Brazilian Free-Tail Bat Outflight

From April through mid-October, visitors watch the nightly spectacle of several hundred thousand Brazilian free-tail bats exiting Carlsbad Cavern in search of food.

NPS Photo by Nick Hristov.

 

What triggers emergence of the bats from the cave at night is something of a mystery. The only scientific correlation found with the emergence of bats is civil twilight (28 minutes past sunset). Bats flying around the roost site can see light entering Bat Cave from Carlsbad Cavern’s second natural entrance. But based on the variability of the bats emergence, civil twilight is not the only explanation.

The outflight can last up to three hours, depending on a variety of factors, including the number of bats in the colony. Bats can begin returning at any time, particularly when they have pups to nurse (in which case they typically head out to feed again before morning). The number of bats returning usually peaks around dawn. When the bats fly over the amphitheater, you can hear their wings and also smell them. The Brazilian (Mexican) free-tail bats have a unique odor—not all bat species have an obvious odor. The bats spiral out of the cave in a counter-clockwise direction. It is not known why they choose to spiral counter-clockwise, but current research suggest a variety of factors play roles. One of these may be an internal ‘compass’ in the bats that is based on the earth’s magnetic poles.

For more information on the park’s evening bat flight program, click here.