Hi Kenneth. In response (somewhat delayed... sorry) to your question, I don't think there is a definitive list of what birds go in what category. If in doubt, you could always do a search of the
Gallery for the bird in question and see what category others have put it in, or just make your most reasoned judgement. I'm pretty sure there are some overlapping categories; e.g. there are 24 Eider in Seabirds, and 59 in Waterfowl :). And there's a few obviously wrong uns too - a Nuthatch in with the Herons, and a Snow Bunting in with the Finches, to name but two. So I don't think it's too serious an offence, and if it doesn't obviously fit in any category, then Birds should be fine. :)