Infra-red cameras have captured the grisly moments in which days-old African greater honeyguide chicks slaughter their nest mates.
Like cuckoos, the honeyguide lays its eggs in other birds' nests, leaving these foster parents to raise their brood. While it had been long inferred that the honeyguide chicks kill their foster brothers and sisters, a University of Cambridge project is the first to capture this on film. "We buried infra-red video cameras within the hosts' underground nests to see what happened," said Claire Spottiswoode, the lead author of the paper describing the project. "While the apparent violence with which young honeyguides attacked their newly hatched foster siblings was quite shocking at first sight, it shows the power of evolution to shape amazing adaptations in parasites."
The honeyguide chicks are usually hatched in the nests of bee-eater birds and are born with a pair of needle-sharp hooks at the tips of their beaks. The graphic video evidence filmed in Zambia showed the attacks launched by honeyguide chicks, which hatch before the bee-eater chicks and grow to three times their weight (See video above and gallery below, but be warned -- some images contain potentially upsetting content).
Spottiswoode adds that the unlucky chicks are those who have survived an earlier assault by the honeyguide mother. "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," she explains. "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."
The footage revealed that the honeyguide will usually attack for around one to five minutes, ceasing their attack when the smaller chick stops moving -- but, horrifically, it can take up to seven hours for the bee-eater chick to die. The host parents, say the authors, remained "apparently blithely unaware of what is happening" even trying to feed the honeyguide chick as it attacked.
By the time, the honeyguide chick emerges from the nesting burrow, its beak hooks have disappeared.
Says Spottiswoode: "The behaviour is exactly analogous to that of young cuckoos, which hoist host eggs or chicks onto their backs and tip them over the rim of the nest. But because honeyguide hosts breed in tree holes or underground burrows, honeyguides can't eject host chicks and have instead evolved this highly effective killing behaviour to make sure that they alone monopolise the nest. Each time brood parasitism has evolved we see specialised adaptations for parasitic exploitation, which are no less astonishing for being sometimes rather gruesome."
This article was originally published by WIRED UK
