Hattiegun, sorry I lost track for a few days . . .
Looks like we have no boys in the flock. But the girls have been actively displaying breeding behaviors - treading, flattening out, the usual stuff. As I mentioned, there has been some milky discharge from their vents. Holderread's advice was to start with the extra calcium a month before laying. If yours, a small breed, are thirteen weeks, I would start giving them extra calcium, at least once a week, now.
WadeMD, I have noticed no constant protrusion of a vent. But Vier especially seems to have filled out in the lower belly. I think she may be the one laying (we now have three eggs in five days).
A friend sent two large cheese boxes, which I stuffed with straw. Most of the ducks were extremely interested in straw and boxes. Someone slept in them last night. The egg this morning was next to a box.
Today they seem ravenous for protein. I gave them a pile of worms, and some cat kibble in their pellets. They went wild for both. I need to get some more oyster shell out here, too. I haven't found a good container for it that they won't turn over. I think I need to get another big cake pan. That seems to be the only thing handy that they don't flip with their feet.