We bought these ducks at an auction 2 months ado and they were sold to us as Mallards. What we thought was a male started to get a little white ring around the neck and a little green on top of the head. Now they all look alike. They are small in stature, about the size of a bantam chicken. They must be at least two to three months old now and are not changing in anyway as far as growth or color. Can anyone tell me what they might be please?