How many dangerous birds are there?

Answer 1

All of the human sized flightless birds like, emus, ostriches, cassowaries, which can if provoked, disembowel a person, could be considered dangerous.

Most of the birds of prey, when protecting their young will mess a human up, no problem. 

Answer 2

How do you define dangerous bird?

Most birds don't mess with you unless you mess with them.

 Ostrichs creep me out tho. They could kill a man.