The University Record, March 8, 1999
By Cara Spindler
News and Information Services
They’ve
been accused of sucking blood, eating people and being blind. They
range from weighing less than a penny to a two-pounder with a
wingspan of six-and-a-half feet. They make up one-quarter of all
mammal species. Bats, known scientifically by their family name
chiroptera, pollinate tropical fruit trees, can each eat 600
mosquitoes an hour and, as a colony, can protect a farmer from more
than 15 million rootworms in a summer.
Like frogs, bats are a good overall indicator of environmental health; a fact that becomes even more important with the realization that 50 percent of American bats are in severe decline or listed as endangered.
Because bats generally have only one offspring per year, they are a particularly vulnerable species. When migrating to an area where harmful herbicides and pesticides are still being used, the bat population becomes even more at risk. Phil Myers, associate professor of biology, says bats don’t suck blood. Rather, they first lick the chosen area with their tongues to desensitize it, then scrape and lap until they’re full. Vampire bats usually gorge themselves until they can’t fly, Myers says, and have to wait until their kidneys filter the material to become airborne.
Bat eyesight ranges from very good to very poor. Most rely on echolocation—the ability of animals that emit high-frequency sounds to orient themselves by means of the reflected sound waves—rather than sight to find food. This high-frequency ultrasound is higher than the range of human hearing and generally comes from the bat’s mouth. A few have evolved to emit the sounds from their noses, freeing their mouths for eating at the same time.
Biologists, using an instrument called a “bat detector,” can monitor bat calls, which average 30 pulses per second when flying. When approaching a target, the pulses can increase to 300 per second.
Myers says a bat can tell an object’s size and distance, how long it will take to reach the target and how fast the object is moving. Some bats, he says, even recognize textures, distinguishing stationary moths from tree trunks.
Bats have modified forelimbs that act as “wings,” with tiny nails at the end for roosting and feeding. Depending on what and how they eat, bats have long strong teeth to get through rinds and dig deep into fruit, or a flap of skin between the hind legs that works like a baseball glove to catch insects. Bats that eat nectar have hardly any teeth, but do have a fluted tongue like a hummingbird’s. Carnivorous bats have thin, sharp incisors to break through skin and tough teeth to tear at the meat.
In Michigan, bats generally feed at dusk during the summer months. Some hibernate during the colder months in protected places, like caves and barns. The red bat, able to withstand cold, hibernates in trees. Other Michigan bats migrate several hundred miles to southern Indiana, while still others head for Mexico.
For more information about bats, search the Museum of Zoology’s Animal Diversity Web page at www.oit.itd.umich.edu/projects/ADW.