Nocturnal "vampire" bats are "excellent runners" and researchers have shown how their metabolism is adapted to work in a different way to most mammals.

Twenty-four bats were captured from Belize in Central America and fed enriched cow blood in a Canadian study.

The researchers looked at the carbon dioxide they exhaled in rutin and found traces of amino acids, the building blocks of proteins. The ratio of carbon dioxide to oxygen (respiratory exchange ratio) remained the same at all speeds.

The study suggests that bats' main source of energy was the protein-rich blood meal, rather than the carbohydrates and stored fat used primarily by most other mammals.

"This shows how strongly metabolism can be shaped by a specialized diet, as the diet of 'vampire' bats is relatively low in carbohydrates and fat," the researchers say.

Nocturnal "vampire" bats are only about 7-9 centimeters long, but can double their weight after a blood-feeding session.

They come out at night to detect prey using heat sensors on their bodies. A strong anticoagulant in their saliva stops the prey's blood from clotting during a meal.

The "vampire" bat is one of the few species that can maneuver dexterously on land. It uses this ability to silently approach sleeping prey, such as cattle, pigs and chickens, before making a cut with its razor-sharp teeth.

The study by Giulia Rossi at McMaster University and Kenneth Welch at the University of Toronto is published in the journal Biology Letters.