Could someone help me identify this warbler for me please. I originally thought it was a Chiffchaff or willow warbler but wasn't certain. But on closer inspection the stripe on its eye looks to me like it starts at its eye and doesn't go past its eye towards the back of its head like it shows in my bird guides. It was seen today sat in a tree at the edge of a grassland/meadow field in buckinghamshire.
It would say it's a Chiffchaff (Phylloscopus collybita). It is browner than the Willow Warbler (P. trochilus). The feet are not clearly visible, but they seem dark? this would be an important character: P. collybita with blackish feet, P. trochilus with lighter feet. Whitish eye ring under eye seems to be P. collybita, but I'm not sure.
If you see more specimens (or photos on the web), you can see that the eye stripe varies from bird to bird. Some have more accentuated front halves, or viceversa.
If you could remember the colour of the legs, this would get you to the right ID.
I hope this helps.
I'm sorry I can't really decide, I'm not that good with these species, and the photo doesn't help me. You could try to compare photos of the two species on this web site:
Willow Warbler, with lighter feet: http://ibc.lynxeds.com/photo/willow-warbler-phylloscopus-trochilus/willow-warbler-ground-so-probably-vicinity-nest
Chiffchaff, with darker feet: http://ibc.lynxeds.com/photo/common-chiffchaff-phylloscopus-collybita/adult-singing-male
All the best,