False sunbirds and asities

(Philepittidae)

Class Aves Order Passeriformes Suborder Tyranni (Suboscines) Family Philepittidae

Thumbnail description

Medium or small birds; two species frugivorous with short bills, two species nectarivorous with long, curved bills; males have brightly colored wattles during the breeding season; plumage usually dark blue, black, or yellow

Size

Number of genera, species

2 genera; 4 species

Habitat

Canopy and understory of tropical rainforest Conservation status

Endangered: 1 species; Near Threatened: 1 species

Distribution

Endemic to Madagascar

Distribution

Endemic to Madagascar

Evolution and systematics

The ecological and morphological diversity of these Madagascan endemics has caused considerable confusion over their proper classification. As currently recognized, the philepittids are a family of suboscine birds including two genera, the asities (Philepitta) and the sunbird-asities (Neodrepanis). With their frugivorous habits and short bills, the asities were originally associated with several of the oscine passerines, including the starlings, sunbirds, and birds of paradise. However, by the late 1800s, it was recognized that these birds were in fact suboscine passerines. Sunbird-asities, with their long, de-curved bills and nectarivorous foraging habits, were also originally assumed to be oscine passerines and classified as sunbirds (Nectariniidae). However, it was not until 1951 that investigations of syrinx morphology demonstrated that these unique birds were also suboscines.

The placement of Philepittidae within the Old World sub-oscines remains problematic. The most recent morphological analysis, published in 1993 by Richard Prum, suggests that philepittids are not a true family, but should be considered a subfamily (Philepittinae) of the Eurylaimidae. Under this hypothesis, the Philepittidae represent a radiation from a broad-

bill ancestor that probably originated from Africa. In contrast, a phylogeny based on nuclear DNA gene sequences published by Martin Irestedt and coworkers in 2001 found strong support for placing the Philepittidae outside the Eurylaimidae, thus justifying its classification as a true family.

Physical characteristics

Of the philepittids, the asities are the larger of the two genera, measuring 4.7-6.3 in (12-16 cm) in length. These birds are primarily frugivorous and have short bills, relatively large heads, round bodies, and short tails. In contrast, sun-bird-asities, like many nectarivorous passerines, are relatively small, measuring only 3.5-4.3 in (9-11 cm) in length. They have long, curved bills, and specialized tongues for extracting nectar from forest flowers. Sunbird-asities have plump bodies and short tails.

The plumage patterns of the philepittids are generally characterized by black, dark blue, olive-green and bright yellow. All species are sexually dimorphic; females are generally olive-green and cryptic, while males have much brighter and contrasting plumage. Perhaps the most unique feature of these birds is the bright blue, yellow, and green caruncles (wattles) of bare facial skin developed by males during the breeding season. Richard Prum has performed an extensive investigation of these structures from velvet asities (Philepitta castena) and common sunbird-asities (Neodrepanis coruscans) and has demonstrated that the bright colors are produced by light reflecting from unique alignments of collagen fibers. This form of structural coloration is not known to occur in any other animals.

Distribution

Asities and sunbird-asities are endemic to the forests of Madagascar.

Habitat

These birds are found in the understory, lower levels of canopy, and occasionally in the canopy of primary rainforest, dry deciduous forest, degraded or logged forest, and in secondary forest. The genus Philepitta occurs in many forest habitats of Madagascar, with one species (P. schlegeli) found on the drier eastern side of the island and the other (P. castanea) found in the moister rainforest on the west side of the island. In contrast, Neodrepanis is found only in the rainforests on the west side of the island. These birds occur from sea level up to 5,900 ft (1,800 m), but some species have strong affinities for relatively narrow altitudinal zones.

Behavior

Philepittids may be found either alone, in pairs, or in small groups. Several individuals may occur together at food resources, such as flowering or fruiting trees. Such aggregations may lead to intraspecific displays and defense of resources, especially among Neodrepanis. Philepittids will also join mixed-species foraging flocks when feeding on fruit or insects.

Males call frequently, especially during the breeding season, and a wide variety of male displays has been recorded. Much of this behavior appears to be the basis of a lek mating system. There is no evidence that philepittids migrate, but the possibility that some species are altitudinal migrants cannot be ruled out.

Feeding ecology and diet

The asities in the genus Philepitta are primarily frugivo-rous, but also feed on nectar and insects. Fruits are consumed while the birds are perched. Although Philepitta does not have the specialized bill morphology of Neodrepanis, nectar is probably an important component of the diet. Initial investigations of tongue morphology have suggested that a brush-like tip and the ability to roll it into a tube-like form may increase the efficiency with which nectar can be consumed. Pollen may also be an important food item.

Sunbird-asities (Neodrepanis) are specialized for consuming nectar. These birds have long, decurved bills for entering flower corollas and long, tube-like tongues for the efficient extraction of nectar. They feed on the nectar of a variety of flowers including Balanophoraceae, Balsaminaceae, Loran-thaceae, Rubiaceae, Clusiaceae, Melastomataceae, and Zin-giberaceae. Insects and spiders are also an important component of their diet. These species have been observed searching in moss and along branches for invertebrates and fly-catching small insects.

Reproductive biology

Although there are few breeding records for any of the philepittids, it appears that most nesting attempts are made between July and January. Local breeding seasonality may be timed so that young fledge at the onset of the rainy season.

Most observations suggest that the philepittids are polyg-ynous. The most convincing evidence comes from detailed observations of the velvet asity. The males of this species defend territories no more than 66-100 ft (20-30 m) in diameter, within which males perform three displays, including wing-flapping, an open-mouth display, and an open-mouth display coupled with hanging inverted from their perch. Other observations, such as groups of male Schlegel's asities (Philepitta schlegeli) calling simultaneously and an upside-down open-mouth display by the yellow false-sunbird, suggest that a polygynous mating system may be widespread in this family.

All philepittids build ragged, pendulant nests hung from the low branches of trees. Nests are built of moss, palm fibers, dead leaves, and fine twigs. Based on observations of velvet asities and common sunbird-asities, nest construction is by the female alone and proceeds in an unique fashion: a complete orb is first constructed, then, once finished, the female pokes a hole through the side to form the entrance.

Clutch size varies from two to three eggs. There is no information on incubation or nestling periods. For most species that have been observed, the female incubates and feeds the young.

Conservation status

The philepittids are especially vulnerable to the widespread destruction of forested habitats occurring on Madagascar. The most seriously threatened species is the yellow-bellied sunbird-asity (Neodrepanis hypoxantha), which is considered Endangered. It was also added to Appendix I of CITES in 1995. This species was recently reclassified from Critically Endangered due to studies that indicate its population may be larger than previously thought. However, it remains threatened because of its very small, fragmented range and continuing decline of its habitat.

Significance to humans

For many years, these small, inconspicuous birds have lived in a remote area inhabited by few people, and have been essentially overlooked. More recently, the growing popularity of bird-watching and ecotourism has lead to an increased interest in these species.

1. Common sunbird-asity (Neodrepanis coruscans); 2. Velvet asity (Philepitta castanea). (Illustration by Dan Erickson)
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