Parenting in the animal kingdom isn't always what we would expect, while there are some parents that would go against much larger animals to defend their children like most mammals, some animals don't really give a crap like a sea turtles.
Birds hold the reputation as one of the most devout parents found in the animal kingdom and with good reason. Birds put in days of effort in building their nests, from finding a secure nesting site to collecting nesting material and carefully placing, stitching or sewing to prepare a suitable nest for their young, later they spend weeks hunting for food until their chick is ready to fly. This is more than most animals would do and even though some birds like the cuckoo lay their eggs in others nests (brood parasitism) the behavior of some birds may make cuckoos look like they deserve a parenting award.
The behavior we're talking about is brood reduction. Brood reduction is a behavioral phenomena which results in parents neglecting the smaller and weaker chick (often younger) leading to starvation, bullying by the older sibling also known as siblicide. Some birds show facultative siblicide, which means they may or may not kill their siblings depending on environmental factors like abundance of food. Others show obligate siblicide in which regardless of the availability of food the stronger offspring will almost certainly kill the the weaker. This behavior allows the stronger offspring to receive more resources and grow into stronger adults.
This already dark story is about to take a darker turn, sometimes the parents themselves kick the weaker chick out of the nest or neglect them on purpose while focusing on raising the stronger chick. Parents can go so far as to murdering their own chick which is also called filial infanticide.
Most of the the times the weaker chick isn't a weak but one that hatched last and hence relatively smaller in size.
According to certain studies brood reduction is just another way of natural selection by eliminating weaker organisms keeping the overall population strong. Nature is filled with bizarre sometimes horrifying yet interesting relationships if you wish to know more about nature make sure you watch our documentaries and blogs . Hit the join the tribe feature to get regular updates about upcoming events.