White throated duck

What's the bird on the left? He looks like a mallard, though he has a white throat and his body is mostly brown rather than grey. The bird on the right is a mallard, which has the usual white ring round his neck. To be honest I'm not sure what it is? My guess is that it is just a genetic variation in the mallard species.

If you think you know, then do tell. You can start by clicking edit above.

Here is another photo of the duck: