Thursday, October 17, 2013

Honeyguide Bird

image by Colin Beale
There is a species of bird in Africa called the greater honeyguide (Indicator indicator), which likes to eat beeswax, the only vertebrate to do so.  It will also eat bees, bee larvae, and wax moths if it can get access to an open hive.  But it's a small bird and beehives are notoriously well-defended, so the species has a unique adaptation.  It knows every hive in a 200 mile radius.  If it finds humans within a few kilometers of a hive it will fly up to them, calling and flitting back and forth, flashing its tail.  If the humans are willing to grab an ax and follow the bird, it will lead them to the colony.  (Some traditional African honey-hunters blow a loud whistle, called a fuulido before they set out in search of honey in order to solicit a honeyguide.)  Once the humans have broken into the hive (usually a hollow tree) the bird can feast on the wax and the grubs.

The behavior is innate rather than learned - an evolved behavior.  By analyzing the difference between subspecies scientists calculate that the behavior is at least 3 million years old.

There are two theories about how it came about.  The first is that it co-evolved with the honey badger, who will use their claws to tear open a hive if they can find one.  But in 30 years of trying scientists have never been able to observe the birds interacting with a badger, so they remain skeptical.  A honeyguide was once observed to solicit baboons, but the baboons weren't interested.

The other theory is put forth by the anthropologist and primatologist Richard Wrangham.  He believes that the behavior evolved with human ancestors.  Wrangham's primary interest is in human evolution, and in particular he believes that the most important innovation which enabled the development of Homo sapiens was the mastery of fire.  He studied chimpanzees and noted that they spend fully half of their waking hours chewing.  He himself tried and failed to subsist on their raw diet.   The ability to cook food frees up nutrients that are otherwise inaccessible and this increase in the amount and quality of nutrients allowed human evolution to take it's unique path -- a shrinking digestive tract and a shrinking jaw, but most importantly that large, extremely energy-intensive brain.  

Cooking food is what enabled our human ancestors to support and feed those ever larger brains, and gave them the time and energy to be human.

But hominid brains have been growing for over two million years and there is no archeological evidence of fire use back that far - so Wrangham isn't able prove that cooking had anything to do with kicking off brain growth.  

This is where the greater honeyguide comes in.  Wrangham observed that chimpanzees love honey, but can't get it.  Humans love honey, and they can get it.  The difference?  Fire.  The use of fire and smoke is universal among honey hunters to confuse the bees and derail their defensive behaviors.  If honeyguide birds have been bringing humans to beehives for three million years, then it stands to reason that humans and their ancestors have probably had fire for the past three million years to help them despoil the hives.

It's not an air-tight case by any means, but I love this story of a magical partnership between a meddlesome wax-eating bird and these honey-loving, torch-wielding hominids - a partnership that has stood the test of a whirlwind millions-years ride from ape to human.