One theory suggests gliding saves energy, so researchers test that idea using colugos, mammals from southeast Asia that turns into giant skin sails when they stretch out their legs. The scientist place accelerometer on the back of 16 compliant colugos, the data packed revealed that each colugo glide in average a quarter mile each night, but gliding isn't as effortless as it looks, researchers calculation suggests that flying actually requires one and half times energy than conventional traverse, that's because colugo prepare for a launch by climbing higher up to the tree, and climbing is a lot more strenuous than walking. That finding appears in the Journal experimental Biology. 

 

So why do it, the upside is speed, colugo can sail ten time faster than they tightrope through the canopy, which leave more time to snack, plus leaping in the air is easy get away from predators, in the end, it's not different from human fly,cost more, way faster.