A baby bat is called a pup. Most bat species give birth to just one pup per year, and that single newborn can weigh up to a third of its mother’s body weight, with some species producing pups that reach 43 percent of the mother’s weight. Bats are mammals, so pups are born live, nurse on milk, and depend entirely on their mothers during their first weeks of life.
Why Most Bats Have Only One Pup
Given how large a bat pup is relative to its mother, carrying more than one is rare. Imagine giving birth to something that weighs nearly half of what you do, and you begin to understand why twins are uncommon. The few exceptions belong to a group of tree-roosting bats that includes red bats and hoary bats, which regularly have twins and can produce litters of four or five pups. For the vast majority of the world’s 1,400-plus bat species, though, one pup per year is the norm.
What a Newborn Bat Looks Like
Bat pups are born hairless and with their eyes closed. They look nothing like the fuzzy, winged adults most people picture. Immediately after birth, the newborn crawls to its mother’s nipple, latches on, and begins to feed. In these early days, a pup clings tightly to its mother’s body, sometimes even while she flies. The pup’s grip strength is remarkable for its size, since falling from a roost or from a flying mother would be fatal.
How Pups Grow and Learn to Fly
Development happens fast. Pups are typically weaned within the first three weeks after birth, which means they transition from milk to solid food (usually insects or fruit, depending on the species) in under a month. Flight comes shortly after. Observations in the wild show that newborn bats can fly as early as 22 days old. This rapid timeline isn’t optional. A pup that can’t fly and forage on its own will starve, so the pressure to develop quickly is intense.
Despite this speed, first-year survival rates are low. Data on little brown bats, one of the most studied species in North America, shows that juvenile female survival in the first year ranges from just 23 to 46 percent. The main bottleneck is the first winter. Young bats often haven’t built up enough fat reserves to survive hibernation. Those that make it through their first year have much better odds going forward, with annual survival rates climbing to 60 to 90 percent in subsequent years.
How Mothers Find Their Pups
Many bat species form maternity colonies, large gatherings of females that roost together to give birth and raise their young. These colonies can number in the hundreds or thousands, which creates a challenge: how does a returning mother find her own pup among a crowd of nearly identical babies?
Bats solve this with a combination of sound and smell. Each pup produces unique vocalizations that its mother learns to recognize. But scent plays an equally important role. Research on flat-headed bats found that mothers were significantly more attracted to the scent of their own pups compared to other pups in the colony. This dual identification system, voice plus smell, allows a mother to reliably locate her pup even in a dense, noisy roost.
What Bat Milk Provides
Bat milk varies by species, but it generally delivers a concentrated package of fat and protein to fuel rapid growth. In fruit bats, milk fat content ranges from about 6 to 8.5 percent of wet mass, roughly double the fat content of cow’s milk (about 3 percent). Protein levels hover around 2.6 to 3.4 percent, comparable to bovine milk.
Insect-eating bats produce even richer milk. Their milk is generally higher in fat, protein, and overall energy content than what fruit bats produce. This makes sense: insectivorous bats tend to be smaller with faster metabolisms, and their pups need to pack on weight quickly to survive their first migration or hibernation season.
What to Do If You Find a Baby Bat
A pup found on the ground has likely fallen from its roost. It may look helpless, and the instinct to pick it up is understandable, but you should not touch it with bare hands. Bats are the most commonly reported rabid animal in the United States, and bat bites can be so small you may not realize you’ve been bitten.
If you find a grounded pup, keep children and pets away and contact your local animal control or public health department. They can assess whether the pup can be safely returned to its colony or transferred to a wildlife rehabilitator. If you must move the bat to protect it from immediate danger, wear thick leather work gloves. You can place a box or container over the bat, slide a piece of cardboard underneath, and secure it with tape, punching small air holes for ventilation.
Signs that any bat, adult or pup, may be sick include being active during the day, inability to fly, resting in an unusual location like the ground or inside a home, or allowing you to approach closely. Healthy bats avoid humans. If you’ve had any physical contact with a bat, wash the area with soap and water and contact a healthcare professional, even if you don’t see a bite mark.