Weighing less than 6 grams (0.2 oz), the goldcrest is the smallest bird in the United Kingdom. Its Latin name, 'Regulus regulus', means 'petty king', which refers to both its size and its golden crest (head) feathers. The birds only grow to between 8.5-9.5 cm (3.3-3.7 in) in length and have a wingspan of 13.5-15.5 cm (5.3-6.1 in).

A goldcrest has olive-green upperparts, buff-white underparts, a white line at the top of its wings, and a light brown face. Its crown has black sides and a yellow centre, although the males also have a tinge of orange. Their small, thin bill is black, and their legs are dark brown.

Goldcrests breed in coniferous woodlands and gardens. They build compact, layered nests on tree branches and lay around ten to twelve eggs at a time. The female birds incubate the eggs until they hatch, and the chicks are fed by both parents.

The goldcrest is also the smallest bird in Europe and has appeared in literature throughout history. Roman philosophers and writers, such as Aristotle (384-322 BC) and Pliny (23-79 AD), wrote about a legendary contest between all birds to see who should be their king. The one that could fly highest would be crowned the winner. Most expected the eagle to win, but when he began to tire, a small bird, which had hidden under the eagle's tail feathers, emerged and flew even higher. This was the goldcrest and it was crowned king. That is allegedly how it got its golden crest.

More Info: en.wikipedia.org