Is it possible to assert that there are useful and harmful birds in nature?

It is categorically impossible. A bird can be good for one species and bad for another. We always talk about the usefulness of an organism by considering its effects on us or on the species we use. But birds, which are carriers of dangerous diseases, destroy plants, other animals – a component of natural selection factors. If there were no pests, parasites and other harmful organisms, then evolution would simply stop. Also, we must not forget that birds are in food chains, and their violation affects other organisms.