One summer evening when I was still at the junior school in Wexham Road, Slough we went to an event at the school. Afterwards I was asked to wait in the playground while the adults did something or other. (I don't even remember whether I ever knew why.) It was a fine warm evening and it was just beginning to get dark. A number of bats were flying about over the centre of the playground, no doubt feeding on insects. As they flapped and swooped about, they made high-pitched squeaking sounds and so, thereafter, I knew what sound bats made.
It was some years later that somebody said (on the radio, I think) that the sounds bats made were too high to be audible to humans. My reaction was: "Well, I can hear them." I dismissed the contention as nonsense, but over the years I have heard this said many times. Clearly, at least some of the sounds hunting bats make are low-pitched enough for humans to hear. Mind you, I have never heard bats since then, and so I imagine that as we get older the ability to hear high-frequency sounds diminishes.
Now that we have the internet, I have been able to research the matter and have discovered that a lot of people claim to have heard bats. I checked on the range of frequencies emitted by bats and the range of human hearing and I found that they do in fact overlap. So if some idiot tells you that bats' squeaks are far too high for humans to hear, tell them they are talking nonsense.
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