Visit Ridgefield in the winter and you’ll see waterfowl diving under the water to feed, such as this bufflehead at sunset above, or the coot below, its red eye visible just above the water. I like to sit and watch them and have been struck by the many differences in the bodies of coots and diving ducks, even though they both spend much of their lives diving underwater to feed. There are differences in their bills, and their feet (ducks having fully-webbed feet, coots not), but my favorite difference is most visible when they dive.
Both diving ducks and coots spring forward and break the surface tension of the water with their beaks, but ducks leave a vortex behind them at the start of the dive while coots do not, a difference that begins with their ends. Diving ducks like the bufflehead have broad tails that they spread out horizontally on the water before they dive, enabling them to push their tails down and themselves forward as they start their dive. You can see the pattern of their tail feathers, shown below as water flips off the bufflehead’s tail as he finishes the dive, in the water behind the duck in the first picture.
Compare the bufflehead’s tail above to the coot’s below and you’ll see the coot has a stubby little tail and can’t use it to push forward like the diving ducks can. While it might seem that the diving ducks have solved the diving problem much more efficiently than the coots, I should point out that the coots at Ridgefield far outnumber any species of diving duck at the refuge.
A trait they share in common is that they have to get a long run across the water to take to the air, so if a bald eagle attacks, they prefer to dive under the water as a means of escape. It’s usually effective, but sometimes you’ll see an eagle keep flying over a duck or coot repeatedly until its prey tires and surfaces at just the wrong moment and is captured in the eagle’s talons. I’ve seen eagles with a variety of waterfowl in their talons, but coots more than any others, not surprising given their large numbers.