My Japanese friend uses the work ｢アヒル」when referring to ducks in a public park. However, another Japanese friend uses 「鴨」（かも）in similar situations.
In English, as far as my limited knowledge of the animal kingdom goes, we just have the word "duck". Can anyone explain the difference between these two words? Which is more common (and more correct) in the situation I've outlined? And do the rules change if we're talking about duck as a dish in a restaurant?
Referring to Japanese Wikipedia, it seems the main difference is that アヒル is used for domestic ducks and 鴨 for wild ducks.
According to this Chiebukuro post, 家鴨{あひる} "house duck" came about due to selective breeding from 真鴨{まがも} "true duck" or "mallards". Apparently the former is a tame duck created for food and enjoyment.
I think there's a fair amount of overlap in practical usage, but that アヒル might sound slightly more feminine/cuter than 鴨. This is just anecdotal, but I've often seen アヒル used in that kind of way in Anime etc, and I've seen some females use pen-names of アヒル but never カモ. It also might be worth noting アヒル口, which is apparently regarded for it's "cuteness" and "sexiness" according to Wikipedia.
Ahiru are white and kamo are the other ducks. Duck in cooking is usually kamo. I was corrected for referring to ducks on a lake which were not white as ahiru.
