Similar size to Mallard and congregates with Mallards
No interactions present.
They look like so-called Magpie Ducks...
My Flickr photos...
I did look at Magpie Ducks, I wasn't sure they quite fitted, very near though. The scientific name was the same as Mallard.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Lat/Lng: 53.8407, -1.7951
OS grid ref: SE135382
Seen on the Leeds Liverpool canal at Saltaire, Shipley, West Yorks.