Biology Reference
In-Depth Information
is now. For a long time now we've known better, however. Notwithstanding their small, furry, mouse
like appearance and their German name,
Fledermaus,
bats are not close relatives of mice at all. Indeed,
the connection between mice and bats is actually so tenuous that bats are much more closely related to
humans than to mice.
What
are
the bat's closest relatives? Scientific opinion varies somewhat regarding this question. The
most widely accepted theory is that lemurs are the leading candidates. These small, arboreal mammals,
found chiefly in Madagascar, are primitive primates. Since humans are also primates, this indeed con-
nects our species to the bats.
Bats come in an extremely wide range of sizes. In recognition of that fact, all bats are divided
into two groups, Megachiroptera and Microchiroptera. The Megachiroptera—the megabats or large
bats—are fruit bats. These bats of the Old World tropics seek their food by sight rather than by echo-
location. They include the world's largest bats, the so-called flying foxes; the biggest of these, a native
of Java, can weigh nearly three and a half pounds, with a wingspan that may exceed six feet.
In contrast, the micro, or small, bats, which include our North American bats, are insect-eaters and
hunt by echolocation. Microbats include the world's smallest bat, the bumblebee bat of Thailand. This
tiny creature is well named, for its wingspan is less than five inches, and it weighs less than
four one-
hundredths
of an ounce.
Our North American bats, though larger than this minuscule creature, are nonetheless extremely
small. Their size is deceptive because of their large wing surface, but they weigh astonishingly little.
For example, the big brown bat weighs only one-half ounce, and the little brown bat one-third to one-
quarter of an ounce.
In addition to being the only mammal that truly flies, bats have other unique features. For one thing,
bats roost hanging head-down. Whereas other mammals, including humans, would suffer serious ill ef-
fects if they remained upside down for any length of time, this evolutionary quirk obviously suits the
bat very well. In addition to turning the world upside down for the duration of the long summer daylight
hours, hibernating bats may spend weeks—even months—roosting with their heads down.
This unusual behavior is made possible by physical and chemical adaptations in the bat's body that
restrict the flow of blood to the head. In turn, hanging head-down offers bats the advantage of being
able to see approaching danger and to spring into instant flight. No doubt this evolutionary twist has
enhanced bat survival over millions of years.
Even in their reproductive habits, bats display unique qualities. Most of our bats bear a single young
per year, although some species may have two. The baby bat, known as a pup, weighs at birth a quarter
of its mother's weight. The human equivalent would be a 120-pound woman giving birth to a thirty-
pound baby! As an added feature found only in bats, the mother nurses her young with teats on the
sides
of her body, rather than the front.
Depending somewhat on the species, the mother bat may carry her pup, clinging to her furry skirts,
on her nightly hunting forays. As the pup grows and becomes too much of a burden, the mother simply
