As a guide who has spent countless hours exploring the captivating landscapes of Londolozi, I have often marvelled at the symphony of calls around me. However, there has been one call in particular that I have heard others talk of, but that I had not yet heard for myself – the whistle of a Klipspringer. Recently, I finally got my chance as I gazed up towards a prominent cluster of boulders, and there I saw a Klipspringer giving off a whistled alarm call at what we assumed was a predator that remained undetected.

Antelopes, such as the Klipspringer, can modify the airflow through their nasal passages by adjusting the position and shape of their soft palate. By manipulating the flow of air, they can create different sounds, including whistles, snorts, or nasal calls.

Now that I had heard this unique call for myself, it really got me pondering how mammals can produce such a diverse array of calls. From the whistle of a klipspringer to the bark of a kudu, or the snorts and grunts of a hippo, how do they produce these vocalisations and how do they differ from the echoing call of a lion’s roar?

The Evolution of the Voice Box

The voice box, also known as the larynx, is the key organ for vocalisation in most land-dwelling mammals, including humans. It has an interesting evolutionary history, originating from structures that protected a buoyancy organ in fish called the swim bladder. In mammals, the larynx serves to safeguard the “windpipe” (trachea) and lungs by preventing the entry of foreign substances. It is sealed by a pair of vocal folds or cords, while tall cartilages (the epiglottic and corniculate) act as protective barriers, deflecting food and water away from the opening. These cartilages, along with the soft palate and the posterior wall of the airspace, interlock the larynx with the back of the nasal cavity, creating separate pathways for breathing and swallowing. This allows mammals to breathe and swallow simultaneously, enabling them to detect predators’ scents even while constantly feeding.

Here is an illustration of the human larynx and associated structures. The broad strokes of this can be carried across to most other mammals.

Now that we have covered most of the technical anatomy, we can focus on the vocal cords or vocal folds. These folds of tissue within the larynx vibrate as air passes through them, generating sounds that can be modulated to produce a wide range of vocalisations. The length, thickness, and tension of the vocal cords contribute to the pitch and timbre of the sounds produced.

How do vocalisations differ in mammals?

Klipspringers, along with other antelopes and ungulates, possess less specialised laryngeal structures for complex vocalisations. They do not have distinct vocal cords or folds, relying instead on modifications in airflow and other anatomical features to produce simpler calls.

The reliable bark of a kudu is produced as it forces air from their lungs through the vocal cords, causing them to vibrate. The bark is further amplified and shaped by the resonating chambers in the kudu’s throat, mouth, and nasal cavities. Additionally, the hyoid apparatus, a set of bones that supports the tongue and larynx, plays a crucial role in modulating the sound. This combination of airflow, vocal cord vibration, and the intricate positioning of the hyoid apparatus contributes to the distinct bark-like vocalisation.

Unlike primates and other mammals, klipspringers communicate primarily through non-vocal signals like body postures, facial expressions, scent marking, and visual displays. Klipspringers can produce limited vocalisations, they are generally less varied and serve functions such as alarm calls, warnings, or maintaining contact within their herd.

Three klipspringers

A herd of impalas gathered together to alarm at a leopard as it moves past them by producing a snorting sound through their nostrils. These snorts are typically short and sharp, used to alert other members of their group of potential danger. Rutting impala males also retract the larynx during their rutting calls.

While non-vocal signs are also essential between predators, lions have specialised vocal cords that allow them to produce powerful and resonant roars, along with growls and grunts, which play crucial roles in their social communication and territorial displays. The robust structure of the lion’s vocal cords, combined with their larger size and adaptations in the suspensorium, enables them to generate intense and low-frequency roars that convey dominance and intimidate rivals or intruders.

Cheetahs and other small cats, in comparison to lions and leopards, have a voice box that is fixed in structure with divided vocal cords that vibrate with both inward and outward breaths. This enables cheetahs to purr continuously, but it limits the range of other sounds and therefore prevents them from being able to roar.

Where do we fit in?

In the case of humans, our larynx has undergone significant changes over time. Through the process of evolution, the position and length of the vocal tract have been modified, resulting in a more descended larynx compared to other primates. This descent contributes to the unique resonance and tone quality of human speech. Humans have developed highly versatile vocal cords that enable us to produce a wide range of speech sounds and engage in complex communication. The intricate control of the muscles surrounding the larynx, coupled with the intricate neural connections, allows us to convey nuanced meanings and express ourselves through speech.

While humans have the most versatile vocal abilities, antelopes and lions have evolved adaptations that suit their specific ecological needs. Antelopes rely on a combination of simple vocalisations and other communication methods, such as visual displays and body language. Lions, on the other hand, have developed vocalisations specialised for their social structure and ecological role as apex predators. Overall, the differences in vocal cord structure and function among humans, antelopes, and lions reflect the diversity of vocal adaptations across species, shaped by their evolutionary history, ecological niche, and social behaviours. So, the next time you hear the symphony of calls in the wilderness, take a moment to appreciate the incredible diversity of vocalisations among mammals.

The larynx of a hippo is relatively large and muscular, allowing for greater control and modulation of sound. The vocal cords themselves are thick and flexible, capable of producing deep and resonant tones. As the air passes through the vocal cords and resonates within the vocal tract, it produces the characteristic grunts and snorts that are synonymous with hippos.