Kinglets are small forest birds in the subfamily Silviinae, family Muscicapidae, within the largest of the avian orders, Passeriformes, the perching birds. Kinglets are the most common North American representatives of their rather large subfamily, which is much more diverse in Europe, Asia, and Australia, and includes some 279 species.
There are two species of kinglets in North America, both of which are very active insectivorous feeders that breed in northern and montane conifer-dominated forests. The golden-crowned kinglet (Regulus satrapa) is a small bird, only about 3-4 in (9-10 cm) long, with an olive-green body and a white eye-stripe. The bird is a very active hunter of insects, spiders, and other small arthropods. Its song is a high-pitched series of notes followed by a chatter. The kinglet's nest is generally located within dense foliage high in the outer part of the crown of a conifer tree, and can contain as many as 10 eggs, which together may weigh more than the female bird. Both sexes have a bright yellow head-cap, but in male birds this feature is crowned by an orange-red cap, which is apparent only during a courtship display. Although insectivorous feeders, the golden-crowned kinglets can winter in boreal conifer forests as well as in temperate broadleaf forests, where, despite the cold, the kinglet successfully removes bark, twigs, and foliage in search of hibernating arthropods and their eggs. This species also winters as far south as parts of Central America. Wintering birds can often be seen in mixed flocks with other small species of birds, such as chickadees, nuthatches, creepers, and smaller woodpeckers.
The ruby-crowned kinglet (Regulus calendula) is also a common breeding bird in many coniferous forests of North America. This small, 3-4.3 in (9-11 cm) long bird also has an olive-green body and a distinctive white eye-ring, and is a very energetic gleaner of small arthropods, sometimes hunting at branch tips using brief fluttering flights. The song is somewhat of an ascending chatter, with elements often repeated in threes, and the final parts are amazingly loud for such a tiny bird. The male ruby-crowned kinglet has a vermillion patch on the top of its head which is only apparent when the bird raises the crest during courtship display. This species winters farther to the south than the golden-crowned kinglet, mostly in southern North America and northern Central America.
Two very closely related species of Eurasia are the goldcrest (Regulus regulus) and the firecrest (Regulus ingicapillus), which also breed in northern or temperate conifer-dominated or mixed-wood forests.