This misunderstood mammal provides numerous ecological benefits.
By Lowell and Kaye Christie, F45246
Bats get a bad rap. Often they are photographed with their mouths open, snarling in self defense. What type of reaction would you expect from a shy creature that spends its life in a low-light environment and suddenly has flashing bright lights in its face?
Actually, most bats are quite gentle, mind their own business, and help keep the world’s population of annoying insects in check. The next time you’re out walking along a lakeshore at dusk, just remember that the flitting bats you observe are eating as many as 1,000 mosquitoes an hour.
Although few people notice bats, the Chiroptera (meaning hand-wing) order is actually the second-largest group of mammals, making up between 20 to 25 percent of all mammal species, and is exceeded only by the many types of rodents. We’ve never quite understood why people find chipmunks cute but overlook the soft, furry bats that zip through the night, keeping us safe from insect bites. It’s probably because most folks don’t know enough about bats.
Bats can be found worldwide, except for the polar regions. Their many species can be separated into two groups “” megachiroptera and microchiroptera. As the names suggest, these are the large and small bats. The large species are found in the tropical rain forests of Australia, Asia, and Africa. They are also called “flying foxes,” as some of them have dog-like faces. The largest is the Malayan flying fox, found in Asia. It can weigh as much as 2 pounds and has a wingspan of almost 6 feet. (In case you’re worried, the big bats subsist on fruit, nectar, or pollen.)
At the other extreme are the microbats, smaller bats that are found worldwide. All of the bats that inhabit North America are from this group. The smallest species of all is the Kitty’s hog-nose bat, which is native to Thailand. Also known as the bumblebee bat, it has a 6-inch wingspan and weighs about as much as a dime.
Bats are the only mammals that actually fly. The flying squirrel doesn’t count, because it only glides. Bats have four fingers and a thumb, just as we do, but these extremities are proportionally much longer than ours. The wing itself is a double membrane of skin that stretches between the elongated finger bones to the hind legs and tail.
The small bats are known best for their method of finding and capturing prey. They use echolocation, which combines the bat’s vocal qualities with its exceptional hearing. When searching for insects, the bat emits high-pitched sounds (up to 100,000 hertz) that are far outside the range of human hearing. By listening to the bounced return (the echo), the bat creates a mental map of its environment, including flying insects it might want for dinner. As it homes in on an insect, it increases the rate of its sound emissions to fine-tune its approach, reaching as many as 200 squeaks per second. The bat may capture its prey in its mouth, or use its wings as a net to scoop the meal out of the air.
You might think that the bat has an unfair advantage against insects, using the equivalent of sonar and nets against unsuspecting prey. But while humans can’t hear the bat’s echolocation sounds, some of the insects the bat hunts can. Rather than catch dinner one tiny mosquito at a time, a bat may concentrate on much larger moths. Some moths have developed a response to the high-frequency sounds by waiting until the bat starts increasing the rate of its transmissions and then actually falling out of the air to the ground in an attempt to avoid capture. Another moth has learned to send its own high-frequency sounds back at the bat. This moth can make up to 450 ultrasonic clicks in a tenth of a second, trying to confuse the bat. In experimental videos you can actually see the bat hesitate as the moth begins its “vocal” counterattack.
Bats live in most areas where they can find food “” fruit for larger bats, pollen for others, and insects for most of the rest. Many plants in the world’s rain forests depend on the bats to either spread their seeds or to carry pollen from one plant to another. In the desert of the Southwestern United States, the giant saguaro cactus depends upon bats that migrate north from Mexico for pollination.
Because they are warm-blooded animals, bats that live in northern areas have to find a way to cope with cold weather and the absence of food during winter. Approximately 45 percent of North American birds solve the problem by migrating, but only about 3 percent of the bat population follows this example. The rest either hibernate; or, in milder areas, go into a state of torpor when temperatures drop.
Bats often hibernate in caves, where they may spend many months of the year. A hibernating bat’s heart slows down to approximately 11 beats per minute, and its body temperature drops to 40 to 60 degrees Fahrenheit. Compare that to a heart rate as high as 1,000 beats per minute when a bat is alert and flying. In order to conserve heat, many species of bats roost together in large numbers, sometimes consisting of hundreds of bats per square foot.
Some researchers believe that the amount of time bats spend hibernating contributes to their long lifespan. Depending upon the species, a bat may live for 10 to 30 years, and one bat in Europe was recaptured at 41 years of age.
As long as the weather is warm enough for insects, it’s worth looking for bats at dusk. We have a small lake near our house, and evening walks are often accompanied by the flutter of bat wings close overhead. The easiest way to see bats is to watch over water in the direction of the sunset. The reflection of the setting sun’s light will highlight the bats as they attempt to capture insects that rise off the water. What you will see is Mother Nature’s insect patrol at work.