Duck eggs contain
twice as much potassium and Vitamin A,
three times as much iron, and
five times as much Vitamin B12.
They also are higher in these nutrients: protein, calcium, magnesium, phosporus, zinc, copper, manganese, selenium, thiamin, niacin, Vitamin B6, folate, and retinol. They contain twice the amount of monounsaturated fatty acids which lower total cholesterol and LDL cholesterol (the bad cholesterol) while increasing HDL cholesterol (the good cholesterol) .
Their cholesterol content is higher; approximately twice that of chicken eggs.
They have more albumin (protein) which gives them more structure - more fluffiness in baking.
Free range eggs have significantly higher vitamins and Omega 3 fatty acids while less fat and cholesterol.
Many people who are allergic to chicken eggs are able to eat duck eggs without allergic reactions due to different proteins.
That being said, there are a few who can be allergic to the proteins in duck eggs but not chicken eggs.
Because of their higher protein and cholesterol content, their taste is richer - gamey if their diet is higher in proteins from worms, bugs or fish. Due to the higher albumin content, overcooking them can make them VERY firm, almost rubbery, especially in fried or hard boiled eggs. However, after eating my ducks eggs, chicken eggs taste anemic. The taste is well worth the extra care making egg sandwiches.
www.lsshaftsfarm.com
Sources: local harvest.org; buzzle.com; itdfarm.com; 101sweetpastry.com; Wikipedia.org; newagrarian.com