As winter approaches, bats face significant challenges due to the scarcity of their primary food sources. Their survival through colder months relies on remarkable adaptations.
Hibernation: A Winter Fast
For many bat species in temperate regions, hibernation is their main winter survival strategy. This deep state of inactivity involves significantly lowered body temperature and a drastically reduced metabolic rate. A bat’s heart rate can slow from 200-300 beats per minute to as few as 10, with breathing becoming infrequent. This physiological slowdown allows bats to conserve up to 98% of their energy.
During hibernation, bats do not eat, relying on energy stored in their fat reserves. They choose secluded locations like caves, mines, or attics, known as hibernacula, where temperatures remain stable. While bats may briefly awaken from torpor, they generally do not feed, as foraging expends too much energy.
Building Reserves for Winter Survival
In late summer and autumn, bats engage in intensive feeding to accumulate energy reserves for hibernation. They consume large quantities of insects, building significant fat stores necessary for survival.
These fat reserves are the sole energy source fueling bats throughout hibernation. A bat can consume up to its body weight in insects each night during peak feeding times. This ensures they have enough energy for months without food, including periodic arousals.
When Bats Remain Active
While hibernation is common, some bat species in warmer climates remain active and feed throughout winter. In regions where insect activity persists year-round, bats continue their regular foraging. This includes areas with consistently mild temperatures, like parts of the southeastern United States or Florida. These active bats primarily consume available insects such as moths, beetles, flies, and mosquitoes.
Some bat species may also tolerate cooler temperatures to forage when conditions allow, even if they typically hibernate. Research indicates that bats active in winter consume various insect prey, including agricultural and forest pests like green clover worms, Nantucket pine tip moths, and pale weevils. Depending on species and location, their diet might also include nectar or fruit if available.
Migration: A Seasonal Shift
Another winter survival strategy for certain bat species is migration to warmer regions. Instead of hibernating, these bats escape cold temperatures and food scarcity by relocating. This seasonal shift allows them to access environments where food remains abundant.
Migratory bats continue to feed during their journey and in their warmer wintering grounds. Some species, like the Nathusius’ bat, can travel up to 2000 kilometers to find suitable climates. Their diet in these areas largely consists of insects, or for some species, fruit and nectar.