Newborn bats are remarkably small at birth. Understanding their initial size, rapid development, and species-specific variations provides insight into their life cycle and adaptations.
Initial Dimensions at Birth
Newborn bats, often called pups, typically measure 1 to 2 inches (2.5 to 5 centimeters) in length. They can weigh as little as 0.1 ounces (a few grams), comparable to half a teaspoon of sugar. While these are general averages, some microbat pups can weigh up to 28.3% of their mother’s body mass at birth.
For example, a big brown bat pup might weigh around 3 grams, while its adult mother weighs approximately 17 grams. A little brown bat pup typically weighs about 2.2 grams when born. This initial size underscores their complete dependence on their mothers during the first few weeks of life.
Appearance and Rapid Development
Newborn bat pups are often born hairless or with very fine, sparse hair, giving them a pinkish hue. Their eyes are typically closed at birth. Despite this, they undergo rapid growth and development.
Within a week or two, pups of many bat species begin to open their eyes, and their fur starts to develop, becoming thicker. This accelerated development is important for their survival. Pups often grow to nearly full size within three weeks, thanks to the rich milk provided by their mothers. Around this same time, they begin their first attempts at flight.
Varying Sizes Among Bat Species
The term “baby bat” encompasses a wide spectrum of sizes, reflecting the diversity within the nearly 1,400 known bat species worldwide. A newborn’s size is largely determined by its species.
The smallest bat species, and arguably the smallest mammal, is the Kitti’s hog-nosed bat, also known as the bumblebee bat. An adult of this species measures 1.1 to 1.3 inches (2.8 to 3.3 centimeters) in length and weighs approximately 2 grams. This means an adult bumblebee bat is comparable in size to the pups of many other bat species.
In stark contrast, the largest bat species, such as the giant golden-crowned flying fox, can have a wingspan of up to 5.6 feet (1.7 meters) and weigh up to 3.5 pounds (1.2 kilograms) as adults. While their pups are still small at birth relative to the adult size, they are significantly larger than the adult Kitti’s hog-nosed bat. For instance, a female fruit bat weighing around 300 grams can give birth to a pup weighing about 50 grams, demonstrating the considerable size of some newborn bats relative to their mothers.