<<30,000 ft, eh? That's a good distance. I'm willing to bet some of the birds that are natural soarers (raptors, etc.) could make it down; they get way the heck up there on their own anyway. But I'm no expert.>> Bold added.
Heard back from my naturalist friend. For some reason I found the bold part humerous, maybe it's just the phrase "way the heck up there".
Zenmervolt