[Ferret]

I think it is generally accepted that a species that has arrived under its own steam is native as soon as it has a self supporting population that no longer relies on vagrants to support its population. So Collard Dove was added, I suspect, to the BTO’s official list as soon as this could be proved.

To be ‘official’ it needs to be on someone’s list i.e. DEFRA or a local council, this probably wont happen until someone decides it either needs protecting or exterminating, probably both. Although it will probably be added to semi-official lists before that i.e. RSPB, BTO, British Dragonfly Society, Butterfly Conservation, etc.

At the end of the day if its here its here, and if its not going to be a pest or a threat to other species nobody if likely to put to much effort into where it came from, especially if it looks like it could be a natural expansion of its range. Some species that we consider as British species i.e. Painted Lady, Red Admiral and Hummingbird Hawkmoth probably still rely on migrants and do not have self sustaining populations.

Awkward little buggers aren’t they; just refuse to fit into our neat little lists

Ferret