Bats are unique among mammals because they are the only group capable of sustained, powered flight. A baby bat, known as a pup, is born into a world where this ability is still several weeks away. Unlike the young of many bird species, bat pups are not born ready to fly or even glide. They are born dependent on their mothers. This inability to fly is a direct consequence of their altricial nature and the complex physical requirements of their specialized anatomy.
When Bat Pups Take Their First Flight
The age at which a pup takes its first flight varies significantly across the thousands of bat species. For most small insect-eating bats, or microbats, the timeline from birth to independence is fast. Pups generally begin to test their wings and take short, clumsy practice flights within the roost around three to five weeks of age.
True sustained flight, which signals independence, typically occurs around six weeks for many microbat species. This period coincides with their weaning, as they must now forage for themselves. Larger species, such as some fruit bats (megabats), may take longer, sometimes requiring up to eight weeks before achieving confident flight. This rapid development is necessary, as the young bats must quickly master flight and foraging before the colder months arrive.
Dependence and Early Life in the Roost
Before they can fly, young bats spend their first weeks sheltered in specialized maternity roosts. These roosts are warm, safe places where pregnant females gather to give birth and raise their young, often containing hundreds or even thousands of individuals. Pups are born altricial, meaning they are initially blind, furless, and weighing about one-third of their mother’s weight in some species.
Mothers nurse their pups for approximately four to five weeks, providing the high-fat milk necessary for their rapid growth. While the mother is away foraging during the night, pups are often left clustered together in groups known as creches, which helps them conserve warmth. This communal roosting is important because the warm environment helps accelerate the pup’s development. Though the colony is dense, a mother is able to locate and nurse her own offspring upon returning, often using specific vocalizations to identify her pup.
Physical Development for Sustained Flight
The delay in a pup’s flight capability is due to the anatomical development required for powered flight. At birth, the pup’s wingspan and wing area are too small, and the muscles are not yet strong enough to overcome the force of gravity. The wing structure, composed of skin membrane (patagium) stretched over elongated finger bones and forelimbs, must grow significantly.
The growth of the forearm bones, wingspan, and wing area typically outpaces the increase in body mass during the pre-flight period. During this time, the pup engages in pre-flight exercises like “push-ups” and wing flapping, which strengthen the developing bones and the large pectoral flight muscles. This physical training and rapid growth are necessary to reduce wing loading—the ratio of body weight to wing area—to a point where the young bat can lift its body and achieve aerodynamic stability.