Pitta  

Holozoa

Pittas are a family, Pittidae, of passerine birds mainly found in tropical Asia and Australasia, although a couple of species live in Africa. Pittas are all similar in general structure and habits, and have often been placed in a single genus, Pitta, although they are now split into two extra genera, Erythropitta and Hydrornis. The name is derived from the word pitta in the Telugu language of Andhra Pradesh in India and is a generic local name used for all small birds.

Pittas are medium-sized by passerine standards, at 15 to 25 centimetres in length, and stocky, with longish strong legs and long feet. They have very short tails and stout, slightly decurved bills. Many, but not all, have brightly coloured plumage.^[1]

These are fairly terrestrial birds of wet forest floors. They eat snails, insects and similar invertebrate prey. Pittas are mostly solitary and lay up to six eggs in a large spherical nest in a tree or shrub, or sometimes on the ground. Both parents care for the young.^[1]

Many species of pittas are migratory, and they often end up in unexpected places like house-gardens during migration.

A number of species of pitta are threatened with extinction. One of these, the Gurney's Pitta, is listed as endangered by the IUCN,^[2], a further eight species are listed as vulnerable.^[3] The main threat to pittas is habitat loss in the form of rapid deforestation.

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Taxonomy and systematics

Pittas were first described scientifically by Carl Linnaeus in 1766 in his revised 12th edition of the Systema Naturae. He placed the Indian Pitta in the crow family and genus Corvus. Ten years later it was placed in the thrush family, due to similarities of morphology and behaviour, before being placed in its own genus, Pitta in 1816 by Louis Vieillot. Vieillot was also the first to consider the genus a family in its own right.^[4] The family's closest relatives have for a long time assumed to be the other suboscine birds, and particularly the Old World broadbills and asities (formerly treated as two families, now either lumped into one or split into four). A 2006 study confirmed that these were the closest relatives of the pittas.^[5]

The number of pitta genera has varied considerably, ranging from one to as many as nine. In his 1863 work A Monograph of the Pittidae Daniel Elliot split the pittas into two genera, Pitta for the species with comparatively long tails and Brachyurus for the shorter tailed species. Barely two decades later, in 1880/81, John Gould split the family into nine genera, to which he also included the Lesser Melampitta (Melampitta), a species which despite uncertain affinities is now at least no longer considered related to the pittas. Soon afterwards Philip Sclater's Catalogue of the Birds of the British Museum brought the number back down to three. Modern treatments vary as well. A 1975 checklist included six genera, whereas the 2003 volume of the Handbook of the Birds of the World, which covered the family, placed all the pittas in a single genus.^[4] The family was not well studied using modern anatomical or phylogenetic techniques; two studies, in 1987 and 1990, each used only four species, and comparisons amongst the family as a whole have relied mostly on external features and appearances.^[5]

The Banded Pitta has recently been split into three species, making this male a Javan Banded Pitta

A 2009 study of the nuclear DNA of the pittas, using study skins from museums, was the first to examine most representatives of the family, and found evidence of three major clades of pitta. Based on the study it proposed splitting the pittas into three genera. The first clade, using the genus name Erythropitta, includes six species that had previously been considered closely related on external features. They are all generally small species with small tails, extensive amounts of crimson or red on the underparts, and greenish or blueish backs. The second genus, Hydrornis, includes a number of variable Oriental species. These species are unified morphologically in exhibiting sexual dimorphism in their plumage, as well as in possessing cryptic juvenile plumage (in all the species thus far studied). Into this second clade is included the Eared Pitta, which had often been placed into its own genus, Anthocincla, on account of its apparent primitive characteristics. The final genus, Pitta, is the most widespread clade. Most species in this genus have green upperparts with a blue wing-patch, dark upperparts and cinnamon-buff underparts. This clade contains all the migratory species of pitta, and it is thought that many of the pitta species from islands are derived from migratory species.^[5] This division of the pittas into three genera was adopted by the International Ornithological Congress' Birds of the World: Recommended English Names.^[6]

As with genera, there has been considerable variation in the number of recorded pitta species. The checklists of Sclater and Elliot at the end of the 19th century contained 48 and 47 species each. More recent checklists have had fewer than this, one listing just 24 species. Since the 1990s the figure has been between 30 and 32 species; the Handbook of the Birds of the World recognises 30. Two potential species not recognised by the Handbook include the Black-crowned Pitta, which is treated as a subspecies of either the Garnet Pitta or the Graceful Pitta, and the Sula Pitta, which can be treated as a subspecies of the Red-bellied Pitta.^[4] More recently the Banded Pitta has been split into three new species, one endemic to Java, one endemic to Borneo and one found in Sumatra and the Malay Peninsula.^[7]

Description

The plumage of the juvenile Garnet Pitta (right) is drabber than that of the adult (left)

The pittas are small to medium sized passerines, ranging in size from the Blue-banded Pitta at 15 cm (5.9 in) to the Giant Pitta, which can be up to 29 cm (11 in) in length. In weight they range from 42–210 g (1.5–7.4 oz). Pittas are stout bodied birds with long, strong tarsi (lower leg bones) and long feet. There is considerable variation in the colour of the legs and feet, this may be used by females in judging the quality of males. The wings have ten primaries are generally rounded and short Those of the four migratory species, however, are more pointed. The tails range from being short to very short, and is composed of twelve feathers.^[4][8]

Distribution, habitat and movements

The pittas are generally birds of tropical forests, semi-forests and scrub. Of particular importance to most species are forests with lots of cover, a rich understory, and leaf litter for feeding. Pittas often frequent areas near waterways as well. Some species inhabit swamps and bamboos forests,^[4] and the Mangrove Pitta, as its name suggests, is a mangrove specialist.^[9] A number of species are lowland forest specialists, for example the Rainbow Pitta is not found above 400 m (1,300 ft), whereas other species may occur at much higher elevations, for example Rusty-naped Pittas have been found up to 2,600 m (8,500 ft). This varies in the Fairy Pitta across its range, reaching up to 1,300 m (4,300 ft) in Taiwan but at much lower levels in Japan.^[4] In addition to natural habitats pittas may use human altered habitats, for example migrating Blue-winged Pittas and Hooded Pittas use parks and urban gardens in Singapore.^[9]

The greatest diversity of pittas are found in South-east Asia. Of the three recently proposed genera, the large genus Pitta is the most widespread. The two species found in Africa are from this clade, as are the most northerly species (the Fairy Pitta) and the most southerly (the Noisy Pitta). The most remote insular endemics are in this group as well, including the Black-faced Pitta, which is endemic to the Solomon Islands. The pittas of the clade Erythropitta are mostly found in Asia with one widespread species, the Red-bellied Pitta, reaching the north of Australia. The Hydrornis pittas are exclusively Asian.^[5][4] Some pittas have large distributions, like the Hooded Pitta, which ranges from Nepal to New Guinea, others have much smaller ones, like the Superb Pitta, which is endemic to the tiny island of Manus in the Admiralty Islands.^[4][10]

Behaviour

Pittas are diurnal, requiring light in order to find their often cryptic prey. They are nevertheless often found in darker areas and are highly secretive, though they will respond to imitations of their calls. They are generally found as single birds, with even young birds not associating with their parents unless they are being fed. Small groups have been observed during migration.^[4]

The pittas are strongly territorial, with territories varying in size from 3000 m² in the African Pitta to 10,000m² in the Rainbow Pitta. Pittas will perform territory defence displays on the edges of their territories, although fights between rivals have only been recorded once. Migratory species will defend non-breeding feeding territories in addition to their breeding ones.^[4]

Diet and feeding

The anvil of a Noisy Pitta, used to smash snails against in order to remove the shells

Earthworms form the major part of the diet of pittas, followed by snails in order of importance. Earthworms may however become seasonally unavailable in dry conditions when the worms move deeper into the soil. In addition a wide range of invertebrate prey is eaten, including many insects groups such as termites, ants, beetles, true bugs, and lepidopterans; as well as centipedes, millipedes, and spiders.^[4]

Pittas feed in a thrush-like fashion, moving aside leaves with a sweeping motion of the bill. They have also been observed to probe the moist soil with their bills in order to locate earthworms. It has been suggested that they are able to locate earthworms by smell; a suggestion supported by a study which found that they have the largest olfactory bulb of 25 passerines examined.^[11] Some species will also use tree roots and rocks as anvils on which to smash open snails in order to eat.^[12]

Breeding

Like most birds the pittas are monogamous breeders, and defend breeding territories. Most species are seasonal breeders, timing their breeding to occur at the onset of the rainy season. An exception to this is the Superb Pitta, which breeds almost year round, as the island of Manus which it breeds on remains wet all year. The courtship behaviours of the family are poorly known, but the elaborate dance of the African Pitta includes jumping into the air with a puffed out breast and parachuting down back down to the perch.^[4]

The pittas build a rudimentary nest that is a dome with a side entrance. The nest is as large as a rugby ball, and is usually well camouflaged amongst vines or vegetation of some kind. The nests can either be placed on the ground or in trees. Both sexes help to build the nest, but the male does most of the work. It takes around two to eight days to build a new nest; this probably varies depending on the experience of the birds involved. A new nest is constructed for each nesting attempt.^[4]

The clutch size varies by species. Typically three to five eggs are laid, but two is typical for the Garnet Pitta, whereas six is more common for the Blue-winged Pitta and the Indian Pitta. It is thought that species with higher levels of predation tend to have smaller clutches, as smaller clutches involve fewer provisioning trips that might alert a predator to the presence of a nest, and the loss of a smaller clutch is less costly to replace. Clutch size may vary within a species depending on latitude. A study of Noisy Pitta found that birds in the tropics had smaller clutch sizes than those in more temperate environments.^[13] The eggs of pittas are ovoid, with one end slightly pointed, and generally smooth (the deeply pitted eggs of the Superb Pitta being the exception to this). The size of eggs varies by species, with smaller species laying smaller eggs. There is also some variation in egg size within a species in species with large ranges. For example the eggs of Noisy Pittas are smaller closer to the tropics.^[4]

Status and conservation

Blue-headed Pittas (male left, female right) are threatened by rapid deforestation in Borneo

Pittas are generally forest birds and as such are vulnerable to habitat loss caused by rapid deforestation. One species is considered to be endangered and a further eight are listed as vulnerable. The Gurney's Pitta was not seen for thirty four years between 1952 and 1986, before a small population was discovered in southern Thailand. This small population continued to decline since its rediscovery, and by 2000 it had reached a low of 10 pairs, and was listed as critically endangered. In 2003 the species was found in Burma for the first time since 1914, and in large numbers, between 9 and 35 thousand pairs. Although the species was considerably less threatened than thought, it is still of considerable conservation concern as deforestation of the habitat in Burma continues.^[14] The rapid rate of deforestation in Borneo has pushed the Blue-headed Pitta, previously considered common and secure as recently as 1996, into the list of species considered vulnerable.^[15]

Species

Species in taxonomic order:

• Genus: Hydrornis
  • Eared Pitta, Hydrornis phayrei
  • Blue-naped Pitta, Hydrornis nipalensis
  • Blue-rumped Pitta, Hydrornis soror
  • Rusty-naped Pitta, Hydrornis oatesi
  • Schneider's Pitta, Hydrornis schneideri
  • Giant Pitta, Hydrornis caerulea
  • Blue-headed Pitta, Hydrornis baudii
  • Blue Pitta, Hydrornis cyanea
  • Bar-bellied Pitta, Hydrornis elliotii
  • Banded Pitta, Hydrornis guajana
    • Javan Banded Pitta, Hydrornis guajana
    • Malayan Banded Pitta, Hydrornis (guajana) irena
    • Bornean Banded Pitta, Hydrornis (guajana) schwaneri
  • Gurney's Pitta, Hydrornis gurneyi
• Genus: Erythropitta
  • Whiskered Pitta, Erythropitta kochi
  • Red-bellied Pitta, Erythropitta erythrogaster
  • Blue-banded Pitta, Erythropitta arcuata
  • Garnet Pitta, Erythropitta granatina
  • Graceful Pitta, Erythropitta venusta
  • Black-headed Pitta, Erythropitta ussheri
• Genus: Pitta
  • Hooded Pitta, Pitta sordida
  • Ivory-breasted Pitta, Pitta maxima
  • Superb Pitta, Pitta superba
  • Azure-breasted Pitta, Pitta steerii
  • Sula Pitta, Pitta dohertyi
  • African Pitta, Pitta angolensis
  • Green-breasted Pitta, Pitta reichenowi
  • Indian Pitta, Pitta brachyura
  • Fairy Pitta, Pitta nympha
  • Blue-winged Pitta, Pitta moluccensis
  • Mangrove Pitta, Pitta megarhyncha
  • Elegant Pitta, Pitta elegans
  • Noisy Pitta, Pitta versicolor
  • Black-faced Pitta, Pitta anerythra
  • Rainbow Pitta, Pitta iris

References