Taxonomy
The Eurasian Treecreeper was first described under its current scientific name by Linnaeus in his Systema naturae in 1758. The binomial name is derived from Greek kerthios, a small tree-dwelling bird described by Aristotle and others, and Latin familiaris, 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 sreeh. Species in the southern group, in contrast, have a faster-paced trill without the sreeh 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.
There are nine to twelve subspecies of Eurasian Treecreeper, depending on the taxonomic view taken, which are all very similar and often interbreed in areas where their ranges overlap. There is a general cline in appearance from west to east across Eurasia, with subspecies becoming greyer above and whiter below, but this trend reverses east of the Amur River. The currently recognised subspecies are as follows:
| Subspecies | Range | Notes |
|---|---|---|
| C. f. britannica | Great Britain and Ireland | Irish treecreepers, slightly darker than British ones, have sometimes been given subspecific status |
| C. f. macrodactyla | Western Europe | Paler above and whiter below than C. f. britannica |
| C. f. corsa | Corsica | Buff-tinged underparts and more contrasted upperparts than C. f. macrodactyla |
| C. f. familiaris | Scandinavia and eastern Europe east to western Siberia | Nominate subspecies. Paler above than C. f. macrodactyla, white underparts |
| C. f. daurica | Eastern Siberia, northern Mongolia | Paler and greyer than the nominate subspecies |
| C. f. orientalis | Amur basin, northeast China and Korea | Similar to nominate, but with stronger streaking above |
| C. f. japonica | Japan | Darker and more rufous than C. f. duarica |
| C. f. persica | The Crimea and Turkey east to northern Iran | Duller and less rufous than the nominate form |
| C. f. tianchanica | Northwestern China and adjacent regions of the former USSR | Paler and more rufous than nominate subspecies |
| C. f. hodgsoni | Western Himalayas of, Kashmir | Often treated as a full species, Hodgson's Treecreeper, C. hodgsonii. |
| C. f. mandellii | Eastern Himalayas of India, Nepal | Often now treated as a subspecies of Hodgson's Treecreeper |
| C. f. khamensis | China, Sichuan | Often now treated as a subspecies of Hodgson's Treecreeper |
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