Rüppell's Griffon are cliff-nesting vultures which travel widely in search of carrion. In the Mara there are no nesting/roosting cliffs so these vultures are long-distance commuters from suitable sites in the Rift Valley such as Hell's Gate.
All your birds are fantastic but this is my favorite! Of course, I am partial to vultures. I love that you were able to get a perfectly parallel flight shot with such clarity of the eye. Way to go!