By Dan Schneider and Peter Pautler
As the only flying mammals in the world, bats can make an impressive claim to fame. Eight species of these nocturnal creatures live in Ontario. Agile and predatory, bats are capable of extremely sophisticated bio-sonar, also called echolocation, meaning that they emit pulses of sound and can detect echoes bouncing back from objects, including their prey. Human beings are incapable of hearing the ultrasonic pulses bats emit. The sounds insect-eating bats make range in frequency from about 20,000 hertz (Hz, or cycles per second) to about 60,000 Hz. Our limit of hearing is about 20,000 Hz. (Human voices range from 100 Hz to 1,700 Hz, while a piano’s upper limit is 3,600 Hz.)
A bat’s keen sense of hearing allows it to detect returning echoes from nearby prey, and its remarkable agility allows it to then react and capture flying insects. A bat can execute a change of direction in as little as one-sixteenth of a second. Because they usually detect insects that are within a few metres, bats appear to be flying erratically as they rapidly change direction to capture prey. A red bat can emit a sound five times per second; when the bat is closing in for the kill, the rate increases to an amazing 200 times per second. Sometimes bats capture insects with their mouth, but a bat can also use its tail or wings to scoop up an insect and transfer it to its mouth “acrobatically” while in flight.
As insectivores, Ontario’s bats are beneficial to humans. A lactating little brown bat needs to consume her full body weight in insects every night (twice her normal consumption), equivalent to some 5,000 mosquitoes. One examination of the stomach contents of a little brown bat revealed as many as 145 mosquitoes.
If their prey seems small, consider the size of a bat. Ontario’s bats range from the eastern small-footed bat, which at about four grams is less than half the weight of a chickadee, to Ontario’s biggest bat, the hoary bat, which at 30 grams (on average) weighs about as much as a house mouse. At roughly eight grams, a little brown bat weighs twice as much as a small-footed bat, but still only as much as two nickels and a dime.Yet their wingspan (22 to 27 centimetres for a little brown bat), with the skin stretched thinly between elongated finger bones, creates the illusion of a bigger animal.
Comparatively speaking, bat babies are giants. A newborn little brown bat weighs an astonishing 25 percent of its mother’s weight (in comparison, a human baby weighs about 6 percent of its mother’s weight). An eastern pipistrelle bat’s twins may collectively weigh one half of the mother’s weight. Little brown, northern long-eared and small-footed bats give birth to a single offspring; all other Ontario species produce litters of two or three offspring. Mating occurs in late summer or early fall, and a delayed fertilization occurs in early spring. The gestation period lasts seven to 14 weeks. Offspring are born in late spring and early summer, in nursery colonies found in tree cavities, attics and tree branches.
Watching a bat’s acrobatic aerial manoeuvring can be mesmerizing, but identifying them by species is challenging. Using a bat detector (a device that lowers the frequencies of bat voices, thus making them audible to us) helps with identification.
Some nature centres, naturalist clubs or conservation authorities host “bat walks,” which can be quite informative. Ontario’s bats have returned with the summer season. After the sun sets, enjoy the experience of a few close encounters.