When the sun sets, bats come alive.
By Kristen Pope
As night falls, and humans wind down for the evening, bats get ready to leave their daytime roosts for a long night ahead. Bats use the evening hours to forage for food, find water, and engage in other vital pursuits.
To celebrate bats’ nighttime activities, bat lovers have held International Bat Night every August since 1997, and the event is now observed in more than 30 countries.
While they fly under cover of darkness, bats can use their amazing echolocation abilities to seek out prey. Bats send out high-frequency sounds which bounce off insects and other prey, letting the bats know just where these targets are located.
One example of a bat that uses echolocation to feed at night is the Mexican free-tailed bat (Tadarida brasiliensis). A maternal colony of 15 million of these bats lives in Bracken Cave (located near San Antonio, Texas) during the summer months.
They emerge each evening to forage, but Fran Hutchins, Director of Bracken Cave Preserve, points out, “They’re not completely nocturnal. It doesn’t have to be completely, totally dark for the bats to be out foraging.”
Hutchins says they emerge around 6:30 p.m. each night in late summer, a few hours before the sun sets, which is around 9 p.m.
When they head out for a night of foraging, adult Mexican free-tailed bats can travel up to 60 miles each way in search of insects to eat. They hunt in crop fields, and sometimes fly up to 10,000 feet in the air to devour high-flying swarms of insects. Juveniles stay closer to their roost, lacking the energy reserves to travel as far as the adults.
When they emerge in the evening—and return in the morning—they form a swirling vortex dubbed a “batnado.”
“In the morning these bats are coming in from hundreds of feet up in the air, so it literally rains bats into the cave in the morning,” Hutchins says. It takes a couple hours for them to return around dawn, and they must dodge aerial predators like raptors and hawks as they fly, as well as ground-dwelling predators like snakes and raccoons.
After a long night of foraging for food, sipping water while flying, and dodging predators to re-enter the cave, they’re ready for a day of rest before doing it all again.