They eat snails and slugs which helps the goats as the white tail deer carry some worms that co mingle with snails and slug (https://easternalliancekatahdins.com/meningeal-worm/). They are hardier, more tolerant to cold and rain and snow. Also they lay the same if not more eggs, and more early in the spring and later in the late fall. Also we charge more for duck eggs as they are less common and better for baking and have bigger yokes, more protein and minerals.
Supposedly you can tell early on with the duck bill color but I have not figured it out yet. I have suspicions who is male by how they act probably around 4 weeks but you really are not sure until the tail curls and head turns green around 12-16 weeks. This is with khaki Campbell and Welsh harlequin