A friend pointed me to a NY Times article,
http://www.nytimes.com/2008/03/04/sc...gewanted=print
which referenced the original publication,
http://www.pnas.org/cgi/content/abstract/0707711105v1

The Abstract states:
Gliding saves much energy, and to make large distances using only this
form of flight represents a great challenge for both birds and people.
The solution is to make use of the so-called thermals, which are
localized, warmer regions in the atmosphere moving upwards with a
speed exceeding the descent rate of bird and plane. Whereas birds use
this technique mainly for foraging, humans do it as a sporting
activity. Thermalling involves efficient optimization including the
skilful localization of thermals, trying to guess the most favorable
route, estimating the best descending rate, etc. In this study, we
address the question whether there are any analogies between the
solutions birds and humans find to handle the above task. High-
resolution track logs were taken from thermalling falcons and
paraglider pilots to determine the essential parameters of the flight
patterns. We find that there are relevant common features in the ways
birds and humans use thermals. In particular, falcons seem to
reproduce the MacCready formula widely used by gliders to calculate
the best slope to take before an upcoming thermal.