Amongst the Pteropodidae, the biggest family of non-echolocating bats, several species of the genus Rousettus are known to produce clicks using their tongue (Roberts 1975).
Recent research has also shown that some members of the family are capable of echolocating with their wings! (Boonman et al. 2014)
That’s all great but why such a diversity?
I’m certain all of you have at one point or another in your life, have found yourself in a busy shopping mall, or café. How easy is it to have a normal conversation in there? Not that easy at all! That’s because all the sound waves are interfering with each other, resulting in a despicable noise.
Now, replace the humans in the shopping centre with bats. And turn off the lights. All those bats have to find food, listening to their own echo to picture their environment. Wouldn’t be easier if each bat has its own characteristic echolocation call?
While that’s not the case, strong variability between species allows different species to find different kinds of prey in the same environment, without disturbing one another.
Small bats will usually have a call of high frequency because it gives them the resolution required to find small prey whereas larger species will usually look for larger prey, thus having a lower call.
The specialised calls of Hipposideridae and Rhinolophidae work in a different way. They have a constant frequency and the bats listen for modulations in that frequency in the echo. Those modulations are the result of the Doppler effect. If you don’t know what that is, you’re far from the only one. But also, you do know what it is. When you hear an ambulance, you know if it’s in front or behind you. The sound changes as it goes past you. That’s the Doppler effect, in very short. If you want to know more, the internet is a much better teacher than I am.
This highly specialised method allows them to perceive the flutter of the flying insects, enabling them to not only distinguish a flying, living prey from a falling leaf but also to distinguish between different types of prey.
What about bats of the same species then?
Well… They also want to find food and avoid collision. What bats of the same species will usually do is slightly modulate their frequency to avoid interference. They will also emit “social calls” aimed at reminding the intruder that it’s their turf. Not so social after all.