White-breasted nuthatch

The white-breasted nuthatch (Sitta carolinensis) is a species of bird in the nuthatch family Sittidae. It is a medium-sized nuthatch, measuring approximately 15.5 cm (6.1 in) in length. Coloration varies somewhat along the species' range, but the upperparts are light blue-gray, with a black crown and nape in males, while females have a dark gray crown. The underparts are whitish, with a reddish tinge on the lower abdomen. Despite not being closely related, the white-breasted nuthatch and the white wagtail are very similar in plumage.

The white-breasted nuthatch is a noisy bird. It has a nasal voice and often utters little cries or vocalizations, often composed of repetitions of small invariant whistles. In summer, it is an exclusively insectivorous bird, consuming a wide range of arthropods, but in winter its diet consists mainly of seeds. The nest is located in the cavity of a tree. The clutch consists of five to nine eggs, incubated for two weeks by the female, who is fed by the male. The two adults then feed the young until they fledge, and for a few weeks after that.

The white-breasted nuthatch breeds throughout much of North America, except in the cooler and drier areas. It is mainly found at low elevations, in deciduous forests or in mixed woodlands. Seven to nine subspecies are generally distinguished by their slightly distinct distributions, vocalizations, and coloration. The species was once thought to be related to the white-cheeked nuthatch (S leucopsis) and Przewalski's nuthatch (S. przewalskii), two species from southern Asia, but is actually more closely related to the giant nuthatch (S. magna), also from Southeast Asia.

The white-breasted nuthatch is a medium-sized nuthatch, measuring about 15.5 cm (6.1 in) in length. Like other members of its genus, it has a large head, short tail, short wings, a powerful bill and strong feet; it is 13–14 cm (5.1–5.5 in) long, with a wingspan of 20–27 cm (7.9–10.6 in) and a weight of 18–30 g (0.63–1.06 oz).

The adult male of the nominate subspecies, S. c. carolinensis, has pale blue-gray upperparts, a glossy black cap (crown of the head), and a black band on the upper back. The wing coverts and flight feathers are very dark gray with paler fringes, and the closed wing is pale gray and black, with a thin white wing bar. The face and the underparts are white. The outer tail feathers are black with broad diagonal white bands across the outer three feathers, a feature readily visible in flight.

The female has, on average, a narrower black back band, slightly duller upperparts and buffer underparts than the male. Her cap may be gray, but many females have black caps and cannot be reliably distinguished from the male in the field. In the northeastern United States, at least 10% of females have black caps, but the proportion rises to 40–80% in the Rocky Mountains, Mexico and the southeastern U.S. Juveniles are similar to the adult, but duller plumaged.

Three other, significantly smaller, nuthatches have ranges which overlap that of white-breasted, but none has white plumage completely surrounding the eye. Further distinctions are that the red-breasted nuthatch has a black eye line and reddish underparts, and the brown-headed and pygmy nuthatches each have a brown cap, and a white patch on the nape of the neck.

The white-breasted nuthatch has nine subspecies, although the differences are small and change gradually across the range. The subspecies are sometimes treated as three groups based on close similarities in morphology, habitat usage, and vocalizations. These groups cover eastern North America, the Great Basin and central Mexico, and the Pacific coastal regions. The subspecies of the western interior have the darkest upperparts, and eastern S. c. carolinensis has the palest back. The eastern form also has a thicker bill and broader dark cap stripe than the interior and Pacific races. The calls of the three groups differ, as described above.

Only three other species of nuthatches inhabit North America: the red-breasted nuthatch (S. canadensis), the pygmy nuthatch (S. pygmaea) and the brown-headed nuthatch (S. pusilla), and their distributions overlap with those of the white-breasted nuthatch. They are, however, clearly distinct and much smaller, since they are the smallest nuthatches, measuring 10 centimeters long and weighing around 10 grams. The red-breasted nuthatch has reddish underparts and has a black stripe on the eye. The pygmy nuthatch and the brown-headed nuthatch have a brown crown with a white spot on the nape.