Public domain or low cost nature recordings?

["Matthew Capowski"]

Greetings,

I've Googled for 'public domain nature recordings' but didn't really
find what I was looking for.  I'm curious if any of you have favorite
sites for such things?

I'm working on a video project that needs to satisfy our errors and
emissions insurance policy so the source of the recordings needs to be
'trusted' by the community, so to speak.  Of course I will pay if I
have to/that's the only way but my project is pretty low budget.

Thanks in advance.

MC