A Rare Example of Mutualism Between Humans and Free-living Wild Animal
A new study confirms the existence of mutual partnership between humans and a free living bird species. When the honey-hunters of the Yao tribe call for the greater honeyguides, the bird recognizes, understands and responds to the hunters call and leads them to honey in the forest.
Collaboration among different plant and animal species for mutual benefit is a known phenomenon. The mutualism between oxpecker – a kind of bird and the rhinoceros/zebra, bees and flowers, spider crab and algae, leaf-cutter ants and fungi are some examples. But it is very rare to see such an adaptive collaboration between human-beings and animals.
A research study published in the journal Science, gives concrete evidence of the existence of cooperation between the bird species, greater honeyguide and the Yao tribe in Mozambique. The honeyguides (Indicator Indicator) recognize and responds to the specific sound signals from honey-hunters by flitting from tree to tree and guiding the hunters to the tree with bee-hive. Hunters take the honey, while the honeyguides relish on the bee-wax.
To study this unique partnership, Dr. Claire Spottiswoode went to the Niassa National Reserve in northern Mozambique. The region is known for honey and bee-wax production for many centuries and trails all the way back to Arab Trading times. This economically important occupation is still continued by the present Yao people who harvest honey by traditional methods.
“This work by evolutionary biologist Claire Spottiswoode and her team is the first to provide clear and direct evidence that honeyguides respond to specialized human signals … and that the birds associate those signals with potential benefits,” says John Thompson, an evolutionary biologist at the University of California, Santa Cruz.
Few examples of partnership between humans and animals for mutual benefit exist. Humans have taken help from animals like dogs, cormorants, falcons for foraging. In these cases, the animals are trained or domesticated for cooperation.
But the existence of mutualism between humans and a free living animal in the natural world is very rare. Many reported evidence exists about cooperation between artisanal fisherman and free-living dolphins and of men calling dolphins for hunting, but lacks scientific evidences.
For the first time, clear scientific evidences has been reported on this unusual association between a bird species and human-beings. Long back, Joao dos Santos, a Portuguese missionary in the 1588 during his stay in Sofala (in present day Mozambique) wrote about a small bird which used to fly through the cracks in the mission church walls and nibble the wax from the candle sticks. He also reported the same bird species guiding the hunters to bee-hives located deep in the forest.
The present research work by Dr. Claire Spottiswoode confirms this ancient observation. The study shows that, the probability of finding a bee-hive under honeyguides guidance increased by 75 percent.
When a honey guide finds its treasure deep in the forest, it fly’s to the nearby Yao settlement and starts calling it’s human partner by a loud chattering call, a call that is different from their usual territorial sounds. Along with the call, they distinctly gesture the direction in which the beehive is located by flitting from tree to tree, until their human follower follows them and finds the tree with the bee’s nest.
By themselves, they are incapable of stealing the wax from a beehive. But with collaboration with humans, they get the delicious wax, while the human partner gets the honey.
To attract the greater honeyguides, the Yao tribe in Mozambique makes use of a distinct sound – a loud trill followed by a grunt ‘brrr-hm’. The Yao tribe members say, they learnt it from their forefathers and use it only for hunting purpose. They feel, this call is the best way to attract honeyguides and hold their attention.
To understand the efficiency and effectiveness of this unusual partnership, Dr. Claire constructed a couple of experiments. The first experiment was aimed to verify whether or not the birds gave reliable information and actually guided the hunters to the bee’s nests and the second one was tailored to check whether the honey-hunters provided reliable information to the honeyguides and the birds’ in-turn associated this specific vocal sound to a specific meaning.
To find whether the guiding behavior gave accurate directions to the beehive coordinates and consequently to successful finding of the hive by the humans, the movements of the honey-hunters trailing the bird were tracked using GPS. Interestingly, 75 percent of the guided walks led to the successful discovery by humans of at-least one bees’ nest.
Next, to test whether the birds associated the ‘brrr-hm’ sound to a specific meaning, the research team recorded three sounds – the hunter’s trill grunt, a ring-necked dove’s song and an unrelated Yao call, of same amplitude. Then Claire and two Yao honey-hunters walked while playing one of the three sounds once in every 7 seconds for a period of 15 min and tracked the birds’ responses.
The honeyguides responded more to the ‘brrr-hm’ sound than to the other two control calls. Compared to the other 2 control sounds, Yao’s call increased the probability of guided by a honeyguide from 33% to 66% and the overall probability of been shown a bee’s nest from 17% to 54 %.
The finding clearly confirms the human-animal collaboration and the bird’s ability to attach a specific meaning to a human call for cooperation and partnership.
“The honeyguide literally understands what the human is saying,” says Stuart West, an evolutionary biologist at the University of Oxford in the United Kingdom. “It suggests that the honeyguide and human behavior have co-evolved in response to each other.”
Another honey-hunter researcher, Brian Wood from Yale University says, 1000 kms away, the Hadza community in the neighboring Tanzania use an all together a different sound signal – a melodious whistle, to the same effectiveness. In this case also the birds discriminate the specific sound from other calls and responds appropriately showing their willingness to cooperate.
Responding to a recruitment signal from a human being for foraging activity was previously associated with domesticated animals such as dogs. What is unusual about this human-honeyguide mutualism is that, it involves a free-living wild animal, whose interactions with humans must have evolved through natural selection.
But what is puzzling is how and from what age these birds start to recognize this sound. Just like cuckoo birds, they lay their eggs in the nests of other species. Young honeyguides don’t get tutored in partnering with humans from their parents, as just like cuckoos, honeyguides lay their eggs in other birds nest and the youngsters spend their childhood with non-biological siblings.
One hypothesis the researchers believe-in to explain this mystery is that, learning might be occurring socially from other older honeyguides in the vicinity of bees’ nests, resulting in a local cultural tradition among honeyguides that reflects the customs of their human collaborators.
Unfortunately, there is not much time left to solve these mysteries, as age old traditional occupations like honey-hunting is rapidly disappearing.
“The historical connections between humans and wild animals are becoming altered at unprecedented rates,” Thompson says, and “the possibility of studying these kinds of relationships in any historically meaningful way are decreasing quickly.”
“Reciprocal signaling in honeyguide-human mutualism”, Claire N. Spottiswoode et al, Science, Issue 6297, 22 July 2016.
“Wild bird comes when honey hunters call for help”, Elizabeth Pennisi, AAAS, July 2016.