Identifying scoters by shape

I was recently studying and sketching the three species of American scoters in Revere, Massachusetts, and I was struck by the differences in head and body shapes. I thought those differences deserved to be highlighted in some new sketches, which are shown below. If you enjoy quizzes, you can try to identify the three species, or just go straight to the discussion below.

The three North American scoters can be distinguished readily by details of the head and bill, but like many birds of open water they are often seen at a great distance in bad light, when details such as bill shape and plumage patterns cannot be ascertained. More subtle (but equally diagnostic) differences in silhouette then become important.

A – White-winged Scoter

• bill relatively large but fine-tipped, with sloped or slightly “scooped” forehead
• head relatively small with crown angled down to inconspicuous corner on hind-crown, but much shorter distance to hind-peak than on Surf
• neck thicker at base
• back of neck angles down and back
• back relatively flat, highest near front and sloping gradually to tail
• tail relatively short and less often raised

B – Surf Scoter

• bill large and bulky, angled slightly down
• peak on forehead and long slope to very strong corner on hind-crown
• neck evenly thick
• back of neck more or less vertical
• back peaked in center, not as rounded as Black
• tail fairly long and sometimes raised, but less conspicuous than Black

C – Black Scoter

• bill small, slightly upturned and with strongly “scooped” forehead
• rounded crown with very slight corner on hind crown
• neck thinner than other two species
• back of neck curved
• back rounded, riding higher in water
• tail long and often conspicuously raised