any mic really..i would think that an omni directional pattern would be the best. sound professionals makes some low cost omnis that will probably serve you well.(i think the part number is sp-bmc-3??)
A condenser mic with a 3 micron diaphragm will pick up the subtle sounds a little easier, rather than a 6 micron. The problem is you'll need phantom and that isn't easy to supply out in the woods.