to murder hatched

How does Gozel Haobil take care of himself for ideal living conditions? He kills his neighbors. Why does this happen and where has the hook gone with which the murder is carried out? The answers, including a video of Haovil in action, in the article before you

Yonat Ashhar and Noam Levithan Galileo

In a burrow in the ground a small chick hatches from its egg into complete darkness. He does not know it, but he is not the first chick to inhabit the underground nest: a larger chick, which hatched some time before him, is waiting for him in the darkness. The big chick is a killer equipped with two formidable hooks that protrude from its beak. A few minutes later he went into action.

Under the cover of darkness, he pounces on the little chick, and with movements that seem uncharacteristic of a bald chick that looks so helpless, he grabs his victim, opens and closes his beak, terrorizing the little body and shaking it.

This horror scenario was photographed, in black and white with an infrared camera, by Claire Spottiswoode from the University of Cambridge in England and Joron Koorevar from ECO Logisch in the Netherlands. In the video we see a baby shrew (Merops pusillus) being attacked by its step-brother - a baby shrew (Indicator indicator).

social parasites
The honeybee is a small African bird, known for connecting with humans and leading them to beehives (hence its English name: Honeyguide). When the people drive the bees away with smoke and open the hive, the birds eat the bee eggs, larvae and wax.

There are persistent rumors that the beekeepers lead other animals to beehives - especially the honey badger, which is resistant to bites and is able to open the beehive for the birds. But unfortunately, there is no reliable evidence that such cooperation actually takes place and the only nature film in which this behavior is "documented" was directed with the help of a tamed and stuffed badger of Obil.

Aviles have another unique feature: they are social parasites, meaning the females lay their eggs in the nests of other birds. Social parasitism is not uncommon among birds. In some species, the parasitic chicks grow up with the "legal" chicks - for example, the cuckoos that live in Israel lay their eggs in crows' nests and the chicks grow up together relatively peacefully. In contrast, nestlings of other cuckoo species tend to throw the host's eggs or nestlings from the nest to their deaths.

assaulting a person
For years, scientists suspected that the obilis were also engaged in killing their step-siblings. Since the nests of the crickets are underground (in Africa they are mainly found in the burrows of shrews), the owls cannot throw the eggs from the nest: it was assumed that they take a more direct approach. The sharp hooks on the beaks of the chicks hinted at this possibility, and to this must be added the fact that no more chicks were ever found in the nests where there were ovile chicks.

The only case where such an attack was observed was in 1952: Gordon Ranger held two chicks in his hand, a parasite chick and a host chick, and the parasite chick attacked the smaller chick and killed it. It's unclear what Gordon tried to do next with the murderous chick, but it somehow managed to pierce Gordon's tongue.

To watch the video showing the lead chick murdering its nestmate

The disappearance of the murder weapon

In the article published by Spotizud and Korfar in the journal Biology Letters, they presented for the first time a video showing the aggressive behavior of the Obil chicks under natural circumstances. The chicks attacked their step-siblings in all ten nests that were photographed. The attacks lasted less than three minutes, and in all cases the surrogate chicks died. About two weeks later, having completed what was apparently their only task, the hooks were absorbed into the developing chick's beak and gradually disappeared.

The researchers discovered that the owls have another method for getting rid of the surrogate chicks, even before they are born: when the owl female lays her egg in the nest, she punctures the other eggs in the nest in her beak and thus prevents their development. The chick eliminates the shrew chicks that manage to survive this attack
.
The reason for this behavior, as cruel as it may seem to us, is clear: the lead chick receives more food and care from its adoptive parents when it has no competitors. In most birds, chicks that grow up together in a nest share much of their DNA with each other, so natural selection does not create a preference for fratricide.

In the case of a social parasite, there are no such restrictions, and this is how the strategy we see in the leaders developed: the behavior of the mother, the behavior of the chick, and also its physical characteristics - especially the hooks on its beak and its strong bite - are all aimed at creating an ideal breeding environment for the chick. There is no doubt that the parasitism of the ovules is a serious problem for crickets in the southern part of Zambia, where the study was conducted.

Out of 172 shrew nests examined, about two-thirds were visited by the parasitic bird. It seems that the shrews are trying to combat this: more than half of the nests that contained the eggs of the honeyguides have been abandoned. If the crickets are destined to lose their chicks, it is better for them to give up the nest before they invest many resources in it, and when they still have a chance to start a new nest. In other places where social parasitism is common the hosts sometimes recognize the foreign egg and throw it out of the nest. Considering the high cost of this parasitism for the shrews, it is possible that such a strategy will develop in the future for them as well.

for further reading:

The original article:
Spottiswoode, C. & Koorevaar, J. A stab in the dark: chick killing by brood parasitic honeyguides. Biol. Letters (2011). http://bit.ly/nzaYPT

Ed Jung's blog post

The full article was published in Galileo magazine, December 2011