Bats employ hibernation, a specialized survival strategy, to endure periods of scarce food, especially in colder months. This deep, sleep-like state involves physiological changes, enabling them to conserve energy and survive extended periods without feeding.
Understanding Bat Hibernation
Bat hibernation involves torpor, a state of reduced metabolic activity. During this time, a bat’s body temperature drops dramatically, often nearing the ambient temperature of its surroundings, sometimes as low as 0-2 degrees Celsius (32-35.6 degrees Fahrenheit).
A hibernating bat’s heart rate slows considerably, from hundreds of beats per minute when active to as few as 5-20 beats per minute. Respiration also slows, with bats taking only a few breaths per minute, sometimes going minutes without a single breath. These physiological reductions allow bats to burn fewer calories, relying on fat reserves accumulated during warmer months. Bats may spontaneously wake up for short periods, lasting from 30 minutes to an hour, which requires substantial energy to raise their body temperature back to normal.
Hibernation Locations and Timing
Bats typically hibernate during the winter months when their primary food source, insects, becomes unavailable. The duration of hibernation can vary, with some species, like the little brown bat, hibernating for more than six months until insects reappear in the spring. This extended period necessitates a stable environment.
Bats seek out locations, known as hibernacula, which provide stable temperatures, high humidity, and minimal disturbance. These sites often include caves, abandoned mines, and rock crevices. Some species may also use old buildings or hollow trees as hibernacula. Bats generally prefer temperatures around 5 degrees Celsius (41 degrees Fahrenheit) and high relative humidity (often 90-100%) to prevent dehydration during their dormant state.
Threats to Hibernating Bats
Hibernating bats face several dangers due to their vulnerable state. White-Nose Syndrome (WNS) is a fungal disease caused by Pseudogymnoascus destructans (Pd), which thrives in the cold, moist conditions found in hibernacula. The fungus grows on the bat’s bare skin, including its muzzle, ears, and wings, causing physiological disruption.
WNS causes bats to awaken more frequently from torpor, prematurely depleting the fat reserves they need to survive the winter. This increased arousal, combined with wing damage that can lead to dehydration, often results in starvation or death. Human disturbance, even minor incidents like noise, light, or touching, can also cause bats to wake up, expending energy reserves and potentially leading to their demise. Habitat loss, including the destruction or alteration of suitable hibernacula, further threatens bat populations by reducing the availability of safe wintering sites.