http://theconversation.com/how-vultures-use-each-other-as-guides-through-the-turbulent-skies-106870

There is a well known theory, by aeronautical engineer Paul
MacCready, which states that birds and gliders should glide at high airspeed
when they have just left a strong thermal and expect to be approaching another
strong thermal. But gliding quickly is risky, as the flyer is more likely to hit
the ground before reaching the next thermal. So our hypothesis was that these
vultures, and other soaring birds, are able to take this risk and glide quickly
when they have clues provided by the soaring of others, on the whereabouts of
the next thermal.

When we mapped the movements of all the vultures and analysed their gliding
airspeeds, we found that – on making a decision to leave one thermal and glide
to the next – vultures which had tapped into this extra information by
“eavesdropping” on the movements of others (they weren’t flocked together but
were watching how the other vultures were acting) chose to take the risk and
adopt significantly higher airspeeds than those going it alone.

Thanks to John Simon.