By Kaitlyn Fletcher
Tucked into the western slope of the Sangre de Cristo Mountains, an abandoned iron mine hosts the largest known roost of Brazilian Free-tailed Bats in North America. June marks the annual return of these 250,000 summertime residents.
“Brazilian free-tailed bats form some of the largest aggregations of mammals anywhere in the world,” said Daniel Neubaum, the Conservation Species Program Manager at Colorado Parks and Wildlife, who was ‘tagged’ by the agency for bats. While most male bats prefer to live alone, this species is an “exception to the rule.”
Other large seasonal roosts are located in Grand Junction and throughout the Colorado National Monument. Bachelor colonies typically consist of hundreds to thousands of bats.
Migrating from the borderlands of Mexico, the nocturnal visitors come for the San Luis Valley’s resources, rich in insectivore delights.
Aerial warfare for agriculture
Every night, an enormous army of bats swarms into the skies. Typically about 9 centimeters, these tiny soldiers can reach speeds of 60 mph while feasting on “metric tons of insects” across the landscapes.
Insects thrive in the valley’s rich agricultural fields, wetlands and other moist habitats. This bat’s diet consists mainly of small moths, sometimes snacking on mosquitoes, beetles and other insects. Many are major agricultural pests, providing “a bonus for the agricultural community because fewer bugs are eating their crops,” Neubaum said.
Hungry bats save the U.S. agricultural industry at least $3 billion annually in pest control. Bats hunt insects using echolocation, which involves using sound waves to target their preferred prey’s size and shape. Researchers used hot air balloons equipped with acoustic detectors to document these fast fliers foraging on moths almost two miles above the surface.
“Some moths try to jam the echolocation signals of bats by emitting their own noises,” Neubaum said. “It’s like aerial warfare out there where bats change their pitch and type of call to get the best information on the bug’s location. Moths fight back with different clicks and calls.”
As the sun rises over the mountains, the large plume — visible even from weather radar — returns to camp in the Orient Mine to nestle in the darkness.
More than an abandoned mine
Orient Mine is tapped into an existing cave system with five-plus levels to separate different bat species. Each passage differs in its climate, accommodating a variety of needs. This bachelor pad is within a huge multi-level room where the ceiling collapsed, creating an outside access point now labelled as the Glory Hole.
The abandoned mine and its inhabitants are now protected within the 2,200-acre Orient Land Trust, which also preserves the surrounding natural and cultural resources, including Emerson Ranch and Valley View Hot Springs. The trust offers free public tours to view this immersive wildlife experience, among other educational programs.
Aaron Sidder, the Ecology and Compliance Coordinator for Bat Conservation International, helps get “boots on the ground.” BCI works with federal partners to protect bat habitat, mostly on BLM lands, through watershed restoration and mine closures, to name a few of their efforts.
Designed to allow bats to pass, the Glory Hole is fenced off from the public to protect both parties.
“(Bat gates) protect people from themselves because these mines are hazardous places,” Sidder said. “The BLM especially doesn’t want people exploring these things in the dark. There can be air hazards,” vertical drops, weakened infrastructure and other invisible dangers, Sidder said.
It is a misconception that bats only find homes in caves and mines. They will also use rock crevices and trees. Season-dependent, bats rely on numerous local habitats to roost, feed and hibernate, including vulnerable riparian habitats.
Threats to bats
Detected for the first time in June 2022, white-nose syndrome attacks bats during hibernation, causing starvation and irreversible wing damage. Although flagged as potential carriers of this fungus, Brazilian free-tailed bats have yet to show signs of this mammal’s biggest threat. It has not spread to the Orient Mine.
“If you take (the fungus) into a warm environment, the spores can survive, but they generally don’t reproduce, propagate, or grow. So when bats come back to a warm summer roost, they can clean the spores off their bodies and get them out of their system.”
This deadly fungus thrives and persists in cold climates, mirroring its hibernation habitat.
“Arousing bats from winter hibernation can be detrimental to their health,” Sidder said. “That’s what white-nose syndrome does: (the irritation) arouses them from torpor and then they starve to death because there’s inadequate insect availability at that time.”
Other threats include habitat loss, energy development, particularly windmills and extermination in urban areas.
Brazilian free-tails and beyond
Colorado has an estimated 19 species of bats, about half of which have been recorded in the San Luis Valley. These include several Myotis species, the common Big Brown Bat and another migratory species, the Hoary Bat. Some are considered Species of Concern.
Brazilian free-tailed bats cover one of the biggest ranges in the Americas, occurring through Central and South America. Neubaum describes this species as “highly diversified,” surviving the humid tropics and up into cool temperate zones.
Other famous roosts, such as Bracken Cave in Texas and Carlsbad Caverns in New Mexico, are maternity colonies where females raise the next generation of fliers. Mothers often only raise a single pup.
Maternity roosts are warm, humid environments that can reach 120 degrees, explained Neubaum, joking that he’s “never seen a sweaty bat.” Ideal homes have high exit points to protect juniors learning to spread their wings. Chosen winter spaces are co-ed, cold and constant to promote hibernation.
Most of the valley’s bats hibernate within Colorado, including the Big Brown Bat and Townsend’s Big-Eared Bat, while a select few migrate into the state for the summer season. Most hibernate in elusive spots inaccessible to humans.
“Believe it or not, 20 years ago, we didn’t know where most of our Colorado bats spent the winter. That’s the beauty about bats…,” Neaubaum said. “There’s still a lot left to learn. Many mysteries to solve.”
If you find a grounded bat, call Colorado Parks and Wildlife (303-291-7771) or Colorado BatCREW (866-909-2287) immediately for resources. Do not touch bats.