‘Brown’ Warblers
To pair up with the essentially brown pipits, we have brown warblers. This is not a ‘proper’ grouping of course, and we have included members of four genera among this bunch. Of these, Grasshopper and Cetti’s Warbler are notoriously skulking and Garden Warbler (more of a woodland bird than the others) can also be very difficult to get a good look at.
Upperpart colours
Though all these birds are essentially brown, note the presence or absence of streaking and the tone of the brown involved. Only Sedge and Grasshopper Warblers are streaked on their upperparts.
Head shape and pattern
Though head shape is variable (as the feathers can be moved by the bird), it is still useful. But, face pattern is even more useful. Note that it is only Sedge Warbler which has such a broad and long pale supercilium (‘eyebrow’). Garden Warbler is notoriously plain-faced.
Song
Though impossible to convey on an ID card, songs are extremely useful for distinguishing warblers in spring. All five of these warblers have very distinct songs (though some people struggle between the rhythmic Reed Warbler and the more random-sounding Sedge Warbler songs; and Garden Warblers sound very like Blackcaps). Learn these songs and it will save a lot of time and effort!