Simon, I try to pick lists that look like they had some thought put into them. The only ones I can really guarantee are the ones that are either produced by myself or ones from places I have been to (as I heavily research everywhere I go).
Sometimes, with these lists, people don't go into areas which might have particular species and thus get missed on a list. At the local park, if I decide not to walk by the pond and count the water birds, I can completely miss that subset of species on a day list. On the other side, I can chose to bird parts of the park not usually birded by anyone else and turn up several bird species not usual to the park. As far as I am aware, I think Mute Swan is not a native resident in most of Spain (?) so you are absolutely correct on that and other points.
Carlos
PS: Oh, and by the way, JoanT is correct that the list is from New Mexico, USA. But where exactly?