Prey animals usually prefer to stay out of reach of predators, but researchers have observed a pair of birds and a group of bird-hunting bats residing in the same tree cavity in north-east Italy.
Wildlife photographer was monitoring greater noctules (Nyctalus lasiopterus), a species of carnivorous bat, in a forest near Udine as part of a study led by , an ecologist at the University of Naples Federico II. One spring afternoon she heard birds close to an ash tree that bats had been known to use as a roosting site for years. She then spotted a Eurasian blue tit (Cyanistes caeruleus) flying close to the entrance that the bats used.
鈥淚 was almost jumping from happiness,鈥� says M盲enurm. 鈥淲hat I had discovered was something unbelievable.鈥�
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The ash tree had a vertical crack over 1 metre long where bats roosted year-round. Around 25 greater noctules resided in the cavity鈥檚 upper section while a nest of Eurasian blue tits lay in the lower section.
M盲enurm and her colleagues monitored the nest for a month, during which time they observed the blue tit parents bringing worms to the nest and, later, feeding two fledglings outside of it. In the following days, the birds were no longer present, suggesting that the chicks had successfully fledged, she says.
The greater noctule usually feeds on insects in summers but preys upon birds, including blue tits, when the birds are migrating.
Russo describes the bat as a fast flyer that is thought to capture birds mid-flight. However, some researchers believe that greater noctules capture birds in their nests.
鈥淥ur observation shows that when sharing the same cavity, the bats simply ignore the birds, and the birds seem not to be threatened by the bats,鈥� says Russo.
This bizarre coexistence indirectly suggests that these bats exclusively hunt birds in flight, he says. If the bats only prey on birds in flight and in open spaces, then they wouldn鈥檛 perceive a nesting bird as an edible target and the bird wouldn鈥檛 perceive the predator鈥檚 presence as a threat.
鈥淭he fact that this pair of Eurasian blue tits selected this tree roost, which was already occupied by bats, for nesting is very surprising,鈥� says at the University of Costa Rica. 鈥淢ore surprising yet is that the parent birds, and their fledglings, were not consumed by the bats during the entire month when observations were made.鈥�
Ecology and Evolution
