Fact of the week: Bad is complicated

I use to think that the only avian brood parasite was cuckoos. I was wrong. There are also cowbirds. These cowbirds are even more vindictive than cuckoos. If the host eliminates the cuckoo's egg, the cuckoo will at most try to lay another egg to replace the lost egg. The cuckoo does not literally put all her eggs in one basket so she has to monitor several nests with her egg.

Side note: 

Cuckoo also have a problem with their own counterparts. If they see a nest that already has another egg that is different from the host, that egg is going to damage by hook (actually beak) or by crook (Gravity). It is a game of bluff and double bluff. 

The cowbird does things differently. It lays its egg in the host and then drops by to see if its egg is still present. If it is missing, the cowbird will destroy all the eggs in the host's nest. Note that the nest is otherwise left intact. This leaves a message to the host bird to lay another batch of eggs and accept them as their own.    

This looks more merciless but then the cowbird's chicks are less murderous to the host's chicks. The cuckoo's chick will push everybody else overboard. Egg or hatchling.