The African savanna, a vast and vibrant ecosystem, is characterized not only by its stunning landscapes and diverse wildlife but also by its unique soundscape. The sounds of the savanna are shaped by a variety of factors, including the animals that inhabit it and the environmental conditions that influence sound transmission.
Among the most iconic sounds of the African savanna are those produced by elephants. These intelligent and social animals have developed a sophisticated communication system that relies heavily on sound. Let's delve into the characteristics of these sounds and how they are influenced by their environment.
Elephant Communication: The Power of Infrasound
Elephants are family-oriented animals with complex social lives. Related females live together for life in herds and raise offspring together. All members of a herd defer to one leader, the oldest and wisest female in the family group, known as the matriarch. As male elephants reach adolescence, they strike out on a different path from their female relatives. They leave their birth herds. Young males often seek out other males their age and form close bonds. Younger males also may associate with older males in loose groups known as bachelor herds. Adult male elephants also are inclined instinctively to spend much of their time alone.
Elephants have a highly developed system of communication through sounds. Elephants produce a broad range of sounds from very low frequency, inaudible infrasound to soft rumbles, trumpets, snorts, roars, and even growls. Standing up close to an elephant making an infrasonic call, you might hear or feel a low rumble.
The low frequency, or infrasound, allows elephants to communicate across miles. It is below the range of sound that the human ear can detect. Another elephant would be able to hear that infrasonic call up to 12 miles away! Elephants detect the low vibrations through their ears, feet, and trunk tip. Elephants affect their environment perhaps more than any other creature on earth.
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Elephants also communicate through touch, sight, smell, and chemical processing. Body language is highly developed in elephants. Their sense of smell is as exceptional as their sense of hearing, and they also exhibit long-term memory.
African savanna elephants are highly social and exhibit a complex vocal communication system. They use a low-frequency contact call (termed ‘rumble’) to maintain social contact over long distances. Their most frequent call-type is the ‘rumble’, with a fundamental frequency (which refers to the lowest vocal fold vibration rate when producing a vocalization) near or in the infrasonic range.
Rumbles are used in a wide variety of behavioral contexts, for short- and long-distance communication, and convey contextual and physical information. For example, maturity (age and size) is encoded in male rumbles by formant frequencies (the resonance frequencies of the vocal tract), having the most informative power.
Factors Affecting Sound Transmission
As sound travels through the environment, however, its intensity level decreases. In general, as sound waves propagate through the environment, the spectral and temporal structure degrades progressively with distance, yielding a 6 dB attenuation of the signal amplitude (source intensity that corresponds to sound pressure) per distance doubling (termed ‘spherical spreading’) under frictionless open field conditions, i.e., far from any obstructions. This potentially constrains the signal’s active space and thus affects decoding acoustic information by receivers.
Further factors causing ‘excess attenuation’ are ambient noise, fluctuations or changes of atmospheric conditions, vegetation strata, topography, and reverberation (frequency-dependent repeated reflections of a signal). Attenuation of higher frequencies and reverberation are more pronounced in dense habitats due to tree trunks, branches, and foliage, whereas open field habitats possess fewer reflecting barriers. In open habitats, however, irregular atmospheric conditions, such as high wind speeds or temperature, may affect sound propagation.
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Elephants can communicate with each other over long distances through sound, including low-frequency infrasound that humans can’t hear. Given their tremendous size and strength, and because they gather in groups, elephants have few predators to worry about. Lions, hyenas, and crocodiles may attempt to prey on young or sick elephants.
However, elephants are often successful at fending off predators, protecting their young, and defending sick or injured herd mates. For example, when a matriarch detects a nearby predator, she will herd offspring together and all other adult females in the group will form an outward facing circle around them, providing many layers of protection from the would-be attacker.
Interestingly and unlike previous findings, the transmission of formants was better than that of the fundamental frequency. Our findings demonstrate the importance of formant frequencies for the efficiency of rumble propagation and the transmission of information content in a savanna elephant’s natural habitat.
Sound propagation in the African savannah is best after sunset and 1-2 h before sunrise when ground level temperature cools down under dry and low wind conditions.
How Elephants Listen...With Their Feet | Deep Look
Other Sounds of the Savanna
The African savanna is not just home to elephants; it is teeming with a wide variety of other animals, each contributing to the soundscape. Here are some examples:
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- Kudu: Males are normally larger then females, and vocalize more using large grunt noises. There is white fur on the backside of the short tail, used as a warning signal to others when predators are near.
- Lion: The lion’s displays pack mentality, and only one male is allowed mating rights in a pride. Males are very territorial and will fight to keep their territory. The hunt antelope and larger mammals and will pick off the weakest link.
- Red-billed Hornbill: The long curved bill is nicely adapted to dig for food. Hornbills are omnivores and eat a variety of food such as insects, seeds and fruits, they are very opportunistic and like to stay within there territory.
- Lappet faced vulture: They use their powerful beak to tare through thick skin and can be very aggressive towards their own species during feeding.
- Greater Honeyguide: They use wavering and special vocals to get the attention of people to guide them to the bee colonies.
These are just a few examples of the many animals that contribute to the rich soundscape of the African savanna. Each species has its own unique vocalizations and behaviors that shape the acoustic environment.
Human Impact and Conservation
Elephants are most vulnerable to, and threatened by, humans. Demand for elephant tusks - the main source of commercial ivory - has led to aggressive poaching that has decimated elephant populations across Africa. Elephants may also fall victim to farmers defending their crops or local residents fearful of interactions with elephants.
African elephants are listed as endangered by the IUCN, the world’s leading conservation organization. Conservation issues affecting African elephants are complicated. Despite an international ban on ivory trade passed in 1989, poaching remains a significant threat. Competition with humans for limited space and resources is an equally significant threat.
As a result, their natural habitats are fragmented and there can end up being too many elephants in too little space, yet those that range outside of protected borders are quite likely to come into conflict with people or to be killed by poachers.
It is crucial to protect these animals and their habitats to preserve the unique soundscape of the African savanna for future generations.
