My ducks are about 4 months old, we have a large woodshed they sleep in at night and a nice stream running through our property where they hang out during the day.

So as you can see 2 of the ducks are busy finding things to eat while the guy in the front is just kinda floating there with his eyes closed. Every now and then I see him stick his head under the water and nibble at things but for the most part he just floats there while the other 2 are constantly moving around looking for things. This has been going on for 2 days now and I'm worried there's something wrong with him. Has anybody seen anything like this? I've looked through some sites that have general Duck ailments but nothing quite fits this description.

Unrelated question, I'm pretty sure this is a Male Mallard, the Green area on his head has been getting larger (all the pics I see they have a full head of green), I assume this happens over time?

Any help appreciated, thx.