Common chiffchaff one of the first avian signs that spring has returned. Its call is a "hweet", less disyllabic than the "hooeet" of the willow warbler or "hu-it" of the western Bonelli's warbler. The song differs from that of the Iberian chiffchaff, which has a shorter . However, mixed singers occur in the hybridisation zone and elsewhere, and can be difficult to allocate to species. When not singing, the common chiffchaff can be difficult to distinguish from other leaf warblers with greenish upperparts and whitish underparts, particularly the willow warbler. However, that species has a longer primary projection, a sleeker, brighter appearance
The Sibley Guide to Birds North American and one for the eastern half. The guide was favorably reviewed by "The New York Times", "The Wilson Bulletin" (now "The Wilson Journal of Ornithology"), and the journal "Western Birds". The Sibley Guide to Birds The Sibley Guide to Birds is a reference work and field guide for the birds found in the continental United States and Canada. It is written and illustrated by ornithologist David Allen Sibley. The book provides details on 810 species of birds, with information about identification, life history, vocalizations, and geographic distribution. It contains several paintings of each species, and is critically acclaimed