Bats are the only flying mammals. Their wings are delicate membranes stretched between the greatly lengthened bones of the hand. In some species a tail membrane between the legs provides an additional aid for flight. Except for these membranes, bats, like other mammals, are furred. They have sharp-pointed teeth and suckle their young. The ability to avoid obstacles by detecting echoes of high-pitched sounds is characteristic of the smaller bats. This faculty enables them to fly safely in dark caves, which frequently form daytime roosts, and it is also important for locating their insect food. Two species of bat occur in New Zealand. They are the only known native land mammals and are representatives of two distinct bat lineages. The Maoris called them “pekapeka” and they were the subject of an old native proverb predicting evil. They are named, respectively, the long-tailed and short-tailed bat.