I've nothing against Hybrid species of Birds. To me, Birds are either interesting, or they're not; although I've not found any that fit into the "not" category yet.
But don't you see that your logic, and that of AnimalAid will lead to
less interesting bird species to see, because two groups of different birds on either side of the ocean will become two groups of the same bird due to man bringing one to meet the other?
It boils down to a very simple question - do you want to have White-headed Ducks and Ruddy Ducks in the World, or just Ruddy Ducks? Because without shooting the Ruddy Ducks in Europe (leaving many tens of thousands in America) you cannot have both. The science is very clear. Those in AnimalAid etc who say it isn't just don't understand it. The people who
do understand the science (BirdLife International, Natural England and many other scientists) say that we have to get rid of the Ruddies in Europe if we want to keep White-headed Ducks.
Notice that all of the people who object to the cull are not ornithologists/scientists, and all of the organisation that back the cull are specialists in ornithology/science.
Would you ask AnimalAid for their opinion on the best way to reduce the economic deficit? No, because they are not economists - I'd ask an economist. By the same token, AnimalAid's opinion on genetic swamping and competition in ducks is worth about the same amount of attention. Which is none. When it comes to those subjects, we have specialists at BirdLife, RSPB, Natural England and British and Spanish universities.
When it comes to the ethics of veal crates or dog cruelty, of course, then AnimalAid and RSPCA have some valid things to say. But we don't hear the RSPB chipping in, do we? Horses for courses.