Rock Stars
Text: Tim Jackson. Pictures: Anup Shah/Digital Source. Article from the December 2012 issue of Africa Geographic Magazine.
What does a rock hyrax have in common with Mick Jagger? They’re both singers, of course. Whereas Jagger sings to entertain, though, the rock hyrax’s wails and snorts perform a suite of suite complex functions, as several researchers from Israel recently discovered.
Science editor Tim Jackson was intrigued by their study of the animal’s vocal talents, songs and sex appeal.
Singing is something we all take pretty much for granted. Everywhere we go we are confronted with people, headphones firmly in place, listening to some form of music device. But if you examine singing in general, you’ll be struck by one glaring fact: mammals are not particularly good at it.
There are exceptions of course. Whale song (if you regard their calls as singing) is one such example. It’s not that mammals aren’t vocal. My dog barking at the front gate as I write this article is one obvious reminder, but let’s face it, there’s not a lot of complexity in a dog’s vocalisation. Nor are the calls of most other mammals especially insightful. A call might communicate important information to other individuals, but it is hardly going to top the billboard charts. An example is the alarm call made by a meerkat or primate before it ducks for cover. If you are another individual in the group, you’ll learn something about the type of predator approaching and hopefully take the right sort of action.
Calls do not only signify warnings, of course. The constant roaring of a male impala in rut might help to warn other males of his superior breeding status or his amorous intentions towards a mate, but it’s not a love song.
Things get more interesting when you link individual vocalisations together into a longer chain. Their order and syntax – or the individual ‘syllables’ if you like – can convey more detailed information. This sort of structure is commonly found in birdsong, but mammals seemingly provide a dearth of examples. Bats are one of the few groups that have been studied, and in fact the complexity of their vocal repertoire is similar to that of birds. Whales – and cetaceans in general – also communicate with one another using complex ‘syllables’ and a recognisable order.
Quite why mammals as diverse as whales, primates and bats chat in this way isn’t really understood at all. One line of thought suggests that such powers are vested in some of the seemingly more intelligent mammal species. Another theory puts forward that whereas the individuals of many species are able to rely on their powers of hearing and sight, other species – those that live in the ocean depths, for example, or, like bats, hang out at night – benefit from being able to communicate with sounds.
There is one known exception to these hypotheses. The rock hyrax, or dassie. This small, unassuming animal doesn’t fit the chatterbox mould, and yet it’s right up there with the best of them in terms of communication. ‘Male hyraxes produce long, complex songs lasting up to 10 minutes,’ says Arik Kershenbaum of the University of Haifa, Israel. His team has been studying the animals in that country, but hyraxes are widespread through Africa and the Middle East. Kershenbaum co-authored the findings, which were published in Proceedings of the Royal Society B earlier this year.
‘A hyrax song typically consists of a series of bouts,’ he explains. The songsters usually perform their recital from a conspicuous post like the top of a large boulder. ‘Each bout is made up of a sequence of “syllables” followed by a short pause,’ he adds. ‘The repertoire males use consists of five different sounds: wails, chucks, snorts, squeaks and tweets, and a bout usually contains up to 30 syllables.’
Hyraxes whose ranges are just a few kilometres apart tend to have similar repertoires – they sing similar songs
Kershenbaum’s research group teased apart the songs of different hyraxes by looking at the order of syllables in them. ‘We found that hyraxes living in different regions had their own distinctive dialects,’ he elaborates. The animals whose ranges are just a few kilometres apart tend to have similar repertoires, so neighbouring individuals and groups sing similar songs. ‘These regional dialects probably evolve and are maintained through learning the songs of other individuals, copying them and improvising,’ Kershenbaum reasons. Typically, male hyraxes disperse a few kilometres from their natal colonies, taking with them features from songs they learned there. These are then absorbed into the repertoire of other hyraxes in the new neighbourhoods, where imprecise copying or improvisations are likely to lead to a revised version.
‘We do not know if and what information is transmitted via song structure,’ Kershenbaum concludes. ‘But our results suggest that vocalisations like these in mammals aren’t restricted to cetaceans, bats and primates – they may be common in other mammals too.’
It’s unclear why male hyraxes sing, but it seems to be a way they advertise themselves. We know that males with a higher social rank sing more often,’ says Kershenbaum, indicating that the vocalisation performs a similar function to birdsong. Only male hyraxes sing; females don’t. All resident males and about a third of bachelor males sing (see ‘Group chat’). All are adults who have moved away from their natal groups.
The calls contain a lot of information about the singer. He is obviously male, but his song also hints at his body weight, size, condition and social status. Heavier males, for instance, sing longer songs for longer periods, producing more ‘chuck’ notes in their melodies – up to 51 chucks repeated in a row – have been recorded. Most of the songs begin with a ‘wail’ note followed by a series of other elements, often multiple chucks and sometimes snorts.
Singing seems to be practised by hyraxes that have elevated levels of stress hormones, or Cortisols. The increased Cortisol could indicate that the animal is ‘fired up’ and is also associated with social rank – the higher the singer’s standing in a colony, the more stress hormones he produces. The powerful males also tend to be older, but they do get to mate more. Their songs then broadcast their dominant status. Non-singers rarely breed with the females.
Neighbouring males often sing in response to one another, but they are less tolerant of outsiders, getting involved in three times as many aggressive interactions. Singing is almost certainly used as a signal, both to females and rival males, to indicate high hyrax status. In the case of breeding, a sure sign of the importance of singing is that the songs stop abruptly for a few months after the mating period.
When hyraxes call they wish to focus attention on themselves, but there’s no-one to provide the fanfare. In the absence of such an announcement, the males cue in to the screams that pups make as a signal to start singing. ‘We think that songsters enhance their singing display by exploiting these rarely emitted pup screams,’ says Amiyaal Ilany from Tel Aviv University, whose research on hyrax calls was published in Public Library of Science. ‘The pups’ screams are presumably produced only in the presence of imminent danger, so they probably elicit
The repertoire males use consists of five different sounds: wails, chucks, snorts, squeaks and tweets, and a bout usually contains up to 30 syllables
strong attention from hyraxes in the vicinity,’ he says. ‘As far as we know, our findings are the first indication that animals exploit the calls of others to bring more attention to their own calls.’
Just like rock stars.
Group chat
Rock hyraxes are quite social, living together in mixed-sexed groups that usually include one mature ‘resident’ male that has joined the group from elsewhere; several adult males that will later disperse; and some five to 20 adult females and their pups. The pups reach sexual maturity at about 16 months of age, at which point most adolescent males up to 24 months old are forced to leave their natal groups and will join the other evicted bachelors on the outskirts of the colonies. Adult females make up the core of the group; resident males generally stay with a breeding group for several years, until they are eventually ousted by a rival male.
Although male hyrax songs can be remarkable, most of the animals’ vocalisations are restricted to quiet communications between individuals in a group. Except when danger threatens, that is, when both males and females will make a loud, repetitive trill.
We were entertained and astonished at the singing skills of hyraxes.
Amiyaal Ilany has kindly allowed us to share a soundclip of a song; you’ll find it and other really interesting facts about the animals on the Africa Geographic blog blog.africageographic.com.
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