Spoonbill bird beaks

Bills, Bills, Bills! Form and Function in Bird Beaks

Anyone who has spent even a short time watching birds will have noticed the huge variety in bill size and shape between (and sometimes even within) species. From toucans with their huge, oversized bills to the tiny, needle-like ones of most warblers, there are beaks from one extreme to the other. The main reason for this diversity is that different species have different feeding strategies. Put simply, over time, their beaks have adapted to help them fill particular ecological niches. This means that just by looking at a bird’s beak, you can tell an awful lot about what and how it eats. Read on to find out more about some of these amazing bird beaks.

What Are Beaks?

They may look like noses, but beaks (or bills; the term is interchangeable) are actually modified jaw bones. This means that they are largely made of bone rather than the cartilage that makes up mammal noses. The beak’s bony inside is covered by a sheath of keratin. This is the same substance that constitutes our hair and nails. Beak colour is determined by this outer layer, although it isn’t fixed and can change in some species depending on what time of year it is. Most birds have two nostril-like holes in the beak called nares.

Puffin bird beaks
Puffins only sport colourful beaks in summer. In winter, they are largely grey

Although birds of course use their beaks primarily for feeding, they also help them in other ways. Some birds use them to advertise their suitability to the opposite sex. This is probably why Atlantic puffins grow a colourful bill for the breeding season but shed the outer plates to sport a dull, grey beak in the winter. Toucans’ large beaks help them keep cool in the tropics. The size increases blood flow which in turn helps more heat radiate out and away from the bird. Birds also use beaks to communicate, fight off rivals or predators and help them preen. Lastly, beaks act as a third ‘hand’, helping replace the two limbs that became wings. As such, birds can perform incredibly dextrous actions, such as nest-building, with their beaks.

Black-headed weaver bird beaks
Black-headed weavers use their beaks to make beautifully intricate nests

All Manner of Beaks

Following the discovery of Archaeopteryx in 1861, palaeontologists began suggesting that modern birds evolved from dinosaurs. However, it wasn’t until the last few decades that fossil finds in China proved this link conclusively. More recent research still has revealed some of the specific evolutionary steps involved, including how dinosaur jaws might have evolved into beaks. Millions of years of evolution later, and those first beaks have diversified into almost every shape and size imaginable, largely to help individual species deal with particular food items.

Bar-tailed godwit and curlew bird beaks
Two waders with quite different beaks: bar-tailed godwit (left) and curlew

Famously, Charles Darwin recognised this link between natural selection and food availability in the finch specimens he collected in the Galapagos Islands in 1835. Once ornithologist John Gould had identified them as 12 related species, Darwin suggested that they had all evolved from one original pioneer species. They had then developed different beak shapes depending on the food available in each area they settled in. So, what do different species’ bill shapes tell us about their feeding habit today?

Cracking Seeds and Nuts

It’s not just finch species in the Galapagos that have different beaks and different feeding strategies. Although fairly closely related, finches in the UK have also evolved to fit slightly different niches. Although youngsters are often fed protein-rich insects, adult finches all eat seeds. Thick, short, cone-shaped beaks help them extract these seeds from cones, fruits or seedhead. Crucially, different species favour certain plants to avoid competition with each other. Their beaks reflect this beautifully.

Goldfinch bird beaks
This goldfinch’s cone-shaped beak helps it feed on teasel and thistle seedheads

Hawfinches, for example, have extremely large, sturdy beaks. These help them cope with hard seeds such as beech mast, cherry stones and hawthorn seeds. Siskins, meanwhile, have much smaller daintier beaks to help them extract seeds from the fiddly gaps in pine, spruce and alder cones. Goldfinches have medium-sized beaks designed to suit dandelion, thistle and teasel seeds. Crossbills have the most specialist beaks of all our finches in the UK. As their name suggests, their bills cross at the end. This arrangement makes the perfect tool for separating pine scales to get at the seeds.

Crossbill bird beaks
This crossbill’s crossed mandibles are used for prising out pine seeds

Catching Insects

Insectivorous birds likewise have different beaks depending on how they get hold of them. Warblers, such as blackcaps, chiffchaffs and willow warblers, have small, thin, tweezer-like beaks. These enable them to pick tiny insects off leaf-surfaces as they move through trees and shrubs. Treecreepers likewise have thin, dainty beaks but theirs are curved, enabling them to reach insects from small bark crevices. Flycatchers, martins, nightjars and swifts, meanwhile, tend to have short, flat beaks that combine with a wide gape to help them catch insects in flight.

Wood warbler
Like all warblers, wood warblers have thin, pointy beaks for picking insects off leaves
Treecreepers use their thin, curved beaks to get into bark crevices

Some birds have to use a bit more brute force to feed, and this too is reflected in bill size and shape. Starlings are fairly generalist, eating pretty much anything. Insects in the soil and under stones form a large part of their diet, however, and their fairly long, pointed beak helps them do this. When probing the ground, strong muscles allow them to partially open their beaks and grasp prey. Rooks also probe the ground for food with their large, strong bills. Great spotted woodpeckers have the ultimate brute force tool when it comes to insectivores. Although they readily eat nuts and fat at feeding stations, their beaks are specially adapted to hammer at bark and get at beetle grubs hidden underneath.

Great spotted woodpecker bird beaks
Woodpeckers have strong, chisel-like beaks for hammering into wood

Fishing and Meat-eating

Those fish-eating birds that hunt with their beaks rather than their feet often have long, spear-like bills. These aren’t exclusively for catching the fish themselves, but also help them break the water efficiently. Herons, gannets and kingfishers all fit into this category. Sawbill ducks, such as goosanders and red-breasted mergansers, have serrated bills edges to help them hold the fish. Pelicans, such as the Dalmatian pelican which became extinct here around the time of the Roman occupation, have a different strategy. They use a large, pouched structure attached to the lower mandible to scoop fish up. They then contract muscles in the pouch to squeeze out all the water also brought up.

Goosander feeding
Goosanders and other sawbills have serrated bills for holding fish firmly
Brown pelican
Like all pelicans, this brown pelican has a large muscular scoop on its lower mandible

Birds of prey are almost exclusively meat-eaters, so their beaks and talons need to be able to pierce the relatively tough skin of their prey items. They all have strong, curved, sharp beaks as a result. These help them tear up meat for themselves, as well as feed their young with manageable portions. Falcons have an extra adaptation, helping them make up for the fact they are smaller than other raptors and lack the strength to always out muscle their prey. A tooth-like projection on the top mandible called a tomial tooth aligns with a divot in the lower mandible, forming a strong cutting tool. They use this to severe their prey’s spinal cord and kill them instantly.

Peregrine falcon bird beaks
Peregrine falcons can break their prey’s spinal cord with their beaks

Filter Feeding and Sweeping

Some water birds, including many ducks and swans, are filter feeders. As they swing their heads side to side through the water, small crustaceans, insects, seeds and fish are trapped by tiny, comb-like structures attached to the bill. Some birds will also push water through these lamellae with their tongues to speed up the process. The shoveler, with its wide, spatulate bill, is particularly well-adapted to feeding in this way. Flamingos are one of the most unusual filter feeders. Famously, they hold their heads upside down in the water to feed. As a result, their bill structure is opposite to that of most birds, with their lower mandibles stronger and larger than the upper.

Shovelers use their wide beaks for filter feeding
Greater famingo
Flamingos have larger lower mandibles than upper, as seen in this greater flamingo

Spoonbills also sweep their long, spatulate beaks through shallow water. However, instead of catching prey indiscriminately and filtering it out, they have sensitive cells called papillae in their beaks to help detect prey items in murky water or at night. Once they sense their target, usually small fish, crustaceans and aquatic invertebrates, they lift it out of the water and throw it back into their throats. Avocets also sometimes use touch to locate prey. This beautiful wader often picks small invertebrates from the water surface. But if unable to see well, it sweeps its thin, upturned bill from side to side through mud or water to seek out prey.

Two spoonbills feeding
Avocet bird beaks
Avocets have upturned bills for scything through water

Probing for Food

Many wader species probe for food, both in mudflats at the coast and fields inland. By sporting a vast array of different bill shapes and lengths, they are all able to access food at different levels within the soil or mud, avoiding competition. Curlews, for example, have long, curved bills that are able to reach deeper than any other UK wader. The curvature may also help them reach more food when picking between stones and seaweed. And female curlews have beaks that are up to 18% longer than male bills. This is likely to be so that they avoid competing with each other. For instance, during very cold weather, coastal lugworms retreat further below the surface. There is a possibility that females can still reach them at these greater depths while males are forced to find earthworms inland instead.

This curlew is using its long, curved beak to good effect

Another probing adaptation is the ability to open the tip of the top mandible independently of the rest of the bill. Many of our wader species are able to do this to some extent, but it is most noticeable in those with longer beaks such as curlews, godwits and snipe. Called rhynchokinesis, this flexibility gives them the dexterity to catch small prey items in the mud, even though they can’t see anything. The tips of their bills are also full of sensors. These detect movement within mud and murky water, even that of invertebrates a few centimetres away.

Snipe can open the tip of their bills independently of the rest of the beak to help them grab prey

Beautifully Adapted Beaks

These are just some of the incredible adaptations illustrated by bird beaks, with most of these examples UK species. Further afield, there are a whole host of other developments, of course, from the nectar probes of hummingbirds and honeyeaters to the huge, clog-shaped beak of the shoebill, designed to catch large waterborne prey including fish and baby crocodiles. And then there are the generalists. These are birds, such as members of the corvid family, who take advantage of whatever food source they can lay their beaks on. Generalists tend to have in-between beaks that are just long and strong enough to cope with all sorts of situations. So, next time you look at a bird, remember that its beak can give you an insight into what it eats and how it lives its life.

Anna's Hummingbird
Hummingbirds, like this Anna’s hummingbird, have thin beaks for accessing nectar

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