Corsican nuthatch

The Corsican nuthatch (''Sitta whiteheadi'') is a species of bird in the nuthatch family Sittidae. It is a relatively small nuthatch, measuring about in overall length. The are bluish gray, the grayish white. The male is distinguished from the female by its entirely black . The species is sedentary, territorial and not very shy. It often feeds high in Corsican pines, consuming mainly pine nuts, but also catching some flying insects. The breeding season takes place between April and May; the nest is placed in the trunk of an old pine, and the clutch has five to six eggs. The young fledge 22 to 24 days after hatching.

The Corsican nuthatch is found only on the island of Corsica, where it populates the old forests of high altitude laricio pines, descending lower in winter. Its scientific name comes from John Whitehead, the ornithologist who brought the bird to the attention of the scientific community in 1883. The Corsican nuthatch is closely related to the Chinese nuthatch (''S. villosa'') and the red-breasted nuthatch (''S. canadensis''). It is threatened by loss of nesting sites and habitat fragmentation, with an estimated population size of about 2,000 individuals, possibly in moderate decline. Due to the small population size and the limited range, the conservation status of the Corsican nuthatch is classed as " vulnerable" by the International Union for Conservation of Nature.

Taxonomy

Discovery and studies

The Corsican nuthatch was discovered when ornithologist John Whitehead went to observe alpine swift (''Tachymarptis melba'') on June 13, 1883. Whitehead, who had spent much of the previous years in Corsica, spotted and shot a male Corsican nuthatch. He kept the specimen's skin and did not bother with it until October, when he asked Richard Bowdler Sharpe for help in naming some small birds he had collected; although the bird's head was damaged by the collection method, Sharpe assured him that the species was not yet described. Whitehead thought the bird was extremely localized and did not give the precise locality where he collected the first specimens for fear that the species would be exterminated by additional collections.

Whitehead returned to Corsica in May 1884 and found a male, which he recognized by its black . After killing it, he waited to see the accompanying female, killed it as well, and then collected three more specimens from a small flock. In the following days, he observed a pair coming and going with nesting material in a hole six meters above the ground in the trunk of a very old pine. He located other nests, some above the ground, and opened two of them, finding 5 eggs in each, which he collected.

The Italian ornithologist Enrico Hillyer Giglioli reported in 1890 that he had observed the bird on September 16, 1877, at Ponte Leccia, almost six years before Whitehead, but mistaking it for a Eurasian nuthatch (''S. europaea''), he did not bother to shoot it. In the spring of 1896, the German naturalist Alexander Koenig visited the forest of Vizzavona and collected with great difficulty five specimens; in the early autumn of 1900, Arnold Duer Sapsworth brought back some skins. For the first, the breeding season had not begun at the time of his visit and for the second, it was over; no additional eggs were therefore brought back during this period. The next collections were made between 1908 and 1909 by the British ornithologist Francis Jourdain, who provided some additional field notes and explained the difficulty of accessing the nests.

The first works concerning the biology of the bird were only carried out in the 1960s by the German ornithologist Hans Löhrl, who studied the reproduction, feeding and behavior of the species. In 1976, Claude Chappuis described the voice of the species in an article dedicated to the vocalizations of birds from Corsica and the Balearic Islands. In the 1980s, the Italian ornithologists Pierandrea Brichetti and Carlo Di Capi studied the reproduction of the Corsican nuthatch. Since the 1990s, the species has been studied closely by local groups, and in particular by ornithologists Jean-Claude Thibault, Pascal Villard and Jean-François Seguin.

In the summer of 2006, Dutchmen participating in an entomological expedition incidentally observed a pair of nuthatches in the Altai, near the meeting point of China, Kazakhstan, Mongolia and Russia, in a pure larch forest (''Larix sp.''). The male has a black crown, and the female does not, and both have a dark topped by a white supercilium. The closest species geographically that might fit this description is the Chinese nuthatch (''S. villosa''), which would then be far from its known distribution, and which has more buffy underparts than the observed individuals. This record could be indicative of a much wider distribution of the Chinese species, or the bird could be an as yet undescribed species related to ''S. whiteheadi'' and ''S. villosa''.

Nomenclature

The Corsican nuthatch was described by Sharpe in March 1884, based on the first male specimen collected by Whitehead, who was thus given the specific name. Whitehead sent a second male to Sharpe, who presented it in May to the ''Zoological Society of London''. In June, Sharpe completed the description of the species after Whitehead sent him a female. The Corsican nuthatch is sometimes placed in a subgenus, ''Micrositta'', described by the Russian ornithologist Sergei Buturlin in 1916, and has no subspecies.

The Corsican nuthatch was subsequently considered a subspecies of the red-breasted nuthatch (''S. canadensis'') from 1911 until the 1950s. In 1957, American ornithologist Charles Vaurie explained that the morphology did not allow one to be sure that the Corsican nuthatch was a distinct species, and that it was probably better to consider it as belonging to the "''canadensis''" group, regrouping the species ''S. canadensis'', ''S. whiteheadi'' and ''S. villosa''; The German ornithologist Hans Löhrl, after studying the ecology and behavior of the birds of Latin America and Corsica, and through the publication of his field notes between 1960 and 1961, disagreed with Vaurie's position. In 1976, the French ornithologist Jacques Vielliard described the Algerian nuthatch (''S. ledanti''), just discovered in Algeria by Jean-Paul Ledant. He devoted part of his article on the possible relationships of the different species and their evolutionary history. Vielliard suggests that Vaurie stopped at "a superficial morphological similarity" to bring the Corsican nuthatch closer to the red-breasted nuthatch, and that the Corsican species should rather form with Krüper's nuthatch (''S. krueperi'') a group known as the "Mesogean nuthatches", "where ''S. ledanti'' providentially fits in".

Molecular phylogeny and evolution

In 1998, Eric Pasquet studied the cytochrome b of the mitochondrial DNA of a dozen nuthatch species, including the various species of the ''Sitta canadensis'' group, which he defined as comprising six species, which are also those of what is sometimes treated as the subgenus Sitta (''Micrositta''): ''canadensis'', ''villosa'', ''yunnanensis'', ''whiteheadi'', ''krueperi'' and ''ledanti''. Pasquet concludes that the Corsican nuthatch is phylogenetically related to the Chinese nuthatch and the red-breasted nuthatch, these three species forming the sister group of a clade including Krüper's nuthatch and the Algerian nuthatch. The first three species would even be close enough to constitute subspecies, rejecting Vielliard's "mesogean" theory and thus confirming Vaurie's conclusions. For the sake of taxonomic stability, however, all retain their full species status. In 2014, Eric Pasquet and colleagues published a phylogeny based on nuclear and mitochondrial DNA of 21 nuthatch species and confirmed the relationships of the 1998 study within the "''canadensis'' group", adding the Yunnan nuthatch, which was found to be the most basal of the species. The study findings align with the morphology of the species, the red-breasted nuthatch, Corsican nuthatch and Chinese nuthatch sharing as a derived character the entirely black crown only present in males, a unique trait in the Sittidae and related families. The second clade, which includes Krüper's and Algerian nuthatches, would have a black front crown in males, this sexual dimorphism being absent in young individuals.

The phylogeny established, Pasquet concludes that the paleogeographic history of the group would be as follows: the divergence between the two main clades of the "''canadensis'' group" appears more than five million years ago, at the end of the Miocene, when the clade of ''krueperi'' and ''ledanti'' settles in the Mediterranean basin at the time of the Messinian salinity crisis; the two species constituting it diverge 1.75 million years ago. The other clade split into three with populations leaving Asia from the east, giving rise to the red-breasted nuthatch, and then from the west, about one million years ago, marking the separation between the Corsican and Chinese nuthatches. Current distributions do not necessarily accurately reflect ancestral ones, however, and the Corsican nuthatch may be a paleoendemic that once had a much wider distribution and underwent reductions in pine distribution; "trapped" in Corsica, it would have evolved by vicariance.

The simplified cladogram below is based on the phylogenetic analysis of Packert and colleagues (2014):

Description

Plumage and measurements

The Corsican nuthatch is a small bird, measuring long with a wingspan of and a weight of . The folded wing measures , the relatively short tail measures , and the tarsus and beak measure . The head is small and the is short for a nuthatch. It is thin and blackish gray, black on its tip. The eyes are black, the legs and toes are light brown.

The are overall bluish gray, the belly pale grayish buff with the throat whiter. The male has a black crown and forehead, and a black eyestripe, separated from the crown by a broad, sharp white supercilium. In females, the crown and eyebrow line are the same gray as the back. In both sexes, the sides of the head as well as the throat are white; the , overall grayish white, are more or less shaded with buff. The outer rectrices are black with white spots and gray tips. The birds undergo a complete moult every year after the breeding season. Sexual dimorphism appears eleven days after hatching, and fledged young have a plumage close to that of adults. As juveniles, they remain duller, with some brown on the large coverts.

Vocalizations

The contact call is a light, whistling ''pu'', which the bird repeats in series of five to six notes, in ''pupupupu''. When agitated, this nuthatch emits a "rough and stretched, slowly repeated" ''pchèèhr'', as might a common starling (''Sturnus vulgaris''), or a ''psch-psch-psch'' that turns into a ''chay-chay-chay'' or ''sch-wer'', ''sch-wer'' when more agitated. The song, described as a "clear, sonorous, rapid ''dididididi'' nd ofvariable rhythm," meanwhile, is reminiscent of the alpine swift; the contact call is a similar trill. It "sings fairly regularly in the spring," but is more discreet during the breeding season.

Similar species

The Corsican nuthatch is the only nuthatch found in Corsica, however, it may be reminiscent of the coal tit ''(Parus ater)'', which is common in Corsican forests and has similar markings on its head. The Eurasian nuthatch which inhabits nearby mainland France is larger, has no black on the crown and has yellow (or white for some subspecies) underparts tending to orange around the rump. In the original description, Sharpe likened it morphologically to the Chinese nuthatch, which however has more brightly colored underparts, and to Krüper's nuthatch, which is the same size and has the same color upperparts, but has a reddish-brown area on the underparts that is absent in the Corsican species. The Corsican nuthatch is also similar to the red-breasted nuthatch, which is found only in North America, but has yellowish underparts. Finally, the Corsican species most closely resembles the Algerian nuthatch, from Babor Mountains, which can be distinguished by its paler underparts, whitish sides of the head, and by the male's crown, which has only the black front.

Distribution and habitat

The Corsican nuthatch is the only species of bird endemic to Corsica, and even to metropolitan France. Its range covers the majority of the island, which is very mountainous. This bird is found from the Tartagine-Melaja forest in the north to the Ospedale forest in the south, but it is particularly abundant in the Monte Cinto, Monte Rotondo, Monte Renoso and Monte Incudine massifs. There are also two isolated populations, in Castagniccia in the northeast of the island, and in the Cagna mountain in the south.

The Corsican nuthatch favors Corsican pines ''(Pinus nigra laricio)'' forests interspersed with clearings; this habitat is fairly dry in the summer (three weeks to two months of drought) and experiences heavy rainfall in the off-season ( per year). This nuthatch is sedentary; it generally lives in deep valleys between and above sea level between April and October, but can be found from above sea level, although the more open forests at higher elevations are less suitable. It descends lower in winter, and may then inhabit mixed forests of Corsican and maritime pines ''(Pinus pinaster)'' or forests of white fir ''(Abies alba)''; however, its stand indices are significantly lower than in pure Corsican pines forests. It avoids hardwood-dominated or mixed woodlands.

Old pines provide the nuthatch with abundant food, and the species is absent from sectors where trees are less than in diameter, and where the Corsican pine is in the minority compared to other species. The places most likely to shelter the Corsican nuthatch have large trees (over high) and large diameter (over ). The preference of the bird for the Corsican pine over the maritime pine could be explained by the toughness of the seeds of the latter. From a historical perspective, Thibault and colleagues explain in 2002 that "the Corsican nuthatch and the Corsican pine, probably present on the island since at least the middle of the Quaternary, had to face the last climatic fluctuations of the Pleistocene, which caused deep modifications in the composition and distribution of the vegetation. It is likely that the nuthatch survived in the Corsican pines throughout this period.

Behaviour and ecology

Like all nuthatches, the Corsican nuthatch can move head down along branches, and is rarely found on the ground. It is a territorial bird and are not shy. It lives in monogamous couples evolving all year long on the same territory of three to ten hectares, the two birds of the couple defending it from intruders, of the same species or of another. The home range, the area where the birds generally live within their territory, varies in size, depending on the season and age of the birds, but especially on the cone production of the pines.

Food and feeding

The Corsican nuthatch consumes mainly pine nuts, but also small flying insects in summer. From March to November, small arthropods (adult insects and their larvae, spiders) represent the main part of its diet; it catches them in flight but more generally in the trees; it makes a quarter of its captures in flight, from a lookout post, and exploits the rest of the time the substrates provided by the trees. In spring and summer, it is more likely to be found in the treetops, foraging high up in the foliage of pine trees, at the end of branches, like a chickadee; in autumn, however, it searches for food along the trunks and on large branches, and may also form mixed feeding flocks with other small passerines outside the breeding season. November marks the beginning of the opening of pine cones, from which the Corsican nuthatch extracts seeds with its fine bill. In years of high production, the nuthatch may find food resources in the cones until March. As nuthatches often do, the Corsican nuthatch hides some seeds under the bark or under lichens

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