The curious case of the Honeyguide

According to rock paintings scattered throughout Africa, humans have been collecting honey for at least 20, 000 years. This is not surprising really seeing as it is a readily available and palatable food that has a sweet taste and high energy output. What is surprising however, is that many African tribes (which still collect honey using traditional techniques), frequently work in partnership with a bird that leads them to any bee colonies that it has discovered in trees, rock crevasses and disused termite mounds! There are anecdotal records of this partnership extending as far back as the 17th Century - a partnership that has been of great interest to many biologists.

The Greater Honeyguide, Indicator indicator, is related to the family of woodpeckers and is native to sub-Saharan Africa.

This remarkable partnership between the Greater Honeyguide and humans is fairly complex and requires the active participation of both parties in order for it to work effectively. To begin it, African honey-gatherers first draw the attention of the bird when they set out on an expedition by using a distinctive whistle that can be heard from more than a 1 km away. This call, known as the 'Fuulido' among the Boran tribes of Kenya, is made by blowing air into closed fists, modified shells or hollow nuts and more than doubles their chances of encountering the bird. Once a Honeyguide has located humans that are interested in foraging for honey, it becomes excited and flits rapidly between perches that are close to the party while emitting a double-noted and persistent call. African honey-gatherers claim that this call signals that the bird knows of a nearby bee colony, which it will lead them to. Thereafter this behaviour, the Honeyguide flies away in a straight line for up to few minutes before returning. Once it has returned to the foraging party it sits on a conspicuous perch until the honey-gatherers approach it, at which point it flies off again in the same direction (while calling). In this manner, it leads the humans to the site of the colony with each flight getting shorter and each perch getting lower as the distance to the hive decreases. Once the Honeyguide has reached the site of the hive, it circles it and emits a lower 'indication call' that is softer, with a greater gap between notes to signal their arrival.

Researchers have found that this communication system is extremely successful and have calculated that by following the bird, African honey-gatherers can reduce their foraging times by 64% (Isack & Reyer, 1989)! Despite its obvious success and benefits to humans however, many scientists were once baffled as to why the system evolved in the first place. Mainly, because it would have been an evolutionary nightmare: with both counterparts to the system having to learn how to communicate with the other and what parts to play simultaneously... It is plausible however when you consider the fact that humans and Honeyguides have coexisted in Africa for millions of years, providing a long 'window' that this could have taken place in. Furthermore, the evolution of such a system makes sense logically. Humans benefit from following the Honeyguide since the bird leads them to bee colonies and saves them many hours that they could have spent fruitlessly searching for. Once at the nests, humans can break them open using tools and smoke (an old bee-keepers trick that makes bees very docile, effectively sending them to sleep) to extract the honey and thus, get a food reward. The Honeyguide benefits from leading humans to any nests that it has found since humans can break the nests much more easily than they can. Thus, they can get their own food reward (wax and larvae) without the risk of being stung. Thus, both parties directly benefit from participating in the arrangement and it should logically, be under positive selection pressure.

Many biologists argue that the communication system between humans and the Honeyguide actually evolved between the bird and the Honey Badger, Mellivora capensis, and that humans merely 'hijacked' their way into it. This is highly doubtful however, due to two main reasons. Firstly, Honeyguides are diurnal (active during the day) and Honey Badgers are nocturnal (active during the night) so the animals would rarely meet under natural circumstances and definitely not enough to allow such a sophisticated communication system to have evolved. Secondly, because no-one has ever seen a Honeyguide lead a Honey Badger to a bee colony nor are there any historical anecdotes of this occurring.

Interspecific communication systems such as this are very rare in nature and have only seldom evolved. This is mainly due to the fact that different species are usually in direct competition with each other for resources so would normally selfishly exploit such a system for their own ends and due to the difficulties in the genetics and learning that underlies such behaviours (which were mentioned earlier). Thus, the relationship between humans and the Greater Honeyguide is a remarkable feat of communicative engineering and is a superb example of the ingenuity of Nature.

Reference

Isack H. A. & Reyer H. U. (1989). Honeyguides and Honey Gathers: Interspecific Communication in a Symbiotic Relationship. Science 243, 1343-1346.