The blood diet of vampire bats has reduced their ability to detect bitter and otherwise yucky tasting flavors, according to a new study that could help explain the unusual cravings of these flying mammals.

The study, published in the latest issue of the Proceedings of the Royal Society B, puts vampire bats on the growing list of animals with unusual senses of taste. That list includes marine mammals such as dolphins, which swallow their food whole and so don’t spend a lot of time savoring flavor.

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Vampire bats aren't foodies either, unless that term includes raw blood cravers.

"Vampire bats are the only mammals that feed exclusively on blood," authors Wei Hong and Huabin Zhao of Wuhan University said. They explained "the extreme narrowness" of the bat's diet might have turned the bats into "poor tasters."

For the study, the researchers looked at taste receptor genes in all three species of vampire bats, as well as in 11 other types of bats. They also examined prior behavioral tests on vampire bats, which essentially determined whether or not the bats turned their nose up on certain flavors or liked them.

Vampire bats showed indifference to sweet flavors, so we now know they don't have a sweet tooth. These bats also had trouble detecting bitter, salty and sour tastes. That's significant, the researchers believe.

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"Mammals typically have five primary taste modalities dedicated to the evaluation of diets, of which the bitter taste serves as an important natural defense against the ingestion of poisonous foods and is thus believed to be indispensable in animals," they wrote.

So much for that theory about being indispensable, since vampire bats have lost much of their ability to taste bitter flavors.

Hong and Zhao say that vampire bats find their food, not by taste, but by using a combination of smell, echolocation and heat detection. All of these allow them to "find their prey and locate the skin with rich capillaries."

It remains a mystery as to when and how vampire bats first got on their unusual all-blood diet. If the ancestors of the bats ate other things, then these animals might have once possessed a better ability to taste multiple flavors. That ability then could have been lost over time as the bats sipped more blood.

On the other hand, maybe vampire bats have almost always been this way. Researchers hope to solve the mystery as they’re trying to unravel the evolution of bitter taste detection in animals.

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Just this week, at the 2014 Institute of Food Technologists Annual Meeting & Food Expo in New Orleans, food scientists announced that they plan to block, mask and/or distract from bitter tastes in human foods to make them more palatable to consumers. Coffee without bitterness appears to be catching on, for example.

Some people, in particular, are genetically more sensitive to bitter tastes — just the opposite of vampire bats in terms of food tasting ability.

Photo: A vampire bat. Credit: Getty Images