There is an article on vultures in NY Times this last week. It is all about how these birds are super smart, and how they had to adapt to feed on carrion.
But they also talk about vultures (and condors are vultures) and flying. Flapping their wings takes up about 30x the energy of perching. But gliding on air currents and updrafts is only 2x of the energy. So they have posted this. It is very cool.