tHATS A GOOD QUESTION THAT I DONT HAVE AN ANSWER FOR SINCE I JUST STARTED RAISING CHICKENS A MONTH OR SO AGO. I LIVE IN THE PINEY WOODS OF EAST TEXAS AND HAVE TONS OF PINE NEEDLES. hELP!
I use pine straw in a corner of my aviary as well. My ducks don't really use it much, but sometimes play in it. They love to root around in it, though.
From what i heard in the duck section, it's very hard to get moldy, which was the main reason i went with it.
I was previously going to use some dried grasses like meadow hays, but nearly all of them are green and i noticed all the green hays seem to mold over within a week in my climate.
If you are lucky to have a pine tree, you can get it for free or just buy a bale of it, much like Hay. I bought a 25 or 40 pound bale, for about $20.