While snakes are well-known enemies to bats, their preying on the winged mammals has hardly been recorded. Furthermore, no bat as big and heavy as the common vampire, has been described being killed and eaten prior to the present study, published in the open access journal Subterranean Biology.
The study, where scientists, led by Sarah Martin-Solano, Universidad de las Fuerzas Armadas, ESPE, Ecuador, record a rainbow boa catching the bat, is the first known such case to have taken place on a cave's floor. The documented observation serves to confirm that snakes do predate on bats in caves, and is also the first such case known from Ecuador.
Apart from the detailed description, the scientists also provide a film, showing almost in full the event of a rainbow boa catching, killing and swallowing an adult female common vampire bat.
The predation has been observed in a 450-metre-long cave in Tena, Ecuador. There, an adult female common vampire bat, one of the three bat species to feed exclusively on blood, was seen to fly into the cave right over the boa's head and its waiting open jaws, raised some 30-35 centimetres above the ground.
The approximately 140-centimetre-long snake snatched the bat by the head and immediately brought it down to the floor. Having been strangled by the boa, the bat appeared to give up its resistance about two minutes later, although the predator did not let it go for another seven minutes. Once assured the mammal is dead, the snake started trying different positions from which to fit the bat in its mouth. However, this seemed particularly difficult due to the mammal's size and the stiffness of its shoulder joints.
Eventually, the rainbow boa began constricting the body once again. Then, starting from the head, the snake managed to swallow the whole bat in 4 minutes and 50 seconds, with the predation measured to last about 25 minutes in total.
In conclusion, the authors suggest that more research needs to be undertaken, so that scientists can find out how common is for snakes to prey on bats in caves.