Crime scene
Nature has written the best crime novel with some birds. In many cases, the fight for survival starts really early. From the first second of their life, chicks have to manage to avoid infanticide, fratricide or murder of any kind.
Infanticide is produced when an adult bird violently kills a chick of its own species. To illustrate this phenomenon we can move to the tropical lakes and ponds where the Northern Jacana (Jacana spinosa) lives. The male of this species is the one who incubates the eggs and takes care of the nestlings. When a female wants to court a male, she destroys the eggs or kills the chicks in order to mate with him. This way, the infanticide will get her own offspring. Males cannot prevent the fatal ending because they are smaller in size than the females.
The Good Son
Another crime, more cruel if possible, is filicide. This happens when a parent kills its own offspring. When the availability of food decreases, some species, like the Black Stork, harass the youngest —and thus weakest— chick until it dies of exhaustion or falls out of the nest.
Cain Vs Abel
Cainism is the murder of the weakest chicks by their own siblings, so they can get the exclusive attention of the parents and more food. Sometimes, the crime is produced in the presence of the parents, like in the case of the Golden Eagle, and some other times, when the parents are absent from the nest.
The Great Egret starts incubating the first egg before laying the second one (hatching asynchrony); for this reason, there is a big size difference between the two nestlings. It is common for Great Egret chicks, in a constant fight for food, to kill their own siblings. This is due to an adaptive response: if food is scarce, the oldest chick decides to kill the youngest one. This way, the chances that some of the nestlings survive are increased.
In a research on the Black Eagle, it was observed that the eldest chick killed its brother by pecking him 1500 times along 38 attacks. During this process, the killer increased its weight in 50 grams and the victim lost 80 grams. Although this practice may seem very cruel, another research proved it to be really effective. Cattle Egret eggs were incubated, getting chicks of similar size which were administered the necessary amount of food. Despite what it could seem in the beginning, researchers reached the conclusion that it was possible to support more chicks with this natural system.
One Flew Over the Cuckoo’s Nest
If we look among the small-sized killers, we find the species that parasitize the nests. An example of this would be the cuckoo. The female cuckoo doesn’t brood its own eggs, but lays them in nests of other species. The gullible step-parents will take care of the chick thinking it is their own, unaware of the upcoming tragedy. The young cuckoo is born before its stepbrothers, which he will throw to the void when the parents are not present, granting its own survival and leading to one of the most curious scenes in nature: not long afterwards, he will be fed by step-parents that are half its size.
In the case of endangered species, ornithologists use techniques to avoid these natural behaviours. With the purpose of increasing the productivity of the nests, supplementary feeding programmes are usually carried out in order to let the parents support the whole offspring. When this is not possible, the youngest chick can be rescued and raised in captivity.
All these crimes may give you the chills, but, like Aristotle said, nature never makes anything without a purpose. As we have seen, the female Northern Jacana pursues an individual benefit, in order to ensure the persistence of its genes. The fratricide of egrets and eagles achieves a collective benefit by adjusting the number of chicks to the availability of food, and the cainism of the cuckoo pursues the survival of the species: due to its long size, there wouldn’t be enough food to share with its stepbrothers.
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