Common Eiders dine on a winter caviar treat: Nature News –

Winter is a great time to go to the beach. You won’t find much warm sand but will find a wonderful array of sea birds. Case in point, last week I decided to head to the coast to look for sea ducks. There, behind a sandbar at the mouth of the Mousam River, I got to know the common eider (Somateria mollissima) in an entirely new way.  Eiders are one of my favorite ducks because of my obsession with the North. These are a species of the north; they nest in the tundra and along rocky shores and are found along the coastlines of both the northern Pacific and Atlantic oceans.  
Hanging out in a tidal inlet were two gorgeous cinnamon colored female eiders.  These large (the largest duck in the northern hemisphere) sea ducks have a very distinctive long, sloping lobe of the bill that extends up the forehead.  The adult males are easy to identify with their striking black and white plumage, but to my eye these two females were even more striking. They almost glowed. When I looked them up in Sibleys’ Guide to Birds (just to double check) I learned something new.  There are regional differences in plumage, especially in the females.  Our eastern Atlantic female eiders are dark rufous (they get even redder-brown in winter) whereas the western Arctic group is more gray-brown and the East Arctic and Hudson Bay groups are grayer.  I couldn’t find information about why this is except for some speculation on regional camouflage needs. 
These eiders were hanging out in a wide spot of a tidal creek, just before where it narrowed to go under a bridge.  There were two females and a herring gull.  The two eiders would dive underwater while the gull and I watched for bubble patterns to try to figure out where they would come up. I was interested in getting a photo, whereas it turns out the herring gull was interested in stealing their meal. More often than not when they popped up at the surface with their prize the gull would swoop at them and occasionally startle them into abandoning their prey.  
The eiders were just close enough that I was able to see that they were bringing up crabs. They would toss the crab around, do something with it underwater, work it around in their bills and eventually gulp it down. It amazes me that they could swallow those things whole. All that tossing and manipulating is called ‘handling’ and what they were doing with the crabs was disarticulating them (taking off the pointy legs) to make them more palatable.  They do this with urchins, another favorite food, rotating in the mouth to flatten the spines. Cornell Lab’s “Birds of the World” explains how they process these crunchy treats. “Feeding cycles or bouts generally last 20 to 35 minutes and are composed of about 13 to 23 minutes of active feeding and 8 to 17 minutes of rest.  During resting phases, food items stored in the gullet (esophageal cavity) move through the gizzard where items are crushed and passed into the intestine for digestion.” Interestingly those resting periods can be a function of prey type. “For example, individuals spent more time in foraging bouts when seeking crabs than when selecting sessile blue mussels and sea urchins.”
When I got a close look at the crabs I could see they were carrying eggs, like icing on the cake for these ducks, a caviar treat!  What’s icing on the cake for local ecosystems is that these looked to be mostly green crabs. These were females who breed late in the summer and carry their eggs all winter. The eiders were doing their part in helping to control the population of this invasive and incredibly destructive species of crab.  
This is what I love about bird watching, I think it’s the same reason some people fish, while we shouldn’t need an excuse it gives us one to get outside and explore. When on the lookout for birds there is never a bad time to go to the beach. 
Susan Pike, a researcher and an environmental sciences and biology teacher at Dover High School, welcomes your ideas for future column topics. Send your photos and observations to Read more of her Nature News columns online at and, and follow her on Instagram @pikeshikes.