Small passerine bird in the kinglet family
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The goldcrest (Regulus regulus) is a very small passerine bird in the kinglet family. Its colourful golden crest feathers, as well as being called the "king of the birds" in European folklore, gives rise to its English and scientific names. The scientific name, "R. regulus", means 'petty king' or prince. Several subspecies are recognised across the very large distribution range that includes much of the Palearctic and the islands of Macaronesia and Iceland. Birds from the north and east of its breeding range migrate to winter further south.
This kinglet has greenish upper-parts, whitish under-parts, and has two white wingbars. It has a plain face contrasting black irises and a bright head crest, orange and yellow in the male and yellow in the female, which is displayed during breeding. It superficially resembles the common firecrest ("Regulus ignicapilla"), which largely shares its European range, but the latter's bronze shoulders and strong face pattern are distinctive. The song is a repetition of high thin notes, slightly higher-pitched than those of its relative. Birds on the Canary Islands are now separated into two subspecies of the goldcrest, but were formerly considered to be a subspecies of the firecrest or a separate species, "Regulus teneriffae".
The goldcrest breeds in coniferous woodland and gardens, building its compact, three-layered nest on a tree branch. Ten to twelve eggs are incubated by the female alone, and the chicks are fed by both parents; second broods are common. This kinglet is constantly on the move as it searches for insects to eat, and in winter it is often found with flocks of tits. It may be killed by birds of prey or carry parasites, but its large range and population mean that it is not considered to present any significant conservation concerns.
Description.
The goldcrest is the smallest European bird, in length, with a wingspan and a weight of . It is similar in appearance to a warbler, with olive-green upper-parts, buff-white underparts, two white wing bars, and a plain face with conspicuous black irises. The crown of the head has black sides and a narrow black front, and a bright crest, yellow with an orange centre in the male, and entirely yellow in the female; the crest is erected in display, making the distinctive orange stripe of the male much more conspicuous. The small, thin bill is black, and the legs are dark flesh-brown. 
Apart from the crest colour, the sexes are alike, although in fresh plumage, the female may have very slightly paler upper-parts and greyer underparts than the adult male. The juvenile is similar to the adult, but has duller upper-parts and lacks the coloured crown. Although the tail and flight feathers may be retained into the first winter, by then the young birds are almost indistinguishable from adults in the field. The flight is distinctive; it consists of whirring wing-beats with occasional sudden changes of direction. Shorter flights while feeding are a mix of dashing and fluttering with frequent hovering. It moves restlessly among foliage, regularly creeping on branches and up and down trunks.
Identification.
The goldcrest is usually easily distinguished from other small birds in its range, but poor views could possibly lead to confusion with the common firecrest or yellow-browed warbler. The adult common firecrest has a distinguishing face pattern showing a bright white supercilium (eyebrow) and black eye-stripe, and the juvenile usually shows enough of this face pattern to be readily distinguished from the plain-faced goldcrest. The yellow-browed warbler has a yellowish supercilium and pale crown stripe, so also shows a different head pattern. 
The ruby-crowned kinglet, an American "Regulus" species and a potential vagrant in Europe, could be more difficult to distinguish. It has a plain face like its Old World cousin, but the male has a red crest without any yellow or a black border. Female and juvenile ruby-crowned kinglets lack the ruby-red crown patch, but compared with the similarly crestless juvenile goldcrest, the American bird is larger in size, has an obvious whitish eyering, and yellowish wing bars.
Voice.
The typical contact call of the goldcrest is a thin, high-pitched "zee" given at intervals of 1–4 seconds, with all the notes at the same pitch. It sometimes has a more clipped ending, or is delivered more rapidly. The call is higher and less rough than that of the firecrest. The song of the male goldcrest is a very high, thin double note "cedar", repeated 5–7 times and ending in a flourish, "cedarcedar-cedar-cedar-cedar-stichi-see-pee". The entire song lasts 3–4 seconds and is repeated 5–7 times a minute. This song, often uttered while the male is foraging, can be heard in most months of the year. There is also a subdued rambling subsong. Male goldcrests sometimes show a territorial response to recordings of the songs or calls of the common firecrest, but the reverse is apparently not true, since the songs of the common firecrest are simpler in construction than those of its relatives.
The songs of mainland goldcrests vary only slightly across their range and consist of a single song type, but much more divergence has occurred in the isolated Macaronesian populations. Not only are there variations between islands and within an island, but individual males on the Azores can have up to three song types. The dialects on the Azores fall into two main groups, neither of which elicited a response from male European goldcrests in playback experiments. There are also two main dialect groups on the Canary islands, a widespread group similar to the European version, and another that is restricted to the mountains of Tenerife. The song variations have been used to investigate the colonisation pattern of the Macaronesian islands by goldcrests, and identified a previously unknown subspecies.
Taxonomy.
The kinglets are a small group of birds sometimes included in the Old World warblers, but frequently given family status, especially as recent research shows that despite superficial similarities, they are phylogenetically remote from the warblers. The names of the family Regulidae, and the genus "Regulus", are derived from the Latin , a diminutive of , a king. The goldcrest was first described by Carl Linnaeus in his in 1758 as "Motacilla regulus" (characterised as ). It was moved to the warbler genus "Sylvia" by English naturalist John Latham in 1790, and to its current genus by French zoologist Georges Cuvier in 1800.
The relationships of the flamecrest or Taiwan firecrest ("Regulus goodfellowi") of Taiwan have also been a source of much debate. It is sometimes viewed as a race of firecrest, but its territorial song resembles those of the Himalayan races of goldcrest, and genetic data show that it is the closest relative of that species, and, despite its alternative name, only distantly related to the firecrest. The flamecrest diverged from the goldcrest 3.0–3.1 mya (million years ago).
Subspecies.
Continental Eurasia.
Several subspecies of the goldcrest have been described. In continental Eurasia, there are nine generally accepted and very similar subspecies, differing only in details such as plumage shade. At the genetic level, the two Central Asian forms, "R. r. sikkimensis" and "R. r. himalayensis", are very close to each other, and have differentiated only in the recent past, but they diverged from the western subspecies around 2.8 mya.
The Atlantic islands.
Two groups of goldcrest taxa are found on the Atlantic islands of Macaronesia. Birds on the Canary Islands are ancient colonists, whereas those on the Azores are of more recent origin. There are no goldcrests on Madeira, where the Madeira firecrest is the only "Regulus" species.
The Canary Islands were colonised in two waves. The first step was the occupation of Tenerife and La Gomera 1.9–2.3 million years ago, followed by a separate invasion of El Hierro and La Palma 1.3–1.8 mya.
Birds from the Canary Islands are particularly distinctive having a black forehead, pink-buff underparts and a darker closed wing, and have been sometimes treated either as a subspecies of the common firecrest or as a different "Regulus" species altogether. They were sometimes called the Tenerife goldcrest, no matter which of the islands they lived on; however, a 2006 study of the vocalisations of these birds indicate that they actually comprise two subspecies of the goldcrest that are separable on voice; "R. r. teneriffae" occurring on Tenerife and the newly described subspecies, "R. r. ellenthalerae", the western Canary Islands goldcrest, occurring on the smaller islands of La Palma and El Hierro. 
Differences in songs, genetics and morphology suggests that the Azores were colonised in a single invasion in the late Pleistocene, about 100,000 years ago. It is likely that the initial colonisation was of the easternmost islands, with a subsequent spread to the central and western island groups from the western caldera of São Miguel, where both eastern and western song types are found.
Fossils.
There are a few Pleistocene (2.6 million to 12,000 years BP) records from Europe of extant "Regulus" species, mostly goldcrests or unidentifiable to species. The only fossil of an extinct "Regulus" is a left ulna from 2.6–1.95 mya in Bulgaria, which was identified as belonging to an extinct species, "Regulus bulgaricus". The goldcrest lineage diverged from this apparent ancestor of the common firecrest in the Middle Pleistocene.
Distribution and habitat.
The goldcrest breeds in mature lowland and mountain coniferous woodlands, mainly up to , and occasionally to . It uses spruce, larch, Scots pine, silver fir and mountain pine, and in man-made landscapes also introduced conifers such as douglas fir. Breeding densities of up to 591 pairs per square km (1,530 pairs per square mile) have been recorded in Norway spruce in Ireland, and goldcrests constituted over 60% of all birds found in Welsh Douglas fir and Norway spruce plantations. Broad-leaved woods are used only when some spruce or firs are also present. Sites such as parks and cemeteries are used only when they offer suitable conifers that are not otherwise locally available. The height and nature of any undergrowth is irrelevant. 
Unlike more specialised birds such as the Eurasian nuthatch and the Eurasian treecreeper, both of which forage on tree trunks, the kinglets do not need large woodlands, and their population density is independent of forest size. Once breeding is over, this species will readily move into deciduous trees and shrubs, heathland and similar more open habitats.
The Tenerife subspecies occurs in the mountain region previously occupied by laurisilva, but now dominated by tree heaths. It is common only in that habitat, becoming rare in pine forest, where it occurs only where tree-heath is also available.
The goldcrest has a huge range in Eurasia, breeding from Macaronesia to Japan. It is common in middle and northern temperate and boreal latitudes of Europe, between the July isotherms, and thus predominantly in cooler climates than the firecrest. Further east it occurs discontinuously through southern Siberia to Sakhalin and Japan, in the Tian Shan mountains, northern Iran, and from the Himalayas east to central China.
This species has bred in Iceland since about 1999, and was widespread by 2004, although numbers are affected by hard winters. Breeding occurs intermittently in the Faroes. The goldcrest has occurred as a vagrant in Jordan and Morocco.
This species is partly migratory, northernmost populations deserting their breeding areas in winter. Birds winter in Europe and Asia south of the breeding range. Birds in northern Fennoscandia and Russia vacate their territories between late August and early November, with most leaving in late September to mid-October as the first cold weather arrives. Adverse conditions may lead to disorientation, large numbers gathering on ships on overcast or wet nights. Large influxes include 15,000 birds on the Isle of May in October 1982, and nearly 21,000 birds through a single site in Latvia during September and October 1983. Spring migration is complete by late March on the Mediterranean islands, but continues to late April or early May in northern Europe. The spring passage is much lighter than in autumn, suggesting high mortality on migration.
A study in the Baltic region showed that northern goldcrests were more likely to migrate, and increased their body mass beforehand; non-migratory southern birds did not increase their fat reserves. The travel speed of migrating goldcrests increased for those leaving later in the autumn, and was greater for the northernmost populations. Migration was faster on routes that crossed the Baltic Sea than on coastal routes, and the birds with the largest fat reserves travelled at the highest speeds. The ability to lay down fat is adversely affected