The Goldcrest (Regulus regulus) is a very small passerine bird in the kinglet family. Its colourful golden crest feathers gives rise to its English and scientific names, and possibly to it being called the “king of the birds” in European folklore.
The Goldcrest is the smallest European bird, 8.5–9.5 cm (3.3–3.7 in) in length,with a 13.5–15.5 cm (5.3–6.1 in) wingspan and a weight of 4.5–7.0 g (0.16–0.25 oz). It is similar in appearance to a warbler, with olive-green upperparts, 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 upperparts and greyer underparts than the adult male. The juvenile is similar to the adult, but has duller upperparts and lacks the coloured crown.