son, those are most definately hens.
if you look at the beaks, they are orange.
Black ducks have a greenish yellow bill.
also look at their feet, mallards are all orange, while the webbed part on a black duck is black.
and you can look at their wings to help you tell the difference.
just some advice, make sure you know what your shooting before you shoot it, it will keep you out of trouble with the warden.
GREAT LOOKIN DUCKS though!