Common Eiders have a design problem, which they try to overcome with two distinctive defensive moves. Their problem is that their bodies are too heavy and broad to overcome their “bow” waves and get enough “hull” speed to fly up quickly when they sense a predator in the water (e.g., a seal), air (e.g., bald eagle), or land (e.g., human).
Rather than try to fly up, they collect closer in their group (a “paddling” of Eiders) to make it difficult for a predator to isolate on a single target, as do zebras.
Then, as you see here with these Eiders in Blue Hill Bay, they perform their first distinctive maneuver, what researchers call “steaming”: they increase speed by using their wings as oars that both propel them and lift them up a bit.
If need be, they convert their steaming into what has been called by researchers “paddle-assisted flying.” (See them beginning this in the image in the first Comment space.) In this maneuver, they lift off the water, but stay low and use their powerful legs to assist their air-beating wings in giving them more speed to skim over the water. (Brooklin Maine; Leighton Archive images used)
For more on this subject, see: Gough, et al., “Aquatic burst locomotion by hydroplaning and paddling in common eiders (Somateria mollissima),” Journal of Experimental Biology 2015 218: 1632-1638; doi: 10.1242/jeb.114140