It is widely accepted that many birds, particularly the larger species such as albatross, condors and eagles glide in flight to save energy. This adaptation requires highly specific wing characteristics all conforming to wonderfully complex mathematical equations that boggle the mind, however it is remarkable for reasons other than its complexity. Gliding has evolved separately many times across the animal kingdom in some mammals, reptiles, amphibians and even fish. This repetition of a trait without any common ancestor is known as convergent evolution and is a wonderful example of nature repeatedly yet randomly finding synonymous solutions to similar problems.
It was assumed based on its uses in birds, that this adaptation must also assist energy conservation in all species that possess it. Colugos are arboreal gliding mammals native to South-East Asia. Their gliding capabilities exceed that of the other mammals sporting the trait, and they can cover distances of up to 150M between treetops with no significant loss of altitude. They are hunted for both meat and fur and are the preferred prey of the critically endangered Philippine eagle.
A recent study carried out by scientists at the University of California, Berkley shows that in colugos the notion of gliding for energy conservation may not apply. The University scientists attached radio transmitters with in-built accelerometers to the backs of 6 individual colugos measuring their glide trajectories and the distances covered. From this they saw that the colugos only climbed relatively small heights to enter into their long flights, an average of 8M to glide between 30-50M; looking good for energy saving so far. The next step was to assess the energy consumption of this glide (the energy used to climb 8M) and compare it with the energy used to simply crawl to the end point. Rather surprisingly the calculations suggested that the colugos consume up to 1.5 times more energy climbing up the tree to take off than they would by making their way clumsily along from branch to branch.
This begins to challenge the traditional supposition that all gliding is energy saving and caused the scientists to reassess its purpose in this case. One obvious advantage stood out, speed. Watching colugos move is a slightly clumsy and slow affair. Gliding allows them to move up to 10 times faster between locations therefore covering a more widespread range and allowing much more time to forage. The team also speculate that it is beneficial for evading predators and reduces the risk of falling from the canopy tops.
Inevitably other gliding mammals, as well as the other taxa displaying the gliding trait will need to be investigated to see whether this is a unique use of this adaptation, or whether natures perfect answer to many entirely different problems is wonderfully unified.
The natural world is constantly surprising us and just when we think we might fully understand a concept, a discovery is made to generate new and exciting perspectives. This is a wonderful example of what we can achieve when we question pre-existing answers, and highlights the value of curiosity and research. Long may the dynamics continue.
