Bats are nocturnal, coming out at night. They are the only mammals capable of true (meaning, flapping) flight, because the other so-
Although some bats have remarkable faces and behavior, wings are the most conspicuous features of the flying bats. Upon landing, bats immediately fold their wings so they appear to shrink in size. Small size is another distinctive feature of bats. While a few species weigh more than 3.5 oz (100 g) as adults, most weigh less than 1.7 oz (less than 50 g), and the majority less than 0.9 oz (less than 25 g). The smallest bats in the world (hog-
Flying foxes and their allies (family Pteropodidae) usually have claws on their second fingers, but some species (dawn bats, genus Eonycteris, and naked-
Although some bats have quite muscular forearms, their wing bones tend to be lightly muscled. In most bats, the folds of skin (wings) enclose some connective tissue, nerves, and blood vessels. Some free-
Although both can fly, bats differ from birds. While living birds such as ostriches, emus, and penguins, and fossils like elephant birds have lost the ability to fly, there are no living or fossil flightless bats. Bats have teeth, while living birds do not. Bats give birth to live young, while birds lay eggs. Since teeth are heavy, having them at the front end of a flying animal could create aerodynamic problems. Additionally, laying eggs could be more efficient and less costly for a flying animal than bearing live young. The diversity of birds (more than 8,000 species) suggests that their approach is more successful than that of bats (1,000 species).
In birds, the wings do not involve the hind limbs as they do in bats. The hind limbs of bats tend to be spindly and poorly muscled, and many bats are not mobile on the ground. Most birds are much more mobile on the ground, and their robust hind legs reflect this reality. Mobility in the air, on the ground, and beyond (as for penguins) may partly account for differences in diversity between bats and birds. In addition to the obvious (i.e., bird wings are made of feathers, while bat wings are folds of skin), there are other differences between these animals. In bats, the division of power generation across nine pairs of muscles means that they are thin in profile through the chest. In birds, two pairs of muscles power flight: one the down-
In most bats, the thumbs are free of the wings, appearing there as claws. In some bats, notably thumbless ones (family Furipteridae) and some ghost bats (genus Diclidurus, family Emballonuridae), the thumbs are greatly reduced in size and may lack claws. At the other extreme are the very long thumbs of vampire bats (Desmodus rotundus). Vampire bats’ thumbs act like “throwing sticks,” giving the bats extra leverage for taking off from the ground. Bats’ wing membranes usually join along the side of the body, but in two groups they meet in mid-
Most bats have tails. But while tails of some (e.g., mousetailed bats, Rhinopomatidae, and some Pteropodidae) are long and slender, others (e.g., free-