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 Origin of Birds in fact, was decidedly reptilian and generally opposed to that of modern birds. This included the pelvis, which lacks a pectineal process and has a very different os sacrum from modern birds, as well as the carpus, which Heilmann wrote exhibited the same phenomena found in the wrists of modern reptiles. Its tail was also noted by Heilmann as being extremely reptilian and resembling nothing known of modern birds. He goes on to state that other features of "Archaeopteryx", however, are remarkably birdlike and bear little resemblance to their reptilian analogues. The hand of "Archaeopteryx" is observed as being one