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| Here in the California deserts there are more than a dozen species of
bat—Earth’s only flying mammal. This oft-misunderstood animal
has existed for approximately 55 million years, an estimate derived from
the discovery of Icaronycteris, a fossil bat. Over that unimaginable period
of time, bats have evolved a stunning array of adaptations that continue
to dazzle the biologists who study them and the naturalists who observe
them. |
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| What about flying squirrels? you might be asking yourself right now. Aren’t
they mammals? Aren’t they also able to fly? The answer is yes, squirrels
certainly are mammals, and some species are able to soar. But no, those
that glide are not equipped with wings that allow them to ascend—so
it cannot be said that they are truly capable of flight. |
| Bats comprise almost one quarter of all mammals. This is significant when
one considers that approximately 4,000 species of mammal have been classified
thus far. Doing the math, we find that there are almost 1,000 species of
bat on Earth! The diversity of these species is equally impressive: bats
range from the palm-sized bumblebee bat weighing less than a penny, to the
flying foxes of Asia, which boast an average three-foot wingspan. Biologists
divide bats into two main groups: megabats (the larger, primarily fruit-eating
bats) and microbats (generally smaller and insect-eating). Bats demonstrate
surprising diversity in their diets. Most of our desert bats are insectivorous,
gobbling up thousands of moths, mosquitoes and beetles during their nightly
forages. Tropical bats, however, might subsist on a diet of fruit, nectar,
pollen, or even frogs! |
| The pallid bat of the southwestern deserts favors an odd delicacy:
scorpions. Apparently, pallid bats are immune to scorpion venom, so
their culinary preferences help to keep that arachnid’s populations
in check without harming the bats. Bats whose diet consists of animal
prey use echolocation to hunt, navigate and avoid collision with other
bats. Scientists are only beginning to decipher the banks of acoustic
signatures, or bat calls they have collected, and it is often difficult
to distinguish one bat’s sounds from another, or one type of
communication from another. The same species of bat, for example,
might echolocate at different frequencies depending on whether it
is looking for prey, engaged in a feeding frenzy, looking for a mate,
or warning others of danger. |
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| Vampire bats, whose saliva is being studied by pharmacologists for its
superior anticoagulant properties, live in Latin America, from Mexico to
northern Chile and Argentina. Of the three vampire species, two prey on
birds, and the third tends to favor mammalian species. In no case is the
host animal seriously affected by the feeding process, although a vampire
bat might infect its host animal with any of a number of diseases. |
| When we think of bats, we may picture millions of them emerging from a
cave at sunset. Most of our local bats, however, do not occur in such large
numbers—nor do they inhabit caves. In general, bats choose dark, quiet,
undisturbed places as their homes: caves, rock crevices, trees, abandoned
buildings, abandoned mines, bridges and tunnels. Those that live here in
the desert usually squeeze themselves inside a rock crevice, or perhaps
roost in an abandoned mine. If they are disturbed while hibernating, bats
may burn up their stored energy supplies and perish before the weather permits
them to go out hunting again, so it is important to leave bats alone. Do
not forget that they are wild animals, capable of transmitting diseases
such as rabies—although it must be said that fewer than a tenth of
one percent of our local bats have been found to be rabid. |
| Most bats hang upside down when they roost, using their sharp curved claws
to cling to roosting surfaces. How then, do they manage to nurse their young—or,
for that matter, eliminate waste—without spilling, soiling themselves,
or getting a headache? Several strategies help them stay dry and clear-headed:
a system of valves controls the flow of blood; nursing is conducted through
a kind of gravity-feed system; and a quick arch of the back at the appropriate
moment keeps the bat’s fur clean and silky. Bat biologists believe
that their unique roosting posture and the ability to squeeze into narrow
spaces have given bats an advantage by allowing them to avoid competing
with other animals for more conventional types of habitat. |
| Although bats have sometimes been mistaken for flying mice (in French,
the word for bat is “chauve-souris,” or “bald mouse,”
and in German it is “Fledermaus,” or “flying mouse”),
there are few similarities between the two animals. A bat mother will usually
give birth to one pup a year; twins are uncommon, and triplets even more
so. Many bats do not have tails, and some have such large ears that they
resemble rabbits or dogs more than mice. Dentition, or the size and shape
of teeth, is another good indication of the vast difference between bats
and mice. Bat teeth are designed for eating insects (which involves biting
off the prey’s head and wings, discarding them, and dining on the body),
whereas mouse teeth are adapted to a diet of seeds, grass and grains. |
| Mother bats have a remarkably well-tuned reproductive system: they are
able to re-absorb their embryo if the upcoming season looks unpromising
due to a lack of sufficient food and water for their young. In addition,
the development of the fetus can be delayed or sped up depending upon the
maternity roost’s temperature. Once they are born, the juveniles must
develop enough fat in their first year to survive hibernation or migration,
and they must learn to fly! No wonder nature has provided so many options
in the bat’s reproductive process! |
| As a family, bats are impressively diverse animals. They are found on
every continent except Antarctica. They range in size from a few inches
across to a wingspan of more than three feet; they may eat insects, frogs,
scorpions or fish, or feed on nectar, fruit or blood. There are almost 1,000
species on Earth that are busily controlling pests, dispersing seeds and
pollinating flowers. Sadly, bats are often misunderstood, and their numbers
are dwindling due to loss of habitat and misguided “pest control”
programs. If you see a bat, please leave it alone. If it is lying on the
ground, do not touch it: that is not normal behavior for a bat, and it may
be ill. Here at Joshua Tree National Park all bat species are protected.
Look for them at dawn or dusk in desert washes, which make up 80 to 90 percent
of their foraging territory. Enjoy them, but respect them—they remain,
in spite of their timid nature, wild animals. |
by Park Ranger Caryn Davidson
Illustration from a painting by Andrea Peyton |
