[gweinberg]

It's amazing how high birds can fly http://en.wikipedia.org/wiki/List_of_birds_by_flight_heights

[dm2]

Unfortunately it's likely that many many types of animals take advantage of low-altitude wind-streams, especially during migrations.

But maybe we could place several of them into the jet-stream (at 10-15 km) which is higher than all birds except one type of vulture.

Edit: Nevermind, Google is working on exactly that: http://www.gizmag.com/google-x-makani-power-airborne-wind-tu...

The cable seems to be the most difficult part: http://en.wikipedia.org/wiki/High-altitude_wind_power