Although there is no evidence as yet of any White-headed x Speckled Mousebird intergrades, the two are sympatric in several areas, and the mystery individual depicted in these photographs shows a remarkable resemblance to the form
Colius striatus marangu described by Van Someren in 1939 from specimens from South Kilimanjaro, Moshi and the lowlands north of Mt Meru.
In 1939 (Journal EANHS Vol 14: 54-55) Van Someren commented on Speckled Mousebirds on either side of the Kenya-Tanzania boundary line.
These birds were nearest to the race cinerascens but differed being less pure grey on the crown and mantle, and it seemed many had brown eyes, not the yellowish or creamy eyes in cinerascens.
The two photographs attached by Adam show an individual with a decidedly grey crest, dark eyes and plain pale brownish underparts.The location lies to the west of South Kilimanjaro, and appears not to fit with any of the currently recognised races of Speckled Mousebird. It is possible that they are closest to what van Someren described as Colius striatus marangu but which has largely been lost or forgotten over the years since 1939, and submerged within cinerascens in all recent books.
Del Hoyo & Collar (2016) comment that. "those from Mt Kilimanjaro (N Tanzania) previously separated as race marangu, were probably a hybrid population and are generally placed with cinerascens;” They clearly followed Dr Herbert Schifter (the Mousebird authority) who had earlier considered the South Kilimanjaro birds a hybrid population that may have originated from adjoining dry country populations, and were characterised by having brown or parti-coloured irises.
Don Turner