White-necked raven (Corvus albicollis) at the last rest area before Kibo.
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 several even around Kibo huts, at 4700m amsl.
They fly to those higher altitudes looking for food during the day, but return to lower elevations to nest.