Mesmerizing Footage Shows Stream of Bats Emerge from Huge Cave

A huge swarm of bats flying out of a massive Mexican cave in unison has gone viral on Reddit.

The video, posted to Reddit by user u/Erne385291 and originally put online by Twitter user @BeAcevedoTachna, shows what appears to be thousands of bats streaming out of the Cueva de Los Murciélagos, situated around 27 miles south of Monterrey, Mexico.

Bats are the only mammals that can truly fly in a sustained fashion. They comprise around 20 percent of all mammal species and are extremely well-adapted to their environment and methods of hunting on the wing.

Chief scientist at Bat Conservation International, Winifred Frick, an associate research professor in ecology and evolutionary biology at University of California Santa Cruz, told Newsweek: "Many different species of bats live in caves and form large colonies."

According to Frick, bats live in caves because they are generally safe places to roost during the day, when the animals need shelter from predators and the weather.

About 40 percent of the world's bat species live in caves, but bats can also live in other kinds of features such as trees and, increasingly, in buildings or under bridges.

Karen J. Vanderwolf, a bat researcher at the University of Waterloo in Ontario, told Newsweek: "There are over 1,400 bat species, and more are being described every year. Like humans, bats are very social and live in groups.

"When they emerge in these big groups to go eat for the night, they do interfere with each other's echolocation, and they do bump into each other during flight.

"They are very good at recovering from collisions, though, and injuries are rare. This was discovered through the use of slow-motion videos," Vanderwolf said.

According to Vanderwolf, there are multiple species of bat present in the cave shown in the video, and it is likely that the Mexican free-tail bat, a species known for forming huge colonies in caves, is one of them.

"Mexican free-tailed bats can form very large colonies like the ones shown in the video and often fly out together in those impressive ribbons of bats," Frick said.

"In Texas, the most spectacular example is from Bracken Cave, which is owned and protected by Bat Conservation International.

"The bats leave the roost together at sunset and then hunt for nocturnal insects in the night sky – eating moths and other nocturnal insects, including agricultural crop pests."

Flying as a group has several advantages, including there being less risk of predation as an individual, according to Frick.

Bats use specialized echolocation to navigate and hunt, sending out chirping sounds at steady intervals, and using the amount of time the sound takes to bounce back to their ears to calculate the distance to the object it rebounded from.

Their hearing is extremely sensitive, and their brains have adapted to calculate the position of prey based on the noises they hear.

Bats have also adapted to change their pulse-emission frequency in relation to their flight speed, to ensure that echoes still return in their optimal hearing range.

However, with so many bats flying together, this may impact the ability of individuals to use their echolocation effectively.

"From an echolocation perspective [flying in these large groups] definitely poses a great acoustic sensing challenge," Marc Holderied, a professor of sensory biology at the University of Bristol, southwest England, told Newsweek.

"Each echolocator depends on being able to hear the faint echoes from the environment it needs for navigation.

"Unless the target is very close, these echoes are much lower in amplitude than the emitted calls, so the calls of your neighbors would flood your ears with high intensity sounds thereby masking the echoes," said Holderied.

"Several researchers have tried working out just how bats cope nonetheless, and here are some of their ideas: Bats might not call at full amplitude and only depend on the echoes from the bats flying right next to them.

"This reduces the general noise level and the number of neighbors contributing to the background noise; only a subset of individuals might call, with the silent others 'parasitizing' on the callers' echoes; or a combination with other senses compensates the partial loss of echolocation," Holderied said.