Toucans (Ramphastidae)

(Ramphastidae)

Class: Aves

Order: Piciformes

Family: Ramphastidae

Thumbnail description
Medium-sized to large birds, instantly recognizable by their strikingly large and colorful bills; often associate in small flocks when foraging

Size
13–24 in (33–60 cm); 4–30 oz (113–850 g)

Number of genera, species
6 genera; 41 species

Habitat
Predominately tropical and montane rainforest

Conservation status
Endangered: 1; Near Threatened: 3

Distribution
South America south to northern Argentina

Evolution and systematics

The toucans (Ramphastidae) are a very striking group. No fossilized remains of this family are known; recent remains of a toco toucan (Ramphastos toco), from the Pleistocene (20,000 years old) have been found, in Minas Gerais, Brazil.

The toucans' closest relatives are barbets (Capitonidae), and the two groups are thought to have evolved from a common ancestor; in their landmark 1993 study, Sibley and Ahlquist describe toucans as "New World barbets with big bills." Woodpeckers (Picidae) are closely allied to the toucans, which are also similar to hornbills (Bucerotidae), albeit more distantly related.

J. Haffer proposed the most widely accepted theory of speciation in toucans, and his model has since been applied to other Amazonian bird groups. Toucan speciation apparently occurred during Pleistocene glaciations (characterized by dry forest expansions) and interglaciations (characterized by tropical forest expansions). The rapid formation and disappearance of new Pleistocene biomes enhanced speciation rates in this region. Species derived from drier biomes later became sympatric (inhabiting the same range but not interbreeding) when tropical forest expanded in Amazonia, forcing the dry forest specialists to adapt to tropical forest or perish. There are 6 genera with 41 species. The green toucanets (Aulacorhynchus) are represented by seven species; the aracaris (Pteroglossus) by 12 species; the black toucanets (Selenidera) by six species; the saffron toucanet (Baillonius) is monotypic and in Peters is lumped into genus Andigena; the mountain toucans (Andigena) are represented by four species; and the true toucans (Ramphastos) by 11 species.

Social mimicry, a relatively rare evolutionary event in nature, is seen in this group. Social mimicry is the situation in which two or more distantly related species are more similar to one another than they are to other, more closely related species. Among toucans, it is apparent in the yellow-ridged toucan (Ramphastos vitellinus culminatus), which mimics the color and appearance of the larger white-throated toucan (Ramphastos tucanus cuvieri). The mimic benefits because it avoids being attacked by the larger model, while its appearance deters smaller species from trying to share feeding sites.

Physical characteristics

Toucans are characterized by brightly colored plumage and an unusually long and bulky, but very lightweight, bill with a downcurved tip and serrated edges. Another trait characteristic of toucans is a tongue with a bristly or brushy tip. Toucans range in length from 13–24 in (33–60 cm). In almost all species, male and female look alike; only the black toucanets (Selenidera) and green aracari (Pteroglossus viridis) are sexually dimorphic.

The toe arrangement is zygodactylous, with two toes projecting towards the front and two to the back.

Naturalists have long puzzled over the significance of the toucan's large bill. Originally, observers suggested that the bill was a weapon used to defend the nest cavity. This is not so; when toucans sense danger, they come out of the cavity entrance in a hurry, threatening the enemy only out in the open, if at all. Instead, a long bill enables these rather heavy birds to pluck berries from the tips of branches without leaving a stable perch. A thin, dark-colored bill would, however, be just as useful for this purpose. Possibly the toucan's bill plays a role in pair formation and in the social life of the group. According to E. Thomas Gilliard, it acts as a signal. However, toucans can also use their bills to threaten those birds whose nests they plunder. Tyrant flycatchers and even small raptors are frightened by the giant bill, which is even more effective because of its lively colors, and they fly about helplessly while the toucans devour their young or eggs. Other birds will attack a toucan only while it is in flight, because it is then unable to defend itself with its bill.

Distribution

Toucans are restricted to the Neotropics, where they are distributed through most of tropical South America as far as northern Argentina, with some individuals found as far north as Mexico. Although most species are lowland residents, there are some exceptions: most of the toucanets (Aulacorhynchus) have home ranges at 8,200 ft (2,500 m) or higher in Central America, and the mountain toucans (Andigena) range 3,900– 11,000 ft (1,200–3,350 m) in the South American Andes.

The nation with by far the highest diversity of toucans is Colombia, with 21 species; Venezuela, Ecuador, and Brazil are home to 17 species each. The country with the lowest diversity of toucans is Trinidad, with a single species, the channel-billed toucan (Ramphastos vitellinus).

Habitat

Most toucans are canopy specialists in tropical or montane rainforest. Secondary vegetation may be inhabited by true toucanets, aracaris, and some of the true toucans. Some of the aracaris and the toco toucan are riverine specialists, and species such as red-breasted (Ramphastos dicolorus) and toco toucans may inhabit palm savanna.

Behavior

Toucans wander through the forests and adjacent clearings in small family groups and flocks; such flocks rarely consist of more than twelve birds. Toucans are not intensely sociable; they never take flight in a tight group, but instead wander about in loose groups. The agile aracaris fly swiftly and in a straight line; large toucans are poor fliers. After beating their wings a few times, they hold them out and glide downward, as if pulled down by the weight of their large bills. Then they begin to beat their wings again. The flight, as a result, is both undulating and brief.

Toucans preen one another, particularly on the head and nape, with the tip of the bill. When sleeping, toucans lay the bill up over the back, and tip up the tail, forming a roof over the back and bill. One can see how advantageous such a "feather ball" is to the aracaris, which sometimes sleep five or six together in an old woodpecker tree hole or in rotted hollow tree trunks; the last bird to squeeze in enters the hole backwards, with its tail laid over its back.

Toucans utter melodious calls many times in the late afternoon, continuing when most other birds have gone to rest, but are inactive at night. They also vocalize more during morning hours, and after rains. They prefer to remain high in trees, even bathing in the rainwater pools that form in the fork of a tree or on a thick horizontal branch.

Although many species have ranges that overlap, D. Brooks found that species living in the same region have bills of different lengths and take different prey, thus avoiding competition. The only case of competitive exclusion where two similar-sized species coexist involves pale-billed aracaris (Pteroglossus flavirostris), a species that is restricted to the forest canopy in the Peruvian Amazon by chestnut-eared aracaris (Pteroglossus castanotis), which occupy forest edge almost exclusively. Competitive exclusion is assumed because pale-billed aracaris in Venezuela will use edge forest, not just forest canopy, in the absence of chestnut-eared aracaris; meanwhile chestnut-eared aracaris in Paraguay, where there are no pale-billed aracaris, remain in forest-edge habitat.

Most toucan species are year-round residents in their home range but montane species may undergo seasonal altitudinal migrations, moving downslope in fall and upslope in spring. For some lowland species there are records of huge flocks invading areas with fruiting trees after the breeding season, when fruits become scarce.

Feeding ecology and diet

All toucans forage in the forest canopy (as opposed to the understory or on the ground). Fruits (and some flowers) are a toucan's primary food. Fruits eaten include those of palms (such as Mauritia, Euterpe, Oenocarpus), nutmeg (Virola), figs (Ficus), guava (Psidium), red pepper (Capsicum fructescens), and other fruits such as Casearia corymbosa, Cecropia, Didymopanax, Phytolacca, Rapanea, and Ehretia tinifolia. Although most of the toucan diet is composed of fruit, these birds occasionally eat small mammals such as bats, plus baby birds and bird eggs. They also eat insects such as crickets, cicadas, spiders, and termites, other small invertebrates, and lizards and snakes. Toucans often drink water from epiphytic bromeliads rather than descend to the ground to drink from a pool or stream. Toucans that plunder nests to eat eggs and chicks are often mobbed by the other birds.

Though specialization on fruit may decrease with increasing body size, toucans as a group are primarily frugivorous. Remsen and his colleagues found fruit in 96.5% of all toucan stomachs they examined. Arthropod prey was found in only 5.5% of stomachs, and vertebrate prey was found in fewer than 1% of samples.

Toucans pluck fruit while perched. Getting a small berry from the tip of the huge bill into the throat is quite a task; toucans perform it by jerking the head back while the bill is open. Large lumps of food are held under the foot and reduced to smaller lumps with the bill. When the soft part of a berry has been digested, large seeds are regurgitated on the spot; smaller seeds pass through the digestive tract and are dispersed. This seed dispersal helps to regenerate the tropical forests where toucans live.

Reproductive biology

Typically the male feeds berries to the female as part of courtship. Mutual preening is also an important aspect of courtship. Toucans form monogamous pairs.

Eggs are ellipitical and white. The clutch typically ranges from two to four eggs, though as many as six may be laid in some species. The egg may be as heavy as 5% of the weight of the female in some species. Incubation lasts approximately 18 days, but this depends on the species. Both parents incubate.

Toucans nest in tree holes, usually high above the ground; the larger species prefer natural cavities in rotted trees, while the smaller ones often use woodpecker holes. Chestnut-eared aracaris will nest in abandoned tree-termite nests. Toucans sometimes drive woodpeckers away from newly excavated nest holes, and then enlarge the entrance if it is too narrow for them. The floor of the hole is typically 3–8 in (8–20 cm) below the opening. Toucans sometimes lay their eggs in the same hole year after year. The eggs lie on wood debris, or often on a lining of seed pellets that the birds have regurgitated before egg laying.

Newly hatched toucans have bare red skin that is not covered with down. Their bills are short, with the lower bill longer and wider than the top, as is the case with young woodpeckers. Thick, horny swellings on the heels protect these joints from friction. The heel pads have sharp outgrowths that may form a ring; these "tarsal calluses" fall off after the young leave the nest.

Both parents brood the naked nestlings, and parents also share the work of feeding their young. They bring some of the food in the tips of the bill, but most food is carried in the throat or esophagus and regurgitated at the nest. Parents and older nestlings clean the nest hole and carry refuse away in their bills. Young toucans open their eyes after they are three weeks old. Their feathers grow so slowly that young still show much bare skin even after they are a month old. Young of the largest species probably remain in the nest for about 50 days. Fledglings typically begin feeding themselves 8–10 days after leaving the nest.

Conservation status

The main enemies of adult toucans seem to be raptors, which sometimes catch toucans almost as large as themselves. Of the 41 toucan species, only the yellow-browed toucanet (Aulacorhynchus huallagae) is considered Endangered. The main threat to this Peruvian species is loss of habitat.

Three additional species are considered Near Threatened, however. The saffron toucanet (Baillonius bailloni) of central South America is threatened by habitat destruction, capture for the cage bird industry, and hunting to some degree. Two of the mountain toucans—the plate-billed (Andigena laminirostris) and gray-breasted (Andigena hypoglauca)—are threatened by habitat destruction in the Andes, where they are endemic.

Significance to humans

A Brazilian folk tale relates that the toucan wanted to be ruler of all birds, so it hid inside a tree cavity with only its large bill visible through the hole. Seeing the massive bill, the other birds accepted the toucan as king—until it emerged from the cavity. Then the thrush noted that despite its large bill, the toucan had a small body, and the toucan was humiliated by all birds.

Amazonian Indians use colorful toucan feathers and bills for decoration, especially those of true toucans (Ramphastos) and aracaris (Pteroglossus). In some cultures toucan flesh is relished, and the birds are regarded as trophies of sorts.

Native South Americans sometimes take young toucans from their nests and keep them as free-flying pets. The first European settlers in South America often kept pet toucans as well. Such tame toucans have been known to dominate chickens in villages and farmyards.

Species accounts

Resources

Birdlife International. Threatened Birds of the World. Barcelona: Lynx Edicions, 2000.

Brooks, D.M. "¿Son la competencia, el tamaño y la superposición de dietas pronosticadores de la composición de Ramphastidae?" In Manejo de Fauna Silvestre en la Amazonia, edited by T.G. Fang et al., pp. 283–288. Bolivia: United Nations Development Program, 1997.

Hilty, Steven L., and William L. Brown. A Guide to the Birds of Colombia. New Jersey: Princeton University Press, 1986.

Ridgely, R.S., and P.J. Greenfield. The Birds of Ecuador. Vol. 1, Status, Distribution, and Taxonomy. Ithaca: Cornell University Press, 2001.

Short, L.L., and J.F.M. Horner. Toucans, Barbets, and Honeyguides. New York: Oxford University Press, 2001.

Sibley, C.G., and J.E. Ahlquist. Phylogeny and Classification of Birds: A Study in Molecular Evolution. New Haven, CT: Yale University Press, 1993.

Sick, Helmut. Birds in Brazil: A Natural History. New Jersey: Princeton University Press, 1993.

Stotz, Douglas F., et al. Neotropical Birds: Ecology and Conservation. Chicago: University of Chicago Press, 1996.

Buhler, P. "Size, Form and Coloration of the Ramphastid Bill as Basis of the Evolutionary Success of the Toucans?" Journal of Ornithology 136 (1995): 187–193.

Haffer, J. "Avian Speciation in Tropical South America." Publication of the Nuttall Ornithology Club 14 (1974).

Remsen, James V., et al. "The Diets of Neotropical Togons, Motmots, Barbets, and Toucans." Condor 95 (1993): 178–192.

The Neotropical Bird Club. c/o The Lodge, Sandy, Bedfordshire SG19 2DL United Kingdom. E-mail: secretary@neotropicalbirdclub.org Web site:

[Article by: Cynthia Ann Berger, MS; Daniel M. Brooks, PhD]