I would think you would be able to tell if it is lonely or mourning. When this happened to us our lone duck just sat on the side of the pond not doing ducky things anymore (no swimming or dabling) once we got another companion duck all duck like activities resumed.
Perhaps your lone duck will get enough socialization with the hens. We've always kept or hens and ducks in separate pens (but next to each other)thru the winter months and the ducks out on the pond spring summer and fall. So you see our duck was truly alone.
Like I said, I think you'll be able to tell. Good luck.

If I had one lonely duck I would give it the companionship of some potatoes, carrots, onions, and a little salt.
But instead, all of my ducks run together and seem MUCH happier that way.

cpp6318,,being a vegetarian,,it's not an option...;)
but he does seem happier these days swimming in his pool ect..just wondered if another was a must. I'll know if and when the right time arises again...till then I guess "one is the lonliest number that he'll ever be"..LOL

cpp6318, Awesome.

so you're saying that a companion is a must right cpp6318?
That's how i took it....??