The Eurasian treecreeper or common treecreeper (Certhia familiaris) is a small passerine bird also known in the British Isles, where it is the only living member of its genus, simply as treecreeper. It is similar to other treecreepers, and has a curved bill, patterned brown upperparts, whitish underparts, and long stiff tail feathers which help it creep up tree trunks. It can be most easily distinguished from the similar short-toed treecreeper, which shares much of its European range, by its different song.
The Eurasian treecreeper has nine or more subspecies which breed in different parts of its range in the Palearctic. This species is found in woodlands of all kinds, but where it overlaps with the short-toed treecreeper in western Europe it is more likely to be found in coniferous forests or at higher altitudes. It nests in tree crevices or behind bark flakes, and favours introduced giant sequoia as nest sites where they are available. The female typically lays five or six pink-speckled white eggs in the lined nest, but eggs and chicks are vulnerable to attack by woodpeckers and mammals, including squirrels.
The Eurasian treecreeper is insectivorous and climbs up tree trunks like a mouse, to search for insects which it picks from crevices in the bark with its fine curved bill. It then flies to the base of another tree with a distinctive erratic flight. This bird is solitary in winter, but may form communal roosts in cold weather.
Description
A Eurasian treecreeper climbing up a tree, leaning on its tail|left|thumb
Similar in appearance, all treecreepers are small birds with streaked and spotted brown upperparts, rufous rumps and whitish underparts. They have long decurved bills, and long rigid tail feathers that provide support as they creep up tree trunks looking for insects. but if they are retained as subspecies of Eurasian, they have to be distinguished from three other South Asian treecreepers. The plain tail of the Eurasian treecreeper differentiates it from the bar-tailed treecreeper, which has a distinctive barred tail pattern, and its white throat is an obvious difference from that of the brown-throated treecreeper. The rusty-flanked treecreeper is more difficult to separate from the Eurasian, but the former has more contrasting cinnamon, rather than buff, flanks. The binomial name is derived from Ancient Greek , a small tree-dwelling bird described by Aristotle and others, and Latin , familiar or common.
This species is one of a group of very similar typical treecreeper species, all placed in the single genus Certhia. Eight species are currently recognised, in two evolutionary lineages: a Holarctic radiation, and a southern Asian group. The Holarctic group has a more warbling song, always (except in C. familiaris from China) starting or ending with a shrill . Species in the southern group, in contrast, have a faster-paced trill without the sound. All the species have distinctive vocalizations and some subspecies have been elevated to species on the basis of their calls.
The Eurasian treecreeper belongs to the northern group, along with the North American brown creeper, C. americana, the short-toed treecreeper, C. brachydactyla, of western Eurasia, and, if it is considered a separate species, Hodgson's treecreeper, C. hodgsoni, from the southern rim of the Himalayas.
The brown creeper has sometimes been considered to be a subspecies of Eurasian treecreeper, but has closer affinities to short-toed treecreeper, and is normally now treated as a full species. Hodgson's treecreeper is a more recent proposed split following studies of its cytochrome b mtDNA sequence and song structure that indicate that it may well be a distinct species from C. familiaris.
The Eurasian treecreeper is non-migratory in the milder west and south of its breeding range, but some northern birds move south in winter, and individuals breeding on mountains may descend to a lower altitude in winter. Winter movements and post-breeding dispersal may lead to vagrancy outside the normal range. Wintering migrants of the Asian subspecies have been recorded in South Korea and China, and the nominate form has been recorded west of its breeding range as far as Orkney, Scotland. The Eurasian treecreeper has also occurred as a vagrant to the Channel Islands (where the short-toed is the resident species), Mallorca and the Faroe Islands. Crevices in buildings or walls are sometimes used, and artificial nest boxes or flaps may be preferred in coniferous woodland. This species is parasitised in the nest by the moorhen flea, Dasypsyllus gallinulae. The juvenile survival rate of this species is unknown, but 47.7% of adults survive each year. The typical lifespan is two years, but the maximum recorded age is eight years and ten months.
This bird may sometimes join mixed-species feeding flocks in winter, but it does not appear to share the resources found by accompanying tits and goldcrests, and may just be benefiting from the extra vigilance of a flock.
Habits
thumbnail|The claws of the treecreeper allows it to attach to the trunks and branches.
As a small woodland bird with cryptic plumage and a quiet call, the Eurasian treecreeper is easily overlooked as it hops mouse-like up a vertical trunk, progressing in short hops, using its stiff tail and widely splayed feet as support. Nevertheless, it is not wary, and is largely indifferent to the presence of humans.