As if it's not enough of a problem for echolocating bats to disentangle echoes from leaves and other surrounding clutter, they also have to worry about interference and jamming from the echolocation calls of other bats in the vicinity. Shizuko Hiryu and her students, Eri Takahashi and Kiri Hyomoto from Doshisha University, Japan, explain that bats must be able to prevent the echolocation calls of nearby bats from jamming their own calls, but it wasn't clear exactly how they modulate their own echolocation shrieks to avoid interference. ‘Doppler-induced error [where the frequency of a call is altered by the animal's own movements] makes it difficult to obtain accurate measurements of echolocation pulses from bats in flight’, Hiryu says. However, this technical challenge didn't disconcert the team. Instead, they constructed minute (0.6 g) microphones that they could mount on the backs of tiny (5–10 g) Japanese house bats to record the minuscule aviators' shrieks as the scientists exposed the animals to simulated jamming calls during flight to find out how the bats adjusted their calls to overcome the interference (p. ).
They discovered that in addition to shifting the frequency of their calls when they overlapped with the jamming sounds, the bats also shifted the calls so that they were out of synch with the simulated jamming shrieks. ‘Our findings demonstrate that bats could adjust their vocalized frequency and emission timing during flight in response to acoustic jamming stimuli’, says the team.
