These birds are are around in the spring, summer and autumn. In fact, they are usually the first migrant to arrive in the spring. They are much more noticeable at this time when they can be heard singing out their loud characteristic song (chiff-chaff chiff-chaff chiff-chaff). They usually perch near the very top of a tree to make the sound travel further. When not singing they can be found hopping around the branches in wooded areas, but they are quite a drab bird, with few characteristic features other than black legs and feet, as can be seen in the photo below...

The one below was heard calling, in the shelter belt in December - obviously one of a few Chiffchaffs that over-winter here in the UK.