Listening to giraffes: looking (literally!) for infra-sounds!
Have you ever heard what the call of a giraffe? No? Well, us neither! This is why 2 French researchers (Thierry Lengagne & Christophe Bonenfant) from Lyon University visited us in November. They brought along a very sensitive microphone to try to decipher whether giraffes talk to each other. Our hypothesis is that if they do so, they would use infrasound (frequencies below 20Hz), which the human ears cannot detect (we can hear from 20 to 20 000Hz). We spent 10 days in the field looking for giraffes and recorded them in different situations. Since we cannot hear infra-sound, we then need to look at the recording frequency domain graph (shown here) to check for the presence of infrasound.
From the picture above, we can clearly identify the cicadas and bird songs (and even flies flying around the microphone)- these we can hear on the recording. However, we can also clearly see evidence of sounds emitted at low frequency but with high energy (compare the 3 energy graph on the bottom line), which is characteristic of infrasound. Now the trouble is that even the slightest breeze produces infrasound as well, so the challenge now is to identify where the infrasound is coming from: giraffes having a chat or wind moving?