I find this site very useful foridentifying bird skulls
I cannot recall any british duck with quite such a short beak, except some of the ornimental races such as the Call Duck.
I have looked at that site, and many other ones..
I have checked jake's blog. ( http://www.jakes-bones.com/ )
but undortunatelly none of the sites I can find are for north american species.
The location of the find does make a big difference. It strikes me that the shape of the skull leading down onto the beak is quite straight where as on most ducks this is curved. I wonder if it may be a small goose, the snow goose has a skull only 8cm long which is the same as this skull, another possible line of enquiry?
unfortunately I don't think it could be any kind of goose...
when I found it, it was a full head. the feathers where irredescent green like a mallard..
so it has to be something with a green head. unless something can cause feathers to turn irredescent green...
and would it be possible that a duck's skull in canada and a duck in uk would have a difference of 4cm? (40mm)
could it be a hybrid?
Goldeneye also has a green head, lives in Canada and has a skull the same size as this skull. Many of the featrures are closer to a Goldeneye than a Mallard, but as I suggested in my first post I would lean towards an ornimental race of duck. I learn't a long time ago to photograph everything before I prepare the skull and despite this I still have skulls which I am uncertain of the correct identity.
Ornimental ducks are specially bred for captivity and are often smaller than the sild ducks that they originated from, here is a link to the Call Duck
Wood ducks are kept in captivity but they are also in the wild, when I use the term ornimental duck I refer to captively bred ducks which have no wild equivalent (unless they escape).