Broadbills

(Eurylaimidae)

Class: Aves

Order: Passeriformes

Suborder: Tyranni (Suboscines)

Family: Eurylaimidae

Thumbnail description
Small to medium-sized birds, some very colorful, most with a broad head, broad bill wide gape, and large eyes

Size
4.5–10.8 in (11.5–27.5 cm); 0.35–6.0 oz (10–171 g)

Number of genera, species
8 genera; 15 species

Habitat
Mostly humid tropical lowland or montane forest

Conservation status
Vulnerable: 3 species; Near Threatened: 3 species

Distribution
Sub-Saharan Africa and Southeast Asia including Hainan Island, Borneo, Sumatra, and Java

Evolution and systematics

The broadbills are a small family with only 15 species and eight genera. Their taxonomic position was somewhat of a mystery for most of the twentieth century, but recent phylogenetic studies using morphological and molecular (DNA sequencing) data have shown that the broadbills form a monophyletic group with the pittas (Pittidae) and asities (Philepittidae). Together, these three families comprise the Old World suboscines, a group that shares a tracheobronchial syrinx, or vocal apparatus. Richard Prum suggests that the asities are the sister group of the African green broadbill (Pseudocalyptomena graueri). His Eurylaimidae thus consists of five subfamilies: Smithornithinae, Calyptomenanae, Eurylaiminae, Pseudocalyptomenanae, and the Philepittinae.

The eight genera in this family are quite distinct and do not appear to be closely related. They may be the last survivors of a once much more diverse group that was slowly replaced by a radiation of oscine songbirds. The origin of the broadbills is still a matter of speculation. Suboscines probably evolved on Gondwana, so it seems reasonable to hypothesize an African origin (giving rise to the ancestors of Smithornis) following the break up with South America. Broadbills then diversified by spreading into Asia (Calyptomena, Eurylaimus, Corydon, Serilophus) and then back to Africa (Pseudocalyptomena and asities).

Physical characteristics

Broadbills are small to medium-sized birds ranging from 4.5 to 10.8 in (11.5–27.5 cm) in length and weighing 0.35–6.0 oz (10–171 g). Broadbills share a host of characters in their syrinx and hindlimb musculature. Except for Calyptomena they are unique among the passerines in having 11 primaries. Most species have an exceptionally wide bill and gape. The dusky broadbill (Corydon sumatranus) beats all records among the passerines with a pink, hooked bill that is as wide as it is long. It even surpasses the skull in width. The more frugivorous Calyptomena and Pseudocalyptomena have a much narrower bill, but have retained a wide gape.

In terms of plumage coloration, the broadbills are a diverse group. Apart from a few dull-colored species, most broadbills are quite colorful, spanning the range from blue to red. Some species also have an area of bare skin around the eyes that is blue in the two Philippine Eurylaimus and pink in the dusky broadbill. Whereas the two sexes look alike in some species, more or less subtle difference can be found in others. Sexual dimorphism is most obvious in Calyptomena. Here the males are more intensely colored and the loral feathers form a forward facing tuft that covers the base of the bill, resembling a small crest.

Distribution

The highly fragmented distribution of broadbills is limited to tropical and subtropical sub-Saharan Africa, Himalayan India, Thailand, Cambodia, Vietnam, extreme southern China (also Hainan Island), Borneo, Sumatra, Java, peninsular Malaysia, and the Philippines. Smithornis and Pseudocalyptomena are the only genera occur in Africa. Hose's broadbill (Calyptomena hosii) and Whitehead's broadbill (C. whiteheadi) are restricted to Borneo and the Mindanao and Visayan wattled broadbill (Eurylaimus steerii and E. samarensis) are restricted to a few islands in the Philippine archipelago.

Habitat

Broadbills are inhabitants of humid forests. Only the African broadbill uses somewhat drier areas. Interestingly, most broad-bills inhabit mountainous terrain. Those species that primarily occur in the tropical lowlands move seasonally into montane forests as a response to changing resource levels. Many species are tolerant of some human caused disturbance, but most require primary forest for long-term persistence.

Behavior

Little is known about broadbill mating systems and general behavior. Most species appear to be monogamous. However, the frugivores (Calyptomena, Pseudocalyptomena) may be polygynous as they appear to form leks. Territoriality is another area that requires more research. Most broadbills join single or mixed species flocks, but it is still unclear if they remain in, or always return to, the same territory. There is evidence, however, that Calyptomena ranges over wide areas in search of fruit.

Broadbills perform a variety of displays that may be related to territory maintenance or courtship. The best-described species are the Smithornis broadbills, which make characteristic elliptical flights, and the green broadbill, which has a series of complex displays. The songs are rather uncomplicated, consisting of whistles, trills, dove-like cooing, and variable series of notes described with different qualities, from bubbly to screaming.

Feeding ecology and diet

Most broadbills are insectivorous. Some species also eat small vertebrates, such as lizards and small fish. The three Calyptomena species are frugivorous, depending to a large degree on figs. Fruit also makes up a large component of the African green broadbill's diet. Most of the food is either gleaned from leaves or branches, or caught in flight. Some broadbills (Smithornis, Cymbirhynchus) also drop to the ground to catch prey.

Reproductive biology

The reproductive season depends mostly on the local rainfall regimes. Some species tend to nest during the dry season and others during the rainy season. All broadbills make pendant nests. Common nest materials include fibers, strips of leaves from monocotyledonous plants, such as grasses, bamboo, and palms, and other leaves. Smithornis also interweave black fungal strands. Spider webs and cocoons, moss, and other materials camouflage the nests. Except in Smithornis and Calyptomena, nests are suspended from the tips of branches, and are hard for predators to reach. Locating the nests above water further deters predators. Cymbirhynchus suspends its nests 5–26 ft (1.5–8 m) above rivers or other water bodies. While protected from predators, nests in the lower range are often destroyed by rising water levels.

Two to six eggs are laid. With the possible exception of Calyptomena, both sexes build the nest. Male parental care appears to be common in most species. The dusky and long-tailed broadbills may even be cooperative breeders as more than two individuals of the species have been observed around nests. As an interesting side note, female green broadbills' heads protrude from the nest entrance. Why? Nobody knows. Much needs to be learned about broadbill reproductive behavior.

Conservation status

Six out of 15 species are on the IUCN Red List. Three species are considered Vulnerable and three Near Threatened. With no more than 10,000 individuals each, the vulnerable species all have tiny ranges that are threatened by deforestation, mining activities, and/or guerilla warfare (on Mindanao, Philippines). Deforestation of lowland forest threatens Hose's, White-head's and black-and-yellow (Eurylaimus ochromalus) broadbills.

Significance to humans

Most broadbills are colorful birds. However, little information is available on their significance in the pet trade. The silver-breasted broadbill (Serilophus lunatusis) is sold at local markets in Thailand. The African broadbill has the distinction of being the first suboscine whose entire mitochondrial genome has been sequenced.

Species accounts

Resources

BirdLife International. Threatened Birds of Asia: The BirdLife International Red Data Book. Cambridge, UK: BirdLife International, 2001.

Lambert, Frank, and Martin Woodcock. Pittas, Broadbills and Asities. Sussex, UK: Pica Press, 1996.

Irstedt, Martin, Ulf S. Johansson, Thomas J. Parsons, and Per G. P. Ericson. "Phylogeny of Major Lineages of Suboscines (Passeriformes) Analysed by Nuclear DNA Sequence Data." Journal of Avian Biology 32 (2001): 15–25.

Prum, Richard O. "Phylogeny, Biogeography, and Evolution of the Broadbills (Eurylaimidae) and Asities (Philepittidae) Based on Morphology." Auk 110 (1993): 304–324.

BirdLife International Indonesia Programme. P. O. Box 310/Boo, Bogor, Indonesia. Phone: +62 251 357222. Fax: +62 251 357961. E-mail: prue@burung.org Web site:

World Conservation Monitoring Center. "Threatened Animals of the World. UNEP-WCMC Animal Database."

[Article by: Markus Patricio Tellkamp, MS]

ADVERTISEMENT