David Attenborough meets the tree dwellers - those mammals that have adapted to a life at height. Some, like meerkats, might hardly seem to qualify but they do regularly climb small trees to scout for danger. Others, like gibbons, live 100 feet or more above the forest floor and never descend to the ground.One third of the world's surface is still covered by forest of one kind or another and mammals from a diverse range of groups have exploited them all.Climbing requires some very specialised adaptations. Hyrax have moist, rubbery feet to help them negotiate slender branches, sun bears rely on sharp claws and strong forearms, coatis go one step further with sharp claws and a long tail for balance. And, when it comes to tails, there's another very effective design. Tamanduas, arboreal anteaters, have gripping tails, which leaves their hands free to break into termite mounds.But climbing into a tree is just the start. The real challenge is how to move between trees. Grey squirrels cope with small gaps by jumping, a technique favoured by many primates as well as bush babies and lemurs. The latter can leap thirty feet in one go but there are other tree dwellers that can travel further than that. By stretching out a membrane between front and back legs, flying squirrels can glide three times that distance, while fruit bats, along with their insect-eating cousins, are the only mammal to have developed powered flight and their strong wings enable them to fly as much as 30 miles in a night in their search for fruiting trees.Life in the Trees is full of strange and unfamiliar animals, such as the Indian slender loris and the fossa, Madagascar's largest arboreal predator, both filmed for the first time in the wild. In this programme, David gets close to many of them, and for some this meant climbing high into the canopy himself.