One of the tougher ID challenges birders may face during the winter months when the sea ducks leave their northern breeding grounds, is telling apart female-type White-winged Scoters and Surf Scoters. Males in adult plumage of these two species don’t really pose much of a challenge. Their bold bills and markings on their head make differentiating these two apart pretty straightforward. But females and juvenile males lack the colorful bills and white markings and so their differences are much more subtle.
With a bit of practice and knowledge of their differences, telling these two apart becomes a much simpler task.
A good place to start with telling the female-types apart is if there is the presence of the White-winged Scoters namesake white wing patches. If you see this feature, problem solved! You have a White-winged Scoter! If not, well, then you have to look towards other field marks to tell which species you have.
Besides the white wing patch, the facial features are your next most obvious field marks you will want to look to for an ID. On both species, two white patches will be on their heads, one below and behind the eye, and one below between the eye and the bill. This is the one we want to pay attention to. On a White-winged Scoter, the feathers go pretty far down the bill, creating a larger, more round white circle, where the feathers on the Surf Scoter end abruptly, creating a more vertical white oval. With the difference of where the feathers on the bill end, this creates vastly different appearances on bill shape.
Head shape also possesses a nice clue to what species you are looking at. A Surf Scoter’s head is more squarish, with a flat top, while a White-winged Scoter’s head is also a bit squarish, but has a more prominent peaked forehead. For head color, the White-winged have a uniformly brown head, while a Surf’s has a black-capped like appearance with the top of the head being noticeably darker than the rest of the head.
At first these features may not be too obvious, but with many more tricky ID’s, with a bit of practice, these two won’t give you much trouble (unless they are miles away on the water…)