Recent sessions at Oxwich Marsh have proved relatively productive. Yesterday, despite the wind picking up mid morning, and very bright conditions (resulting in nets being more visible), Keith Vaughton and I caught 35 birds of 11 species. It was nice to catch both juvenile willow warblers and chiffchaffs, and despite the reedbed seemingly having relatively few reed and sedge warbler territories this year, juveniles of both species continue to be trapped.
The images below are of juvenile bullfinches, three of which were caught, and (bottom) a juvenile willow warbler (left) and a chiffchaff. The latter photo allows a visual comparison of these similar species. The chiffchaff, on the right, is a duller, browner bird with a less distinct supercilium (eye stripe). The willow warbler is far brighter looking. Although not entirely clear from the picture, the chiffchaff had very dark legs, and the willow warbler lighter coloured legs.
In the hand willow warbler tends to show a longer wing and a different wing formula, being a long distance migrant (chiffchaffs do not migrate across the Sahara). Willow warbler shows emargination of the primaries up to P5 and chiffchaff to P6. Despite appearing similar in size and structure in the photo, the willow warbler was also 2 grams heavier.
Owain Gabb 21/07/13