Barbets (Capitonidae)

(Capitonidae)

Class: Aves

Order: Piciformes

Family: Capitonidae

Thumbnail description
Small to medium-sized, colorful, thick-billed, large-headed and short-tailed birds; noticeable bristles around bill; tongue sometimes forked or brush-tipped; foot zygodactyl, two toes pointing backwards

Size
3.2–13.8 in (8–35 cm); 0.3–7.2 oz (8.5–203 g)

Number of genera, species
13 genera, 92 species

Habitat
Mostly tropical forest and forest edge, with some species (including most African ones) thriving in secondary forest, parkland, and even suburbs with many ornamental trees; a few live in drier, thornbush habitats with large termite mounds.

Conservation status
Endangered: 1 species; Near Threatened: 9 species.

Distribution
Northern South America and southern Central America; sub-Saharan Africa; south and Southeast Asia

Evolution and systematics

The order Piciformes includes barbets, toucans, honeyguides, and woodpeckers—on the face of it a varied group but, on closer examination, a range of birds with common characteristics. The toucans and barbets are particularly closely related and share a number of physical features: the tooth-edged bills of toucans are rather like elongated, exaggerated forms of the heavy barbet bills, although the smallest barbets, such as tinkerbirds, have much smaller and simpler bills. Toucans and some barbets are essentially fruit-eaters, with a pivotal role in the dispersal of tree seeds in forests. Almost all barbets can excavate nest holes in trees, as do woodpeckers. Of these various families the barbets are the most generalized. Perhaps small species long ago (12–20 million years ago) gave rise to woodpeckers and honeyguides. American toucans and barbets more certainly arose from a common ancestor some 10 million years ago, but the toucans have become more widespread in range (both to the north and the south of the barbets) and habitat choice. It has been said that, in evolutionary terms, the toucans "left the barbets behind" as they developed while the barbets stayed put in the old, tried-and-tested form.

Physical characteristics

All barbet species perch and climb well and have the two toes forward, two toes back foot structure that allows for an especially good grip on wide branches. This is a grasping or perching rather than climbing foot, and in climbing a near-vertical branch the outer toe may be swung forwards or sideways to give a better purchase. Barbets do not support themselves on their tail feathers, as do woodpeckers, except during brief spells when they are excavating their nests. Unlike woodpeckers, barbets do not have a long, thin, sticky tongue that can be extended and inserted into ant nests, although a few woodpecker species share the brush-tipped tongues of many barbets.

The bill is stout and strong, quite stubby but solid in the smaller species and rather elongated and pointed in the bigger ones. It usually has several tufts of bristles at the base. These can be flattened against the bill and opened up to avoid damage when the bird is pecking or excavating wood, but their precise function is unclear. Some barbet bills are extremely like toucanet bills, the cutting edge of the prominently grooved upper mandible being saw-toothed, but barbet bills are not flattened nor usually keeled in the same way as the larger toucans' extravagant beaks. In many species they are nevertheless used in displays, being brightly colored or contrastingly pale against a dark face.

Neotropical barbets always show marked sexual differences in color or pattern, but males and females are usually alike in Africa and Asia. Many African species are largely black and white with patches of red, yellow, or both in dramatic patterns. African crested and ground barbets are dark above with bold white spots in a rather random, untidy, spangled pattern. Their tails are also black with white or yellowish spots, with a touch of red at the base. The brown barbets of Africa and Asia are, by contrast, mostly dull and weakly marked, uniformly dark brown for the most part. The tinkerbirds of Africa, small and secretive birds of thick foliage, are often strongly patterned, striped black and white or with patches of red or yellow on the head, and vivid orange or yellow rumps: these color marks are often reflected in their names. Asian barbets include many lovely green species, with patterns of red, yellow, purple, brown, and blue in complex bibs, caps, cheek marks, spots, and bars. South American species are often gaudy and differ in appearance from the rest, despite sharing the usual color palette of black, white, red, and yellow. A number have orange breast shields or red breast bands. One genus, Eubucco, contains several small species that are predominantly bright green above, bright red on the head, and red or yellow beneath, topped off by pale yellow bills.

Distribution

Barbets are found in greatest numbers and diversity in tropical Africa; in the Americas they are fewer in species and have a surprisingly restricted range. Asian barbets are also less varied than the African ones. The 15 American barbets are mostly lowland birds of the Amazon basin; only three extend into Central America, in marked contrast with the related toucans. Few spread south of the Amazon and, unlike toucans, there are no southern barbets, and few that live in montane forest.

Barbets occupy most of Africa south of the Sahara, from the Atlantic to Ethiopia and south to South Africa. In Africa, barbets appear to have evolved during a long period of changing forest cover. As vast forests became split into discrete areas, so populations of barbets were isolated. These groups, over time, developed into separate species as forest areas remained apart, each beyond the reach of weak-flying barbets from other forest refuges. This characteristic of everchanging habitat also forced some barbets to occupy drier, bushy places outside proper forest cover, not seen in barbets elsewhere except in recent habitats such as orchards and towns where conditions have quite incidentally been made acceptable to fruit-eating forest birds.

Tropical Asian barbets are less well studied than the others. Five species live in peninsular India, four in Sri Lanka, and five or six in northern India and Nepal, but Southeast Asia has a greater variety. Sumatra has eight species, Java six, and Borneo nine; in all, 21 of 26 Asian barbets are in Southeast Asia. This variety within a spectacular family is wonderful, but its future is surely bleak as forest cover is being destroyed at an unprecedented (and still accelerating) rate. No barbets are found east of Wallace's Line or in Sulawesi: no islands east of Bali have barbets.

Habitat

Lowland tropical forest is typical barbet habitat, especially in Asia and Central and South America. They are often associated with fruiting trees, and many species of ornamental tree that produce copious fruits attract barbets into gardens, towns, and even city parks, particularly in Asia and Africa, where cities such as Nairobi and Harare host barbets all year round. They live in a variety of artificial woodlands, too, from pine to coconut plantations. Dead wood is important for barbets to excavate nesting holes, which they also use for roosting all year round. Over-managed woodland is not really suitable for them.

In East Africa several closely related species live in thorn thickets and bushy places on the fringe of the great wide-open plains, often associated with big termite mounds. In such places D'Arnaud's barbets (Trachyphonus darnaudii) are frequently seen foraging around thickets, ditches, and outbuildings alongside safari lodges, becoming quite bold and confiding. Professor Grzimek must have often seen and heard these lively birds in his camps in and around the Serengeti in Tanzania, unaware of the subsequent debate over their precise classification, as this is a species that has been "split" into two or three in more recent studies. Crested barbets (Trachyphonus vaillantii) are particularly common around termite mounds in open savanna woodland and thornbush, foraging about the tall earthy piles and perching openly upon them in pairs. Where the two occur together, D'Arnaud's prefers the flatter, open spaces between the little cliffs, streamside bluffs, and dry watercourses that the crested occupies. Tinkerbirds prefer tall forest with dense undergrowth, forest edge, and riverside woodland with tangled growth around the base of tall, old trees.

Sometimes two similar species remain separate within a large geographical region through habitat choice. For example, the coppersmith barbet (Megalaima haemocephala) of India favors forest edge, plantations of figs, village and city trees, gardens, orchards, and mangroves—wherever there is fruit to eat and broken branches and stumps to nest in. It does not, however, live in cleared areas where rainforest has been felled, nor the wet rainforest of Sri Lanka, in which areas it is replaced by the crimson-throated barbet (M. rubricapilla). The scarlet-crowned barbet (Capito aurovirens) of Colombia and Ecuador is found close to water, in the varzea or swampy or floodplain forests, and in tall, secondary growth, but it is rarely seen close to the related black-spotted barbet (C. niger), which tends to replace it in the "terra firma" forest of drier, more solid ground. Many species, such as the red-headed barbet (Eubucco bourcierii) of Costa Rica, are found along trails and cut rides in forests, living at the forest edge, but are quickly lost once the original forest is felled. Some, such as the prong-billed barbet (Semnornis frantzii) of Costa Rica and Panama, prefer the high canopy of rich, damp, mountain forest where the trees are draped in long beards of moss and epiphytes.

A number of closely similar species pairs occur in Africa, separated by range rather than habitat. These are examples of allopatric species, sometimes grouped as "superspecies": their ranges are complementary and do not overlap. The bristle-nosed barbet (Gymnobucco peli) lives in lowland forest in West Africa while the nearly identical Sladen's barbet (G. sladeni) replaces it in the forests of Zaire. Whyte's barbet (Stactolaema whytii) occupies woodland from southern Tanzania to eastern Zimbabwe, while the similar Anchieta's barbet (S. anchietae) is found in similar habitats to the west of this range. The range of the red-fronted tinkerbird (Pogoniulus pusillus) of eastern African bush is almost exactly surrounded by the more widespread yellow-fronted tinkerbird (P. chrysoconus). The red-fronted prefers wetter areas than the yellow-fronted in southern Africa, but drier areas in the northeast. Both over-lap with the yellow-rumped tinkerbird (P. bilineatus), an example of sympatric species (found living side by side in the same area, the opposite of allopatric), although where the latter bird is most common the red-fronted is usually absent. Nevertheless, red-fronted and yellow-rumped may even sing from the same tree, but at different times. Where yellow-fronts and yellow-rumps occur together, the yellow-rumped prefers wetter, lusher woodlands; if the yellow-rumped is absent, such woods are, however, occupied by the yellow-fronted.

Two more species with almost exactly complementary ranges are the bearded barbet (Lybius dubius) of West Africa, found in a band of woodland and forest south of the Sahara, and the black-breasted barbet (L. rolleti) just to the east of it, in Chad and Sudan. There is no known overlap but the two may perhaps meet in Chad. The southern edge of the combined range of these two is irregular and "fingered," precisely abutting the similarly fingered range of the double-toothed barbet (L. bidentatus) of more open woodland immediately to the south. These make a trio of species, two with similar habitat but different range, the third replacing them in a slightly different but immediately adjacent habitat.

Behavior

Barbets hop and clamber about trees, move rather heavily through low bushes or on the ground, and often perch quite still for long periods. The bigger species tend to be more sluggish than the tiny ones, which are quite acrobatic when feeding.

They fly well, but look a bit heavy and ungainly in the air and generally fly only for short stretches. The large, colorful species may suddenly appear, flying into a tree with a blurry splash of color, while smaller ones are usually heard but not so easily seen. A number of African barbets perch prominently and call repeatedly from one spot, making them easy to find and watch. The tinkerbirds call repeatedly, with a monotonous and sometimes infuriating repetition of simple notes, keeping out of sight as they do so. Some of these, as well as the coppersmith barbet (Megalaima haemacephala) in India, were among several birds referred to as "brain fever" birds by early European colonists, because of their nonstop calls. Together with the heat, the mosquitoes, and fever, the nonstop repetition of 1,000 or more calls by an invisible tinkerbird was sometimes just too much to bear.

Pairs may "duet" at times, calling in a neat pattern of coordinated notes with remarkable synchrony; this may be taken up and expanded by others within small social groups. It is often impossible to make out which, or even how many, birds are calling in the most perfected duets or choruses, which may produce a rhythmic phrase that is repeated several times in identical form.

They are aggressive birds, but several species (especially the larger ones) are social, with "helpers" at the nest and complicated social lives. Others are strictly territorial, each pair keeping others well away from the nest. They commonly roost in nest holes all year round and data on breeding seasons are poorly known for most species because of this source of potential confusion. A few species "drum" with the bill against a branch in the manner of a woodpecker, while others have aerial displays and noisy wing-rustling displays.

Feeding ecology and diet

Barbets are fruit eaters, but their growing chicks require high protein diets and are fed almost exclusively insects. Barbets have an important role in seed dispersal (although some species regurgitate pellets of undigested seeds from fruit, and then eat them again). In dense forest, there would be little chance of a seed being carried far by wind, or rolling more than several feet along the ground. To get far beyond the parent tree, it is best eaten by a barbet and ejected in a neat package of fertilizer from some far-off perch. Rich, evergreen, tropical forests have many species of fruiting trees, shrubs, and vines that flower and fruit at different times of the year; hence, barbets have a good food source all year round in sizeable forests (but this may become limited or disrupted in areas where forests are cleared or remain only in small patches). In Thailand as many as 100 blue-eared barbets (Megalaima australis) may gather at a single large, fruiting tree, breaking down their normal territories to feed on a temporary abundance of food that is sufficient for all. African barbets have been known to feed on at least 50 different genera of plants, mostly eating fruit but in some cases also taking nectar or blossoms. Figs are especially important food trees in both Africa and Asia and also supply fruits to South American barbets. Cultivated papayas, mangos, bananas, peppers, and avocados are also eaten, probably where natural foods have been reduced by human activity. Usually it is the larger species of barbets that dominate a fruiting tree where several species gather together.

Large fruits are naturally taken only by larger species that are big enough to swallow them. These take longer to digest than smaller food, and a barbet that has eaten some large fruits may then rest for an hour or more while its meal is digested. The red-headed barbet (Eubucco bourcierii) eats flower spikes along with the many insect larvae that find temporary refuge within them, while black-spotted barbets (Capito niger) and several other species, including the scarlet-hooded barbet (E. tucinkae) take both flowers and nectar. African barbets are the most persistently insectivorous species within the family: redand-yellow barbets (Trachyphonus erythrocephalus) will eat almost anything that they can find, including scraps of food put out for them (eagerly taking milk, cereals, meat, bread, and fruit). Snails, worms, lizards, spiders, centipedes, even birds' eggs and young birds are eaten by some African species, as well as the many large insects that abound at certain times. Some even have special "anvils" where they remove the wings of large prey such as locusts. Asian barbets likewise take insects when breeding, but fewer at other times; some also eat birds' eggs, lizards, and centipedes. Several species dig into bark to find beetle larvae and into termite mounds to reach termites. Flying ants and termites are also caught on the wing in quite proficient flycatching sallies from a perch.

At least one South American barbet, the spot-crowned barbet (Capito maculicoronatus), follows swarms of army ants and eats insects that these fearsome columns flush out of hiding places, although it is not a constant companion of the ants in the same way that some woodcreepers and antbirds are, the "professional" followers of ant swarms. Others in this genus tap on bark to stir up insects while birds of the genus Eubucco specialize in foraging among clusters of dead leaves, searching out insects and other small invertebrates that seek food and safety in the brittle bunches. Several of these small barbets join mixed flocks of birds that roam around the forest, eating insects as well as fruit as they move through the treetops.

Reproductive biology

Most barbets have breeding territories and are monogamous, and some pair for life. They proclaim and defend a territory by singing, but their songs may be quite varied: some have 10 or 12 particular calls that are used as song, often in complex male-female duets. Often other birds apart from the breeding pair join in the chorus of songs, apparently serving to strengthen the effect of the song by communicating the size and therefore strength of the group.

Various displays include exposure of color patches on the head, wings, rump, tail, and bill, with feathers being erected to maximize the effect. If there is a difference between the sexes, the male's special color patches are used in such displays. Pairs of barbets focus their courtship activity around the hole that will serve as their nest, and often preen one another. They are long-lived birds with strong pair bonds, supported and cemented by activities such as mutual grooming, which are maintained all year. The pair typically mates for life, so breeding season courtship displays are rather limited, being required only to synchronize breeding condition between male and female.

The nest is in a hole in a tree, usually freshly excavated. Smaller species nest in dead or dying branches, typically digging in from beneath a horizontal bough. Barbets tend to make larger entrance holes than woodpeckers of a similar size. The hole enters a vertical shaft ending in a slightly widened chamber in which the eggs are laid. In more social species several "helpers" may be involved in digging the nest hole over a number of weeks, although in some the helpers at the nest are not involved in the excavation. Wood chips are usually carried away, sometimes being swallowed and then regurgitated elsewhere, presumably to prevent telltale signs from accumulating beneath the tree, giving clues of the nest's whereabouts to predators. The eggs are still not described for many species and incubation and fledging periods are generally little known. Like those of woodpeckers, barbet eggs are, however, always pure white and the clutch size up to six (typically three) in African barbets, two to five (again, most often three) in South American species. Incubation averages around 15 days—12 days for the smallest and up to 19 days for larger species. Once the chicks are hatched, adult barbets keep the nest exceptionally clean in most cases, probably swallowing rather than carrying away the chicks' droppings. Nestlings of small species leave the nest after 17 to 23 days, larger ones remaining as long as 30 or 40 days, notably long periods for such modestly sized birds. Helpers (sometimes young of the pair from previous years) assist the pair in feeding the chicks in some species, while many are strictly territorial and only the breeding pair is involved.

Conservation status

The white-mantled barbet (Capito hypoleucus) of Colombia is classified as Endangered. This species has a small, very fragmented range some parts of which are subject to rapid habitat loss. The population of this species is probably declining as a result.

An additional nine species of barbets—from South America, Africa, and Southeast Asia—are considered Near Threatened. Threats to barbets are all too apparent in all forested habitats. Uncontrolled and frequently illegal logging is increasing, especially in Southeast Asia, where the loss of habitat for barbets and other wildlife is almost incalculable; certainly millions of acres disappear each year.

Good habitat is becoming both reduced in total area and also more patchily distributed, separated by unsuitable areas that barbets are unable to cross. Small populations will inevitably become threatened and less viable, so conservation requires strong protection for forests (including dead trees within them) and also maintenance of corridors that link remaining forest patches. In many areas this appears to be an unachievable aim.

Fires have had severe effects on barbet habitat, too, especially in Indonesia in recent years. In Africa, the barbets that live in open woodland, bush, and savanna will presumably do much better in the long term, but forest-living species face an uncertain future at best.

Significance to humans

Barbets have little or no commercial impact on people, taking some fruits but not usually being sufficiently numerous to be classified as pests. They are, however, very obvious components of a forest's sounds and many species, if not well known visually, are easily recognized by local people by their calls and repetitive songs.

Species accounts

Resources

Fry, C. H., S. Keith, and E. K. Urban., eds. The Birds of Africa. Vol. 3. New York: Academic Press, 1988.

Grimmett, Richard, Carol Inskipp, and Tim Inskipp. A Guide to the Birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and the Maldives. Princeton: Princeton University Press, 1998.

Short, Lester, and Jennifer Horne. Toucans, Barbets, and Honeyguides. Oxford: Oxford University Press, 2001.

Skutch, A. F. Birds of Tropical America. Austin: University of Texas Press, 1983.

Zimmerman, Dale A., Donald A. Turner, and David J. Pearson. Birds of Kenya and Northern Tanzania. Princeton: Princeton University Press, 1996.

[Article by: Robert Arthur Hume, BA]