Pseudo Babblers (Pomatostomidae)

views updated

Pseudo babblers

(Pomatostomidae)

Class Aves

Order Passeriformes

Suborder Passeri (Oscines)

Family Pomatostomidae

Thumbnail description
Large babbler-like songbirds with long tail and scimitar-like bill; plumage is plain russet or patterned with white brows, throat, and tail tip

Size
7–10.5 in (18–27 cm); 1.6–3.2 oz (45–90 g)

Number of genera, species
2 genera; 5 species

Habitat
Shrubberies of woodland, open forest, and tropical rainforest

Conservation status
Not threatened

Distribution
Mainland Australia and lowland New Guinea

Evolution and systematics

So similar in appearance are Australasian pseudo babblers and Asian scimitar babblers that both were formerly grouped together in the same tribe of the babbler family, Timaliidae. However, molecular evidence and examination of the skeleton have shown that the similarities are superficial. Pseudo babblers are divergent members of a quite different assemblage of crow-like songbirds that radiated massively within Australia at least 30 million years ago. Like other crow-like birds, pseudo babblers have a single pneumatised depression (fossa) in the head of the humerus. The sternum (breast bone) is shallowly keeled and processes on the pelvic girdle are much attenuated, both signs that pseudo babblers live more on leg than wing. They have other unique skeletal traits in the palate and skull that interact to support the bill when probing and digging.

The five living pomatostomid species belong to two genera. Garritornis contains a single species (G. isidorei, rufous babbler) endemic to the lowland rainforests of New Guinea. Pomatostomus comprises four species. Gray-crowned babblers (Pomatostomus temporalis) and Hall's babblers (P. halli) are centered in the woodlands of Torresian north Australia, and white-browed babblers (P. superciliosus) and chestnut-crowned babblers (P. ruficeps) are centered in similar habitat across southern Australia. The history of their evolution is unclear.

Physical characteristics

Pseudo babblers are medium-sized songbirds that measure 7–10.5 in (18–27 cm) long and weigh 1.6–3.2 oz (45–90 g). Their wings are short and rounded and equipped with ten well-developed primary feathers and 9–12 uniquely varying secondaries. The tail is long, fan-shaped, and 12-feathered. The bill, vestigially bristled, is long, slender, and downcurved. It lacks terminal notching and is better fitted for probing and digging than for grasping and grabbing. Legs are long and powerful with stoutly muscled calves. Pseudo babblers have scutellate, bilamini-plantar tarsi ("feet") that are adapted for prolonged hopping. Plumage is either plain russet (rufous babblers) or brown and boldly patterned with broad white brows, throat, and tail tip (Pomatostomus). Sexes are alike, and immature birds resemble adults except for their shorter bill. Eyes, which are brown in most species, become light cream in adults of rufous babblers and gray-crowned babblers. Feet are dusky in all species. The bill is yellowish in rufous babblers and mainly dull brown in Pomatostomus.

Distribution

Pseudo babblers live in lowland New Guinea up to 1,500 ft (500 m) altitude, Misool in the western Papuan Islands, and all of mainland Australia except the extreme southeast and southwest coasts and in central and northwest sand deserts. Northern and southern Australian groups of Pomatostomus overlap widely in the central arid zone of Australia.

Habitat

Pseudo babblers inhabit tall open shrubbery under eucalyptus woodland and open forest and, in New Guinea, lowland rainforest. In inland Australia, several species extend widely through mulga (Acacia) woodland; Hall's babblers are confined to it in the Great Artesian basin. Where species overlap there is little obvious partitioning of habitat that might avert competition. Habitat that is little disturbed and has a fairly intact layer of ground litter is critical.

Behavior

Noisy, gregarious, and sedentary, pseudo babblers quarter their foraging grounds energetically in coordinated groups of up to a dozen or more. The group does everything together, including feeding, preening, dust bathing, resting, and roosting. Groups keep within cover as they travel, bounding in powerful hops over the ground and among shrubbery. To keep contact, they call constantly in growls, mews, whistles, and chatterings. Flight, a fluttering of wings broken by long direct glides with short wings fully stretched, is limited to dashes between cover in follow-the-leader fashion. Throughout their territories, pseudo babblers also maintain one or more dormitory nests that are similar in structure and positioning to breeding nests but bulkier; each night, the whole group crams into a single nest to sleep.

Feeding ecology and diet

Pseudo babblers are scansorial insectivores. Each group holds to permanent feeding territories of about 124 acres (5–50 ha) or more year round, depending on productivity, and spends as much as 75% of the day foraging. They use the long bill to toss about in litter, dig and hammer in the ground, and probe the trunks and branches of shrubs and small trees. They eat a range of small to medium-sized arthropods, including beetles, katydids, spiders, crickets, centipedes, termites, grubs, and caterpillars. Seeds, buds, and small reptiles are eaten occasionally. Large prey may be shared among members of a group.

Reproductive biology

Territorial groups usually consist of a senior pair and their offspring and siblings. Breeding may occur erratically year-round in New Guinea but is more limited to spring and early summer in Australian species. The senior pair carries out most of the nest construction. The female incubates and broods alone and is fed on and off the nest by others of her group. All members of the group help in feeding the nestlings, which fledge in about 20–21 days. Nests are rough bulky domes of twigs and fiber that are lined with fine vegetable fiber and animal wool. They are wedged in the upper branches of shrubs and small trees at 6.6–26.2 ft (2–8 m) above the ground. Rufous babblers in New Guinea usually suspend their nest at the ends of palm fronds. Eggs, in clutches of two to five, are pale gray and scribbled all over with fine dusky lines; they hatch in 16–23 days depending on species.

Conservation status

Although no species is threatened, species occurring in southern Australian states are declining due to loss and alienation of habitat (e.g., gray-crowned babblers in South Australia and Victoria and Hall's babblers in New South Wales).

Significance to humans

None known.

Species accounts

List of Species

Rufous babbler
Gray-crowned babbler

Rufous babbler

Garritornis isidorei

taxonomy

Pomatorhinus isidorei Lesson, 1827, Dorei Harbor (Manokwari, Cendrawasi). Two subspecies.

other common names

English: New Guinea babbler, Isidore's babbler; French: Pomatostome Isidore; German: Beutelsäbler; Spanish: Hablantín de Isidore.

physical characteristics

Slender, medium-sized pseudo babbler, 9–10 in (23–25 cm);2.2–2.6 oz (65–75 g). Adults and immature birds are uniformly rich russet-brown all over, with yellowish bill and dusky feet; eyes are pale cream in adults, brown in immature birds.

distribution

All lowland New Guinea and Misool Island up to about 1,500 ft (500 m) altitude.

habitat

Interior lower stages and floor of primary and tall secondary rainforest, usually within 33–49 ft (10–15 m) of ground.

behavior

In permanent territorial groups of usually 5–10 birds, mixing with other species in foraging parties in under-shrubbery and low trees, traveling quickly by powerful hopping. Groups tight and call continually with soft and loud whistles, rasps, and yodels. They apparently roost communally at night in one nest that is used for a season.

feeding ecology and diet

Forages mainly by probing bark and crannies on trunks and branchlets of forest substage but also digs in litter of jungle

floor. Diet includes a range of arthropods; small reptiles also taken.

reproductive biology

Poorly documented. Nests are pensile, massively elongate, and slung from the ends of fronds (usually rattan palms) at 10–26 ft (3–8 m) above the forest floor. Nests are built by the senior pair and helpers. The clutch, probably incubated by the female alone, is usually of two eggs, about 1.1 by 0.7 in (28 by 18 mm), and scribbled all over as in other pseudo babblers. Both parents, at least, feed the young.

conservation status

Not threatened.

significance to humans

Some totemic significance for some lowland tribal groups in New Guinea.

Gray-crowned babbler

Pomatostomus temporalis

taxonomy

Pomatorhinus temporalis Vigors & Horsfield, 1827, Shoalwater Bay, Queensland, Australia. Two subspecies.

other common names

English: Red-breasted babbler, cackler, chatterer, happy jack, pinebird, temporal babbler; French: Pomatostome à calotte gris; German: Grauscheitelsäbler; Spanish: Hablantín de Corona Gris.

physical characteristics

Largest pseudo babbler, 9.5–10.5 in (24–27 cm); 2.2–3.2 oz (65–90 g). Adults and immature birds dull brown with diffuse white brows, broadly white-tipped tail, and a diagnostic pale rufous patch in the outer wings that shows only in flight. Varying according to subspecies, throat is white grading to dull brown over the belly or to deep russet-brown over the breast; upper backs and center crowns are respectively gray or dusky. Bill is brown with a bone-colored ridge on upper mandible, feet are dusky black, and eyes are pale cream in adults and brown in immature birds.

distribution

Drier coastal and subcoastal northern and eastern Australia, northwest to Kimberley Division, and southeast to central west Victoria, with outliers in the Trans-Fly of south New Guinea and in central-west and central Australia.

habitat

Open to dense woodlands with trees of moderate height and under-shrubberies that are sparse to only moderately dense. Dominant trees are species of eucalyptus, paperbarks (Melaleuca), mulga, and cypress (Callitris).

behavior

In territorial groups of about 12, gray-crowned babblers hold foraging territory of 25–37 acres (10–15 ha), or larger in the arid zone, keeping in contact and warning of predators with loud chatterings and whistles. In song, they chorus antiphonally, the lead female braying "ya" and the male responding "ahoo", one following the other in rapid succession. At nightfall, all members of a group cluster to sleep in one of several dormitory nests in their territory.

feeding ecology and diet

Foraging extends well up in shrubs and trees, to as much as 66 ft (20 m) above the ground, because of the nature of the habitat. Arthropods of all kinds are picked from crannies in bark and under branches and from tossing litter and digging on the ground; the babbler even laboriously flies up in attempts to catch winged termites.

reproductive biology

Breeds in spring and early summer in most areas, but also in autumn in Western Australia. Nests are coarse round domes of twigs wedged in forks in upper branches of tall shrubs and small trees at 9.8–32.8 ft (3–10 m) above the ground. Eggs, incubated by senior females, are about 1.1 × 0.7 in (28 × 20 mm) and covered with the fine scribblings characteristic of the family. Two to four eggs form a clutch. Young hatch in 18–23 days and fledge in about 20–22 days. When occasional groups contain several breeding pairs, the pairs use the same nest together and females share incubation of clutches of up to ten or more eggs. Recruitment nevertheless is low, which in turn is offset by longevity; once they have reached adulthood, individual birds may live for 15 years or more.

conservation status

Although most populations of both subspecies are not threatened, those of P. t. temporalis have withdrawn from much of their range in southeast Australia; they are extinct in South Australia and almost extinct in Victoria.