Bats buzz like hornets to scare away owls

(ORDO NEWS) — Italian scientists have found that captured large bats emit “buzzing” sounds, reminiscent of the signals of stinging insects.

As shown by experiments on owls, predators react to the buzzing of a hornet and the “buzzing” of a harmless bat in the same way – they prefer to avoid the source of an alarming sound.

Batesian mimicry , where an edible or harmless species mimics an inedible or dangerous one, has long been known and well studied in a variety of species, from insects to frogs and snakes.

Most often, researchers encounter visual mimicry, when a mimic species acquires an external resemblance to a model species: for example, a harmless milk snake ( Lampropeltis elapsoides ) has the same red-black-yellow stripes on its body as the poisonous coral asps of the genus Micrurus .

Much less often, scientists identify cases of acoustic mimicry, when a mimic species achieves a sound similarity with the model: for example, moth butterflies imitate ultrasonic signals emitted by bear butterflies , whose taste is unpleasant for bats, and bats stop catching them.

However, not only insects “thought of” such an invention: the bats themselves also have enemies, which can also be scared away with the help of sounds reminiscent of the buzzing of wasps and bumblebees.

This is exactly the case recorded by Italian scientists: the big bats ( Myotis myotis ) caught by them, when they were picked up, made “buzzing” sounds, reminiscent of the signals of bees and hornets.

To find out why bats have such strange signals, the researchers first compared recordings of the “buzz” of large bats and hymenopteran insects such as the honey bee ( Apis mellifera ) and the common hornet ( Vespa crabro ).

They then studied the response of owls ( barn owls Tyto alba and gray owls Strix aluco ; four wild birds and four captive-bred birds for each species) to the “buzzing” and “non-buzzing” sounds of two species of bats, as well as to the buzzing of stinging insects. The results of the study are published in the journal Current Biology.

Bats buzz like hornets to scare away owls 2
Structural similarity between the buzzing of hymenoptera insects and the “buzzing” of bats (A) and the behavioral responses of owls to the reproduction of sounds (B, C): Am – buzzing of the honey bee, Mm – “buzzing” of the great bat, Ctrl – control, social signal of the wide-eared folded lip , Vc – buzzing of an ordinary hornet. The reactions of naive and experienced birds were compared, the number of reactions (B) and their intensity (C) were evaluated

It turned out that, in general, the “buzz” of great bats is not particularly similar to the buzz of a hornet: a quadratic discriminant functional analysis (qDFA) with a cross-validation procedure showed 95.4% correct discrimination between insect sounds and bat sounds.

However, this figure dropped to 53.7% when only those call parameters were left that are within the audibility range of owls: in other words, from the point of view of a bird of prey, when trying to catch the source of the “buzzing” sound, the risk of falling into a hornet’s nest and the chance to dine helpless bat are about the same.

In experiments with owls, birds reacted to “buzzing” sounds in somewhat different ways, apparently based on their experience.

The recording of the “non-buzzing” signal of the broad-eared folded bat ( Tadarida teniotis ) most often evoked a predatory reaction in them, but the buzzing of insects and the “buzzing” cries of the great bats more often provoked flight.

Thus, the findings strongly suggest that bats mimic hymenoptera to avoid predators, a first but very promising example of acoustic mimicry among mammals.

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