Bats that Run

01.03.25

By Alyson Brokaw

Starting a new year is a time to reflect on the past and make goals for the future. And if you are like about 50 percent of Americans, one of your New Year’s Resolutions might be related to fitness. Maybe you want to hit the gym regularly this year or maybe start up a running program. If so, you may be able to take inspiration from an unlikely source – bats! While bats are best known as the only mammals capable of flight, at least a couple have adapted to a life on the ground: the common vampire bat (Desmodus rotundus) and the New Zealand lesser short-tailed bat (Mystacina tuberculata). 

With hands and forearms that have been highly modified through evolution into wings, and knees that face backwards (compared to humans), how exactly is it that bats can run anyway? Let’s start by examining the kinematic definition of “running.” If an animal’s gait has an aerial phase, where all four limbs are off the ground, then it meets one of the criteria to be considered a “run.” The second criteria has to do with how much time a limb spends in the air over the course of a stride (or duty cycle) – if in the air for more than 50 percent of this cycle, then it is kinematically a run. 

While bats are best known as the only mammals capable of flight, at least a couple have adapted to a life on the ground.

To measure the kinematics of bats moving on the ground, scientists trained bats to walk on a special treadmill, recording their movements with video. At low speeds, the vampire bats moved with a “cat-like” prowl, using a lateral sequence gait. This gait is common in quadruped animals; when the left front limb moves forward, the back right limb does the same. While the short-tailed bats did not take to the treadmill as readily as the vampire bats, they also used the same lateral sequence walk. However, as the speed on the treadmill increased, the vampire bats shifted their gait from a prowl to a bouncing gallop. Since this bounding gait has a significant aerial phase where all four limbs leave the ground, it meets at least one of the definitions of a run. However, unlike the bounding gait of other mammals like squirrels and rabbits, vampire bats use a front-wheel drive – they initiate their leaps using their front limbs instead of the back legs. 

With hands and forearms that have been highly modified through evolution into wings, and knees that face backwards, how exactly is it that bats can run anyway?

Why would bats be adapted to move efficiently on the ground? The New Zealand lesser short-tailed bat evolved on islands without native land predators like cats or snakes. While they didn’t become flightless like some famous island birds, such as the dodo or kiwi, these bats have adapted to take advantage of ground-based resources. In addition to catching insects in the air, as most insect-eating bats do, short-tailed bats spend up to 30 percent of their time scurrying along the forest floor in search of buried insects, fruits, and nectar. With no major predators around, they’ve never needed to run fast or make quick escapes.

Unlike the bounding gait of other mammals like squirrels and rabbits, vampire bats use a “front-wheel drive.” 

In contrast, common vampire bats use their cat-like prowl to approach their sleeping prey, which includes large livestock like pigs, cows and horses. When feeding under animals that are up to 16,000 times their size, a quick burst of speed can be crucial for dodging a dangerous stomp. Interestingly, the ability to gallop may be unique to common vampire bats. When placed on a treadmill, the white-winged vampire bat (Diaemus youngii) also moved in a lateral sequence gait, but did not transition to a run at higher speeds. White-winged vampire bats, along with the yet-to-be-tested hairy-legged vampire bats (Diphylla ecaudata), primarily feed on birds, so they likely don’t require the same speed to avoid being crushed during a meal.

If you’re planning out your running goals this year, you might be thinking about how to stay in your “fat-burning” zone or perfecting your carb-loading strategy for that big race. After all, humans, like most mammals, rely on metabolizing carbs and fats to fuel endurance activities. However, recent research on vampire bats and their treadmills uncovered an unusual way for mammals to power their workouts. Scientists monitored vampire bat metabolism for up to 90 minutes as the bats walked on the treadmill and found that at much as 60 percent of the bats’ energy came from amino acids, the building blocks of protein, not carbs or fat. This discovery makes sense considering their protein-rich but nutrient-limited diet and highlights just some of the incredible adaptations vampire bats have to support their blood-feeding lifestyle.