A chiffchaff feeds in an apple tree on the Rodwell Trail
Soon the autumn migration will be properly underway and willow warblers will be streaming down through the UK, feeding up before they make the hop onto the continent and then on to Africa. This photo of a chiffchaff a illustrates how dull they are compared to the willow warblers. A typical young willow at this time of year would be a clear yellow-buff underneath with a bold eyestripe and pink legs. These colours are all variable though so the best way is to try to see the wingtips. The shorter wings of a chiffchaff meet neatly over the base of its tail whereas a willow warbler's longer wings are usually held lower down along the tail. I'll try to get a photo of one soon to illustrate, but in the meantime Martin Cade, warden of Portland Bird Observatory, has added a good account of the differences at http://www.portlandbirdobs.org.uk/latest_apr2009.htm
Bob's right in his description and discussion of the differences between chiff-chaffs and willow warblers. At this time of the year the young are easy to identify because of their fresh plumage; but the worn plumage of the adults are much harder and some individuals can be impossible, even in the hand. Individuals may have features which appear to be from both species, therefore you often have to base identification on the majority of features.
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Lat/Lng: 50.5, -2.5
OS grid ref: SY6676