Fences are bad for wildlife

EARTH’S LONGEST artificial structure is usually said to be the Great Wall of China. Just how long that is is hard to say, for northern China actually has many walls, built at different times and not always interconnecting. Earth’s second-longest artificial structure, though, is not a wall, but a fence. Its length is known exactly. It stretches for 5,614km across eastern Australia and is intended to stop the country’s native feral dogs, the dingoes, which live mainly to its north, from preying on sheep, which are farmed mainly to its south.

Australia’s dingo fence is remarkable. But it does not stand alone. Millions of kilometres of fences wrap the world, outstripping the collective length of its roads by something like a factor of ten. Some are intended to curb the movement of animals, some the movement of people, and some merely to mark the limits of territory, so that everyone knows who owns what.