Vampire bats don't learn from bad lunch. (Zoology).

A vampire bat may be the first mammal ever to flunk the ultimate taste test, researchers say.

Mammals that eat something with a novel flavor and then get sick are known to avoid that flavor after just one experience, says John M. Ratcliffe of the University of Toronto. While other bats in a recent test did just that, the common vampire bat came back for more.

Ratcliffe and his colleagues tested an insect-eating species, the big brown bat; the Antillean fruit-eating bat; the Jamaican fruit bat; and the common vampire bat of the New World. Groups of the first three bats were given food flavored with cinnamon, a spice that these Western Hemisphere animals wouldn't have encountered. The vampires ate cow blood dosed with citric acid, a flavor that earlier tests showed vampires reliably detect.

After each group of bats ate, the researchers gave the animals an injection that made them vomit. To see if delay affected the lesson, the researchers injected some bats immediately and others after an hour. Regardless of the delay, when next offered cinnamon-flavored food, the fruit and insect eaters barely nibbled their meal.

The injection made the vampire bats sick, too. Yet they showed no significant aversion to another meal of flavored blood, the researchers report in the February Animal Behaviour.

Vampire bats eat only blood and therefore probably don't encounter toxins in their food, say Ratcliffe and his colleagues. They speculate that the vampire bat may have lost a specialized adaptation for learning a quick lesson from a lousy meal.--S.M.