The little duck in the bottom centre of this picture is a hooded merganser. It was an uncommon visitor to the pond in Springbank Park and a gentleman with a big camera pointed this out to me. I thank him for the tip.
Hooded mergansers have a crest at the back of the head which can be expanded or contracted. In adult males, this crest has a large white patch. It can be quite an impressive display.
Hooded mergansers are short distance migrants and winter in the United States and southern Ontario wherever winter temperatures allow for ice free conditions on ponds, lakes and rivers.