How to recognise a good nature recording:
1. Does it list the name of the recorder. If no one was prepared to put their name on the CD it can't be much good.
2. Does it have a sequence of tracks with smooth transitions. For example: dawn, day, wind, approaching thunder, rain starting, running water, rain clearing, frogs , dusk, etc. This requires much more effort than simply taking a mike to the shower (rain) or running tap (river).
3. Locations are listed. If the recorder actually went to the effort of going on location then the results should be superior. Of course, the birds and frog sounds have to match. For example, Australia has no woodpeckers !
4. List the gear used. Guys with good mikes, binaural head, high technology gear, etc have invested in expensive stuff. The quality shows in the results.
5. List complaints about suffering on location. Recording is an obsession for many guys who spend days/weeks in tents in all weathers in all seasons to get perfect sounds.
6. Listen for background noises. If you can hear planes, cars, doors, pets, talking, then it was probably recorded in the backyard or local park.
7. Nature is random. The same sequence of sounds should never repeat. Too much swishing (white noise) suggests artificial sources.
8. Plenty of variety. I think 20 minutes of river gurgles is really boring. I consider CDs with a single theme or single sound as poor quality.
The random aspect makes nature sounds so unpredictable and special. With a little practice you can separate the CDs which are a unique work from the syndicated productions.