drag’ that is created at the front edge of the gliding membrane where the high pressure below the wing ‘leaks out’ around the tip and produces a downward force to the wing, enabling the animal to more efficiently maintain lift The winglets alter the airflow at the wing-tips and increase the effectiveness of the wing without materially increasing the wingspan They smooth the airflow across the upper wing near the tip and reduce the strength of wing-tip vortices, thus improving the lift-to-drag ratio The changes in airflow also enhance the stability of the glider by reducing ‘rolling’ and ‘yawing’ about the centre of gravity in the glider Aeronautical engineers have determined by experiment that aircraft winglets can reduce drag by approximately 20 per cent and increase the lift-to-drag ratio by approximately 9 per cent

There are other adaptations in the marsupial gliders of the genera Petaurus and Petauroides that improve their gliding ability The skeletons of the smaller

gliding possums show a slight elongation of the bones of the limbs and virtually

no elongation of the tail, compared to similarly sized non-gliding possums

The Greater Glider too has developed comparatively longer bones in both its

forelimbs and hind limbs, compared to its similarly sized non-gliding relatives, the ringtail possums

Unlike the other marsupial gliders, the Feathertail Glider shows no marked elongation of its vertebrae or limb bones, suggesting that in such small animals the presence of the patagium alone is sufficient to provide the necessary increase

in surface area, although this is no doubt assisted by its feather-like tail

The forelimbs and hind limbs of the flying squirrels are also relatively longer than those of similarly sized non-gliding arboreal squirrels As a result of the elongation of the bones in gliding mammals, the shape of the patagium has a roughly square shape compared with non-gliders which, if a patagium were stretched over their limbs, would have a rectangular shape The square shape provides a proportionally greater surface area resulting in more lift and less drag than would a rectangular-shaped patagium In addition, the square shape allows the glider to land at a relatively slower speed and with a high angle of attack, where the head is up and the feet are forward, instead of a low angle of attack, where the animal glides head first.

From top to bottom: The bones of the forearm

and the styliform cartilages of the Siberian

Flying Squirrel, the unciform cartilage of

Lord Derby’s Scaly-tailed Flying Squirrel, and

the extended olecranon at the elbow of the

marsupial Greater Glider

Gliding Mammals of the World

6

The Indochinese Flying Squirrel has a flattened bushy tail which appears to help with ‘pitch’ control during a glide.

The shape of the tail of gliding mammals ranges from feather-like tails for the

smallest species, to bushy, flattened tails or bushy, rounded tails with shortened

fur for medium-sized mammals, to bushy, rounded tails with fluffy fur for the

largest species

Gliding mammals weighing approximately 30 grams or less, such as the

marsupial Feathertail Glider (Acrobates), pygmy flying squirrels (Petaurillus)

and pygmy scaly-tailed flying squirrels (Idiurus) typically have feather-like tails

(known as ‘distichous tails’) which are dorso-ventrally flattened The presence

of a flattened tail appears to help the longitudinal (or ‘pitch’) control during

gliding The Feathertail Glider, for example, has a relatively narrow gliding

membrane along the sides of its body, between the elbow and the knee However,

the effective patagium surface area is increased by long hairs that form a fringe

along the margin of its tail.

The intermediate-sized gliders (weighing more than 30 grams to about 450

grams) have a range of tail types The Arrow-tailed Flying Squirrel has a distichous

tail, while the Hairy-footed Flying Squirrel has a tail that is more thickly furred

but flattened A number of species of the smaller marsupial gliders of the genus

Petaurus and the Dwarf Scaly-tailed Flying Squirrel have a rounded, bushy tail.

Those species weighing more than about 450 grams, with the exception of

the two species of colugos, have rounded, bushy tails, including the marsupial

gliders (Petaurus and Petauroides), the giant flying squirrels (Petaurista), the large

flying squirrels (Aeromys), and the woolly flying squirrels (Eupetaurus), and the

larger scaly-tailed flying squirrels (Anomalurus)

Within those genera whose species have a large variation in body mass there

is typically a degree of variation in tail morphology For example, the smaller

marsupial Sugar Glider has a less bushy tail than the larger heavier members

of the genus Similar observations have been made in the arrow-tailed flying

squirrels (Hylopetes) and dwarf flying squirrels (Petinomys) The smallest dwarf

flying squirrels, such as Temminck’s Flying Squirrel and Vordermann’s Flying

Squirrel, have distichous tails, while heavier species, such as the Whiskered

Flying Squirrel, have compactly furred but flattened tails The still heavier

Hagen’s Flying Squirrel and the Siberut Flying Squirrel, as well as the even

larger Mindanao Flying Squirrel, have bushy, rounded tails.

The ventral tail scales of the scaly-tailed flying squirrels (from left to right):

Pel’s Scaly-tailed Flying Squirrel, Lord Derby’s Scaly-tailed Flying Squirrel, Dwarf Scaly-tailed Flying Squirrel, Beecroft’s Scaly-tailed Flying Squirrel, Long-eared Scaly-tailed Flying Squirrel, Pygmy Scaly-tailed Flying Squirrel.

Introduction 7

Scaly-tailed flying squirrels have relatively long tails whose underside contains

an area of rough, overlapping scales near the base, extending from one-fourth

to one-third the length of the tail It has been proposed that these scales are an ‘anti-skid’ device which the animal uses during landing or climbing The potential for the scales to be actively involved in landing appears to

be supported by observation of these species in the wild that, when the anomalures land, the tail makes a loud clacking sound as it slaps the tree trunk and digs into the bark The tail appears to play only an incidental role

in climbing as the animal does not put its whole body mass onto the scaly tail while climbing, but appears to use it when it is resting.

On the other hand, it has been proposed that the eyes of flying squirrels are placed far to the sides of the head in order to provide a wider field of vision to detect predators This eye placement restricts the field of visual overlap to the front and therefore limits depth perception

Most species of gliding mammals hold their head low in preparation for a launch, crouching down to allow a greater spring off The giant flying squirrels curl their tails tightly like a watch spring and move it up and down quickly three or four times before jumping The marsupial Yellow-bellied Glider has been seen to run along a slender branch and leap without pause to an adjacent tree Similarly Hodgson’s Giant Flying Squirrel may take a short, hobbling run before launching itself into the air to gain momentum for the glide.

During the launch phase, the glider typically raises its tail and kicks into the air with its hind limbs to provide additional momentum Most gliders spread their forelimbs and hind limbs out at right angles to the body quickly after taking off The scaly-tailed flying squirrels, however, appear to wait until they have dropped a metre or more and gained momentum, before stretching out their limbs After take-off, the animal is subject mainly to the force of gravity until its patagium is deployed and begins to generate aerodynamic lift Once its patagium is spread out, the gliding phase begins as aerodynamic forces come into play.

The Taiwan Giant Flying Squirrel curls its tail up

tightly as it launches itself into a glide.

Gliding Mammals of the World

8

Although most gliders launch from a stationary position on a roughly horizontal

surface, the colugos typically launch by jumping backwards from a tree trunk

Once in the air they rotate their body and spread their patagia When feeding

at the end of a branch, the Malayan Colugo has been seen to initiate a glide

without leaping; it just lets go and rotates its body into the glide

There are three main types of glide: the most common is the ‘S-shaped’ glide in

which the glider leaps from the tree, gains a bit of elevation before it assumes a

downward path; the little used ‘J-shaped’ glide in which the animal dives from

the launching place, loses elevation quickly, and then pulls out of the glide to a

more horizontal angle of descent; and the ‘straight-shaped’ glide which involves

launching at approximately the angle of descent of most of the glide

During the glide, the animal must exert some control over the orientation and

stability of its body in order to maintain or adjust its flight direction and angle

of descent so that it will reach a particular destination To maintain a steady

trajectory and avoid spinning or tumbling out of control, it must correct any

inadvertent perturbations that cause its body to rotate At the same time it

must initiate limb movements in order to execute deliberate manoeuvres

The control over the orientation of its body occurs around three axes – in

aerodynamic terms, the roll, the yaw and the pitch.

The gliding possums and flying squirrels glide with their forelimbs and hind

limbs fully extended at right angles to the rest of the body, and their forefeet

flexed slightly upward In contrast, the Greater Glider completes its glides

with its forefeet tucked under its chin and its elbows extended out to the

sides A disadvantage of having the limbs in this position is that the glider

appears to be less manoeuvrable

Most gliding mammals, especially the smaller species, have a remarkable

ability to steer during a glide, allowing them to land accurately at the desired

location They do this by changing the position of the limbs and the tension of

the muscular gliding membrane A left turn is accomplished by lowering the left The gliding stages of the Malayan Colugo.

A Malayan Colugo often launches itself into a glide by jumping backwards from a tree.

Introduction 9

forelimb below the right This increases drag against the left membrane and the glider is spun into a turn It has been suggested that the tail of gliding mammals helps steering by acting as a rudder, which may be partly the case for the smaller species with feather-like or flattened tails It is more likely, especially in the larger species of gliding mammals (except for the colugos), that the tail trails behind the body and either acts to create drag, helping the animal to balance by acting as a stabiliser (similar to the tail on a kite) or that the tail acts to reduce turbulence and drag at the posterior margins of the animal.

During long glides the animal sometimes needs to steer around obstacles such

as non-target trees and branches Most species of gliding mammals are able to

‘bank’ (make turns of 90° or less) and even make a U-turn For example, the Mahogany Glider, Sugar Glider, Greater Glider, Yellow-bellied Glider, giant flying squirrels, Southern Flying Squirrel and the scaly-tailed flying squirrels are all able to make acute turns Due to the increased drag required to make a turn, the animal has to trade the total glide distance for each turn (depending

on the angle) it makes.

Remarkably, it has been claimed that an Arrow-tailed Flying Squirrel was seen to gain 1 metre in elevation over a distance of 6 metres by using vigorous flapping movements of the skin between the fore and hind feet, leading to the idea that active flight developed from gliding flight However, there is considerable doubt about the validity of this observation and it is likely that such movements would dramatically reduce the glide distance Gliders are structurally and aerodynamically different from active fliers A flapping motion by a glider would modify the shape of the patagium causing major shifts in the location of the centre of lift relative to the animal’s centre of mass, thus creating serious problems with stability and lift.

When approaching the landing point the glider moves its forelimbs and hind limbs down and forward, which traps air and creates maximum air resistance This movement allows the patagium to billow like a parachute until the angle

of attack increases from an approximately horizontal position to over 60° and causes drag, via induced turbulence This results in deceleration and allows the glider to make a slight swoop upwards several metres before landing

The gliding stages of the Northern Flying

Squirrel

A Northern Flying Squirrel grabs hold of a tree

with its forehands, as it completes its glide.

Gliding Mammals of the World

10

As the upward swoop continues, the drag increases until the glider stalls

and loses height due to gravity Just before landing, the angle of the body

of the glider increases further to approximately 90° to the horizontal so the

glider is roughly parallel with the tree trunk on which it lands Sometimes the

transition and braking phases of the glide are eliminated so there is no upward

swoop This typically occurs during a shorter glide which has a higher angle of

descent and results in a relatively harder impact when the animal lands.

On landing, the glider usually makes initial contact with the landing point with

its forelimbs as its claws grab hold of the tree This causes the mass of the animal

to rotate downward and its hind limbs make contact shortly afterwards Making

use of all four limbs further reduces the landing forces by spreading the impact

more evenly over the body The Feathertail Glider, and probably the similar

sized smaller gliders, brings its tail well forward before landing, making its body

into somewhat of a parachute.

Apart from the sound of the strong claws gripping the bark, the landing – like

the rest of the glide – is typically almost silent The scaly-tailed flying squirrels,

however, have been reported to land relatively noisily due to the scales on the

tail, and the Greater Glider typically lands with a ‘clop’.

When leaping from tree to tree Lord Derby’s Scaly-tailed Flying Squirrel

assumes the shape of a small umbrella The animal prefers to land on a tree

trunk rather than on the branches of a tree Immediately before reaching the

trunk, its head is at a lower level than the tail, but at the last moment, it

throws its forelegs back over its shoulders, its head comes up, and its tail

sweeps up to meet its head over its back The result is that the whole animal

assumes a vertical position in mid-air Momentum carries it on to the upright

trunk, to which it immediately adheres, before it starts to ascend, using its

front feet together, then pulling up its hind feet and arching its back like a

giant looping caterpillar At the same time, it digs the backwardly directed

scales at the base of its tail into the bark as an added means of support, while

it releases its forefeet and moves upward It can gallop up the smooth trunk of

a giant forest tree at an astonishing speed.

Gliding distance and body mass

The distance an animal glides appears to determine the impact on the tree upon

which it lands Longer glides allow the animal to re-orient the aerodynamic

forces on its body before landing, allowing it to reduce its speed and thus

landing forces, although there are contradictory studies on the landing forces

of gliding mammals A study of captive Northern Flying Squirrels discovered

that they exert between one and 10 times their body weight during take-off

and between three and 10 times their body weight during landing This study

also found increasing forces with increasing glide distance, although these were

over relatively short distances so the flying squirrels may not have been able to

perform a complete braking phase in preparation for landing By contrast, other

research on the wild Malayan Colugo over longer glide distances discovered that

landing forces are greatest for the shorter glides and less for longer glides The

ability of an animal to reduce its velocity before landing allows gliding mammals

to travel long distances between trees with reduced risk of injury.

Lord Derby’s Scaly-tailed Flying Squirrel can move up the trunk of a forest tree at an astonishing speed.

Introduction 11

The relationship between the body mass of

different species of gliding mammals and their

glide distances.

Most gliding mammals, such as this

Sugar Glider, fall into the mass range of

100–500 grams.

The limited data available suggest that among the gliders there is a remarkably consistent angle of descent, which is reflected in the consistent relationship between the body mass and patagium surface area There should also be a most efficient body mass for a species to use gliding and, as the body mass increases or decreases from the optimum, it should become increasingly less efficient until it reaches the upper or lower bounds As the body mass exceeds these thresholds

it becomes too large or small so gliding is no longer advantageous over climbing between destinations.

A comparison of body mass of every species of gliding mammal suggests that the most common body mass range is approximately 100–500 grams, with the next most common being less than 100 grams The difference between climbing horizontally and gliding energy may explain, in small part, the body mass distributions of gliding mammals Above approximately 400 grams, the requirement for gliding has been predicted to decrease until the upper mass limit

is reached, which is approximately 2500 grams This prediction is supported

by research that compared the energetic costs of climbing horizontally to the energetic costs of climbing vertically (required to obtain enough height to glide), in order to achieve the same horizontal distance This study calculated that gliding mammals weighing 400 grams achieve the greatest energetic savings over climbing horizontally, whereas gliding mammals substantially smaller or larger than 400 grams should expend roughly similar energy climbing vertically

to glide as their non-arboreal counterparts do climbing horizontally These observations are supported by the body masses of almost all known species of gliding mammals, which are typically below 2000 grams, with the exception of the Bhutan Giant Flying Squirrel which has been recorded up to 2700 grams.

The relationship between glide distance and body mass suggests that larger gliders must glide further than smaller gliders to save energy over climbing

1–10 11–20 21–30 31–40 41–50 51–60 61–70 71–80 81–90 91–100 100+

Sugar Glider (100 g) Northern Flying Squirrel (130 g) Siberian Flying Squirrel (150 g) Squirrel Glider (230 g) Mahogany Glider (380 g) Yellow-bellied Glider (600 g) Japanese Giant Flying Squrrel (1100 g) Malayan Colugo (1500 g)

Glide distance (metres)

Gliding Mammals of the World

12

horizontally Several glider studies have shown that in order to achieve this,

larger gliders launch higher and glide longer in order to minimise the angle

of descent Therefore short distances are more likely to be reached using

quadrupedal motion by larger gliders than small ones In contrast, small

gliders can be energetically cost effective with steeper glides than larger

gliders so glide short distances more often These observations are supported

by the limited number of studies that show an increase in the average glide

distance with increasing body mass.

Calculations of the relationship between angle of descent and body mass suggest

that gliders weighing less than 19 grams need not have an angle of descent less

than 45° to be cost effective, and can therefore use parachuting and still expend

less energy than required to climb between two points The implication of this

is that gliding membranes are unnecessary for very small mammals Despite

this proposal, several species of gliders do exist that weigh less than 19 grams,

though typically with less developed patagia and uniquely feather-like tails

Marsupial gliders have been observed to glide from less than 10 metres to more

than 100 metres, while the flying squirrels have been recorded to glide more

than 150 metres There are few records of glide distances in scaly-tailed flying

squirrels, although there is one anecdotal record of an individual that glided an

amazing 250 metres over the entire length of an open valley The colugos appear

to be able to consistently glide further than all other gliding mammals with the

help of their extremely well-developed gliding membranes A colugo has been

observed to glide 136 metres with a loss in altitude of only 12 metres.

A detailed view of the different species of Australian gliding marsupials

reveals that heavier species, such as the Yellow-bellied Glider and Mahogany

Glider, make longer glides and launch higher in the tree canopy than smaller

species, such as Sugar Gliders, that typically glide between the mid to lower

canopy Sugar Gliders in southern Australia spend most of their time in the

mid-stratum of the forest in vegetation 10–20 metres high that contains Acacia

trees, while the larger Squirrel Glider spends more time in the upper strata

at 25–30 metres in height Although all gliding mammals make short glides,

it appears that heavier species prefer to climb short distances when there

are interconnecting canopies rather than glide; they launch from a higher

elevation in more open habitat where longer, faster glides can be made In

contrast, smaller species seem to prefer making shorter glides from the mid

to lower storey with a higher tree density and where the turbulence caused

by wind is less These observations suggest that as body mass increases above

the optimal body mass for gliding, the need for longer glides increases as they

are more cost-effective (and maintain glide efficiency), and short distances are

more likely to be traversed by climbing.

Origins and evolution

In order to better understand the different species of gliding mammals that exist

today and where they have come from, we need to look at the hidden treasures

of the fossil record This will help us to understand how the present-day gliding

mammals evolved and where they previously occurred.

The Bhutan Giant Flying Squirrel can weigh nearly 3 kilograms, which is at the upper theoretical limit for gliding efficiency.

Introduction 13

The age of the fossil record of the different groups of gliding mammals varies enormously, ranging from as far back as the early Eocene (50 mya) for the scaly- tailed flying squirrels to the late Eocene (40 mya) for the flying squirrels The fossil record of the enigmatic colugos also appears to extend as far back as the Eocene (50 mya) The gliding marsupials have more recent origins with the fossil record dating back to the late Oligocene to Early Miocene (approximately 24–18 mya).

In addition to the groups of gliding mammals we know today, there are at least three extinct species of gliding mammals from different families that have no surviving relatives The first extinct glider is from the Family Gliridae This

species, Glirulus lissiensis (meaning ‘little dormouse from Lissieu’), was first

collected from the upper Miocene (c 10 mya) deposits in Lissieu, France, and was initially described in 1965 as a non-gliding rodent However, subsequent discoveries of similar fossils from the upper Miocene deposits of Saint-Bauzile (Ardèche) in southern France indicate the presence of a gliding membrane

This species appears to be a distant relative of the Japanese Dormouse (Glirulus

japonicus), which is a non-gliding arboreal rodent and the only surviving

member of this genus that lives in the montane forests of Japan The anatomy

of the fossil glider differs slightly from living forms by the proportions of the segments of the limbs and the greatly elongated bushy tail which is typical of gliding mammals of that size.

Another extinct glider with no subsequent gliding relatives is from the extinct rodent Family Eomyidae, which once had a wide distribution in North America, Europe and Asia The modern rodent groups that are most closely related to this family include the New World pocket mice (Family Heteromyidae) and the

A reconstruction of Glirulus lissiensis, a gliding

rodent from Miocene deposits in France.

Gliding Mammals of the World

14

The geological timescale in millions of years (mya) during the ‘Age of Mammals’, which begins after the Cretaceous Period.

pocket gophers (Family Geomyidae) So far, the only gliding species found of

this family is the early or dawn mouse Eomys quercyi from Oligocene deposits

in Quercy in southern France When described in 1987, it was not at first

recognised as a gliding species, and it was not until 1996, after a well-preserved

specimen was discovered from Oligocene deposits in Enspel, Germany, that

it was identified as a glider Eomys quercyi was approximately 20 centimetres

in length, with its gliding membrane having a low wing loading thus giving it

a manoeuvrability which allowed slow glides in densely forested areas where

there is little air turbulence Abundant fossils of leaves, fruits and seeds where

the rodent was found suggest it inhabited a thick mesophytic forest, which was

widespread in western and central Europe during the late Oligocene.

In 2006 another extinct species of gliding mammal, Volaticotherium antiquus or

‘ancient gliding beast’, was discovered from Inner Mongolia This incredibly

strange creature is so unusual that it has no known relatives and has been

placed in its own family known as the Volaticotheriidae within a new Order

of mammals, called the Volaticotheria This species is also the oldest species

of gliding mammal ever found It extends the earliest record of gliding for

mammals to the Cretaceous some 125 mya This is 75 million years older than

any previously discovered gliding mammal Volaticotherium antiquus was the size

of a squirrel and had an estimated body mass of about 70 grams, similar to that

of the modern Southern Flying Squirrel from the United States of America.

A fourth species of extinct mammal that has been proposed to be a glider is an

undescribed marsupial from Palaeocene deposits (65–56 mya) in Brazil The

conclusion that this species was a glider was derived from features of the humeri

and femora including its exceptionally long and slender structure, similar to

living gliding mammals.

The evolution of gliding

Why did gliding evolve in the first place? There are three primary theories to

explain the evolution of gliding: (a) predator avoidance, (b) optimal foraging,

and (c) cost of foraging.

The ‘predator avoidance’ model suggests that gliding locomotion, nesting

in cavities and nocturnal behaviour reduce the chance of predation Some

evidence supports this as gliding mammals appear to live significantly longer

than non-gliding species Other evidence suggests that predation by birds may

have limited gliding mammal diversity; all species of gliding mammals are

active at night which may be due to the lower number of nocturnal predators

However, it has been proposed that although gliding may provide flying

squirrels with an escape from mammalian and reptilian predators, they may

actually suffer increased levels of predation from owls This is because, despite

being able to make turns during their glides, they are relatively clumsy in the

air compared to the high manoeuvrability of night predators such as owls

Gliding mammals often appear to choose their landing site cautiously before

launching and do not appear to be readily adapted to quickly launching in

order to escape predators Observations that support this include predation

of an estimated 500 Northern Flying Squirrels by Spotted Owls ( Strix

occidentalis ) in a single year and predation of approximately 120 Sugar Gliders

A reconstruction of Eomys quercyi, a gliding

eomyid rodent from Oligocene deposits in Germany.

Introduction 15

by seven breeding pairs of Powerful Owls (Ninox strenua) in a single breeding

season The gliding marsupials may differ from the colugos, flying squirrels and scaly-tailed flying squirrels, as their ancestors were almost certainly already nocturnal, then developed a gliding membrane Whereas at least some

of the eutherian gliding mammals may well have been diurnal, then developed

a gliding membrane and subsequently become nocturnal Either that or the ancestral squirrels were all nocturnal and some of them subsequently became diurnal.

The ‘optimal foraging’ hypothesis argues that gliding locomotion reduces travel time between patches of food Some food types such as nectar, pollen and fruit are typically located in patches which are spread out within the forest, while other food types such as foliage are more ubiquitously available and more clumped together Many gliding mammals use patchily distributed food resources and gliding locomotion allows these animals to forage more quickly and over a wider area than would otherwise be possible by climbing alone In habitats where food is limited and widely spread, adaptations such as gliding may increase mobility and therefore food harvesting rates of the different dietary food items

The ‘cost of foraging’ hypothesis proposes that gliding locomotion is energetically less expensive than quadrupedal locomotion and therefore allows an increased foraging radius The most energetically expensive part of transport is climbing

up tree trunks or vertical branches, so gliders save energy by gliding from tree to tree instead of running down the tree and climbing or running to the next tree During gliding, the animal makes use of potential energy gained during previous climbing up the tree and uses little energy to control and manoeuvre during gliding Thus gliding is theoretically an energetically cheaper way of moving from one place to another, and also much quicker than running or climbing

Apart from allowing the ability to glide, gliding membranes can have other advantages For example, a trapped Mahogany Glider has been seen to pull its patagium over its head, somewhat like an umbrella, when it was raining And some flying squirrels have been observed using their patagia apparently

as a blanket, wrapped around their bodies, presumably to protect themselves from heat loss Similar observations have been made on the Greater Glider During hot weather, the large surface area of the patagium could also allow more effective heat dissipation, enabling the glider to cool down more quickly Gliding membranes thus bring a number of advantages to these animals; however, it remains that their forelimbs are not greatly specialised and remain useful for climbing and the manipulation of food, unlike the forelimbs of true flying animals.

Structural attributes of forests

In addition to the theoretical triggers for the evolution of gliding, the structure of the forests also appears to have been important in facilitating the evolution of gliding, although there are no consistent trends between the different groups of gliding mammals For example, gliding in the Australian possums has historically been thought to have evolved due to the opening

Reconstruction of Volaticotherium antiquus, a

gliding mammal from Cretaceous deposits in

China.

Gliding Mammals of the World

up of the vegetation as Australia dried out during the late Miocene some

10 million years ago Nonetheless the evolution of gliding within Australia’s

rainforests cannot be ruled out as the Northern Glider is found at an elevation

of approximately 1000 metres in undisturbed rainforest on Mount Somoro in

the Torricelli Mountains of northern New Guinea The rainforest origins are

possibly supported by the theoretical split of Petaurus gliders from non-gliding

possums some 20 million years ago when there was widespread rainforest and

other broad-leaf forest types, although the occurrence of eucalypts and acacias

suggests that sclerophyllous communities were becoming more widespread

Further strong support for the evolution of gliding in rainforest is provided

by the fact that most of the other gliding vertebrates are largely restricted

to rainforest; however, their biogeographical distribution in tropical forests

is not uniform For example, the colugos, which are by far the most

well-developed gliding mammals, live in evergreen rainforests of South-East Asia,

while most of the flying squirrels in South-East Asia and the scaly-tailed

squirrels of tropical Africa also occur in rainforest In contrast to the marsupial

Northern Glider, the other gliding marsupials live in relatively open eucalypt

woodlands Similarly the American Northern Flying Squirrel and Southern

Flying Squirrel live in open coniferous and mixed woodlands and the flying

squirrels of Japan and Europe typically occur in coniferous, broad-leaved or

mixed forest with evergreen and deciduous trees.

The overlapping tree crowns in tropical forests often give the illusion of a

continuously connected canopy; however, the mid and lower storeys consist

largely of open space that promotes the selection of long-distance gliding,

especially where lianas to link up adjacent trees are scarce As a result, the

distribution of gliding species in tropical rainforests appears to be correlated

with differences in canopy structure and particularly liana density

Ground-level liana densities have been shown to be highest in tropical African forests,

somewhat lower in non-tropical rainforests, and lowest in Indo-Malayan

forests It has been suggested that prehensile-tailed vertebrates are favoured in

African and especially South American forests where they can bridge canopy

gaps using lianas, whereas in the relatively more open Asian forests gliding is

favoured However, this theory is compromised by the variety of species of

primates and frogs that are known to jump long distances in the Neotropical

region of Central and South America.

Another aspect of forest structure that appears to be important (at least

in some cases) is the greater height of lowland Indo-Malayan rainforests

Although systematic comparative surveys of tropical forest heights are not

available, several observers have noted the extreme heights of Indo-Malayan

forest canopies due to the abundance of trees of the family Dipterocarpaceae

The top of the canopy of lowland dipterocarp forests is typically 45 metres

in height, with some individual trees reaching 60–70 metres Similarly,

canopy heights of four rainforests in New Guinea ranged from 40–60

metres in height In contrast, canopy heights of African and South American

rainforests are significantly lower because there is no predominant family of

tall trees analogous to the Dipterocarpaceae of Indo-Malaya For example,

on Barro Colorado Island in the Republic of Panama, canopy trees in the

Introduction 17

old forest are 30–40 metres tall Similarly, the average height of rainforest

in the Amazonian Terra Firme Forest basin is 30–45 metres, with individual

trees of Dinizia excelsa (Leguminosae) and Bertholletia excelsa (Lecythidaceae)

reaching 50 metres in height Observations of African rainforests are similar

to those of South America

A consequence for gliding animals of an increased forest height, especially from emergent tree species, is that there is a higher point of take-off for

larger gliders to travel above the thicker rainforest below The high point of launch from these emergent trees allows longer glides to be made and results

in substantial energetic advantages, especially for larger species In vertical climbing, energetic costs are proportional to the climbing speed, and vertical climbing prior to a glide is the principal energetic cost of locomotion for gliding animals Therefore the energetic cost of transport can be significantly reduced in gliding animals by increasing glide lengths and, indirectly, by increasing heights of take-off points.

There also appear be a substantial savings of time associated with the ability to make one continuous glide rather than several consecutive glides, especially for larger gliding mammals whose cost of climbing is much more than smaller gliders Consecutive glides necessitate repeated landings and climbing, resulting in a loss of time and kinetic energy The additional time associated with transient residence at intermediate sites may also increase exposure to arboreal predators The greater time in the air during a long glide may allow a greater variety of potential landing sites.

Zoogeography

The fossil record and the locations of the gliders we see today offer important information on the past and present distribution, or zoogeography, of this group of mammals Zoogeography is the science that deals with the distribution of animals and their forerunners (both in time and space) and considers geology and geography through the examination of the fossil record, past and present climates, changes in vegetation, changes in sea level and continental movement.

Zoogeographic regions are areas of the world with distinctive fauna They are based on the taxonomic or evolutionary relationships of animals, and not the adaptations of animals to specific environments Each region maintains a level of homogeneity within its borders that differs from adjacent areas, so the animals within each region are likely to display similarities to each other Therefore the boundaries between zoogeographic regions are drawn according to the distribution of vertebrate taxa, especially families

There are six zoogeographic regions of the world:

s s s including China, Korea and Japan)

The marsupial Northern Glider inhabits

undisturbed rainforest in northern

New Guinea.

Gliding Mammals of the World

Although the system of identifying regions around the globe according to

the relative uniqueness of their fauna was initially developed for birds by

Philip Sclater in 1858, the first to associate mammals with different regions

of world was Andrew Murray in 1866 and subsequently by Alfred Wallace

(1876), Richard Lydekker (1896), and William and Phillip Sclater (1899)

Of the different regions that are recognised, it is that which separates

the placental mammals of the Oriental region with the marsupials of the

Australasia region that is probably the most famous The first zoogeographical

study of this region was undertaken by Salamon Müller in 1846, with a

more thorough assessment undertaken by Alfred Wallace (1863) who placed

a line between Borneo and Sulawesi in the north and, in the south, between

the tiny islands of Bali and Lombok, separated by a mere 32 kilometres,

but for the most part inhabited by different families of mammals and even

birds that have the powers of flight There are several later variations to the

Wallace Line that place it closer to New Guinea.

Although gliding mammals occur in all zoogeographic regions, the diversity of

the different groups of gliding mammals shows some clear regional differences

The marsupials for example are restricted to the Australasian region where all

eight species are found The highest diversity of gliding marsupials is evident in

Australia where six species occur All six are found in Queensland, five occur

in New South Wales and Victoria, four in South Australia, and only the Sugar

Glider is found in the Northern Territory and Tasmania (where it appears to

have been introduced) Outside Australia the diversity of gliding marsupials is

The six zoogeographic regions of the world are areas with distinctive fauna.

Palaearctic

Ethiopian Nearctic

Neotropical Oriental

Oriental

Australasian

The Japanese Giant Flying Squirrel inhabits broad-leaved forest, or mixed forest with both evergreen and deciduous trees, including many large trees such as Japanese Cedar It is capable of gliding up to 160 metres.

Introduction 19

limited though very widespread, being confined to the Sugar Glider that occurs throughout New Guinea and nearly 26 surrounding islands (making it the most

widespread of all Australasian mammals), the Biak Glider (Petaurus biacensis) that

is limited to Biak and Supiori Islands off the north-west coast of New Guinea, and the Northern Glider that occurs only in the Torricelli Mountains in northern New Guinea.

Throughout the Australasian region all marsupial gliders, with the exception

of the Northern Glider, occur primarily within open woodland and forest The Northern Glider appears to be restricted to closed rainforest on Mount Somoro

in northern New Guinea Some populations of Sugar Gliders have been found

to occur in Australian rainforest; however, studies in northern Queensland have found that Mahogany Gliders and Sugar Gliders live in open woodland and rarely enter the adjacent rainforest.

The colugos are restricted to the Oriental region where one species occurs

in the Philippines, while the other occurs on mainland Asia and on more than

40 islands within this region, including Borneo, Sumatra and Java The Sunda Shelf, which is an extension of the continental shelf of mainland South-East Asia (adjacent to the Malay Peninsula, Thailand, Cambodia and Vietnam) links this region with Borneo, Sumatra, Java, Bali and the smaller surrounding islands During the glacial maxima of the Pleistocene, sea levels were as much as

120 metres below those we see today and the entire Sunda Shelf was exposed as dry land This exposure during glacial periods and submersion during interglacial periods may be the mechanism that allowed the broad island distribution of colugos throughout the region.

The flying squirrels have the greatest distribution of the gliding mammals and are represented in four zoogeographic regions There are two species in the Nearctic region of North America, with the distribution of one of these extending slightly into the extreme north of the Neotropical region Only one species of flying squirrel occurs in Europe while the rest of the Palearctic region includes 21 species The highest diversity of flying squirrels occurs in the Oriental region where 41 species are known to occur, of which 13 species also occur in the Palearctic region

Within the Oriental region the greatest diversity of flying squirrels is in Borneo where 15 species can be found Sumatra and Thailand have 13 species; Burma, Sumatra and the Malay Peninsula have 12 species; Vietnam and Bhutan have eight species, while Java has seven species No species of flying squirrel occurs east of the Wallace Line in the Australasian region Many species found

in this region also have populations or subspecies in western and northern Asia including southern China, India, Sri Lanka, Nepal and Pakistan Another five species (two woolly flying squirrels, Kashmir Flying Squirrel, Hodgson’s Giant Flying Squirrel and Bhutan Giant Flying Squirrel) are restricted to north-western Asia in the region of Bhutan, Sikkim in north-eastern India, Nepal, north-western India, Kashmir, Pakistan and Afghanistan The North

Chinese Flying Squirrel, Complex-toothed Flying Squirrel, Red and White Giant Flying Squirrel and Chinese Giant Flying Squirrel are restricted to the

southern parts of the Palaearctic region in southern and central China and eastern Tibet Within China there are 16 species The provinces of Sichuan

During the glacial maxima of the Pleistocene,

the entire Sunda Shelf was exposed as dry land.

Sahul Sunda

Gliding Mammals of the World

20

and Yunnan have the greatest diversity of flying squirrels, with nine species

and 11 species respectively The Siberian Flying Squirrel is the most northerly

flying squirrel and occurs throughout Eastern Europe, Russia, China, Korea

and Japan.

All six of the scaly-tailed flying squirrels occur in the Afrotropical region where

they are restricted to central and western Africa The highest centres of diversity

are in Cameroon, Congo, Equatorial Guinea, Gabon, Liberia and Zaire, each of

which has five species.

Conservation

The conservation status of the different species of gliding mammals varies

enormously, ranging from critically endangered to least concern Of the

65 species of gliding mammals there are two considered critically endangered,

six are endangered, three are vulnerable, five are near threatened, and

32 species are classed as of least concern A reflection of the poor knowledge of

this group of mammals is that 11 are considered data deficient and six have not

been evaluated due to their recent recognition as species The primary threats

faced by gliding mammals throughout their distribution include loss of habitat

as a result of clearing of vegetation for timber and agriculture, the naturally

limited distribution of some species, hunting for food, occurrence of frequent

fires, and their collection from the wild for the pet trade.

The indication from the species with a conservation status of ‘least concern’ is

that these species face little or no threat Sadly this is almost certainly not the

case as most species are in decline in at least part, if not all, of their distribution

It is highly likely that many more species and subspecies should be recognised as

vulnerable or endangered but are not due to the limited information available and

the difficulties associated with species that have a large geographic distribution

over a continent and/or multiple countries

For example, the Siberian Flying Squirrel is considered low risk near threatened

overall However, in Finland and elsewhere, populations have declined severely

during the past few decades as a result of intensive forestry that has removed old

hollowed trees Similarly in Estonia the Siberian Flying Squirrel’s distribution

has declined considerably, with one study showing numbers at five monitoring

sites having declined by 21 per cent between 1940 and 1979 and almost

50 per cent during the period between 1980 and 2001 As a result of habitat

loss the species is vulnerable in Finland, endangered in Estonia (with only a

few hundred animals remaining), and possibly extinct in Latvia, Lithuania

and Belarus In Korea it once occurred throughout most of the northern half

However, due to clearing in the 1960s and 1970s there was a serious decline

in numbers and range, resulting in it occurring in only very small numbers

throughout its former range and was listed as Endangered in 1982.

Similarly, the Northern Flying Squirrel and the Southern Flying Squirrel

from North America each has subspecies that are considered threatened

Therefore it is likely that a more detailed analysis of the distribution of each

species and subspecies level within each country is likely to reveal many more

threatened populations.

In Finland and elsewhere, the Siberian Flying Squirrel, Europe’s only flying squirrel, is in serious decline due to intensive forestry and the resulting loss of old hollowed trees.

Introduction 21

As all species of gliding mammals are arboreal they are typically limited to crossing small gaps in the tree canopy Although they can glide over some gaps such as roads, tracks and power line easements, they cannot move easily through areas where the trees are more widely spaced than their maximum glide distance, which is typically only 30–60 metres (depending on the height

of the trees they launch from and the surrounding terrain) Therefore gliding mammals are highly sensitive to habitat fragmentation as they do not readily travel along the ground If they do come to the ground they are exposed to an increased risk of predation One method which has been used to assist gliding marsupials in Australia has been the placing of power poles on each side of roads which the gliders can use to bridge gaps in the vegetation.

One of the key reasons for raising concerns of the currently recognised conservation status of different species of gliding mammals is highlighted by South-East Asia This region includes approximately half of all species of gliding mammals, yet it has the highest relative rate of deforestation of any major tropical region and could lose three-quarters of its original forest by 2100 and up to

42 per cent of its biodiversity The conversion of natural habitat to other land uses

is considered the major driving force behind worldwide biodiversity loss

One of the immediate impacts of logging activities is the alteration of the unique multilayered and closed tropical canopy Observations in Malaysian forests show that reductions in canopy height, surface area and the crown size

of selectively logged forests are still evident after four decades of regeneration When these forests are cleared the species richness of trees appears to be negatively associated with the intensity of the logging activities, suggesting that logged forests require long periods of time to recover Similarly, recent studies show a trend of declining species richness and population density with increasing forest disturbance through logging activities, agriculture or urbanisation across a range of South-East Asian taxa, including mammals.

Directions for future research

One of the keys to conserving species is knowledge of where they occur and what they require It is clear from these pages that while some species of gliding mammals are comparatively well understood there are many for which even the most basic biological information is not known One of the reasons for this lack

of information is because of their cryptic nature – being nocturnal – they are difficult and expensive to study and survey in order to gain an accurate estimate

of their distribution and abundance.

It is hoped that this text will serve as a motivator for further applied research on this group of mammals Particular areas of research include further taxonomic studies to identify which populations or subspecies should be recognised as distinct species Studies are also needed to determine the ecology of many species including their diet, social behaviour, home range and reproduction The geographical distribution of many species and subspecies also needs to be more accurately determined.

Some of the subspecies of the Southern Flying

Squirrel are considered threatened.

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Gliding Mar

Gliding Mammals of the World

24

Families of gliding marsupials

There are three lineages of gliding marsupials within the possum Suborder

Phalangerida They are placed within three different families, each of which

has gliding and non-gliding members The Feathertail Glider is placed within

the Family Acrobatidae, which includes the non-gliding Feathertail Possum

(Distoechurus pennatus) from New Guinea Most of the gliding marsupials

occur within the Family Petauridae in the genus Petaurus, which includes six

living species This family also includes the non-gliding Leadbeater’s Possum

(Gymnobelideus leadbeateri) and the four species of striped possum of the genus

Dactylopsila that occur in New Guinea, with one of these species also occurring

in Australia The third family, Pseudocheiridae, has the Greater Glider, along

with some 17 species of non-gliding ringtail possum, including the Common

Ringtail Possum (Pseudocheirus peregrinus) which is a familiar resident to many

Australian backyards.

The fossil record

Our knowledge of the evolutionary history of the gliding marsupials remains

quite poor, with continuing debate as to whether the fossil species were

able to glide The oldest petauroid possums discovered so far include two

undescribed species from Geilston Bay in Tasmania, which date back some

30–20 million years, although there is no suggestion at this stage that these

The taxonomic relationships among living possum genera of the Suborder Phalangerida

(derived from Crosby et al 2004).

Gliding Marsupials 25

species could glide Other fossils from approximately 20 million years ago

at Riversleigh in north-western Queensland, Australia, have so far revealed two unnamed genera of petaurids; one genus containing two smaller species and a genus with a single larger species, although it is not known if these were able to glide None of these species is particularly close to any lesser

gliding possums of the genus Petaurus, with one genus labelled ‘pre-Petaurus’

because its teeth are similar to both the lesser gliders and the non-gliding Leadbeater’s Possum It was not known if these species were able to glide The most likely gliding marsupials come from the Hamilton Local Fauna fossil site in Victoria, Australia, which has revealed two petaurids, similar to the living Yellow-bellied Glider and Squirrel Glider, which are approximately five million years old The most recent fossil deposits are the Pleistocene deposits

in the Naracoorte Caves World Heritage Area in South Australia, where fossils most similar to Sugar Gliders have been discovered.

There are two extinct species of possums that were initially described from the early Pliocene deposits in Victoria as non-gliding ringtail possums of the genus

Pseudocheirus However it now seems likely that these species were relatives of

the modern day Greater Glider When these species were first described it was noted that the dental morphology most resembled that of the Greater Glider, but they were placed in the genus of non-gliding ringtail possums because it was not possible to demonstrate that these species could glide More recently,

an extinct Greater Glider, Petauroides ayamaruensis, has been described (with

considerable reservation) from Pleistocene deposits in Papua (western New Guinea), though most recent fossils suggest this may not be a glider after all Other fossils attributed to the modern Greater Glider have also been found from Pleistocene deposits in the Naracoorte Caves in south-eastern South Australia The lineage which includes the Greater Glider could have evolved within rainforest, where the related non-gliding, rainforest-dependent Lemuroid

Ringtail Possum, Hemibelideus lemuroides, still persists in the rainforests of north

Queensland The Lemuroid Ringtail Possum has a vestigial flap of skin, less than

25 millimetres wide, in the groin region of the hind legs It does not glide, but leaps from branch to branch, appearing to flatten its body somewhat It frequently makes leaps of 2–3 metres with its legs outstretched like those of a glider, landing heavily on a cushion of foliage This has led to conclusions that some of these long jumps have the appearance of true glides and that Lemuroid

The Lemuroid Ringtail Possum does not glide

but flattens its body as it leaps from branch to

branch

Probable ancestors of the Greater Glider

have been found from Pleistocene deposits

in the Naracoorte Caves in south-eastern

South Australia.

Gliding Mammals of the World

26

The Squirrel Glider (top) and the Greater Glider

(bottom) from The Voyage of Governor Phillip to

Botany Bay, 1789.

Ringtail Possums should be capable of limited gliding Lemuroid Ringtail

Possums appear to be both morphologically and functionally intermediate

between the gliding and non-gliding members of the Phalangerida and may be

some distance along the road to development as a true glider

The fossil record of the Feathertail Glider remains quite poor, with the first

fossils of the genus not being found until 1985 at Riversleigh A number of

teeth and a whole jaw, approximately 20 million years old, have since been

found, although it has yet to be established whether this taxon is a species of

feathertail glider, most closely related to the non-gliding Feathertail Possum,

or a new taxon structurally between the living forms Fossils most akin to

feathertail gliders have also been discovered from the Pleistocene deposits in

the Naracoorte Caves in South Australia.

It has been argued that marsupial gliders did not proliferate before the

beginning of the Pliocene, five million years ago because open forests were not

widespread in Australia before this time The ability to glide in the marsupials

has been considered to be a response to the opening up of the forests as the

climate dried during the Pliocene As the trees became further apart due to

the change in vegetation from rainforest to open woodland, the possums had

to jump further and further between trees until they had developed a gliding

membrane that allowed them to travel between the spread-out trees that

occur in eucalypt forests.

A Pliocene radiation of the gliding petaurids is supported by genetic studies;

however, the presence of Petaurus-like animals from the Oligo–Miocene epochs

implies they may have been present in rainforest before the forests dried out and

became open woodlands during the late Pliocene It is possible, however, that

they did not glide until the Pleistocene, less than two million years ago

The discovery of five-million-year-old fossils of gliding possums of the genus

Petaurus from the Hamilton Local Fauna site suggests that these could have

been inhabitants of Victorian rainforests, although it is difficult to conceive of

a need to glide in a rainforest where all the crowns of the trees are touching

These same deposits also revealed the presence of a pre-greater glider, so the

idea of rainforest gliders should not be abandoned too quickly.

Early observations

The Squirrel Glider was one of the first marsupial gliders to be discovered by

Europeans In 1789, a year after the First Fleet arrived in Australia, Governor

Arthur Phillip noted that this species ‘inhabits Norfolk Island off the coast of

New South Wales’ and called it the ‘Norfolk Island Flying Squirrel’ It was

subsequently given the name Sciurus norfolcensis in recognition of its supposed

squirrel origin, however it was later recognised as a marsupial and named

Petaurus norfolcensis Despite its name this species has never occurred on Norfolk

Island and is only found down the east coast of Australia.

The Greater Glider was also recorded by Governor Arthur Phillip in 1789, who

detailed several of its features:

The ears are large and erect; the coat or fur is of a much richer texture

or more delicate than the sea otter … on the upper parts of the body, at

Gliding Marsupials 27

The Squirrel Glider (top) and the Greater Glider

(bottom) from George Shaw’s Zoology of New

Holland, 1794.

first sight, appearing of a glossy black, but on a nicer inspection, is really what the French call petit gris, or minever, being mixed with grey; the under parts are white, and on each hip may be observed a tan-coloured spot, nearly as big as a shilling; at this part the fur in thinnest, but at the root of the tail it is so rich and close that the hide cannot be felt through

The fur is also continued to the claws: the membrane, which is expanded

on each side of the body, is situated much as in the grey species, though broader in proportion.

A few years later, in 1794, the English botanist and zoologist George Shaw

described the Squirrel Glider in detail in his Zoology of New Holland:

In its general aspect this animal has so much the appearance of a squirrel, that on a cursory view it might readily pass for such A more exact inspection into its characters will however evince it to be a genuine opossum … The abdominal pouch is of considerable size, and is situated,

as in other opossums, on the lower part of the abdomen The hind feet are furnished with a rounded, unarmed, or mutic thumb Nothing can exceed the softness and delicacy of this animal’s fur … I must also add, that

I have great reason for supposing the Petaurus to be furnished with an abdominal pouch; a particular which I have not yet been able to ascertain;

no living specimens having been yet imported The Opossum now described

is a nocturnal animal, and continues torpid during the greatest part of the day, but during the night is full of activity.

Despite being a marsupial, the Yellow-bellied Glider was described by George Shaw in 1791 as a rodent flying squirrel He noted that:

I thought it best to describe this animal as a species of flying squirrel, and to separate the flying squirrels from the genus Sciurus, with which Linnaeus had conjoined them, and to form them into a genus by the name of Petaurus This perhaps may be thought an unnecessary piece of exactness; yet is something

so peculiar in the expanded processes of skin by which the flying-squirrels are distinguished, that they may properly enough be allowed to form a distinct genus Of all the species then of this genus the animal here figured is the largest and most elegant.

Several years later, in 1800, Shaw noted that ‘the size, colours, and form, of the Petaurine or great flying opossum of New Holland, conspire to render it one of the most beautiful of quadrupeds’ He described it as about ‘the size of a half- grown cat or a small rabbet [sic]’.

The general appearance of the animal is similar to that of a flying squirrel;

an expansile membrane, covered with fur, stretching from the fore legs to the hind on each side of the body, and thus enabling the animal to spring to a considerable distance at pleasure.

In his Zoology of New Holland, Shaw was the first to record the Feathertail Glider: Amongst the most curious quadrupeds yet discovered in the Antarctic regions

… which (exclusive of its diminutive size, not exceeding that of a common domestic mouse) forms as it were a kind of missing link between the genera of

Didelphis and Sciurus, or opossum and squirrel.