Oh that they doo... and the cotton from the cotton woods, and the greener bits of died grass, and the twigs, and the straw itself. LOL...
Like I said, mine eat literally everything. If a piece of straw is too chewy they trot it over and deposit it in their water dish for later. By far and away, straw has been our friend. We use it in our brooder and also in the coop outside. keeps the shat off the floor for the most part, and keeps the water that spills around their inside dish fairly well soaked up. Another thing, as we are in Alaska here and the only grain we can grow with any great success here is Barley, we have taken to feeding it to them. We sprout it for 4 to 7 days, feeding it to them in that period of its growth and they go absolutely ape for it. As do our chickens. You should be able to find a grain of some kind in your local area that you can buy direct from the farmer for a fairly low cost. Ours, shipped something like 500 miles or so, came to just about $6.50 per 50 pound sack. The hay bales were $1.50. Needless to say, once your ducklings get to about 3 to 4 weeks, it is one heck of a lot cheaper than buying all your feed at the pet store. Also, if you have to get any antibiotics and such, go online and buy them from a farming site as they sell it in bulk and cheap for lots.