Bat with tag. Credit: Elena Tena
Europe’s largest bat species, the greater noctule (Nyctalus lasiopterus), has been caught red-handed terrorising songbirds in the night sky above southern Spain.
High-resolution biologging tags affixed to the backs of 14 bats to record their 3-dimensional movements, acceleration, altitude and sounds documented 2 of the predators as they attempted to catch migrating songbirds for their next meal.
One was successful.
It climbed to an altitude of 1200m above the ground and used its low frequency, ultrasound echolocation calls to locate the unsuspecting bird which, unlike certain insects, cannot hear them.
Then, the bat plunged vertically downwards, beating its wings faster and harder to triple its acceleration while emitting continuous attack calls. The chase lasted nearly 3 minutes before ending close to the ground.
The passerine let out 21 distress calls, later identified to have belonged to a European robin (Erithacus rubecula), before going quiet.
“An echolocation pause of ~1 s just before the passerine’s last distress call suggests that the bat likely used its mouth to deliver a lethal bite,” write the authors of a study presenting the findings in the journal Science.
“After the kill, mastication [chewing] sounds, recorded between echolocation calls, confirmed that the bat was eating continuously during flight for 23 minutes without losing altitude.”
Detached bird wings with distinct bite marks from greater noctule bats were found on the ground under the hunting grounds, which according to the researchers, “suggests that the bats, while in flight, bite off the wings to immobilise the passerine, reduce drag and facilitate handling”.
Bat with blood and feathers around its mouth. Credit: Jorge Sereno
“We know that songbirds perform wild evasive manoeuvres such as loops and spirals to escape predators like hawks during the day – and they seem to use the same tactics against bats at night,” says the study’s first author, Laura Stidsholt from the Department of Biology at Aarhus University, Denmark.
“It’s fascinating that bats are not only able to catch them, but also to kill and eat them while flying. A bird like that weighs about half as much as the bat itself – it would be like me catching and eating a 35kg animal while jogging.”
The remains of passerine birds have been found in the faeces of 3 species of large, fast-flying echolocating bats including the greater noctule.
“We knew that the greater noctule catches and eats insects in flight, so we assumed it did the same with birds – but we needed to prove it,” says Carlos Ibáñez from Spain’s Doñana Biological Station, who first discovered feathers in the droppings of greater noctules nearly 25 years ago.
The new study presents evidence which, for the first time, brings to light how the bats go about catching and eating the birds in flight.
“Exciting avenues for future research could include the fine-scale foraging behaviour of the 2 other aerial-hawking, bird-eating bat species, the antipredator behaviour of the targeted passerines, or how changes in timing and intensity of bird migration could affect the diet and population dynamics of these apivorous bats.”