techincally, most any of them will breed together, especially within the same subspeices group, and even out of it.
Have seen wood duck widgeons, widgeon pintails, wood duck goldeneyes, scaup and pintail, etc. Wood ducks and pintails are your biggest threat for mixing to other species from what I have had, and seen pics of, the others arent too bad but, most any can cross breed. The only species I havent seen a cross to yet is a mandarin.
I even saw a ring teal pintail last night.
Trick is to give them plenty of space and evenly paired. I always kept all 3 species of widgeon in the same pens with no problems, but yes, there is a good chance in a small pen they will cross. Also, the 2 hens from these are very similar, so to a new person, you may not be able to tell them apart. I would go with european and chiloe if it were me, they are the prettiest of the 3, and less likely to mix. Plus the chilow stays in color all the time too.
but out of all the birds I have kept in community pens, by keeping them evenly paired and plenty of space, I only had 1-2 crosses over all those years. That's the trick to these community pens, plenty of room, and no odd ball spare birds, especially drakes, if anything, keep a few extra hens for the ones like wood ducks and pintails and you should be fine.
