Thomas's Sac-winged Bat

Fascinating facts about the Thomas's Sac-winged Bat

• A male Thomas's sac-winged bat has two pouches in his wings — one on each forearm — that he fills with a pungent, musky secretion from glands near his shoulders. During the day, while hanging in his roost, he periodically unfolds his wings to waft this scent toward females roosting nearby, essentially turning himself into a living perfume dispenser. The smell is so distinctive that researchers can identify individual males by their signature scent profile. This ritual advertising happens hundreds of times per day, making male Thomas's sac-winged bats the most dedicated fragrance marketers in the animal kingdom.
• Thomas's sac-winged bats are among the few bat species that roost in groups of just 6 to 8 individuals — and they return to the exact same roost site, often a furled leaf or tree cavity, night after night for months or years. This extreme site fidelity means a single colony occupies a territory smaller than a basketball court, and the same animals sleep within centimetres of each other every dawn. Researchers can recognize individual bats by their roost choice, watching the same personalities claim the same spots across decades.
• Unlike most tropical bats that breed seasonally, Thomas's sac-winged bats in Central America breed year-round, with females giving birth roughly every five months. A pregnant female carries a pup that weighs nearly 40 percent of her own body mass — imagine a human mother carrying a 35-kilogram fetus. Despite this burden, she hunts nightly for insects and fruit, diving and weaving through dense vegetation with almost no loss of agility, her metabolism firing at extreme speed to sustain herself and her growing offspring.
• Thomas's sac-winged bats hunt using ultrasonic calls at 120 to 150 kilohertz — frequencies so high that humans cannot hear them even with hearing aids — yet they also produce social calls in the 20 to 40 kilohertz range that other bats and even some insects can detect. Males use these lower-frequency chirps to communicate dominance and territory within their tiny roosting groups. They have essentially invented two parallel languages: a private ultrasonic conversation for finding food and a public frequency for advertising status and defending their leafy home.
• The sac-winged bat's vulnerability to habitat loss is sharply defined: they depend on tropical dry forests where trees still retain water-filled furled leaves and hollow cavities through the dry season. Climate change is extending dry seasons across Central America, causing trees to shed leaves earlier and remain leafless longer, which collapses the roost availability that entire colonies need to survive. A single severe drought can eliminate a multi-year-old roost site within weeks, forcing the same bats that have roosted in the same spot for three years to vanish or relocate — a survival gamble that few can win.

At a glance

About the Thomas's Sac-winged Bat

In the twilight skies of Central America, the Thomas's Sac-winged Bat dances on leathery wings, its delicate form silhouetted against the fading light as it embarks on a nocturnal quest for insects. With each beat of its wings, the bat unleashes a soft whoosh of air, a gentle whisper that belies the remarkable agility with which it navigates the dense forest canopy. As it flits and weaves through the shadows, its sac-like wings, adorned with intricate folds of skin, glow like tiny lanterns, a testament to the remarkable adaptability of this vulnerable creature.

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