Kinglet

The kinglets or crests are a small group of birds sometimes included in the Old World warblers, but are frequently given family status because they also resemble the titmice. The scientific name Regulidae is derived from the Latin word regulus for "petty king" or prince, and comes from the coloured crowns of adult birds. This family has representatives in North America and Eurasia. There are seven species in this family; one, the Madeira Firecrest, Regulus madeirensis, was only recently split from Common Firecrest as a separate species. One species, the Ruby-crowned Kinglet, differs sufficiently in its voice and plumage to occasionally be afforded its own genus, Corthylio.

Description
Kinglets are among the smallest of all passerines, ranging in size from 8–11 cm (3.2–4.3 in) and weighing 6–8 g (0.2–0.3 oz); the sexes are the same size. They have medium-length wings and tails, and small needle-like bills. The plumage is overall grey-green, offset by pale wingbars, and the tail tip is incised. Five species have a single stiff feather covering the nostril, but in the Ruby-crowned Kinglet, this is replaced by several short, stiff bristles. Most kinglets have distinctive head markings, and the males possess a colourful crown patch. In the females, the crown is duller and yellower. The long feathers forming the central crown stripe can be erected; they are inconspicuous most of the time, but are used in courtship and territorial displays when the raised crest is very striking.

There are two species in North America with largely overlapping distributions, and two in Eurasia which also have a considerable shared range. In each continent, one species (Goldcrest in Eurasia and Golden-crowned Kinglet in North America) is a conifer specialist; these have deeply grooved pads on their feet for perching on conifer twigs, and a long hind toe and claw for clinging vertically. The two generalists, Ruby-crowned Kinglet and Common Firecrest hunt more in flight, and have smoother soles, shorter hind claws and a longer tail.

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 showed that, despite superficial similarities, the crests are taxonomically remote from the warblers. The names of the family, Regulidae, and its only genus, Regulus, are derived from the Latin regulus, a diminutive of rex, "a king", and refer to the characteristic orange or yellow crests of adult kinglets. The kinglets were allocated to the warbler genus Sylvia by English naturalist John Latham in 1790, but moved to their current genus by French zoologist Georges Cuvier in 1800.

Several forms have only recently had their status clarified. The Madeira Firecrest was formerly considered to be a subspecies, R. i. madeirensis, of the Common Firecrest R. ignicapillus. A phylogenetic analysis based on the cytochrome b gene showed that the Madeiran form is distinct at the species level from the Firecrest nominate subspecies R. i. ignicapillus. Cytochrome b gene divergence between the Madeira Firecrest and the European bird is 8.5%, comparable with the divergence level between other recognised Regulus species, such as the 9% between the Goldcrest and the Golden-crowned Kinglet. The split was accepted by the Association of European Rarities Committees (AERC) in 2003, but some authorities, like Clements, have not yet recognised the new species. The Golden-crowned Kinglet is similar in appearance to the Common Firecrest and has been considered to be its New World equivalent, but it is actually closer to the Goldcrest.

Goldcrests 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, occurring on the smaller islands of La Palma and El Hierro. The three Goldcrest taxa on the Azores, Santa Maria Goldcrest, Sao Miguel Goldcrest and Western Azores Goldcrest, represent recent colonisations from Europe, and are best treated as subspecies.

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).

Most members of the Regulus genus are similar in size and colour pattern. The exception is the Ruby-crowned Kinglet, the largest species, which has a strongly red crest and no black crown stripes. It has distinctive vocalisations, and is different enough from the Old World kinglets and the other American species, the Golden-crowned Kinglet, to be sometimes assigned to a separate genus, Corthylio.

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
Kinglets are birds of the Nearctic and Palearctic ecozones, with representatives in temperate North America, Europe and Asia, northernmost Africa, Macaronesia and the Himalayas. They are adapted to conifer forests, although there is a certain amount of adaptability and most species will use other habitats, particularly during migration. In Macaronesia, they are adapted to laurisilva and tree heaths.

Diet and feeding
The tiny size and rapid metabolism of kinglets means that they must constantly forage in order to provide their energy needs. They will continue feeding even when nest building. Kinglets prevented from feeding may lose a third of their body weight in twenty minutes and may starve to death in an hour. Kinglets are insectivores, preferentially feeding on insects such as aphids and springtails that have soft cuticles. Prey is generally gleaned from the branches and leaves of trees, although in some circumstances prey may be taken on the wing or from the leaf litter on the ground.

Breeding
The nest are small, very neat cups, almost spherical in shape, made of moss and lichen held together with spiderwebs and hung from twigs near the end of a high branch of a conifer. They are lined with hair and feathers, and a few feathers are placed over the opening. These characteristics provide good insulation against the cold environment. The female lays 7 to 12 eggs, which are white or pale buff, some having fine dark brown spots. Because the nest is small, they are stacked in layers. The female incubates; she pushes her legs (which are well supplied with blood vessels, hence warm) down among the eggs. The eggs hatch after 15 to 17 days. The young stay in the nest for 19 to 24 days. After being fed, nestlings make their way down to the bottom of the nest, pushing their still-hungry siblings up to be fed in their turn (but also to be cold).

Status
The four continental Regulus species all have very large ranges and populations. The two single-island endemics are common within their habitat, and are not thought to be at risk. All kinglets are therefore classed as Least Concern on the IUCN Red List,