On the hunt for their nightly meal, a swarm of Geoffroy's Rousette fruit bats bursts out of a Philippines cave in 2008.
In January 2011 a U.S. cave-mapping expedition stumbled upon an unusually high number of pregnant bats in the Monfort bat colony, in the country's southern Mindanao region (see map). The bat species does not usually give birth in January, making the discovery a "big surprise" and forcing the scientists to halt their mapping project, according to Norma Monfort, founder and president of the Monfort Bat Cave & Conservation Foundation.
The cause of the bat baby boom is unknown, although Monfort suspects one factor may be that the cave is protected from humans as an ecotourism site, which allows their numbers to grow. Monfort's family has owned the property for more than a hundred years.
In most of the bats' Southeast Asian range, people either hunt the mammals for food or disturb them while harvesting guano for fertilizer. If people enter a bat cave, nursing mothers can be easily startled, causing their pups to tumble to their deaths, Monfort said by email. (Interactive: Hear bat calls.)
But at Monfort cave, the 1.8-million-strong colony is not only thriving, in 2010 the Guinness Book of World Records deemed it the world's largest gathering of Old World fruit bats.