There are a number of Passeriformes called "warblers". They are not particularly closely related, but share some characteristics, such as being fairly small, vocal and insectivorous.They are mostly brownish or dull greenish in color.
Tree warblers are medium-sized warblers in the marsh- and tree-warbler family Acrocephalidae. They are found in Europe, Africa and western Asia. Until recently, they were all classified in the single genus Hippolais.
These warblers are associated with trees, though normally in fairly open woodland rather than tight plantations. Compared with the closely related Acrocephalus species, tree warblers have squarer tails and broader bill-bases. Most are unstreaked greenish or brownish above and cream or white below. They are insectivorous, but will occasionally take berries or seeds. The species breeding in temperate regions are mostly strongly migratory. Birds of Glacier National Park