Chiming in from the Bird Photography group: vultures evolved bald heads to avoid soiling their feathers with the rot and bacteria that are commonly found in the corpses they eat. However, not all vulture species eat exactly the same way, so not all species of vultures need bald heads. The Bearded Vulture, like this one, eats the bones of dead animals after much of the meat has been picked off by other carrion birds. Since they don't deal with lots of rotting meat, they have no need for bald heads.
However, the Bearded Vulture is actually a pretty interesting case in and of itself--it doesn't really "fit" with the other vultures, and forms a separate subfamily inside the accipitridae with only a couple other birds, which makes it distinct from what we tend to think of as the "typical" bald-headed vulture.
And, with that said, the Bearded Vulture is my absolute favorite bird in the world, and it this is a stunning, stunning shot.