Crying, laughing… Birds and mammals use different sounds to exchange information and interact. Decryption.
Why do birds sing or some mammals make different sounds? The sound world of animals has long remained inaccessible to researchers. But for about forty years, bioacoustics has lifted the veil over the richness and complexity of these communications. ” This specialty developed thanks to the invention of the tape recorder and the advent of computers. ‘, explains Nicolas Mathevon, who twenty years ago created the bioacoustic research laboratory at the University of Saint-Étienne* (Loire), which has gained worldwide recognition.
Today, scientists can not only record and retransmit the sounds they make, but also analyze them, modify them, or even create artificial calls in order to observe the reactions of animals in the field. They discovered an incredible variety, which Nicolas Mathevon reveals in his book. Animals are talking. Let’s listen to them.
” Some animals express something other than their current emotions. They control their sound productions depending on the context and the interlocutors. says the bioacoustician, not embarrassed to talk about “language”. Language specific to each species, meeting different needs.
1/ Express your dissatisfaction
Spotted hyenas grin despite
In the heart of the African savanna, spotted hyenas live in groups of 6 to 90 individuals, with a complex organization in which females predominate over males. Howls, growls, hisses… To be heard, they have about twenty voice signals, and each of these cries can be modulated (louder, more serious…) depending on the circumstances. One of them is characteristic: a grim smirk, which they use especially during meals, when there is fierce competition around the carcass. A way to express their dissatisfaction when they have to let other people in the group eat in front of them. Acoustic study of this call, which differs in amplitude and frequency, showed that it contains information about the age and hierarchical status of the animal in its clan.
2/ Resolve conflicts
Elephant seals recognize each other by their call
Each year, northern elephant seals migrate from southern Alaska to the Pacific coast to breed. The males then confront each other in fights, sometimes fatal… But they also engage in “vocal duels” consisting of a series of clicks at a rate of several clicks per second. The study of the acoustic structure of screams (rhythm, pitch) turned out to be interesting: contrary to what the researchers thought, it does not reveal information about the strength or motivation for winning a fight. On the contrary, each man demonstrates a certain vocal style. Marine mammals are able to memorize the voices of their fellows in a few days. Better, they remember it from year to year. An elephant memory (the sea!), which explains that when the dominant male starts to make sounds, others recognize him and prefer to run away rather than fight.
3/ Attract a soul mate
Koala puts everything on his second body
For a koala, size matters! To seduce females, the marsupial emits an incredibly piercing cry, similar to a motorcycle engine and close in frequency to an elephant’s cry. Purpose: to appear larger, and therefore more attractive. The researchers found that this feature is due to the presence of a second speech organ located above the larynx, whose membranes are long enough to reproduce very low frequencies. Deception, in order to pretend to be more imposing than he really is, is also the purpose of the deer when he calls: by stretching his head up, he lowers the larynx to the sternum, making the sound deeper.
4/ Mark your territory
White-browed warbler spotting intruders
The white-browed warbler lives in the Brazilian Atlantic forests, whose song follows a clear structure: a few very high notes, then a series of low notes, becoming more and more serious, with a steady decrease. It is used by males to signal their presence, mark their territory, and locate other males from a distance despite vegetation. However, a more detailed analysis showed that the vocalizations of each bird are slightly uneven. The researchers played various recordings through a loudspeaker. Result: the warbler does not respond to the songs of her usual neighbors, whom she knows well. But if we artificially change the unevenness of the melody, the bird will rush to defend its territory from whoever it identifies as an “intruder”!
5/ Find your offspring in the crowd
The voice guides the sea lions
Being able to join your cubs among tens or even thousands of others is sometimes a matter of survival. In some birds, such as penguins, or pinnipeds, such as walruses and sea lions, parents and calves control each other with their voices. The denser the colony, the more effective this recognition system. The subantarctic fur seal lives in the Indian Ocean and breeds on land. But she only stays with her newborn for a few days and has to go back to breastfeeding for two to three weeks… during which the baby has nothing to eat. Specialist Isabelle Charrier showed that at birth, a newborn responds to the voice of any female, but after two to five days, only he can distinguish the voice of his mother. The faster the baby learns, the faster the mother abandons him. And the longer the mother goes, the more the cubs scream about their hunger. Upon her return, the mother hears the child’s vocalizations and replies that the reunion will take place in just ten minutes.
6/ Call for help
Gibbons points out where the danger comes from
In the animal kingdom, the use of sound to warn of a threat is widespread, but some species are more subtle than others. Thus, the study showed that gibbons use a very complex communication, a proto-language close to the language of the first hominids. By modulating their vocalizations, they indicate whether the danger comes from below (snake) or from above (eagle). As for the merion, a very small bird, it has an alarm system with two calls: one to gather in front of an intruder, the other to hide. Even more surprisingly, crocodiles also communicate with sounds: the cubs make distress calls to call for help from their mother. And her reaction is immediate: she jumps up and rushes to the source of the sound.
You can learn to sing!
For a long time, it was believed that the cries of animals are an innate reflex inherent in genetics. For example, the barking of a dog. On the other hand, “singing” birds (thrushes, robins, tits, etc.) must hear their parents and imitate them … otherwise they cannot sing! This phenomenon of cultural transmission is often accompanied by small copying errors, so that from generation to generation songs may be slightly interchanged, for example with a Marseille or Parisian accent.
*Enes, Sensory Neuroethology Group, University of Saint-Étienne – Lyon Neuroscience Research Center (CNRL) – CNRS-Inserm.
> Animals talk. Let’s listen to them Nicolas Mathevon, HumenSciences, 2021. An immersive dive into an extraordinary bioacoustics field experience.