Eider Nest

No sign of the bee-eater though it has been reported as still around. I walked along the shore from Sandside Bay to the Gloup, then back by the road. A melee of birds were gorging maybe on sandeel offshore- At least ten bonxies and four arctic skua among the other birds. I didn't notice an eider duck on her nest until she flew off. I took a quick photo and realised just now that there is a herring gull egg there too. There were about seven gull nests very close by. Was it laid there in error? Or maybe the gull thought the duck would be a good foster mother. The duck defecated on the eggs as she flew off. I've seen that before. Maybe the smell disguises the smell of the eggs? Or maybe it puts off potential predators?