Q: What are some of the adaptations of bats? A: Bats are the only true flying mammals, so many adaptations are for flight. The most widespread view is that they originated from insectivores similar to shrews. The wings have evolved from the front limbs. The upper arms and forearm bones are relatively normal, but their four fingers are greatly elongated and support the wing membrane, composed of a double layer of skin. This skin encloses the fore and hind limbs and the tail. The finger bones are very thin and lack claws. The small thumb consists mainly of a prominent hooked claw, an adaptation for climbing walls or trees. The hindfeet have five very sharp hooked claws, allowing bats to hang in their characteristic position, with their heads down.
The broad wing membranes give the bat the lift for flight and propel it through the air. Slower-flying bats have short wide wings, whereas more rapidly flying bats have long thin wings. The membranes extend back along the side of the body and enclose the legs and tail. This part of the membrane stretching between the upper leg bones (the femora) is called the interfemoral membrane.
Figure 1 Big-eared Bat (Photo by James Kiser )Add to 'My Saved Images'
Most bats are insectivorous and catch much of their insect prey while in flight at night. Bats have small eyes, which they can use in daytime or when there is a bright moon. However, most of their navigation and hunting is accomplished with echolocation (a process analogous to radar or sonar). Bats produce a rapid series of Âclicks which then bounce off an object such as a wall, a tree, or a flying insect and return to the batÂs ear as an echo. The bat can gather information about its environment from these echoes—the size of an object, its shape and distance, and whether it is moving. If the object is an insect, the bat may be able to distinguish between major kinds, such as beetles vs. moths.
Bats have sharp teeth and chew their insect food into very tiny pieces. The external skeleton of flying insects contains chitin, which is tough and hard to digest. Most chitin passes rapidly through the digestive tract of the bat and is largely undigested. However, bats do contain intestinal bacteria that may help digest some chitin. This is important in winter when most bats are not feeding and digest chitin remnants that remain in the intestine for prolonged periods.
Figure 2 Red Bat, adult male. (Photo by Adam Mann )Add to 'My Saved Images'
Not all bats feed on insects. Some eat fruit, blood (vampires  three species in Central and South America), pollen and nectar, and even fish or other small vertebrates. Echolocation is poorly developed and the eyes are large in fruit-eating bats, particularly in Old World species
Many bats in temperate areas mate in fall and hibernate in winter. The sperm do not immediately fertilize the eggs, but remain in the female reproductive tract during winter and fertilize the eggs in spring about the time the bats emerge from hibernation. This process is called delayed fertilization. It allows the bats to mate at a time when food is plentiful rather than in early spring when their food (flying insects) is in short supply. Also, it allows the female bats much more time to become pregnant—anytime in fall and even through the winter and early spring. It is important that most bats become pregnant, because temperate bats have a low reproductive rate (most species have one young per year, a few have two, and very few have more). This low reproductive rate works to maintain bat populations in concert with low predation rates and long life (one little brown bat from New England was known to live 34 years under field conditions, and there are records or Eurasian bats living even longer).
Bats constitute about one-fifth of the worldÂs more than 5000 species of mammals and thus fill many ecological niches. Therefore one finds great variation in the behavior and structural adaptation of bats. Many bats have leaflike projections from the nose or other facial adornments. The size and shape of the ears and also of an upward-projecting earlobe, the tragus, vary greatly. It is not clear how these structural adaptations serve the bat, but many may be involved with echolocation. Some tropical bats have disks on their wings that act as suction cups and help them hold to wet surfaces. The North American red and hoary bats are solitary and hang among the foliage; these species have fur on the upper side of the interfemoral membrane that serves as a blanket when the membrane is wrapped around the bat.
These are only some of the many adaptations that help bats.
Dr. John O. Whitaker, Jr.
