"Drunk" bats have no trouble flying under the influence, a new study says.

Tropical bats of Central and South America regularly eat fermenting fruits and nectar. But they can fly and use their built-in "sonar" just as well while inebriated as while sober—even with blood-alcohol contents that would exceed legal limits for people.

(See more pictures of Central American bats.)

"We went into the study fully expecting that some of the species wouldn’t be able to hold their drink," said study co-author Brock Fenton, a biologist at the University of Western Ontario in Canada.

But "the bats, unfortunately, hadn’t read the proposal," he said.

Buzzed Bats

In April 2009 Fenton and colleagues caught 106 bats representing six different species in northern Belize. The team gave the bats either sugar water or ethanol—the intoxicating agent in liquors—in amounts proportional to the bats' body weights.

The scientists then took saliva samples to gauge the bats' blood-alcohol content (BAC). Some bats had a BAC of more than 0.3 percent—in all 50 U.S. states, it's illegal to drive with a BAC of 0.08 percent.

The flying mammals were placed in a closed obstacle course on the forest floor. "It’s like walking a straight line," Fenton quipped, referring to a common test given to suspected drunk drivers by police —except to succeed, the bats had to maneuver around hanging plastic chains without crashing.

The team also recorded the bats' echolocation calls to see if they'd "slur their words," Fenton said. Bats use echolocation—sound waves that bounce off objects—to sense prey and to navigate. (Interactive: Hear bat calls.)

Surprising the scientists, the buzzed bats passed both tests with flying colors. (Related: "Extinct Walking Bat Found.")

Lightweights to Lushes

The team also discovered that the bat species had varying blood-alcohol contents, suggesting a spectrum of tolerance.

Fenton compared such variation to people, saying there are some who just "sniff the cork [and] they’re gone and others who can soak up two or three bottles and don’t show any sign of impairment."

What's more, tolerance in bats—as in humans—may be dictated in part by how often and how much a bat drinks.

For example, a previous study in Israel had shown that drunk Egyptian fruit bats crashed more frequently in experiments than the New World bats did, Fenton said.

New World bats may handle alcohol better because they eat more fermented foods than Old World bats, according to the study, published February 1 in the online journal PLoS One.

New World bats' high tolerance may have afforded them an evolutionary edge, Fenton added, since they could handle eating fruits that other animals couldn't. This alcohol tolerance may even explain why Central and South American bat species are so much more diverse than in other regions.