There’s nothing subtle about them. The males you can ID from far away. It’s like they have big puffy heads.
I find them to be as shy as a Wood Duck. The only place I ever get consistent opportunities is the ponds around old Magnolia Cemetery. Even there most shots are long.
I waited along a hidden place on the bank of the pond to get these closer than normal, shots.
Below is a female. No crazy colors, but still a puffy head.
Mergansers are diving ducks and prefer fish caught under the surface. So, a shy bird, who swims under water. A good reason they are hard to photograph.
Mergansers spend the winter in the Lowcountry. We do have year round residents but I don’t see many and we are out and about often.