The vampire bats of South American rainforests aren't quite as dangerous as their name implies. But while they may not be changing into immortal humans at night, they are changing their behaviour in a troubling way. New research is uncovering that some of the bats are developing a taste for new kinds of prey, and that shift has scientists worried – because it could also herald a change in the spread of bat-carried diseases.

For 12 years, researchers studying Brazilian ecosystems used remote cameras to keep an eye on large mammals in the country's Pantanal wetlands and Atlantic Forest. Among the more than 10,000 photos and videos captured, they found evidence of the feeding habits of vampire bats. The furry parasites are known to go after domestic livestock, but this research has revealed which wild-roaming species they like to sink their teeth into.

Video credit: Galetti et al., 2016.
The camera trap footage showed the bats riding on the backs or hopping at the heels of victims ranging from native tapirs and deer to free-roaming cattle and feral pigs. Vampire bats are subtle hunters: just a small nip to get at the juicy blood meal flowing through the wound, and if all goes according to plan, the tiny biters aren't even noticed. (Though not all prey is equal. The footage showed that at least some deer were particularly feisty, snapping and kicking at the bats as they swooped in.)

In the Atlantic forest, however, the bats had a preference for pig: they went after feral swine five times more often than the bats in Pantanal. This fits in well with research from last year, which focused on DNA in vampire bat droppings and found that bats in the Amazon rainforest also preferentially dined on pigs.
A common vampire bat riding an invasive feral pig in the Brazilian Pantanal (left). Another bat drinking blood from the ear of a domestic pig. Image: A Keuroghlian/W Uieda via Galetti et al., 2016.

Of all the creatures that fall prey to vampire bats, feral pigs might not get much of our sympathy. After all, these invasive animals are a huge problem in many parts of the world. In the southern United States, for example, they cause many millions of dollars' worth of damage to local agriculture, leading wildlife agents and farmers to turn to various pig-exterminating tactics.

But for the scientists in Brazil, where vampire bats are reportedly the main carriers of rabies, the real worry is disease.

Based on past studies, roughly one in seventy vampire bats in the Atlantic Forest are rabid, and the number can be as high as one in ten in some parts of the Amazon. The bats can also host other dangerous diseases like hantavirus, coronavirus and adenovirus. Rabies has long been a concern for livestock, but while domestic animals can often be vaccinated, the local wildlife – and the wild-roaming feral pigs – don't have any protection. This situation is bringing the threat of rabies uncomfortably close to people.

In the Pantanal region, bushmeat hunters go after the feral pigs for their meat and oil (in fact, this has been hailed as a good method for keeping pig populations in check), potentially putting themselves at risk. Meanwhile, feral pigs infected with rabies can become aggressive towards people, pets or livestock. And what's worse, the pigs are spreading.

Over the past few decades, a lot of land in southern Brazil has changed over from cattle pasture to sugarcane farming, and the Atlantic Forest has experienced some severe wild habitat loss. All of this has resulted in a drop in livestock numbers while feral pig populations are on the rise. And the vampire bats are poised to trade beef for pork in their diet. 

As the feral pigs continue to spread, researchers warn that vampire bats will likely follow. A long history of negative human influences in the region – the introduction of invasive pigs, the destruction of natural habitats and the conversion of wild land for agriculture – may now be culminating to push the spread of dangerous diseases to humans and domesticated animals alike.


Top header image: Roger Le Guen, Flickr