Birds
Toucan
Ramphastidae · also called toucans, toucanets, aracaris
A toucan’s bill looks like it should tip the bird off its perch, and it nearly does nothing of the sort — it is a rigid foam of bony struts under a paper-thin shell, a third of the bird’s length but a twentieth of its weight. The toucan uses it to reach fruit on twigs too thin to stand on, to rob other birds’ nests, and, it turns out, to shed heat like a radiator.
Overview
Toucans are the family Ramphastidae, around 40 species — toucans, toucanets, and aracaris — in the forests of Central and South America. They are mostly fruit eaters, flipping food back into the throat with a toss of the head, but also take insects, lizards, snakes, and the eggs and nestlings of other birds. They are closest to woodpeckers and barbets, not to the Old World hornbills they resemble.
The bill
Big for reach — a perched toucan can lean out to fruit on thin outer twigs — and serrated for grip, the bill is also one of the largest heat-exchange organs of any animal, shedding up to 60% of the bird’s body heat on a hot day and tucking under a wing at night to conserve it. Toucans fence with their bills and toss fruit to each other, behaviour that looks like play.
Borrowed nest holes
Despite the bill, toucans cannot excavate wood and must use natural cavities or old woodpecker holes, sometimes several birds crammed into one, tail folded over the back. Good cavities are scarce, which limits where they can breed.
Status
The family is mostly Least Concern — the toco and keel-billed toucans are still common — but several species are declining or threatened, hit by rainforest clearance, the pet trade, and hunting. As major seed dispersers, their loss slows forest regeneration.
Toucan: common questions
What does a toucan use its big bill for?
Several things, and heat control turned out to be one of the most important. The everyday use is reach and handling, since the long bill lets a heavy bird sit on a solid branch and still pick fruit from the thin outer twigs where it grows, and the serrated edges grip slippery fruit and help tear into other birds' nests. The bill is also a major cooling organ, richly supplied with blood and uninsulated, so a toucan can offload a large share of its body heat through it by increasing blood flow, and reduce heat loss at night by cutting the flow and tucking the bill into its back feathers. The bright colours probably help toucans recognise their own species and may play a role in courtship and social signalling.
How is a toucan's bill so big without weighing it down?
Because it is mostly air. The bill is built as a lightweight lattice of thin bony rods and membranes, a natural rigid foam, covered by a smooth outer shell of keratin only a fraction of a millimetre thick in places. This gives it stiffness and a large surface area at very little weight, so the bill of a toco toucan, though about a third of the bird's total length, makes up only around one twentieth of its body mass. Engineers have studied the structure as a model for strong, light, impact-absorbing materials.
Where do toucans nest if they cannot make holes?
In cavities they did not create. Toucans have weak feet for climbing bark and a bill that, despite its size, cannot chisel into sound wood, so they depend on tree holes formed by rot, broken branches, or, very often, old nest holes abandoned by woodpeckers. Good cavities are scarce, and competition for them is intense, which limits where toucans can breed. Inside, the hole is usually unlined, the parents both incubate the two to four white eggs, and the chicks hatch naked and helpless with special pads on their heels to protect them on the bare wood. This reliance on existing holes is one reason logging that removes large old and dead trees hits toucan populations hard.
What is the difference between a toucan and a hornbill?
They look superficially alike, both being medium to large fruit-eating forest birds with an oversized bill, but they are not related and live on different continents. Toucans are in the family Ramphastidae and are found only in the Americas, and they are closest to woodpeckers and barbets. Hornbills are an Old World family, Bucerotidae, of Africa and tropical Asia, and many have a hollow structure called a casque on top of the bill. The two are a classic example of convergent evolution, with unrelated birds evolving similar big-billed, fruit-eating forms to fill the same ecological role in rainforests half a world apart. One behavioural difference is that most hornbills seal the female inside the nest hole with mud, which toucans never do.