The Birds & Bee-eaters: Murderous African Birds Attack Nestmates

I ought to have posted these when writing them last year, but no time like the present, hm? These articles were written for Dr. Temesvari's BioSc 494: Popular Science Journalism. This appeared in the Fall 2011 issue of Tigra Scientifica which can be downloaded here.

The Birds & Bee-eaters: Murderous African Birds Attack Nestmates

Blindly yet brutally stabbing underground, the invader kills his foster siblings. Although it sounds like the premise for a horror film, this is the reality for African honeyguide chicks and their host families. A study published in the September 2011 Biology Letters, Dr. Claire N. Spottiswoode and Jeroen Koorevaar observed within the underground nest honeyguide chicks killing host chicks (their would-be foster siblings) with specialized hooked bills for the first time.

This murderous behavior is part of brood parasitism- the parents lay eggs in the nest of other birds and do not deal with the responsibility of childrearing. Unlike babies left on doorsteps, however, these youngsters will hatch early and actively take out their nest mates for primacy with their foster parents. Many species of cuckoo are brood parasites; their preferred method of siblicide is pushing the other eggs or chicks out of the nest. It certainly puts a spin on those hourly popouts by a cuckoo clock.

Honeyguides are drab African birds that are roughly the size of a pigeon. Honeyguide interactions with humans are generally positive – they are well known for guiding humans to beehives, eating the grubs left behind when the people take the combs. Their parasitic nature is known; however the only prior description of killing behavior is from 1952, when a chick bit a host chick while being held.

Spottiswoode and Koorevaar placed infrared cameras at the end of common bee-eater bird tunnels. The bee-eater is the most common host for the honeyguides, and they typically nest in underground burrows. Honeyguides visited most of the bee-eater nests that were observed and laid eggs in occupied ones. The parents actually punctured host eggs with their beaks to improve their offspring’s chance of survival. Luckily for the bee-eaters, sometimes they would miss some eggs, or the bee-eaters would lay additional eggs later.

The honeyguide chicks hatch days before the bee-eaters and are very aggressive- the authors noted that chicks immediately tried to bite them with considerable strength when handled. In the videos, the honeyguide chicks attacked the host chicks and held on, blindly stabbing by opening and closing their jaws and shaking the host chick. Although it does not cause open bloodshed, the biting produces bruising and hemorraghing under the skin. Host chick deaths varied from nine minutes to seven hours after initial attacks. In most nests, the corpses stayed and decomposed- a grisly background while the imposter grows and develops.

Without a doubt, this systemically brutal system works for honeyguides. But does such a well-developed system come at a cost? Spottiswoode speculates that accelerated growth and exertion may have a huge energy cost for honeyguides, though more research needs to be done to determine this. Honeyguides are like the fairies of folklore: they leave changlings in nests, equipped with built-in knives and the initial strength to wield them and cause mischief.

Spottiswoode, C. & Koorevaar, J. A stab in the dark: chick killing by brood parasitic honeyguides. Biological Letters. http://dx.doi.org/10.1098/rsbl.2011.0739