Common chiffchaff
The common chiffchaff ("Phylloscopus collybita"), or simply the chiffchaff, is a common and widespread leaf warbler which breeds in open woodlands throughout northern and temperate Europe and the Palearctic. It is a migratory passerine which winters in southern and western Europe, southern Asia and north Africa. Greenish-brown above and off-white below, it is named onomatopoeically for its simple "chiff-chaff" song. It has a number of subspecies, some of which are now treated as full species. The female builds a domed nest on or near the ground, and assumes most of the responsibility for brooding and  feeding the chicks, whilst the male has little involvement in nesting, but defends his territory against rivals, and attacks potential predators. A small insectivorous bird, it is subject to predation by mammals, such as cats and mustelids, and birds, particularly hawks of the genus "Accipiter". Its large range and population mean that its status is secure, although one subspecies is probably extinct. Taxonomy. The British naturalist Gilbert White was one of the first people to separate the similar-looking common chiffchaff, willow warbler and wood warbler by their songs, as detailed in 1789 in "The Natural History and Antiquities of  Selborne", but the common chiffchaff was first formally described as "Sylvia collybita" by French ornithologist Louis Vieillot in 1817 in his "Nouveau Dictionnaire d'Histoire Naturelle". Described by German zoologist Friedrich Boie in 1826, the genus "Phylloscopus" contains about 50 species of small insectivorous Old World woodland warblers which are either greenish or brown above and yellowish, white or buff below. The genus was formerly part of the Old World warbler family Sylvidae, but has now been split off as a separate family Phylloscopidae. The chiffchaff's closest relatives, other than former subspecies, are a group of leaf warblers which similarly  lack crown stripes, a yellow rump or obvious wing bars; they include the willow, Bonelli's, wood and plain leaf warblers. An old synonym, used for the chiffchaff was "Phylloscopus rufus" (Bechstein). The common chiffchaff has three still commonly accepted subspecies, together with some from the Iberian Peninsula, the Canary Islands, and the Caucasus which are now more often treated as full species. Etymology. The common chiffchaff's English name is onomatopoeic, referring to the repetitive ' song of the European subspecies. There are similar names in some other European languages, such as the Dutch , the German , Welsh and Finnish . The  binomial name is of Greek origin; "Phylloscopus" comes from '/, "leaf", and ""/, "to look at" or "to see", since this genus comprises species that spend much of their time feeding in trees, while "collybita" is a corruption of "kollubistes", "money changer", the song being likened to the jingling of coins. In some languages their tree-dwelling habit is hinted in the vernacular name. For example, in Swedish the common chiffchaff is called "gransångare", a compound of "gran" (i.e. "spruce") and "sångare", meaning both "singer" and Old World warbler. Description. The common chiffchaff is a small, dumpy, long leaf warbler. The male  weighs 7–8 grammes (0.28–0.31 oz), and the female 6–7 grammes (0.25–0.28 oz). 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 (extension of the flight feathers beyond the folded wing). 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. This warbler gets its name from its simple distinctive song, a repetitive cheerful '. This song is one of the first avian signs that spring has returned. Its call is a ', less disyllabic than the ' of the willow warbler or ' 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 and generally pale legs. Bonelli's warbler ("P. bonelli)" might be confused with the common chiffchaff subspecies "tristis", but it has a plain face and green in the wings. The common chiffchaff also has rounded wings in flight, and a diagnostic tail movement consisting of a dip, then sidewards wag, that  distinguishes it from other "Phylloscopus" warblers and gives rise to the name "tailwagger" in India. Perhaps the greatest challenge is distinguishing non-singing birds of the nominate subspecies from Iberian chiffchaff in the field. In Great Britain and the Netherlands, all accepted records of vagrant Iberian chiffchaffs relate to singing males. Distribution and habitat. 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. 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 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 ("P. trochilus") prefers younger trees, while the wood warbler ("P. sibilatrix") 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. Behaviour. Territory. The male common chiffchaff is highly territorial during the breeding season, with a core territory  typically 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 point, appears to be used to advertise an established territory and contact the female, rather than as a paternity guard strategy. Beyond the core territory, there is a larger feeding range which is variable in size, but typically ten or more times the area of the breeding territory. It  is believed that the female has a larger feeding range than the male. After breeding has finished, this species abandons its territory, and may join small flocks including other warblers prior to migration. Breeding. 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 high and across. The clutch is two to seven (normally five or six) cream-coloured eggs which have tiny ruddy, purple or blackish spots and are about  long and 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. Feeding. 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 and threats. 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. Status . The common chiffchaff has an enormous range, with an estimated global extent of 10 million square kilometres (3.8 million square miles) and a population of 60–120 million individuals in Europe alone. Although global population trends have not been quantified, the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (that is, declining more than 30 percent in ten years or three generations). For these reasons, the species is evaluated as "least concern". None of the major subspecies is under threat, but "exsul", as noted above, is probably extinct. There is a  slow population increase of common chiffchaff in the Czech Republic. The range of at least "P. c. collybita" seems to be expanding, with northward advances in Scotland, Norway and Sweden and a large population increase in Denmark.