At the start of the 20th century, we had data that told us that...

• bats did not need their eyes or their sense of touch to orientate in complete darkness

• bats relied on their hearing to orientate in darkness

Some people (Spallanzani, Maxim) even had the partly correct idea that bats generate sounds and wait for the reflections of these sounds to gain information about their surroundings. But because nobody could hear bats making any sounds apart from the occasional screechy squeak, this idea was not really popular.

Nobody realised that bats were making very powerful sounds all the time - sounds that we cannot hear because they are too high in frequency....