Watch: Vampire bat on treadmill proves they use blood for fuel

Low-carb, high-protein diet no barrier to creatures’ energetic exercise, scientists find

Vampire bats’ main fuel source is the blood they drink, scientists have confirmed – after putting the creatures on a treadmill.
Most animals, including humans, use carbohydrates as their primary fuel but the vampire bat has a diet consisting of only blood, which is low in carbs and high in protein.
Scientists in Canada built a custom treadmill that went up to a speed of 1.1 mph to exercise wild bats and explore whether they have a special ability to make energy from proteins in the same way as blood-sucking insects such as mosquitoes.
Footage of the bats includes a blooper reel of one trying to avoid the treadmill and falling off the back of it, while the scientists also made a slow-motion clip of one bat strutting sideways to the 2006 song Walk It Out by rap artist Unk.
A total of 24 vampire bats — the only mammal which has to eat blood to survive, known as an obligate sanguinivore — were captured from Belize forests for the study.
They were fed a diet of cows’ blood enriched with certain amino acids, the building blocks of proteins, to allow the scientists to monitor how many amino acids were burned for energy.
The bats were then put on the 26in treadmill, which was turned up to a speed of 0.4mph to allow the animals to get used to the setup, before researchers cranked it up to 0.75mph after a couple of minutes.
Bats then used a sideways gait that was halfway between a walk and a run, the scientists found, which has “occasional hops”.
A couple of minutes later the treadmill was put at full speed of 1.1mph, which was running speed for the bats.
“Hops occurred consistently, each with a notable aerial phase,” the scientists from the University of Toronto write in their study, published in Biology Letters, a Royal Society journal.
Bats in the study went through this process three times while scientists monitored how much oxygen they were using and how much carbon dioxide was being produced by the bat.
Analysis of the air samples revealed the bats were using protein as their primary source of fuel, which came from the blood they had eaten.
Study author Dr Kenneth Welch, associate professor at the University of Toronto, told The Telegraph: “These bats are incredibly intelligent and cunning little animals. And, like us, they prefer not to exert themselves if they don’t need to.
“Our metabolic treadmill had been designed for use with rats but, unlike rats, bats are incredibly dextrous and have long, strong thumbs that they could use to hook these holes and hold themselves up off the moving belt.
“Dr Giulia Rossi, who did the bulk of the work, cleverly patched these up with duct tape to thwart the lazy bats.
“After this, almost all the bats we tried eventually figured out how to walk and run on the treadmill and, for the most part, they were really exercise champs, staying active over a nearly 1.5-hour trial time.”
He added: “They may seem like ungainly walkers to us (I am reminded of walking with crutches; or to the way a gorilla walks), but it certainly works for them.
“Most species of bats are not really capable of running and it seems that in evolving to be aerial specialists, most bats lost their ability to run, and most are pretty lousy on the ground at all.
“But vampire bats need to sneak up on their prey to nip their foot or ankle and start lapping up blood, so they re-evolved the ability to walk well, and even to run, so that they might track a capybara along a forest trail at night.”
The scientists say that the study is proof that the bats have evolved to make energy from blood in a similar way to that of mosquitos.
This, they add, is “a striking example of convergent evolution among both vertebrate and invertebrate obligate blood-feeding animals”.