Vampire bats that live in Latin America have switched to blood meals from cattle instead of from rainforest mammals, ecological physiologists report in the Journal of Comparative Physiology B.

They say that the conversion of rainforests ecosystems into livestock producing farmland resulted in the expansion of vampire bat populations in Latin America.  

Farmers are observing vampire bats satisfying their need for blood by attacking cattle instead of wild mammals. To document this change in behavior, Dr Christian Voigt and colleagues analyzed the stable carbon isotope ratio of exhaled CO2 in vampire bats.

Vampire bat

They fed captive vampires blood that was labeled with the stable (non-radioactive) isotope carbon-13 and then monitored the time period between the blood meal and the appearance of labelled carbon atoms in the exhaled breath.

“Vampire bats used the freshly ingested blood very fast to fuel their metabolism; after less than an hour the stable carbon isotope signature of the vampires’ exhaled breath was similar to that of their latest diet” Dr Voigt states.

Then the researchers collected breath of free-ranging vampire bats in Costa Rica and analysed its stable carbon isotope signature.

“The potential victims of vampires in Costa Rica are either cattle or rainforest mammals such as tapirs and peccaries. These two groups of animals feed on isotopically distinct plants which are grasses in the case of cattle and herbs or shrubs in the case of rainforest mammals. Therefore, we expected that the stable carbon isotope signature in bat breath would change according to their diet,” Dr Voigt noted.

The vampires’ breath clearly indicated that their last blood meal almost always originated from cattle, although rainforest mammals were also present.

The authors argue that the vampire bats do not necessarily prefer cattle blood, but that cattle are much easier to find for vampires than rainforest mammals. Cattle are held fenced-in on open pastures, whereas rainforest mammals roam in dense vegetation.

Converting rainforests into pasture has a large impact on many native mammals of Latin America, usually not to the benefit of the original mammal fauna.

Citation: C C Voigt, P Grasse, K Rex, S K Hetz and J R Speakman (2007). Bat breath reveals metabolic substrate use in free-ranging vampires. Journal of Comparative Physiology B, DOI : 10.1007/s00360-007-0194-z is published online on 16 August 2007.