I also managed this rather distant photo of a montane white-eye. As further support that despite the top of this mountain being only c. 2100m the forests at the top support montane species.
Other non-montane species were groups of cabinis's greenbul, and singles of augur buzzard, yellow-rumped tinkerbird, brown-crowned tchagra.
On the mammal side of things, I did manage to see and photograph a troop of colobus monkeys. While seeing them there wasn't surprising, I can't recall ever having run into them before on the mountain.
Others were syke's monkeys and baboons heard from afar, and dwarf mongoose.
While Ol Donyo is not the easiest park to see birds, it has a lovely bit of forest at the top and apart from some semi-drunk hikers I didn't encounter anyone else. Karibu Thika!
Cheers, Darcy