It’s hard to tell who vampire bats like to feed on just by looking at their feces since they dine exclusively on blood. But now, researchers analyzing DNA isolated from bat droppings reveal that they crave pigs’ blood most, though they’ll settle for chicken blood, according to a new Journal of Mammalogy study.
When trying to identify a forager’s prey preference, you usually inspect their feces for fur, undigested bits, or bone fragments from their meals. To see whose blood is being sucked by common vampire bats (Desmodus rotundus), a trio led by Paulo Bobrowiec from the Instituto Nacional de Pesquisas da Amazônia examined the DNA from fecal samples. They fed eight captive bats blood from chickens, cows, pigs, dogs, and humans—the most frequently attacked prey items during the night in rural areas of the Brazilian Amazonia. The blood was collected from slaughterhouses (cows, pigs) and anesthetized dogs at a vet clinic, and people blood came from a local hematology center; the chickens were provided live within the bat enclosures. The team extracted and amplified DNA from blood samples of each prey species and from 190 fecal samples from these bats (that’s 38 samples of each prey species).
Additionally, the team also captured 157 Desmodus rotundus bats and collected 88 fecal samples from 18 small villages along a lake and two rivers in central-western Brazilian Amazonia. They also measured the availability of domestic animals. No traces of wild, rainforest vertebrates (like deer or tapirs) were identified in the fecal samples—which suggests that they selectively feed on domesticated animals. After all, livestock is more predictable, detectable, and accessible.
Chickens, they found, were the most attacked prey species, making up 61.4 percent of the identifiable samples—but fowl is only exploited as a secondary, complementary food source. When available, pigs were the highly preferred prey. Preference is a measure of the proportion of attacked prey and the proportion of available prey species: The one attacked more than expected by chance is the one that’s preferred. According to Science, the bats were seven times more likely to feed on pigs than chance would predict.
It’s likely that the bats’ thirst for pigs’ blood is related to its higher nutritional value compared with other farm animals, as well as the nighttime corralling of pigs (as opposed to horses and cows who might be allowed to roam free). Furthermore, Desmodus saliva liquefies mammal blood more readily than it does avian blood—making it easier and faster to ingest.