The secret co-evolution between humans and honeybirds

Honeybirds (Indicator indicator), also known as greater indicators or golanera indicators, are a fascinating, grey-olivorous species of piciform birds belonging to the same order as the better-known woodpeckers. Widespread over a wide area of sub-Saharan Africa, these birds feed mainly on insects and other small invertebrates, are fond of larvae and beeswax and, like cuckoos, are known to lay their eggs in the nests of other bird species. In fact, they are a parasitic brood species: as soon as the eggs hatch, the young fledglings - thanks to their peculiar hooked beak - eliminate the other eggs in the nest or kill the young that have already hatched, thus guaranteeing themselves exclusive care and nourishment.

The major indicators are also known for a unique behaviour in nature: they voluntarily guide humans and other predators to wild bee colonies, obtaining in return the opportunity to feed on larvae and the wax present in them, energy-rich foodstuffs inaccessible to them due to their limited bodily capacities. This mutualistic relationship, especially with the honey hunters of the Yao people and the hunter-gatherer population Hadza, has lasted for thousands of years. Indeed, we have records of such behaviour as far back as 1569, when the Portuguese missionary João dos Santos noticed the special passion of these birds for candle wax in his church in Mozambique and described their ability to lead local hunter-gatherers to honey.

In addition to humans, these birds also have another fascinating ally: the honey badger (Mellivora capensis), also known as honey badger or ratele. This formidable predator, belonging to the Mustelidae family, is immune to snake venom and has developed dog-like teeth. In fact, its omnivorous diet includes a wide range of foods, including small mammals, birds, reptiles and insects, but it is above all honey and bees that the badger seems to pay most attention to. Such an intense passion for this foodstuff has in fact led, according to a recent study, to a mutual foraging pact with honeybirds: if the latter is able to locate hives, the badger is able to destroy them. This reciprocal collaboration between the mellivora and indicator birds, although only observed locally, offers an extraordinary example of interspecific adaptation and cooperation.

Recently, it seems that these small birds have developed a predilection for an even more powerful ally: human beings, in particular the Hadza people, a hunter-gatherer community living around Lake Eyasi in Tanzania. In particular, indicator birds attract the attention of honey gatherers withspecific calls and, flying from tree to tree, indicate the presence of the most hidden and inaccessible hives. In this way, humans, armed with axes and smoke, are able to stun the bees and once the honey harvest is over, our wax-loving friends can feed on the remains. A study conducted in 2014 in northern Tanzania showed that thanks to the birds' cues, the success rate in the search for honey by Hadza hunter-gatherers increased up to 560%, providing a significantly higher yield than searches conducted without their help.

However, it is not only the indicator birds that are attracting the attention of the Hadza people. A 2016 research by the University of Cambridge led by Claire Spottiswoode showed that the cooperation between these two species occurs through a two-way communication. Humans also respond to the birds by using specific calls that 'initiate' the action of cooperation and joint foraging. This call is then different according to the population of reference, while the Yao people, who live in Mozambique, use a sound similar to a trill, the Hadza use a melodic whistle. This mutual exchange of vocal gestures, probably produced by a process of natural selection over thousands of years, represents one of the few instances of collaboration between humans and wild animals.

Have honey indicator birds learnt these vocal signals and are they able to recognise their allies among those in their range? This was Dr Spottiswoode's main question that emerged from the 2016 study and is now being answered. In a very recent study published in Science, the researcher, together with anthropologist Brian M. Wood, investigated whether honeybirds showed a greater likelihood of responding to local dialect cues than those of another human culture or arbitrary vocal gestures. Incredibly, through field research experiments, it emerged that honeybirds in the Yao area were three times more likely to respond to the distinctive call of the Yao than the Hadza whistle. In contrast, honeybirds in the Tanzania area were three times more likely to respond to the Hadza's whistle than to the sound emitted by the Yao.

The results of the research suggest an extraordinary evolutionary phenomenon: the geographical variation and correlation between stimulus and response in communication signals between humans and indicator birds could form the basis for the study of a cultural co-evolution. Indeed, the socially learned cultural traditions of one species seem to influence consistent responses in another species, creating a virtuous circle that reinforces the cultural tradition of the former. It is well known that human beings are extremely culturally adaptable and have benefited from mutual learning. Although social learning phenomena have not yet been demonstrated in indicator birds, many studies are highlighting this trait in the animal world. The hypothesis of a cultural co-evolution could contribute to the recognition of 'geographical mosaics' that generate acultural biodiversity, enriching the very concept of biodiversity.

Ancient and deep relationships between wild animals and humans, such as those between honey birds and African peoples, are rare in nature and very few examples are documented worldwide. Moreover, such relationships are increasingly threatened: once widespread throughout the continent, today honey hunting is only practised by a few ethnic groups in East Africa and is gradually declining. Therefore, it is important not only to take action for the conservation and protection of biodiversity, as 3Bee does through concrete nature-based solutions, but also to consider supporting populations in the protection of cultural biodiversity, which is often in agreement with and related to the preservation of our planet itself.