Toucans are scavengers

Beak shapes of birds

Beak shapes of birds

A contribution by Gaby Schulemann-Maier, Wildvogelhilfe team

Show your beaks! The more than 10,000 bird species that exist on earth differ not only in terms of their body shape and size as well as their plumage. Their beaks are also very different and the appearance of this part of the body reveals a lot about the way of life of the respective bird species.

As the birds developed, warm-blooded beings conquered a habitat previously populated only by flying insects and flighty lizards for the first time in the history of the earth: the air. In order to be able to fly, living beings are not allowed to weigh much, which in the course of evolution has led to special adaptations of the body structure. Birds have an extremely light skeleton with long bones and an extremely powerful respiratory system, with the help of which they can absorb enough oxygen to supply their strong flight muscles with this vital gas. Furthermore, the digestion of the birds proceeds extremely quickly, so that the animals do not have to carry unnecessary ballast with them while they are flying. Birds thus embody the ideal of extremely lightweight construction produced by nature.

The organ for ingesting food has also been perfected over time and adapted to the respective way of life of the birds and the ecological niche they have occupied. The bird's beak is the ideal solution for flying animals. Compared to the massive jawbones of mammals, it is extremely light and yet stable. In its basic structure, the beak is the same for all bird species. Your upper beak is attached to the cerebral skull and still movable, the lower beak is connected to the skull via a joint and is therefore freely movable. The beak is made of keratin or beak horn, which, in addition to its low weight, offers another unbeatable advantage: It can take on different shapes, which is why it was possible for the individual groups of birds to occupy special niches in the diverse habitats of the earth adapted beak shape to be able to easily feed and use the air as a medium in which they move.

In the past millions of years, numerous differently shaped beaks have developed, which primarily serve as highly specialized tools for the ingestion of certain food. A look at the beak of a bird species is therefore often enough to draw conclusions about its feeding habits. In this chapter we introduce the basic types of bird's beaks. Simply click on one of the following list entries to get to the short descriptions including illustrations:


Courtship beak

Many bird species not only wear a so-called splendid dress during courtship, i.e. a different colored, usually particularly splendid plumage. Their beaks also change color or form, as in the case of the puffin (Fratercula arctica) noticeable bulges. During the breeding season these seabirds, which are native to the North Atlantic, grow brightly colored beak sheaths. That outer beak cover consists of the horny substance keratin and is not only strikingly colored, but also wavy.

In order to increase the signaling effect of the beaks in their splendid plumage, the birds also have a yellow mating wart on the left and right at the base of the beak, so to speak in the "corner of the mouth". Gray-blue outgrowths form on the eyelids, which are also only present during the reproductive period. In late summer, the brightly colored beak sheath is thrown off, making the beak narrower and less noticeable. The puffins are then back in the so-called plain dress.


Extravagant beak

Some bird species have developed extremely extravagant beaks that they wear all year round and therefore not only during the courtship period, see courtship bill. They include the toucans, for example. The largest member of his family is the giant toucan (Ramphastos toco). These birds, which live in the lowlands of eastern South America, are 56 to 52 cm tall and their beak is an average of 20 cm long. For toucans to be able to fly, their huge beaks must not be massive - otherwise they would be too heavy. The striking structures consist of very light horn, which is stabilized inside by thin, bone-like struts.

Why the toucans produced such extraordinary beaks in the course of their development history has not yet been unequivocally clarified by science. Apparently, the brightly colored giant beaks seem to show particular vitality and therefore to be a meaningful signal in partner recruitment.

Similar extravagant beaks have also developed in some bird species that live in other parts of the world, such as the hornbills native to Asia. With a few exceptions, these animals, also referred to as hornbills in some literature sources, have a bulge-like attachment on their upper beak: the "horn". In many species it is hollow and therefore very light. In addition, there are horn attachments that consist of loosely structured and quite light bone tissue.

The long beak is important for hornbills when rearing their young. In order to protect the breeding female and the young from predators, the old animals wall up the entrance to the nest hole in the trees with mud or clay until there is only a small gap left. The adult birds can put their long, narrow beak through and in this way the food collected by the males reaches the walled-in female and the chicks.


Filtration beak

One of the most notable adaptations to a particular ecological niche is the flamingo's filter beak. Its construction is extremely complicated, as it has to meet the highest requirements in terms of food procurement. The special tool, unique in the bird world, allows the elegant birds to strain algae from waters such as Lake Bogoria in East Africa or lagoons in the French Camargue. In addition, the flamingos feed on small crustaceans and worms, and occasionally small fish. But how do the birds manage to get this food from the water?

To take in their food, flamingos lower their heads into the water so that their upper beak is at the bottom. With the tip pointing backwards, it lies just below the surface of the water because this is where the concentration of prey or algae is greatest. The lower beak of the flamingo has a bulbous thickening and also contains a honeycomb-like structure filled with air. This gives the beak exactly the right amount of buoyancy in the water, so that it can always stay in the best position to eat without exerting any force.

The kink in the flamingo's beak is of great importance. When open, a normally shaped beak gapes considerably wider at its tip than at its base. Thanks to the kink, the two halves of the flamingo beak are approximately the same distance apart over the entire length when slightly open. At the edges, the upper and lower bills have fine, hairy lamellae in which algae or small aquatic creatures get caught when the birds use their tongues to pump water through their beak. You then only need to loosen the food from the lamellae with your tongue and swallow it.

By the way, some duck species with similar horn structures on the sides of their beak can filter the finest components out of the water. The species that are capable of doing this include mallards (Anas platyrhynchos).


Fish eater's bill (diver's bill and thrust diver's bill)

Most of the fish-eating bird species can be recognized by their characteristic beak shape. Pointed, long beaks or beaks reinforced with an additional horn at the edge are ideal for fixing slippery prey. The small barbs on the inner edges of the beak slide under the scales of the prey, which ensures a secure hold when catching. Typical examples of comparatively short, serrated fish catcher beaks can be found in penguins, among others. These birds catch their prey by diving for it and “flying” by flapping their wings underwater. Other bird species whose beak immediately identifies them as fish-eaters are, for example, great crested grebes (Podiceps christatus) and Little Grebe (Tachybaptus ruficollis). In contrast to the penguins, they do not flap their wings when diving underwater, but rather get their propulsion underwater mainly through the movements of their webbed feet.

The long and pointed shape of the beak of many feathered fish catchers can also be found in representatives of the kingfishers family and in terns, as well as in gannets, which catch their prey as shock divers. This means that they stay above the surface of the water, sift them for prey and then suddenly push through the surface of the water from above. Kingfishers dive in relatively far. This also applies to boobies. The fact that its beak is long and pointed doesn't just make it a good tool for catching fish. It is also ideal for shock divers because it has a streamlined design. When diving into the water, the birds first touch the surface of the water with the narrow tip of their beak, with hardly any water splashing on most of the time. Only in the further course of the immersion process do the somewhat wider areas of the beak follow, which is largest at the base of most shock divers.


Fish eater beak with hook

Some species of birds that feed on fish have a modified form of the typical fish-eater's beak. With them, the tip of the upper bill is slightly bent downwards at the front. This means that these birds have a barb on their beak, which should probably make packing the slippery prey much easier. Bird families with such a beak shape include cormorants and frigate birds. The latter rarely actively hunt for live prey. Mostly, like aerial pirates, they attack other seabirds that transport fish in their beak or crop. The large frigate birds attack the other birds until they spit out the prey. Often the dead fish is caught in the air, but sometimes it is fished off the surface of the water if it falls back into the water. The hook on the upper beak is particularly helpful here.

With the cormorant (Phalacrocorax carbo) and in its relatives the upper beak has a downwardly curved tip, which makes it easier to hold on to the prey, © Gaby Schulemann-Maier
Ariel frigate birds (Fregata ariel) pick up easily dead fish from the surface of the water that they have previously chased away from other birds, © Gaby Schulemann-Maier

Flat duck bill

The beak of numerous water bird species from the duck-like group, which includes ducks, geese and swans, is flat and wide. The beaks of these birds have fine lamellar structures on the lateral edges with which they can easily grab and tear off, for example, aquatic plants, but also vegetation on land (e.g. grass). In addition, these lamellae help them to filter the finest food components out of the water. By taking a little water in the beak and then squeezing it out to the side through the two almost completely closed beak halves, these waterfowl ensure that fine parts of plants or the like stick to the lamellar structures. All you have to do is swallow your food. This type of feeding in ducks is also known as gudgeons.

Mallards (Anas platyrhynchos) have fine lamellae on the side at the edge of the beak that help with pounding, © Gaby Schulemann-Maier
This Canada goose (Branta canadensis) the fine lateral lamellae on the beak are just as visible as the bristle-like structures on the tongue, which help to hold the food in place, © Gaby Schulemann-Maier

Hooked beak

In the bird world, for example, parrots and birds of prey have what is known as a hooked bill, which, however, is shaped slightly differently in these two groups. In both cases, it is typical of the hooked bill that the upper bill is more or less strongly curved and is significantly longer than the lower bill. The latter is often hardly or not at all to be seen when the beak is closed, because it is largely covered by the upper beak and the beard feathers.

Many species of parrots feed on seeds and fruits in the wild. Your upper beak has transverse grooves on the inside, which make it easier to fix the food with the lower beak. Because of these grooves, seeds do not slip out of the beak as easily, while the birds skillfully remove the seed coats with their lower bills. The parrot's beak is also sometimes called the crooked beak. Especially in macaws, it is extremely strong and very strongly curved. These large parrots, native to the South American continent, are easily able to crack hard-shelled food such as Brazil nuts.

The sharp hook at the lower end of the upper beak also serves as a climbing aid for the parrots, with which the birds can find support almost anywhere. Therefore, the beak is not only the most important tool for ingesting food for them, but is also the “third leg”, so to speak.

Birds of prey use their strongly curved hooked bill especially when dividing food and often not to kill their prey with it. The name bird of prey is to be taken literally: They grab hold of their sharp claws and later use their beak primarily as an aid to ingesting food. Birds of prey that have a hooked bill include, for example, eagles, buzzards, falcons and owls, all of which mainly hunt for live prey. However, some birds of prey sometimes inflict a fatal bite on the captured and still living prey with their powerful hooked beak, compressing the victim's windpipe or breaking the neck. In some cases, the prey is then plucked or torn open with the pointed beak in order to cut it into beak-sized pieces. Small prey such as mice, on the other hand, are swallowed in one piece.

Carrion-eating birds of prey such as the vulture and the New World vulture have strong hooked beaks. However, they are sometimes not strong enough to open larger carcasses themselves. In the African savannah, for example, vultures often wait until other carnivores - lions or hyenas - have opened the carcasses of dead elephants, rhinos and other large animals. Only then can their hooked beak be used to break up the relatively soft tissue inside the body.

It is also noticeable that the hooked beak of carnivores and fish eaters is usually shorter among birds of prey than is the case with scavengers. This is likely to be a further adaptation of the vultures to their food acquisition, because they often have to stick their heads into openings in carcasses and the further they go with their beak, the more meat they can reach and thanks to the downward curvature they can literally latch into. An elongated beak is therefore of great use to them.


Landing net

If you live on fish as a water bird and also have a stately, heavy body, you need relatively large amounts of food every day in order to provide yourself with sufficient energy. Beaks that are used to simply snap at fish are usually not efficient enough to do this. That is why the evolution of the pelicans took a peculiar and ingenious path: They designed the "landing nose", a long beak to which a large, highly elastic throat pouch is attached. This is the case with the Great White Pelican (Pelecanus onocrotalus) so big that around 13 liters of water fit inside.

Pelicans often patrol over fish-rich waters at a height of a few meters when they are looking for food. As soon as they spot their prey, they change their flight direction and rush headlong towards the surface of the water. If their heads are submerged in the water, they open their beak and the throat pouch in a flash, which creates a negative pressure and ideally sucks the prey into its interior. The birds quickly close their beaks and swim to the surface to let the water run out of the throat sac while the prey remains in it. Sometimes the food is also netted floating. In order to be able to fix the caught fish even better, the beaks of the pelicans have fine hooks on the edges.


Crossbill

The family of the crossbills is a real specialty in the bird world. In the course of development, birds like the crossbills, which are native to large parts of Europe (Loxia curvirostra) specializes in picking the nutritious seeds from the cones of spruce, larch and pine. Their ancestors had a typical straight pointed beak, but an asymmetrical pointed beak is better than a symmetrical, straight pointed beak to get the coveted food. In the past, those ancestors of the crossbills whose bills were not perfectly symmetrical had an advantage over their straight-billed conspecifics in the competition for food, so that over time an extreme asymmetry developed. This means that with crossbills, the upper and lower bills do not lie on top of one another over their entire length as in other pointed-beaked bird species. The two halves of the beak cross at their ends, which means that the birds can easily get to the coveted seeds in the cones (seed heads) of conifers. The crossed beak can be ideally used as a lever to bend up individual scales of a cone, while the animals skillfully extract their favorite food, the fine seeds, with their tongues.


Tubular beak

A very characteristic beak shape has developed in those bird species that specialize in slurping nectar. About 340 species of hummingbirds live in North, Central and South America and the Caribbean, all of which have long, slender beaks. The same ecological niche is occupied by the nectar birds in other parts of the world, but hummingbirds occur exclusively in the New World and they are not closely related to the nectar birds.

If you compare the individual hummingbird species with one another, their beaks look quite different at first glance. However, the variability of the beaks is comparatively low compared to that of other bird groups. In most hummingbird species, the beak reaches a length that corresponds to about a third to a quarter of the head-trunk length of the animals. The beak of hummingbirds is either straight or slightly bent down so that the birds can optimally get to the nectar of the plants in whose food supply they have specialized in each case. In the nectar birds from Africa and Asia, on the other hand, the beak is usually slightly bent downwards.

Unlike the hummingbirds, the nectar birds do not have a real hovering flight. In this special type of flight, hummingbirds fly in the air before a flower and drink nectar. In the meantime, they often come into contact with the pollen of the plants and carry it on. Thus, hummingbirds are important pollinators of numerous plant species. In the high Andes there are few or no insects that could take over the pollination, where hummingbirds are the most important allies of the plants when it comes to pollination.

The long, tubular beak of the hummingbird serves as a tool for the birds to drink the sweet sap from flowers with deep nectar springs, © Gaby Schulemann-Maier
Nectar birds like this malachite nectar bird (Nectarinia famosa) have a curved pipe beak for drinking nectar; they are not related to hummingbirds, © Derek Keats via Flickr

Pointed beak

Quite a number of birds have pointed bills. Typical of this beak shape is that the upper and lower beak are of equal length and taper to a point in front. Overall, pointed beaks can be constructed differently in terms of their width at the base or over the entire length. This variation in the shapes of the pointed beaks stands for certain eating habits.

Conical beak