Richard Collins: Sounding out what it's like to be a bat

But there are more mundane bat issues which it is possible to address. How, for instance, does a bat cope when its echo-location system fails?

Micro-bats transmit sound pulses and monitor their echoes from the surroundings. The pulses are extremely powerful but, fortunately, too high-pitched for our ears to detect — they would probably deafen us. The system is so sophisticated that bats ‘see’ their surroundings in total darkness as effectively as sighted animals see in daylight. Almost a fifth of all mammal species are bats.

Nor are these creatures of the night ‘as blind as bats’. Their small sensitive eyes might provide the equivalent of our emergency lighting units.

But could bats have another fall-back sensory system?

Researchers at Johns Hopkins University have being searching for a ‘bat Plan B’.

In noisy environments, we turn our heads instinctively to hear what’s being said to us and shout to be heard above the din. Birds do likewise. Scientists from Aberystwyth University compared the vocalisations of great tits living in noisy city centres and those of birds in quieter locations. The city birds, the researchers found, sing at higher pitches than do their country cousins. This, the researchers concluded, is a response to noise — higher frequency sounds are more easily heard above the low-pitched cacophony of city traffic.

When developing radar systems during World War II, engineers encountered a problem. The electro-magnetic pulses transmitted had to be so powerful that they damaged the sensitive receivers needed to monitor their echoes. Bats had solved a similar problem. Their ultrasound pulses are so powerful they would damage the sender’s hearing. The solution, for both bats and radar engineers, was to switch off the receiver while a pulse is being transmitted and turn it back on in time to record the echoes.

But does a bat working in a noisy environment make its pulses even louder so that the reflections will be stronger?

The Johns Hopkins researchers trained captive bats to fly along a corridor and exit a window. They then administered a drug which temporarily disabled the bats’ hearing. The effects of the drug lasted for about 90 minutes and, the researchers emphasise, caused no long-term harm.

When released into the corridor, the temporarily deafened bats "struggled but managed" according to neuroscientist Cynthia Moss. They flew along the corridor as usual but did so lower down, and closer to walls, just a blind person might use facial air pressure to detect objects.

Like the great tits, the hearing-impaired bats altered the structure of their transmissions. They varied the number, length, and bandwidth of the pulses. But when bats were released into the corridor repeatedly, their navigation skills didn’t improve. This suggests that their fall-back procedure is innate rather than learned.

Researchers were surprised that the deafened bats could hear at all. Have bats an as yet unknown auditory pathway, they wonder?

• Clarice Diebold et al. Rapid sensorimotor adaptation to auditory midbrain silencing in free-flying bats. Current Biology. 2024