Communication is a necessity found even in the simplest forms of life. It typically develops between individuals of the same species or population in a nonverbal manner, through visual, olfactory, electrical, or acoustic signals. More rarely, forms of communication can also arise between different species through co-evolutionary phenomena of great biological interest.
In my ethology classes, I always mentioned, as an example of interspecific communication, honeyguides. These small birds have evolved a series of acoustic and visual signals. These signals, primarily aimed at the honey badger, later also involved our own species, guiding badgers and humans to wild bee and wasp nests, where they can jointly exploit them for food.
This is a beneficial synergy (a symbiosis) in which the indicator discovers a bee nest and guides the mammal there to break open the wild honeycomb and feed on the honey, leaving the rest behind, while disorienting and scattering the bees with their stings, which the bees cannot resist.
A few words about the primitive actors of symbiosis.
Indicators are part of the woodpecker family and are found throughout much of Africa, with numerous species. Among them, the best-known is the Honey Indicator (Indicator indicator), a small bird about the size of a blackbird whose behaviour has been significantly shaped by evolutionary adaptation. Like the cuckoo, it is a brood parasite, no longer building its own nest and leaving the burdensome task of parental care to others. From the single egg it lays in parasitized nests, a chick hatches that is a real nuisance to its half-siblings, managing to eliminate them by pulling them out of the nest using a small, hooked horny cap that covers both sides of its beak, which it later sheds.
A specialization of the small intestine produces a secretion that allows it to digest honeycomb wax, transforming it into fatty acids which can be used as food (cerophagy). They are also aided in this by a microscopic fungus living in their intestines (Micrococcus cerolyticus). Finally, they have remarkable olfactory abilities, as evidenced by their large olfactory bulbs, which are quite unusual for birds. Some believe these bulbs help them locate bee nests by the scent of wax. In fact, they were the first missionaries to attract the attention of ornithologists by reporting that when they lit beeswax candles on altars, the indicators soon arrived to peck at them.
However, bees and wasps build their hives in well-protected locations, making them inaccessible to small birds. Therefore, it is necessary to find an ally capable of penetrating these hives and willing to share the prey; otherwise, what kind of symbiosis is it if the benefit isn’t mutual?
This is where the “fearless hunter” comes into play: the honey badger (Mellivora capensis), with honey as the common interest of both species. If the bird is somewhat unusual, this badger is no exception!
Courage to spare, teeth to keep foes at bay, always on the prowl for food, as the poor bees know, whose honeycombs it gnaws at, ravenous and impervious to their stings. Even a cobra’s bite has little effect on it, and he fears nothing from scorpions, which their young prey on as soon as they emerge from their dens.
Hyenas and wild dogs attempt to attack him in groups, but more often than not, they give up, leaving him alone after experiencing their bites and sharp claws.
Adorned with elegant fur, black on the undersides and a beautiful silver on the back and head, its skin is so thick and tough that teeth, stingers, and quills are practically unable to penetrate it (Image 1).
(from Grzimek – Vita degli animali (Animal Life). Bramante Editrice, Milan).
Asking these two about the secrets of their alliance and how they manage to understand each other is not an easy task… Fortunately, the man has stepped in, and we can now talk to him.
The indicator and the man.
The Kenyan Boran tribe has developed a method of communicating with the indicator, which has proven receptive to partnering with them in another symbiotic relationship. Their interbreeding behaviours have been studied ethologically, revealing some truly surprising details.
The symbiotic exchange begins when a tribe member wanders through the village until they encounter an indicator placed high in a tree. This indicator emits a series of rhythmic calls, which the man responds to with a distinctive whistle (Image 2).
Image 2 – Sonogram of the indicator’s calls during a drive toward the hive (A) and after arriving at it (B). The arrow indicates the human’s response call, which accelerates the indicator’s call rate during the drive, almost as if to say “follow me again,” but not after arriving, as if to say “we’ve arrived.”
The indicator responds by shortening the duration of its call, then takes off shortly afterwards in a direction that, in hindsight, is statistically correlated with the location of the nest it had discovered, as shown in Image 3 A, which displays the circular diagram of numerous observations of the initial flight directions.
Image 3B shows a typical guidance pattern, consisting of successive flights, always calling and waiting to be reached by the man who maintains vocal contact by emitting his whistle.
From Image 4, we can observe the most interesting fact: as we get closer to the nest to be preyed upon, the flights become shorter and shorter, and the height at which the indicator lands becomes lower, clearly signaling that “we’re almost there”!
At that point, the man has only to look around and locate the nest to which he has been clearly led. He obtains his honey by smoking and chasing away the bees, leaving the remains of the comb on the ground so the little bird can feast on the wax from the cells. Eggs and larvae do not seem to interest it much, as was once thought. After all, its usual food is insects caught in flight, rather than hives to be raided by leading badgers or natives there.
Finally, one might ask, “Who teaches children the indicators to do all this?” The answer seems simple: since children have no contact with their biological parents, they have only instinctive genetic information to follow… and what else?
Credits
Author: N. Emilio Baldaccini, Former Professor of Ethology and Conservation of Zoocenotic Resources at the University of Pisa. He has published over 300 scientific papers in national and international journals. Actively engaged in scientific education, he is also a co-author of academic textbooks on Ethology, General and Systematic Zoology, and Comparative Anatomy.
Translated by Maria Antonietta Sessa
