White-necked raven (Corvus albicollis) at Horombo huts (3720 m). They would sit either on the ground either on roofs, waiting for some food from people.
Here is the info about these big birds: http://en.wikipedia.org/wiki/White-necked_Raven
I've found some "birds of Kenya" website and they say that this bird is common between altitude 1000-3000metres, but I saw flocks of them even in Kibo huts at 4700m amsl.