Pitoui incappucciato

Tassonomia

The hooded pitohui (Pitohui dichrous) was described by the French ornithologist Charles Lucien Bonaparte in 1850. Bonaparte placed it in the genus Rectes which had been erected in the same year by Ludwig Reichenbach as an alternative name for the genus Pitohui, which had been described by René Lesson in 1831. No explanation was given for the preference of the newer name over the established older one, but it was common to prefer Latin names over non-Latin names, and to provide Latin names to those without. Richard Bowdler Sharpe encapsulated that attitude when he wrote in 1903 "Pitohui is doubtless an older name than Rectes, but can surely be laid aside as a barbarous word". Eventually however the principle of priority, which favours the first formal name given to a taxon, was applied, and Rectes was suppressed as the junior synonym of Pitohui.<p>The hooded pitohui was placed in the genus Pitohui with five other species, and the genus was thought to reside within the Australasian whistler family (Pachycephalidae). A 2008 examination of the genus, however, found it to be polyphyletic (meaning that the genus contained unrelated species), with some purported members of the genus not actually falling within the whistlers. The hooded pitohui and the closely related variable pitohui were both found to be related to the Old World orioles (Oriolidae). A 2010 study by the same team confirmed that the hooded pitohui and variable pitohui were orioles and indeed were sister species, and that together with the figbirds they formed a well defined basal clade within the family. As the variable pitohui was the type species for the genus Pitohui, the hooded pitohui was retained in that genus and the four remaining species were moved to other genera.<p>The hooded pitohui is monotypic, lacking any subspecies. Birds in the south east of New Guinea are sometimes separated into a proposed subspecies, P. d. monticola, but the differences are very slight and the supposed subspecies are generally regarded as inseparable.<p>Pitohui, the common name for the group and the genus name, is a Papuan term for rubbish bird, a reference to its inedibility. The specific name dichrous is from the Ancient Greek word dikhrous, meaning 'two coloured'. Alternate names for the hooded pitohui include the black-headed pitohui and lesser pitohui.

Nome scientifico

Pitohui dichrous

Autorità

(Bonaparte, 1850)

Ordine

Passeriformi

Famiglia

Oriolidi

Genere

Pitohui

Areale e habitat

The hooded pitohui is endemic to the islands of New Guinea. It is found widely across the main island, and also on the nearby island of Yapen. It inhabits rainforest, forest edge habitats and secondary growth, and sometimes mangrove forests. It is most commonly found in hills and low mountains, between 350–1,700 m (1,150–5,580 ft), but is found locally down to sea-level and up to 2,000 m (6,600 ft). It typically occurs at higher elevations than the lowland variable pitohui and lower than the (unrelated) black pitohui, although there is some overlap.

Migrazione

Resident species

Comportamento

The hooded pitohui makes a variety of calls, mostly forms of whistles. Its song is a variable collection of three to seven whistles, which can slur up or down with hesitant pauses in between. Usually the song begins with two similar notes followed by an upslur. It also makes an "tuk tuk w’oh tuw’uow" call, two whistled "woiy, woiy" notes, two downslurred whistled "tiuw tow" notes, and three whistles "hui-whui-whooee", which increase in volume.<p>The diet of the hooded pitohui is dominated by fruit, particularly figs of the genus Ficus, grass seeds, some insects and other invertebrates, and possibly small vertebrates. Among the invertebrates found in their diet are beetles, spiders, earwigs, bugs (Hemiptera, including the families Membracidae and Lygaeidae), flies (Diptera), caterpillars and ants. They feed at all levels of the forest, from the forest floor to the canopy, and are reported to do so in small groups, presumably of related birds. The species also regularly joins mixed-species foraging flocks, and on Yapen and between 1,100–1,300 m (3,600–4,300 ft) above sea-level it will often act as the flock leader. This leadership role, and indeed their participation in mixed flocks, is not true across all of their range however.<p>Little is known about the breeding biology of the hooded pitohui and its relatives due to the difficulties of studying the species high in the canopy of New Guinea. Nests with eggs of the hooded pitohui have been found from October through to February. The nest that has been described was 2 m (7 ft) off the ground. The nest is a cup of vine tendrils, lined with finer vines and suspended on thin branches.<p>The clutch is one to two eggs, 27 mm–32.8 mm × 20.5 mm–22.2 mm (1.06 in–1.29 in × 0.81 in–0.87 in), which are creamy or pinkish with brown to black spots and blotches and faint grey patches; in one egg all the markings with at the larger end. The incubation period is not known, but the species is thought to be a cooperative breeder, as more than two birds in a group have been observed defending the nest from intruders and feeding the young. Young birds, which are covered in white down as nestlings before developing their adult plumage, have been observed being fed acorn-shaped red berries and insects. Young birds will make a threat display when approached in the nest, rising up and erecting their head feathers. As chicks develop directly into adult plumage, it has been suggested that this display may be signalling its identity as a toxic species, even though young birds have not developed toxicity at that age. The function of the toxins to the hooded pitohui has been the source of debate and research since its discovery. The initial suggestion was that the toxins acted as a chemical deterrent to predators. Some researchers cautioned this suggestion was premature, and others noted that the levels of batrachotoxins were three orders of magnitude lower than in the poison dart frogs that do use it in this way.<p>Another explanation for the purpose of the toxins is to mitigate the effects of parasites. In experimental conditions chewing lice were shown to avoid toxic feathers of hooded pitohui in favour of feathers with lower concentrations of toxin or no toxins at all. Additionally lice that did live in the toxic feathers did not live as long as control lice, suggesting that the toxins could lessen both the incidence of infestation and the severity. A comparative study of the tick loads of wild birds in New Guinea would seem to support the idea, as hooded pitohuis had considerably fewer ticks than almost all the 30 genera examined. The batrachotoxins do not seem to have an effect on internal parasites such as Haemoproteus or the malaria-causing Plasmodium.<p>A number of authors have noted that the two explanations, as a chemical defence against predators and as a chemical defence against ectoparasites, are not mutually exclusive, and evidence for both explanations exists. The fact that the highest concentrations of toxins are bound in the feathers of the breast and belly, in both pitohuis and ifrits, has caused scientists to suggest that the toxins rub off on eggs and nestlings providing protection against predators and nest parasites.<p>One argument in favour of the toxin acting as a defence against predators is the apparent Müllerian mimicry in some of the various unrelated pitohui species, which all have similar plumage. The species known as pitohuis were long thought congeneric, due to their similarities in plumage, but are now spread through three families, the oriole, whistlers and Australo-Papuan bellbirds. The similarity in appearance therefore presumably evolved as a shared aposematic signal to common predators of their distasteful nature. This signal is reinforced by the species' strong sour odor. There is also evidence that some other birds in New Guinea have evolved Batesian mimicry, where a non-toxic species adopts the appearance of a toxic species. An example of this is the non-toxic juvenile greater melampitta, which has plumage similar to the hooded pitohui.<p>There have also been experiments to test pitohui batrachotoxins on potential predators. They have been shown to irritate the buccal membranes of brown tree snakes and green tree pythons, both of which are avian predators in New Guinea. The unpalatability of the species is also known to local hunters, who otherwise hunt songbirds of the same size.<p>The existence of resistance to batrachotoxins and the use of those toxins as chemical defences by several bird families have led to competing theories as to its evolutionary history. Jønsson (2008) suggested that it was an ancestral adaptation in Corvoidea songbirds, and that further studies would reveal more toxic birds. Dumbacher (2008) argued instead that it was an example of convergent evolution.

Conservazione

Tendenza della popolazione

stable