Toucans are tropical birds found in the rainforests of Central and Southern Americas. There are about 40 species ranging in size from the lettered aracari that measures just 29 cm in length to the toco toucan that measures over 60 cm. They are distant relatives to barbets and woodpeckers.
They have short, compact bodies, rounded tails, short, thick necks, small wings, and large, colourful bills, which in some species can measure more than half the length of its body. They are noisy birds with a repertoire that includes loud barks and growls, bugling calls, and harsh frog-like croaks.
Toucans tend to have brightly coloured plumage. One of the most familiar toucans, the keel-billed toucan or rainbow-billed toucan, for example has black plumage with a bright lemon-yellow neck and chest, which gives it another alternative name, the sulfur-breasted toucan, red and white feathers above and below its tail, and blue feet. Its face is yellow and around the eye is a patch of green skin. The bill is mainly green with orange on the sides and a red tip, and measures about a third of its length.
Despite its size, a toucan’s bill is surprisingly light. It is constructed from a complex, but highly organised matrix of stiff, bony fibres with interconnecting drum-like membranes that create a spongey honeycomb of air-tight cells. The sponge is covered with overlapping layers of keratin, the same material as human fingernails, that measure about 50 micrometres in diameter and 1 micrometre in thickness.
The structure of the beak means it can absorb impacts without damage, and although there is a hollow area in the centre, about half the length of the upper and lower beaks, here it receives very small mechanical stresses.
On the sides of the bill are serrated edges that resemble teeth, which led early naturalists to believe that toucans were carnivorous and used their bills to catch fish. Now we know that they eat mainly fruit, although they will supplement their diet with insects, smaller birds, snakes, frogs, lizards, and eggs. They also prefer animal food for feeding their chicks, as the high protein content will help the baby birds grow.
Toucans grab berries and fruit with the tip of the bill which they then flip into the throat by tossing their head. If they take a piece of fruit that is too large to swallow, they will throw it up into the air several times, squashing it between their beak each time they catch it. They have long, thin feather-like tongues with fraying along each side which help them guide the food down. The fraying also appears to contain taste buds and toucans will quickly reject food if it doesn’t taste right.
Biologists have long debated the purpose of the toucan’s beak. Henry Walter Bates, the British naturalist, who gave the first scientific account of mimicry in animals, spent nearly 11 years in the rainforests of the Amazon from 1848, gathering specimens for museums and private collections. He wrote up his findings in The Naturalist of the River Amazons, with a lengthy section on the toucan and its bill:
No one, on seeing a Toucan, can help asking what is the use of the enormous bill, which, in some species, attains a length of seven inches, and a width of more than two inches. A few remarks on this subject may be here introduced. The early naturalists, having seen only the bill of a Toucan, which was esteemed as a marvellous production by the virtuosi of the sixteenth and seventeenth centuries, concluded that the bird must have belonged to the aquatic and web-footed order, as this contains so many species of remarkable development of beak, adapted for seizing fish. Some travellers also related fabulous stories of Toucans resorting to the banks of rivers to feed on fish, and these accounts also encouraged the erroneous views of the habits of the birds, which, for a long time, prevailed. Toucans, however, are now well known to be eminently arboreal birds, and to belong to a group (including trogons, parrots, and barbets), all of whose members are fruit-eaters. On the Amazons, where these birds are very common, no one pretends ever to have seen a Toucan walking on the ground in its natural state, much less acting the part of a swimming or wading bird. Professor Owen found, on dissection, that the gizzard in Toucans is not so well adapted for the trituration of food as it is in other vegetable feeders, and concluded, therefore, as Broderip had observed the habit of chewing the cud in a tame bird, that the great toothed bill was useful in holding and re-masticating the food. The bill can scarcely be said to be a very good contrivance for seizing and crushing small birds, or taking them from their nests in crevices of trees, habits which have been imputed to Toucans by some writers. The hollow, cellular structure of the interior of the bill, its curved and clumsy shape, and the deficiency of force and precision when it is used to seize objects, suggest a want of fitness, if this be the function of the member. But fruit is undoubtedly the chief food of Toucans, and it is in reference to their mode of obtaining it that the use of their uncouth bills is to be sought.
Flowers and fruits on the crowns of the large trees of South American forests grow, principally, towards the end of slender twigs, which will not bear any considerable weight; all animals, therefore, which feed upon fruit, or on insects contained in flowers, must, of course, have some means of reaching the ends of the stalks from a distance. Monkeys obtain their food by stretching forth their long arms and, in some instances, their tails, to bring the fruit near to their mouths. Humming-birds are endowed with highly-perfected organs of flight, with corresponding muscular development, by which they are enabled to sustain themselves on the wing before blossoms whilst rifling them of their contents. These strong-flying creatures, however, will, whenever they get a chance, remain on their perches whilst probing neighbouring flowers for insects. Trogons have feeble wings, and a dull, inactive temperament. Then mode of obtaining food is to station themselves quietly on low branches in the gloomy shades of the forest, and eye the fruits on the surrounding trees, darting off, as if with an effort, every time they wish to seize a mouthful, and returning to the same perch. Barbets (Capitoninæ) seem to have no especial endowment, either of habits or structure, to enable them to seize fruits; and in this respect they are similar to the Toucans, if we leave the bill out of question, both tribes having heavy bodies, with feeble organs of flight, so that they are disabled from taking their food on the wing. The purpose of the enormous bill here becomes evident. Barbets and Toucans are very closely related; indeed a genus has lately been discovered towards the head waters of the Amazons, which tends to link the two families together; the superior length of the Toucan’s bill gives it an advantage over the Barbet, with its small, conical beak; it can reach and devour immense quantities of fruit whilst remaining seated, and thus its heavy body and gluttonous appetite form no obstacles to the prosperity of the species. It is worthy of note, that the young of the Toucan has a very much smaller beak than the full-grown bird. The relation between the extraordinarily lengthened bill of the Toucan and its mode of obtaining food, is precisely similar to that between the long neck and lips of the Giraffe and the mode of browsing of the animal. The bill of the Toucan can scarcely be considered a very perfectly-formed instrument for the end to which it is applied, as here explained; but nature appears not to shape organs at once for the functions to which they are now adapted, but avails herself, here of one already-existing structure or instinct, there of another, according as they are handy when need for their further modification arises.
In The Descent of Man, published in 1871, Charles Darwin suggested that:
Toucans may owe the enormous size of their beaks to sexual selection, for the sake of displaying the diversified and vivid stripes of colour with which these organs are ornamented. The naked skin, also, at the base of the beak and round the eyes is likewise often brilliantly coloured; and Mr. Gould, in speaking of one species, says that the colours of the beak “are doubtless in the finest and most brilliant state during the time of pairing.” There is no greater improbability that toucans should be encumbered with immense beaks, though rendered as light as possible by their cancellated structure, for the display of fine colours, (an object falsely appearing to us unimportant), than that the male Argus pheasant and some other birds should be encumbered with plumes so long as to impede their flight.
However, most toucans show little sexual dimorphism in their colouring and the male’s bill is only slightly larger than the female’s, and it does not change with the seasons, unlike the puffin’s bill for example. It’s therefore unlikely to play a big part in attracting a mate.
Other explanations have been put forward. It has been suggested that the bill may be a warning to smaller birds so they can take chicks and eggs from nests undisturbed. Because it is so light it is useless for fighting so its sheer size is used to deter rivals.
The bill also helps toucans access food that would usually be out of reach, such as fruit at the end of a branch which would not be able to support their weight.
Toucans are highly sociable birds and after eating they often spend time sparring with their bills perhaps to maintain pair-bonds or to establish dominance in a hierarchy. Markings on the bill may also help individuals recognise each other.
In 2009 a completely new theory was put forward. A team of Brazilian and Canadian scientists claimed that the huge bill helps with regulating body temperature. Toucans, like all birds don’t sweat, so they need to find other ways of keeping themselves cool in the heat of the tropics.
The researchers, who published their findings in the journal Science, used a heat-sensitive camera to film toco toucans, which have the largest bills of all toucan species, growing up to 20 cm in length. The thermal camera showed that a toucan can control its body temperature by contracting blood vessels in its beak. When the bird got too hot, it released heat by sending blood to its beak, and when it got too cold it constricted the blood vessels to conserve heat. With the bill making up about 40% of a toucan’s surface area it can rapidly radiate heat, and depending on air temperature, wind speed, and blood flow, can lose anywhere between 5% and almost 100% of total body heat.
Like many animals, including humans, toucans drop their body temperature just before sleeping. Thermal images of the birds at sunset showed that their bills cooled by around 10° C as they were preparing to sleep. Once it has fallen asleep it snaps its tail forward until it touches its head covering the bill with feathers to prevent any further heat loss.
The scientists also found that the bill may also help keep toucans cool when they’re flying. The camera showed that in flight they lose four times more heat than they produce when at rest.
Juvenile toucans studied in the experiment didn’t have as much control over how much blood flows in and out of their bills. This may be because ability to control the blood vessels takes time to develop, or it may be because the blood vessels are denser in juveniles are thick and therefore harder to control.
The results showed that the toucan’s bill, relative to its size, is one of the largest thermal regulators in the animal kingdom, rivalling the ears of rabbits and elephants, who also don’t sweat, in its ability to radiate body heat.
