Why do Canada geese & Mallard ducks breed with farm poultry? Do any other birds do this?
I have noticed this at parks. I have never seen a Pintail or Wood duck or any other ducks or geese (or Cardinals or English Sparrows, etc.) do this & was wondering why do these 2 do this?
because domestic ducks/geese come from three species the muscovy duck, the mallard and the greylag goose. These were domesticated to make all the forms you see today. Canada Geese can hybridize freely with Greylag geese because they are (quite) closely related. These offspring can also reproduce Mallards often mate with farmyard ducks because farmyard ducks are often just funny coloured mallards so no problems there. Muscovy ducks and mallards frequently interbreed making an infertile hybrid or mule duck (which tastes good!). Pintail are able to hybridize with farmyard ducks as they are the same genera as Mallards (anas) but they dont unless they are in collections because they have a choice of mates in the wild. Wood Ducks are in a genera apart from mallards called Aix, which they share with mandarin ducks from china. Due to this they are less likely to mate with mallards but it is possible because most potential hybrids are possible although not always as fertile young. Other birds dont get involved because waterfowl like to keep it in the family 
Chicken / Duck Poultry Nipple Drinkers Waterers CCONLY