Native Enough?

Last week, I went bird watching at a wildlife refuge - not too far away from me, but still far enough that I'd never been before.  Without the use of my binoculars, I spotted a few white shapes drifting across the surface of the water.  Pelicans, I thought, perhaps - or maybe rare trumpeter swans, slowly making a comeback.  

When I finally got close enough and saw the birds through the binoculars, I was a little disappointed.  The orange beaks, the dainty posture of the wings - they were mute swans.  Unlike the native trumpeter and tundra swans, mute swans are an invasive species from Europe, which has proliferated in America and caused considerable damage to native waterfowl populations and wetland habitats.  Seeing so many of them here, in the heart of a wildlife refuge, saddened me a bit.

Still, I have to acknowledge that, despite heroic efforts to control their numbers, mute swans seem to be here to stay.  I don't foresee any real reduction in their numbers, and for every trumpeter swan I've seen in the wild, I'm pretty sure I've seen a dozen mute swans.

Photo Credit: Trumpeter Swan Society

At what point, then, do we say that the mute swan is a de facto native?  When do we stop trying, and just accept it?  

Follow up question - would I put mute swans in a native-species themed area of a zoo?  I've seen nutria in such exhibits in Louisiana, and Burmese pythons in Florida, though neither of those are native species.  Does doing so normalize their presence in the landscape in the minds of visitors, suggesting that they do, in fact, belong here?  Or does it provide more a context for us to talk about the threat of invasive species?  If I had to guess - based on the prevalence of sign-reading among visitors - I'd say the former.

Also, do we want to be devoting resources to the upkeep on invasive species in zoos?  I could put mute swans on a pond in our facility (and not much else, probably - they have a reputation for being bullies).  Or, I could devote that space to trumpeter swans, which zoos are working to breed for reintroduction into the wild.  Or injured, non-releasable tundra swans, a native species,.  If someone brought me a non-releasable mute swan, my gut inclination would be to go for euthanasia, though I'd be more than happy to see it rehomed at a facility that wanted it and could guarantee that it wouldn't a) breed or b) have any negative impact on native wildlife?

Ideally, I'd love to be able to do everything - house all sorts of animals for the education of the public and provide for the welfare of all animals that need care, be they native, exotic, or invasive.  Still, all facilities have limited resources, and we have to use them as best as we can.  If I had to make a decision between devoting those resources to the trumpeter swan or the mute swan, I know who I'm supporting.