Dear All,
Clive Mann very kindly forwarded the images of the White Wagtail in
NNP and the query about the birds pattern to HeinVan Grouw at the
Natural History Museum in UK, who gave a very rapid response as
follows;

"Hard to tell from the photos only what is going on with this Wagtail but I
assume, as Brian already suggested, that this bird has a ‘disturbed’
moulting pattern and therefore already shows (partly) breeding plumage.

I cannot think of any (heritable) melanin aberration which could cause this
plumage pattern.

All the best

Hein"

On 1/5/19, Brian Finch birdfinch@gmail.com [kenyabirdsnet]
<kenyabirdsnet-noreply@yahoogroups.com> wrote:
> Dear All,
> I was in Nairobi National Park yesterday (4th January 2019), with
> Nigel Hunter and his grandson Dillon. The weather was periodically
> foul with heavy squalls.
> We were at the Ox-bow along the Mbagathi, sitting out the latest
> downpour, when I spotted some movement on a patch of mud. I put my
> binoculars up and saw it was a White Wagtail this was surprisingly
> only the second individual the Park has ever seen, the last being a
> pair at Athi Dam fifteen years ago. So the record was exciting enough,
> but it looked like no White Wagtail I had ever seen, but was
> unquestionable M. alba alba and not some unusual eastern form.
>
> It was the 4th January, but the large breast patch was pitch black
> right up to the throat, so this was an adult male in summer (breeding)
> plumage, but the head was pale grey, the cheeks were pale grey, in
> breeding plumage the males show contrasting black crowns with white
> face patches, but this was showing the head of an adult male in winter
> plumage. The short black superciliary line maybe related to the future
> appearance of the black crown but that is only supposition.
>
> It is difficult to conceive what moult pattern is taking place on this
> individual to portray two different times of year at the same time,
> and one grossly out of kilter.
>
> Has anyone any idea what is happening here, or seen anything similar.
> Itai with all the thousands you must see every season, have you ever
> come across this combination? Are some White Wagtails with you already
> showing considerable amounts of breeding plumage?
>
> Best to all
> Brian
>