The Corsican nuthatch (Sitta whiteheadi) is a small passerine bird that is endemic to Corsica, where it is the only nuthatch. It is restricted to mature stands of Corsican pine (Pinus nigra spp. laricio) which grow at altitudes of from 800 to 1,600 m (2,600 to 5,200 ft).
The nuthatches are a genus (sitta) of passerine birds with short tails and wings, compact bodies and longish pointed bills. They have grey or bluish upperparts, a black eyestripe and strong feet. Their tails have 12 feathers (rectrices) and their wings have ten primary flight feathers. In 2015 the International Ornithological Committee listed 28 different species.
The Corsican nuthatch was discovered by the English collector John Whitehead in June 1883 when he shot a specimen while on a trip in the Corsican mountains. When he showed the skin to Bowdler Sharpe who was the curator of the bird collection at the British Museum, Sharpe recognised that the bird represented an undocumented species and published a short description. Whitehead returned to Corsica in May 1884 to collect additional specimens and discovered that the species was sexually dimorphic in colour; the bird he had shot the previous year had been a male bird. Sharpe used the additional specimens gathered by Whitehead to publish a fuller description of the species.
Within the genus the Corsican nuthatch belongs to the canadensis group which also includes the red-breasted nuthatch (S. canadensis), the Chinese nuthatch (S. villosa), Krüper's nuthatch (S. krueperi) and the Algerian nuthatch (S. ledanti). These six species usually excavate their own nests and all except the Algerian nuthatch specialize in extracting seeds from pine cones. All members of the group also exhibit sexually dimorphism in the colour of their head feathers. Analysis of ribosomal and mitochondrial DNA indicated that the Corsican nuthatch is most closely related to the Chinese nuthatch and that they diverged from a common ancestor around 0.96 million years ago. The large distance separating the ranges of the two sister species is very unusual for Palaearctic passerines. The Yunnan nuthatch is a sister species to the canadensis group and has many common features.
Cladogram of the candensis group based on Pasquet et al. (2014)
The adult male is 12 cm (4.7 in) long and weighs 11.8–14.4 g (0.42–0.51 oz). It has a black crown and eyestripe separated by a white supercilium. The upperparts are blue-grey and the throat and underparts are greyish-buff. The flight feathers are dark grey-brown fringed with blue-grey. The bill is black to grey-brown becoming pale grey on the base of the lower mandible, the iris is dark brown and the legs and feet are grey-brown or greyish. The female is similar to the male but has a grey crown and eyestripe. Young birds are duller versions of the adults.
The Corsican nuthatch has a pu-pu-pu call and a trilled hididididididi song.
Adults have a complete moult after breeding. Juveniles have a partial moult beginning about 8 weeks after fledging. The adult annual survival rate for male birds is 62 per cent which corresponds to an average lifetime of 2 years and 1 month. The maximum recorded age is 5 years and 7 months.
The Corsican nuthatch is a resident bird of the mountain forests of Corsica, and is closely associated with Corsican pine (Pinus nigra spp. laricio) preferably with some very old trees aged 300 years or more for nesting.
This territorial species nests in holes in dead and decaying Corsican pines, which are usually self-excavated.
The clutch is typically 4–6 eggs (mean 5.1). The eggs are white with red-brown speckles especially at the larger end and are 17.2 mm × 13 mm (0.68 in × 0.51 in) in size. The female incubates the eggs for 14–17 days until they hatch. She is fed on the nest by the male. The female then broods the altricial downy chicks for the first 8 days. The chicks are fed by both adults and fledge when they are around 20 days old.
During the winter months the diet of the Corsican nuthatch consists almost entirely of seeds from Corsican pines. The birds use their long pointed bills to extract the seeds from mature cones that open in fine weather between November and March. Many of the individual seeds are hoarded by the birds in crevices in the bark. These cached seeds are recovered during bad weather when the cones do not open as unlike crossbills, nuthatches are unable to extract seeds from closed cones. In the spring, during the breeding season, the birds feed mainly on arthropods. In May 1884 when Whitehead opened the gizzards of birds that he had shot, he found that they contained small beetles and other insects.
It has the ability, like other nuthatches, to climb down trees, unlike species such as woodpeckers which can only go upwards, and will also flycatch.
Predation is an important cause for the breeding failure of the Corsican nuthatch. The most important predator is believed to be the great spotted woodpecker which is relatively abundant in the pine forests. The Corsican nuthatch takes no action to protect its nest from predation unlike other nuthatch species such as the Eurasian nuthatch that reduces the size of the entrance hole with mud or the red-breasted nuthatch that covers the inner surfaces with pine resin. Instead the Corsican nuthatch excavates its own nest and creates only a narrow entrance hole of around 3.2 cm (1.3 in). This compares with the 5–6 cm (2.0–2.4 in) hole made by the great spotted woodpecker for the entrance to its own nest.
The garden dormouse (Eliomys quercinus) has been proposed as another possible nest predator. Its small size would allow it to pass through entrance hole of the nest but it is not known to climb high up tree trunks.
The population is about 2,000 pairs; the main threats are fire, which destroys the habitat, and predation by great spotted woodpeckers. Since 2010 this bird is considered as a vulnerable species.