Bats are the only mammals that can achieve true flight. Their wings are thinner and more delicate than those of birds. There are some other mammals that can glide through the air, but this is not considered flying.
There are more than 900 species of bats throughout the world, though some estimates range up to 1,200. Bats range in size from very small, weighing just a few grams, to the largest recorded size, weighing up to 2.2 pounds. The flying fox is the largest of the flying mammals and weighs up to 2.2 pounds, with a wingspan of up to 6 feet. Bats are a varied species, and though the species are mostly nocturnal, they have been rarely known to be active during the daytime. Although bats have notoriously bad eyesight, they use echolocation and are graceful, accurate fliers even in the dark of night or caves. The eating habits of bats range from blood and insects to fruits.
Gliding animals are relatively common, but are limited to small mammals, such as squirrels and small possums. Gliding mammals do not have wings, but rely on extra skin between their limbs to catch the air. These mammals leap from high places and ride the air to the next landing area. They typically only glide short distances, such as between two trees. Human BASE jumpers base their glide suits off of this type of mammal.