Common chiffchaff

Appearance

The common chiffchaff is a small, dumpy, 10–12 centimetres long leaf warbler. The male weighs 7–8 grammes, and the female 6–7 grammes. The spring adult of the western nominate subspecies " P. c. collybita" has brown-washed dull green upperparts, off-white underparts becoming yellowish on the flanks, and a short whitish supercilium. It has dark legs, a fine dark bill, and short primary projection. As the plumage wears, it gets duller and browner, and the yellow on the flanks tends to be lost, but after the breeding season there is a prolonged complete moult before migration. The newly fledged juvenile is browner above than the adult, with yellow-white underparts, but moults about 10 weeks after acquiring its first plumage. After moulting, both the adult and the juvenile have brighter and greener upperparts and a paler supercilium.

Naming

This warbler gets its name from its simple distinctive song, a repetitive cheerful "chiff-chaff". This song is 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 "djup djup djup wheep wheep chittichittichiittichitta". However, mixed singers occur in the hybridisation zone and elsewhere, and can be difficult to allocate to species.

Distribution

The common chiffchaff breeds across Europe and Asia east to eastern Siberia and north to about 70°N, with isolated populations in northwest Africa, northern and western Turkey and northwestern Iran. It is migratory, but it is one of the first passerine birds to return to its breeding areas in the spring and among the last to leave in late autumn.

Habitat

When breeding, it is a bird of open woodlands with some taller trees and ground cover for nesting purposes. These trees are typically at least 5 metres high, with undergrowth that is an open, poor to medium mix of grasses, bracken, nettles or similar plants. Its breeding habitat is quite specific, and even near relatives do not share it; for example, the willow warbler prefers younger trees, while the wood warbler prefers less undergrowth. In winter, the common chiffchaff uses a wider range of habitats including scrub, and is not so dependent on trees. It is often found near water, unlike the willow warbler which tolerates drier habitats. There is an increasing tendency to winter in western Europe well north of the traditional areas, especially in coastal southern England and the mild urban microclimate 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.

Reproduction

The male common chiffchaff returns to its breeding territory two or three weeks before the female and immediately starts singing to establish ownership and attract a female. When a female is located, the male will use a slow butterfly-like flight as part of the courtship ritual, but once a pair-bond has been established, other females will be driven from the territory. The male has little involvement in the nesting process other than defending the territory. The female's nest is built on or near the ground in a concealed site in brambles, nettles or other dense low vegetation. The domed nest has a side entrance, and is constructed from coarse plant material such as dead leaves and grass, with finer material used on the interior before the addition of a lining of feathers. The typical nest is 12.5 centimetres high and 11 centimetres across.

The clutch is two to seven cream-coloured eggs which have tiny ruddy, purple or blackish spots and are about 1.5 centimetres long and 1.2 centimetres across. They are incubated by the female for 13–14 days before hatching as naked, blind altricial chicks. The female broods and feeds the chicks for another 14–15 days until they fledge. The male rarely participates in feeding, although this sometimes occurs, especially when bad weather limits insect supplies or if the female disappears. After fledging, the young stay in the vicinity of the nest for three to four weeks, and are fed by and roost with the female, although these interactions reduce after approximately the first 14 days. In the north of the range there is only time to raise one brood, due to the short summer, but a second brood is common in central and southern areas.

Although pairs stay together during the breeding season and polygamy is uncommon, even if the male and female return to the same site in the following year there is no apparent recognition or fidelity. Interbreeding with other species, other than those formerly considered as subspecies of "P. collybita", is rare, but a few examples are known of hybridisation with the willow warbler. Such hybrids give mixed songs, but the latter alone is not proof of interspecific breeding.

Food

Like most Old World warblers, this small species is insectivorous, moving restlessly through foliage or briefly hovering. It has been recorded as taking insects, mainly flies, from more than 50 families, along with other small and medium-sized invertebrates. It will take the eggs and larvae of butterflies and moths, particularly those of the winter moth. The chiffchaff has been estimated to require about one-third of its weight in insects daily, and it feeds almost continuously in the autumn to put on extra fat as fuel for the long migration flight.

Predators

As with most small birds, mortality in the first year of life is high, but adults aged three to four years are regularly recorded, and the record is more than seven years. Eggs, chicks and fledglings of this ground-nesting species are taken by stoats, weasels and crows such as the European magpie, and the adults are hunted by birds of prey, particularly the sparrowhawk. Small birds are also at the mercy of the weather, particularly when migrating, but also on the breeding and wintering grounds.

The common chiffchaff is occasionally a host of brood parasitic cuckoos, including the common and Horsfield's cuckoos, but it recognises and rejects non-mimetic eggs and is therefore only rarely successfully brood-parasitised. Like other passerine birds, the common chiffchaff can also acquire intestinal nematode parasites and external ticks.

The main effect of humans on this species is indirect, through woodland clearance which affects the habitat, predation by cats, and collisions with windows, buildings and cars. Only the first of these has the potential to seriously affect populations, but given the huge geographical spread of "P. c. abietinus" and "P. c. tristis", and woodland conservation policies in the range of "P. c. collybita", the chiffchaff's future seems assured.