Northamptonshire’s fourth-ever Northern Willow Warbler was pulled from the nets of the Stanford Ringing Group, at Stanford Reservoir, this morning.
Willow Warbler comprises three subspecies – nominate trochilus from Britain, central Europe and southern Scandinavia, acredula (‘Northern Willow Warbler’) from northern Scandinavia, Russia and western Siberia and yakutensis (‘Siberian Willow Warbler’) from central and eastern Siberia. However, the subspecies are not well defined and there is extensive intergradation. Furthermore, variation is not linear, and birds showing the characters of one subspecies occur regularly within the range of another (BWP).
Fortunately, visual characteristics, when combined with in-hand biometrics allow identification of acredula to be made. Trying to do so in the field, however, is more than a challenge on an out of range individual! This one is a typical, cold, pallid individual, with reduced yellow tones and quite a striking supercilium.
This is the fourth record of acredula for Northants, all of which to date have been trapped at Stanford! Previous records were 23rd August 2008, 30th June 2011 and 8th September 2014.