Gliding mammals of the world

About the author

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.

FullCOV_GlidingMammals_FNL copy.indd 1

Stephen Jackson

About the artist

Illustrated by Peter Schouten

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.

Gliding Mammals of the World

T

he 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.

Stephen Jackson
Illustrated by
Peter Schouten

Gliding
Mammals
of the

World

7/06/12 11:23 AM


Gliding
Mammals
of the

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Gliding
Mammals
of the

World

Stephen Jackson
Illustrated by Peter Schouten


© 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.
9780643092600 (hbk.)
9780643104051 (epdf)
9780643104068 (epub)
Includes bibliographical references and index.
Gliders (Mammals).
Mammals – Flight.

599.369
Published by
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Collingwood VIC 3066
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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
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Original print edition:
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beneficial and economically viable management of the world’s forests.


Contents
Preface
Acknowledgements
List of species
1 Introduction

vi
viii
x
1

2 Gliding Marsupials

23

3 Colugos

47

4 Flying Squirrels

57

5 Scaly-tailed Flying Squirrels

163

Appendix 1: Subspecies

180

Appendix 2: Gliding mammal localities

182

Appendix 3: IUCN Red List Categories

189

Glossary

190

References

192

Index

214

v


Preface
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

vi

Gliding Mammals of the World


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

Preface

vii


Acknowledgements
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 scalytailed 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

viii

Gliding Mammals of the World

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.

Acknowledgements

ix


List of species
DIPROTODONTIA
Acrobatidae
Acrobates pygmaeus

Feathertail Glider

30

Northern Glider
Yellow-bellied Glider
Biak Glider
Sugar Glider
Mahogany Glider
Squirrel Glider

32
34
36
38
40
42

Greater Glider

44

Philippine Colugo
Malayan Colugo

52
54

North Chinese Flying Squirrel
Black Flying Squirrel
Thomas’s Flying Squirrel
Hairy-footed Flying Squirrel
Namdapha Flying Squirrel
Kashmir Flying Squirrel
Pakistan Woolly Flying Squirrel
Tibetan Woolly Flying Squirrel
Northern Flying Squirrel
Southern Flying Squirrel
Particolored Flying Squirrel
Bartel’s Flying Squirrel
Palawan Flying Squirrel
Indochinese Flying Squirrel
Grey-cheeked Flying Squirrel
Arrow-tailed Flying Squirrel
Sipora Flying Squirrel
Red-cheeked Flying Squirrel

64

66
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98

Petauridae
Petaurus abidi
Petaurus australis
Petaurus biacensis
Petaurus breviceps
Petaurus gracilis
Petaurus norfolcensis

Pseudocheiridae
Petauroides volans

DERMOPTERA

Cynocephalidae
Cynocephalus volans
Galeopterus variegatus

RODENTIA
Sciuridae, Pteromyini
Aeretes melanopterus
Aeromys tephromelas
Aeromys thomasi
Belomys pearsonii
Biswamoyopterus biswasi
Eoglaucomys fimbriatus
Eupetaurus cinereus
Eupetaurus sp.
Glaucomys sabrinus
Glaucomys volans
Hylopetes alboniger
Hylopetes bartelsi
Hylopetes nigripes
Hylopetes phayrei
Hylopetes platyurus
Hylopetes sagitta
Hylopetes sipora
Hylopetes spadiceus

x

Gliding Mammals of the World

Hylopetes winstoni
Iomys horsfieldi
Iomys sipora
Petaurillus emiliae
Petaurillus hosei
Petaurillus kinlochii
Petaurista albiventer
Petaurista alborufus
Petaurista caniceps
Petaurista elegans
Petaurista hainana
Petaurista lena
Petaurista leucogenys
Petaurista magnificus
Petaurista nobilis
Petaurista petaurista
Petaurista philippensis
Petaurista xanthotis
Petaurista yunanensis
Petinomys crinitus
Petinomys fuscocapillus
Petinomys genibarbis
Petinomys hageni
Petinomys lugens
Petinomys mindanensis
Petinomys setosus
Petinomys vordermanni
Pteromys momonga
Pteromys volans
Pteromyscus pulverulentus

Trogopterus xanthipes

Sumatran Flying Squirrel
Javanese Flying Squirrel
Mentawai Flying Squirrel
Lesser Pygmy Flying Squirrel
Hose’s Pygmy Flying Squirrel
Selangor Pygmy Flying Squirrel
White-bellied Giant Flying Squirrel
Red and White Giant Flying Squirrel
Gray-headed Giant Flying Squirrel
Spotted Giant Flying Squirrel
Hainan Giant Flying Squirrel
Taiwan Giant Flying Squirrel
Japanese Giant Flying Squirrel
Hodgson’s Giant Flying Squirrel
Bhutan Giant Flying Squirrel
Red Giant Flying Squirrel
Indian Giant Flying Squirrel
Chinese Giant Flying Squirrel
Yunnan Giant Flying Squirrel
Basilan Flying Squirrel
Travancore Flying Squirrel
Whiskered Flying Squirrel
Hagen’s Flying Squirrel
Siberut Flying Squirrel
Mindanao Flying Squirrel
Temminck’s Flying Squirrel
Vordermann’s Flying Squirrel
Japanese Flying Squirrel

Siberian Flying Squirrel
Smoky Flying Squirrel
Complex-toothed Flying Squirrel

100
102
104
106
108
110
112
114
116
118
120
122
124
126
128
130
132
134
136
138
140
142
144
146
148
150

152
154
156
158
160

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

168
170
172
174
176
178

Anomaluridae
Anomalurops beecrofti
Anomalurus derbianus
Anomalurus pelii
Anomalurus pusillus
Idiurus macrotis
Idiurus zenkeri

List of species

xi


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Introduction


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

2

Gliding Mammals of the World

The Japanese Flying Squirrel weighs about
200 grams and is capable of gliding up to
100 metres.


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.

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).

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), Fringe-limbed Treefrog (Hyla miliaria) and Rabb’s Fringelimbed Treefrog (Ecnomiohyla rabborum) and may also have the ability to glide.
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

Introduction

3


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 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.

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.

4

Gliding Mammals of the World


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.

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.

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.

Introduction

5


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).

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

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.

6

Gliding Mammals of the World


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.

Gliding behaviour
There are five basic stages to any glide: preparation, launch, glide, braking and
landing.
In preparation for a glide, the animal usually climbs towards the end of a
branch in a position that may be anything from horizontal to vertical, although
a horizontal position seems to be preferred. Once in the launch position, the
glider generally sways or weaves from side to side and often bobs its head up

and down seemingly to assess the landing point. This has been interpreted as a
method of triangulation to estimate the distance from the launch point to the
landing point. This hypothesis is supported by observations that arboreal and
gliding rodents have more widely spaced eyes than ground-dwelling forms, thus
improving their perception of depth. Similarly, an examination of the interorbital
widths of the marsupial gliders compared with other non-gliding possums has
revealed that, with the exception of the Greater Glider, marsupial gliders have a
wider interorbital width than the majority of non-gliding possums.
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.
The Taiwan Giant Flying Squirrel curls its tail up
tightly as it launches itself into a glide.

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.

Introduction

7


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

8

Gliding Mammals of the World

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

The gliding stages of the Malayan Colugo.


The gliding stages of the Northern Flying
Squirrel.

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.

A Northern Flying Squirrel grabs hold of a tree
with its forehands, as it completes its glide.

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.

Introduction

9

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.

10

Gliding Mammals of the World

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


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.

Most gliding mammals, such as this
Sugar Glider, fall into the mass range of
100–500 grams.

The relationship between the body mass of

different species of gliding mammals and their
glide distances.

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

60

Sugar Glider (100 g)
Northern Flying Squirrel (130 g)

Percentage of glides

50

Siberian Flying Squirrel (150 g)
Squirrel Glider (230 g)

40

Mahogany Glider (380 g)
30

Yellow-bellied Glider (600 g)
Japanese Giant Flying Squrrel (1100 g)

20
Malayan Colugo (1500 g)
10

0
1–10

11–20

21–30

31–40

41–50

51–60

61–70

71–80

81–90

91–100

100+

Glide distance (metres)

Introduction

11

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.

12

Gliding Mammals of the World

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