Li Clinton, a resource educator at Olympic National Park,says, "... its primary food is coniferous seeds but it will supplement that diet in summer with insects, especially beetles. Most likely what the birds were after was salt as they are common residents around stock salt blocks. The crab molts are coated in salt and the birds will come and lick the salt off. There is no current record of them being interested in the sand fleas. Keep in mind that most of the Dungeness Crab shells you find on the beach are not dead crabs but the molted shells of growing crabs."
Richard Schneider
Port Angeles