From the Battle for Wesnoth team:
Wesnoth is sponsoring a $200 bounty for an environmental sound loop.
We're looking for background audio, explicitly NOT MUSIC, but just recordings of the sound made in a natural environment. We're asking for this because the available sounds in public-domain libraries, that we can find, are not suitable for our needs - we probably want you to go out and record something new. We may post a series of these bounties, if this pans out nicely.