salt glands that eiders and other sea birds have to enable them to survive without fresh water by taking in sea water and excreting the excess salts.
Wandering along the Bamburgh shore the other day, I was surprised to see a male eider swimming towards me. Usually they move away rather than come closer. Then it came out of the water and padded up onto the shore right in front of me. It seemed oblivious to my presence - which again is unusual. Then the penny dropped. It was heading straight for a small pool of fresh water that had collected among the rocks from a small drainage run coming off the land. It obviously knew it was there and nothing was going to stop it. This was a duck on a mission. It drank at least half a dozen times, throwing its head back each time, before waddling off back into the sea.
So, salt glands or not, eider rather have the fresh stuff thank you very much.