What animal has the lowest preference for mercy?

 Does giving birth to a second offspring for a back-up and then killing it later, count? If so, meet Mr. and Mrs. Shoebill.

Shoebills are found in the plains of Amboseli, Africa and are one of the rare birds that starkly exhibit resemblance to their dino-ancestors. See for yourself.

These large heavy birds make nests on the ground and lay not more than 3 eggs at time. They are silent by nature and merciless by birth. After the chicks hatch, while the parents are away, searching for food, the first born chick, which is usually the strongest one, starts dominating the others. The eldest one will push the other eggs/chick away from the nest, pick on its delicate feathers and not allow any attention to the other eggs.

To make matters more serious, parent shoebills do not raise more than one chick at a time and lay the other eggs as a back-up, in case the first one doesn’t make it. After coming back with their bellies full, ready to bird feed, the parents assess the situation, at the nest. They prioritize the stronger chick and simply kill the rest.

I know this is nature’s way of explaining the concept of survival of the fittest, but this is pure ruthlessness. Shoebill takes the prize for introducing ‘back-up-just-in-case’ babies.