Responses to acoustic competition in tree hyraxes

Acoustic communication of tree hyraxes living in Kenya and Tanzania is amazingly diverse, loud, and unique among animals.

Tree hyraxes are curious relict species, it is related to elephants and manatees.

These tree hyraxes sing songs and in just in one location, number of calls may be more than 4000 during one night.

Tree hyraxes have been believed to be solitary, however this belief was based on very limited observations, and then repeated without questioning.

It also shows how little is known about tree hyraxes

As tree hyraxes are highly vocal, but difficult to observe, as they are nocturnal and live in the canopy of the forest, bioacoustics is the best method available to study their behavioral ecology.

This post explains the highlights of the open access, peer reviewed article in Mammalian Biology

https://link.springer.com/article/10.1007/s42991-023-00370-7

Acoustic competition

In the tropical cloud forest acoustic competition is caused by rain, chorusing orthopterans and greater galagos (Otolemur garnettii).

Rain is very powerful acoustic competitor, when rain reaches 4 KhZ, tree hyraxes quit calling almost entirely.

Chorusing orthopterans usually use the band between 5 kHz and 12 kHz. This chorus, no matter how intense it is has no impact on tree hyraxes. They have adapted to each other during millions of years. The most important and loud part of the call is under 5 kHz, meaning that the message will get through even during loud chorus.

Greater galagos, Otolemurs are loud callers, and they do call on the same frequencies. However their calling is random and tree hyraxes can’t avoid calling at the same time.

Interestingly tree hyraxes call less during full moon, this may be a so called “ghost from the past” phenomenon. At some point there may have been a nocturnal, big predator bird, that was hunting also big tree hyraxes, that weight 2-5 kg. Now this predator is extinct, but behavior still continues.

For more information and graphs, see original article https://link.springer.com/article/10.1007/s42991-023-00370-7

Data used in analysis is available at: https://zenodo.org/records/7408368