Reading this thread in anticipation of our first ducks this spring. We are near Olympia.
What I like as a base layer for our chicken day pen is arborists tree chips. The ones we spread were from a large pile that had already cooled down substantially, so not fresh and the initial fungal activity had subsided. This was a nice layer which, when I harvested it along with the layers of litter on top, was chock full of worms and no funky smell (granted-- chickens, not ducks). So, I am likely to try this with our ducks as well and I hope I can have a better answer for you next year. The issue I think about the most for PNWers is the leaching of nutrients (and possible pollution) from manure/litter exposed to the constant autumn and winter (and spring) rain, especially when nothing is growing to use the excess nitrogen. If the pen is covered and not in an area where the water collects, it will be good and dry under there, unless you have the water channeled into the pen area from the hillside.
