Not entirely correct. Some bird species assess how much food is in their area and will starve and evict the weaker-looking chicks so that the stronger-looking ones have a better chance of survival. That is why you will see chicks in the nest beg incessantly for food from the very beginning because the chick willing to step over their sibling for more food is perceived as the stronger and healthier one so they are often rewarded with more food while the bullied chick gets less.
Survival of the fittest. In the wild, it is the law of the jungle.
Not that this has anything to do with these horrible parents. What they did is unspeakable evil.
Also, #21.