The white-breasted nuthatch (Sitta carolinensis) is a species of bird in the nuthatch family Sittidae. It is a medium-sized nuthatch, measuring approximately in length. Coloration varies somewhat along the species' range, but the are light blue-gray, with a black and nape in males, while females have a dark gray crown. The 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 chatty 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. except in the cooler and drier areas. It is mainly found at low elevations, in deciduous forests or in mixed woodlands. Sitta is derived from , Ancient Greek for nuthatch, and carolinensis means "of Carolina" in Latin. The white-breasted nuthatch was first described by English ornithologist John Latham in his 1790 work, the Index Ornithologicus. German ornithologist Hans Edmund Wolters proposed the division of the genus Sitta into subgenera in 1975–1982. The white-breasted nuthatch is placed in Sitta (Leptositta) <small>(Buturlin, 1916)</small>, alongside the white-cheeked nuthatch (S. leucopsis) and Przewalski's nuthatch (S. przewalskii).
Nuthatch taxonomy is complex, with geographically separated species sometimes closely resembling each other. In appearance, the white-breasted nuthatch is similar to the white-cheeked nuthatch of the Himalayas, and was historically sometimes even considered to be conspecific with it. A study published in 2012 showed that four distinct lineages were genetically isolated from each other and could represent different species, recognizable by morphology and song. Molecular phylogenies published in 2014 and 2020 and including all main species' lineages within nuthatches concluded that the white-breasted nuthatch was more closely related to the giant nuthatch (S. magna) than to either white-cheeked or Przewalski's nuthatches; these latter two turned out to be basal in the family.
The simplified cladogram below is based on the phylogenetic analysis by Päckert and colleagues (2020): Like other members of its genus, it has a large head, short tail, short wings, a powerful bill and strong feet; it is long, with a wingspan of and a weight of .
The adult male of the nominate subspecies, S. c. carolinensis, has pale blue-gray , a glossy black cap ( 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 are white. The outer tail feathers are black with broad diagonal white bands across the outer three feathers, a feature readily visible in flight.
Geographical variation
The white-breasted nuthatch currently has seven accepted subspecies, although the differences are small and change gradually across the range. The subspecies are treated in two to four 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. this was not passed due to insufficient evidence, but with an expectation to revisit the status when further evidence becomes available. The subspecies of the western interior have the darkest upperparts but a narrower dark crown above the white cheeks, and eastern S. c. carolinensis has the palest back, but a broader dark crown above the cheeks.
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!width=10% | Subspecies The white-breasted nuthatch is the only North American nuthatch usually found in deciduous trees; red-breasted, pygmy and brown-headed nuthatches prefer pines or other conifers. Although suitable habitat is distributed continentally, it is discontinuous. The separate populations of this non-migratory species have diverged to form distinct regional subspecies.
The white-breasted nuthatch, like most of its genus, is non-migratory, and the adults normally stay in their territory year-round. There may be more noticeable dispersal due to seed failure or high reproductive success in some years,
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File:White-breasted nuthatch 3145.jpg|In flight
File:White-breasted Nuthatch (Sitta carolinensis) in flight.jpg|In flight, from above
File:NuthatchThreat122713.jpg|In a threatening position
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Breeding
The white-breasted nuthatch is monogamous, and pairs form following a courtship in which the male bows to the female, spreading his tail and drooping his wings while swaying back and forth; he also feeds her morsels of food. The pair establish a territory of in woodland, and up to in semi-wooded habitats, and then remain together year-round until one partner dies or disappears. The nest cavity is usually a natural hole in a decaying tree, sometimes an old woodpecker nest.
The white-breasted nuthatch is omnivorous, eating insects and seeds. It places large food items such as acorns or hickory nuts in crevices in tree trunks, and then hammers them open with its strong beak; surplus seeds are cached under loose bark or crevices of trees. This bird will occasionally feed on the ground, and readily visits feeding stations for nuts, suet and sunflower seeds, the last of which it often takes away to store.
Predators and parasites
Predators of adult nuthatches include owls and diurnal birds of prey (such as sharp-shinned and Cooper's hawks), and nestlings and eggs are eaten by woodpeckers, small squirrels, and climbing snakes such as the western rat snake. The white-breasted nuthatch responds to predators near the nest by flicking its wings while making hn-hn calls. When a bird leaves the nest hole, it wipes around the entrance with a piece of fur or vegetation; this makes it more difficult for a predator to find the nest using its sense of smell. The estimated average lifespan of the white-breasted nuthatch is two years,
The white-breasted nuthatch can be a host for certain parasites such as the protists Leucocytozoon or Trypanosoma. The white-breasted nuthatch is the typical host of another protist species, Haemoproteus sittae. Trematodes, such as Collyriclum faba, have also been recorded in this species. The white-breasted nuthatch can also be the target of hematophagous flies of the family Hippoboscidae, such as Ornithoica confluenta and Ornithomya anchineuria or of certain mites, such as Knemidokoptes jamaicensis, which produces scabies.
Conservation status
Bird feeders provide a supplementary source of food.|thumb
The white-breasted nuthatch is a common species with a large range, estimated at . Its total population is estimated at 10 million individuals, and there is evidence of an overall population increase, so it is not believed to approach either the size criterion (fewer than 10,000 mature individuals) or the population decline criterion (declining more than 30% in ten years or three generations) of the IUCN Red List. For these reasons, the species is evaluated as least concern by the International Union for the Conservation of Nature. The white-breasted nuthatch is protected under the Migratory Bird Treaty Act of 1918, to which the three countries in which it occurs (Canada, Mexico, and the United States) are all signatories.