On my walk home from work I regularly pass a large gathering of ducks, geese and swans. Over the past couple of days I noticed a few of the Male ducks are much larger and seem to have much darker heads than the others (not the best photo, but best I could muster with low light on a cycle path). The two in the background are examples of these, would anyone be able to help identify these? They stand in a much more upright stance and have considerably longer torsos. I tried to search for them on google but was unable to find anything with the same colourings and shape. Many thanks! Update: I was able to find the two ducks again and have some slightly better comparison photos(posted above original photo), I could spot them from a distance of about 30 feet as they are that much larger than the other ~20 mallards. They seem to lack the white neck ring all of the other male ducks have and the elongated, swollen shape of their backsides is completely different.
I agree with Hazel (sorry Hazel, I know my ID record isn't great ) . Colour variations in mallards are significant, and also the iridescence can be misleading depending on the light conditions, I've seen some that look blue headed from one direction, but green headed from the other, simply because of the way the light was on them