Bats are the only mammal capable of true sustained flight, and with over 1,300 species and counting, they make up the second largest order of mammals. Organized into the order Chiroptera, meaning “hand wing” in Ancient Greek, their wings consist of elongated hand bones joined by a membrane of skin. Although bats are in fact not blind, most species are nocturnal and use echolocation, a form of biological sonar, to supplement their night-time vision. Species of bats are found all over the world except in the most remote Arctic and Antarctic regions, and therefore much variation is seen among species. Most bats eat fruit or insects, but some species have also been observed eating rodents, fish, frogs, birds, smaller bats, and the blood of livestock and birds.