Whilst ringing on 7 June 2015 I caught an unusual
looking Willow Warbler. The bird did not look like the typical birds we get in
Saudi Arabia where we catch what appears to be two types of birds. Birds
resembling nominate trochilus and acredula/yakutensis types with
the former being much more common. This bird did not appear to be like nominate
trochilus as it was too brown and white and the measurements were small
compared to the acredula/yakutensis types we catch. The trouble with
this group is that only the extremes can be separated with any degree of
confidence i.e. the most obviously yellow- and olive-tinged trochilus
in the west and the paler grey-brown and white yakutensis in the
extreme east, which lack olive and yellow almost entirely. Between these two
the form acredula appears to be very variable in appearance and, even in
a given area, there is a lot of variation. Among acredula, the more
‘brown and white’ types have been referred to as ‘eversmanni’ but such
birds are known to occur alongside more typical acredula and ‘eversmanni’
is not deemed to have any taxonomic validity. Svensson indicates that some acredula
(presumably ‘eversmanni’ types) and yakutensis ‘can look just the
same’. The form yakutensis is rather larger on average but your measurements
of wing and tail fit quite comfortably with acredula and do not hint at yakutensis.
I would like to thank Alan Dean for valuable comments on this odd looking
Willow Warbler (for us in Saudi Arabia at least).
