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Vampire Bats Attacking Cattle as Rain Forest Falls

James Owen
for National Geographic News
August 20, 2007
 
Vampire bats in Latin America are turning their fangs on cattle as rain forest is being cleared to make way for livestock, new research shows.

Scientists made the find by studying changes in the breath of vampire bats in Costa Rica.

The researchers discovered that the bats are finding meatier victims to sink their fangs into as the habitat of wild forest mammals disappears and is turned into livestock pasture.

A study led by Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany, found the blood-seeking bats are switching to cattle from rain forest prey such as tapirs and piglike peccaries.

The study team investigated which animals the bats were targeting by analyzing the chemical signatures, called isotopes, in the carbon dioxide they exhaled soon after eating.

Cattle and rain forest mammals feed on different plants that can be distinguished by their carbon isotopes. Since these chemical clues are present in prey's blood, the signature in the bats' breath varies with their meals.

The study clearly indicated that the vampires' most recent victims were almost always cattle, the team said.

The findings don't mean that vampire bats prefer bovine blood, the team said. Instead, they suggest that livestock are simply easier for the bats to find.

Voigt compared the vampire's dining options to that of a hungry human looking for a hot dog.

"One supplier is moving with a small van through the streets of the town, and it is not predictable for you where the van shows up," he said.

"The other supplier is in a snack bar with a permanent address. You most likely wouldn't go searching [for] the hot dog van but [would instead] go to the snack bar. Vampires are basically doing the same."

Vampires on the Rise

The research, which is published online in the Journal of Comparative Physiology B, came in response to reports from Costa Rican cattle ranchers of increased vampire attacks in the region.

Only three bat species are vampires, all of which are confined to Latin America. Just one of these, the common vampire bat, feeds on mammal blood.

Attacking at night, the bat doesn't suck its victims' blood but laps it up from tiny puncture wounds made with two sharp fangs. An anticoagulant in the bat's saliva keeps its nutritious meal from clotting.

Anecdotal evidence suggests that vampire bat numbers have increased significantly over the past 50 years, Voigt said.

This rise is widely attributed to deforestation, a theory bolstered by recent surveys of bat populations conducted by Voigt's team, he added.

A survey in virgin rain forest in the remote Amazon detected only a few vampires, Voigt said, but a survey of disturbed rain forest in the Andean foothills showed the winged blood-seekers to be the most abundant bat species.

No livestock were found near the Amazonian site, Voigt said, "whereas at the other site numerous pastures with cattle were present."

Livestock farming is seen as a leading cause of rain forest destruction in Central and South America.

(Related: "Amazon Deforestation Drops 25 Percent, Brazil Says" [August 14, 2007].)

In the Amazon, around 60 percent of deforestation between 2000 and 2005 can be attributed to cattle ranching, according to estimates based on figures from the Brazilian National Institute of Space Research and the United Nations Food and Agriculture Organization.

Rabies Threat

The growing number of vampire bats in cattle-ranching areas has also been blamed for the spread of disease among both humans and domesticated animals.

In just two months in 2005, 1,300 people in northern Brazil were treated for rabies after suffering bat bites. Twenty-three of the patients died, according to reports.

Voigt said that habitat conservation, along with efforts to reduce wildlife poaching, is crucial to minimizing the overall impact of vampire bats and their late-night raids.

"If rain forest mammals such as tapirs and peccaries are … killed, there is no alternative left for vampires to get blood from," he said.

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