A noisy business: listening to rock hyraxes on Ongava
Wildlife produces a lot of sound. From insects to mammals, including fish and birds, auditory communication –signals emitted through the acoustic channel – is widespread in the animal kingdom. Bioacoustics studies aim to unravel the mystery of the sounds produced by animals. At the Ongava Research Centre, we focused on rock hyraxes (Procavia capensis), a small, widespread and noisy but still mysterious African mammal.
A rock hyrax at Ongava Lodge
With a brownish-gray fur, an average weight of 4 kg, good agility, small round ears, a visible dorsal gland, rock hyraxes – or dassies – are close relatives of elephants, despite their rodent-like appearance. They indeed belong to the super-order Afrotheria, which also includes, among others, elephants, manatees, aardvark and elephant shrews. If you look closely, you can see their long incisors protruding from their mouths in a manner reminiscent of elephant tusks. You can see them during the day in rocky outcrops, their natural habitat which offers them sunny terraces, cooler shaded areas and plenty of hiding places from predators. Sociality is another life history trait that hyraxes share with their big-eared cousins. As a social mammal, you will see them in groups of up to several dozen individuals, engaging in all kinds of social interactions: huddling, fighting, mating, playing, … If you are careful, you will be able to hear the noises they make while going about their day.
However, some hyrax vocalizations are not so subtle. This is the case with loud calls, which are easily heard repeated vocalizations and produced only by males. Loud calls form complex vocal sequences that can last up to several minutes. They are composed of several calls emitted in series, each of them made of several notes.
These sequences of loud calls vary in their organization, such number of calls per sequence, number of notes per call, duration of silence between calls… Loud calls also vary in terms of acoustic structure: note duration, energy distribution in the frequency spectrum, frequency modulation pattern … So there is a lot of diversity within these sound emissions!
However, to date, we don’t really know what the hyraxes are saying with these calls: who they are, where they are, where they come from, what they want…?
To better understand these calls and what they mean for the species, the Ongava Research Centre has joined forces with French ethologists from the University of Rennes 1 and the CNRS (France) to study hyrax bioacoustics. We conducted acoustic recordings and behavioral observations at Ongava Lodges and Ongava Tented Camp, two places in Ongava Game Reserve where dassies can be easily approached.
We are now analyzing the recorded calls using spectrograms, visual representations of the sounds (yes, the best way to study a sound you hear is with your eyes!). A spectrogram is a visual representation of the spectrum of frequencies (vertical axis) of a signal as it varies with time (horizontal axis), with darker shades indicating more acoustic energy located at those frequencies.
Sonogram from a loud call (sound up!)
An interesting fact is that different subspecies of hyraxes live throughout Africa. For example, in Southern Africa alone, at least two subspecies occur: Procavia capensis welwitschii in Ongava (Namibia), Procavia capensis capensis in South Africa. This fact only multiplies the number of scientific questions that can be addressed regarding hyrax vocal communication: do the subspecies differ acoustically, does the local habitat influence the vocal behavior of a population, do the different populations have their own dialect…?
We hope that the analysis of hyrax calls will tell us more soon!
Author: Aglaé Thieffry, MSc Student, University of Rennes 1