Logo: Gliding mammals of the world

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 Europe and North America, the scaly-tailed flying squirrels from central Africa and the gliding possums of Australia and New Guinea.

Intro: 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 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 welldeveloped 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. Groundlevel 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.

It has previously been thought that gliding in the marsupials evolved due to the opening up of the vegetation as Australia dried out during the Miocene Period
It has previously been thought that gliding in the marsupials evolved due to the opening up of the vegetation as Australia dried out during the Miocene Period.

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 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.

The marsupial Northern Glider inhabits undisturbed rainforest in northern New Guinea
The marsupial Northern Glider inhabits undisturbed rainforest in northern New Guinea.

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.

Random species

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-color 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.