Dear Titus,
I went back through images I had taken of Parrot-billed and Swahili,
Under Parrot-billed I had this image, photographed at Ol Tukai,
Amboseli. It is almost certainly where the visitor took the images
under discussion. By an amazing coincidence I seem to have captured
both a Parrot-bill and a Swahili together, and never noticed it.
With the bird on the left, unfortunately you cannot see the throat,
but I thought you could see an indication of white on the chin and
throat of the submitted image. The bill looks slight, the head is pale
grey, extending to the entire back and on to the wing coverts. The
white patch is small but bright. The underparts are pale with an
indication of a dark mottling. The sides of the tail, vent and
undertail coverts (apart from the mottling) are nearly white. I think
the bird is smaller than the accompanying Parrot-billed Sparrow, but
it is so hard to judge from a photograph.
The Parrot-bill appears to have a heavy all blackish bill, head grey
but back rusty washed like wing coverts, and no white mark on wing.
The underparts are uniform darkish grey and lack the indication of
mottling. The under tail and sides are difficult to discern but look
dark.
The differences between these bird on the same photo are much the same
as the differences between the two submitted images.
Amboseli could be an overlap zone of Swahili and Parrot-billed, we
shall have to pay more attention to the sparrows in this area.
Best to all
Brian