A treadmill run revealed unique metabolic traits of common vampires.

During their nocturnal hunts, vampire bats target sleeping birds or mammals, including livestock and humans. To silently approach their prey, these bloodsuckers often land nearby and sneak up on foot, relying on their folded wings.

This type of pursuit can consume a significant amount of energy. Meanwhile, the blood that makes up the diet of desmodus is rich in iron and protein but contains minimal fats and carbohydrates, which most other mammals use to meet their energy needs. A recent study, published in the journal Biology Letters, revealed how common vampires have adapted to this challenge.

Some blood-feeding insects, such as African tsetse flies Glossina spp., manage to cope with physical exertion on a low-calorie diet of blood by oxidizing the amino acid proline. Biologists from the University of Toronto (Canada) hypothesized that Desmodus rotundus may have developed a similar capability.

To test this hypothesis, researchers captured over two dozen vampire bats in the tropical forests of Central America. They conducted experiments on a specially designed treadmill, which allowed for air sampling to analyze the levels of oxygen, carbon dioxide, and water vapor.

Before the study, the bats were fed cow's blood from a local slaughterhouse, which had been enriched with two amino acids—glycine and leucine—labeled with carbon isotopes to accurately track the metabolic processes of the vampires. The experiment also included three control animals that were fed blood without the added amino acids.

In a series of trials, the researchers gradually increased the treadmill speed from 10 to 20, and then to 30 meters per minute, causing the subjects to transition from walking to running with jumps. Short breaks were taken between runs at different speeds to allow the animals to rest, refresh the air in the treadmill chamber, and for additional blood feeding.

During the experiments, scientists measured the bats' oxygen consumption and carbon dioxide output through breath samples, enabling them to assess metabolic rates. They also tracked the oxidation of the labeled amino acids in the exhaled CO2.

The results revealed that the breakdown of glycine and leucine from the enriched blood consumed by the vampires provided over 60 percent of the energy required for movement. Thus, the experiments demonstrated Desmodus rotundus's ability to almost instantly convert ingested amino acids into usable energy.

However, this adaptation comes with drawbacks: as a result of specializing in a specific diet, the desmodus organism has significantly lost its ability to store energy for later use. This has made them vulnerable to starvation—prolonged food scarcity is deadly for vampire bats.

Nevertheless, bloodsuckers have adapted to this challenge as well. In colonies, successfully hunting individuals often share their acquired blood with less fortunate relatives by regurgitating the consumed meal "mouth to mouth." Naked Science previously elaborated on the friendship among vampire bats in a separate article.