Scientists have long believed the African Greater Honeyguide bird survived childhood by killing its siblings and getting more food from their parents. And now a group of scientists at University of Cambridge have proven this hypothesis by shooting video of one baby chick killing another right after they've broken free of their eggs.
What kind of twisted evolutionary adaptation are we witnessing here?
Honeyguides are an unusual kind of parasite that steals parental care from other birds. Adult honeyguides lay their eggs in other birds' nests — usually smallish bee-eaters — and the baby honeyguides are left to fend for themselves in a nest full of foster siblings. They have a few advantages, though. Gestated for a day longer than their victims, they are born bigger. Plus, they are born with a sharp hook on their beaks, which they use to stab and kill their foster siblings before they have a chance to take any valuable food away from the honeyguide chick. As you can see in this video, the honeyguide bites and shakes its victims until they stop moving.
The entire bloodcurdling drama takes place in the darkness of the honeyeaters' underground nest, and the adult birds seem oblivious to the fact that their children are being murdered by an interloper.
A release from University of Cambridge offered more details about the research:
"The killing behaviour is actually the culmination of a sequence of specialised adaptations that ensure that the young honeyguide has sole access to the food the host parents bring to the nest," said [biologist Claire] Spottiswoode. "The honeyguide mother ensures her chick hatches first by internally incubating the egg for an extra day before laying it, so it has a head start in development compared to the host, and she also punctures host eggs when she lays her own. But some host eggs are overlooked or survive puncturing, and it is these eggs that precipitate chick killing by the young honeyguide has soon as they hatch."
Because the honeyguide hatches first, it has grown to about three times the weight of a hatchling bee-eater by the time it sets about killing it. The research showed that just one to five minutes of active biting time was enough to inflict sufficient injuries to cause host death. However, after maimed chicks stopped moving honeyguides often ceased their attacks and, as a result, hosts sometimes took over seven hours to die.
Host parents are apparently blithely unaware of what is happening and, in the darkness of their burrows, even attempted to feed a honeyguide chick busy attacking their own young. The researchers also filmed one instance of the honeyguide biting its foster parent by accident. By the time the honeyguide emerges from the burrow after about a month of assiduous care by its foster parents, however, its bill hook has grown out and there is no trace of its siblicidal beginnings.
Spottiswoode noted that baby cuckoo birds use a similar survival strategy, parasitizing parental care by shoving the eggs of their foster siblings out of the nest before they can hatch.
Honeyguides don't just begin their lives with murderous betrayal. They actually make a career out of it. Their name comes from the birds' habit of befriending humans and leading them to bees' nests. There the birds wait for humans to destroy the nests for honey so that the honeyguides can get at the tasty, inaccessible wax inside the nest. Helping humans kill a few bees for a tasty snack is just par for the course after killing your siblings to get food from your foster parents.
Top image via Shutterstock