Question: Why do you think that some birds are predators?

Anthony Caravaggi answered on 15 Mar 2017:

There are predators among all forms of life, from single-celled organisms, through to mammals, birds, reptiles and amphibians. There are even predatory plants!

Predators exist because the bodies of other animals are a very good source of lots of different nutrients, including vitamins, proteins and fats. Some animals evolved to get their nutrients from plants, some evolved to get theirs from the flesh and bones of other animals. Others eat both.

Flesh-eating may be the original state for birds. Birds evolved from meat-eating therapod dinosaurs. Maybe the first birds were predators, and their ancestors only started eating seeds and plants, much later.