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
Common chiffchaff of London. These overwintering common chiffchaffs include some visitors of the eastern subspecies "abietinus" and "tristis", so they are certainly not all birds which have bred locally, although some undoubtedly are. The male common chiffchaff is highly territorial during the breeding season, with a core territory typically 20 metres (66 ft) across, which is fiercely defended against other males. Other small birds may also be attacked. The male is inquisitive and fearless, attacking even dangerous predators like the stoat if they approach the nest, as well as egg-thieves like the Eurasian jay. His song, given from a favoured prominent vantage