Food, glorious food
Food is fuel for flight, so birds have to eat plenty and often. Small birds have to eat the most. A hummingbird may eat twice its own body weight in a day.
How birds eat their food
A bird’s digestive system is adapted to get the most from its food in the shortest time. This means birds can quickly turn food into fat, to survive a hard winter or a long migration flight. A sedge warbler can increase its body weight from 10 to 18 grams in the two weeks before migration.
Fast digestion also means young birds grow up quickly. A willow warbler is ready to fly to Africa within two months of hatching from its egg.
Getting it down
Birds have no teeth, so they can’t chew their food. Instead, they just drop it down their throat. Some birds, such as pigeons and game birds, have a pouch in their throat called the crop. Here they store food when feeding in a hurry, ready to digest it later.
Most insect-eating birds use saliva to stick their food together and make it easier to swallow. Others, such as swallows use it as glue when making their nests. Cave swiftlets in eastern Asia make their nests entirely out of saliva, which hardens in the air.
Breaking it down
Inside a bird’s stomach, food is bathed in digestive juices and then passes into a special muscular organ called the gizzard. This grinds it down into smaller pieces for easy digestion. Some birds, such as ostriches, swallow pebbles to help the grinding process.
Coughing it up
Birds of prey use their gizzards to store indigestible bits of what they have eaten, such as fur, bones and feathers. They then cough them all up in a ball, called a pellet. You can find owl pellets underneath the trees that owls roost in. If you put an owl pellet in warm water, it will fall apart and you can see mouse skulls or the remains of what the owl had for dinner. Make sure you wash your hands thoroughly after touching owl pellets.
About bird beaks
Birds don't have bony jaws and teeth for eating: these would make them too heavy to fly. Neither do they have hands for gathering food, since their front limbs have become wings. Instead, they have a special lightweight tool for both jobs: the beak.
A bird’s beak, sometimes called a bill, is made out of keratin, the same as our fingernails. This means that even a huge beak, such as a toucan’s, is surprisingly light. The two halves are called mandibles. Most birds can only move the lower mandible, though some, including parrots, can move both giving them a better grip.
A beak is used for many other jobs, not just feeding. It can be a comb for cleaning feathers, or a handy trowel for digging a nest hole. It can perform delicate tasks, such as turning eggs or weaving nest material together. Woodpeckers can conduct heavy-duty hammering to get to food.
Some birds’ beaks help to attract attention. A toucan’s beak is designed to impress a female; the bigger and more colourful the better. The bright colours of a male puffin’s beak come from tiny scales that grow during spring, also to help attract a mate. After breeding, this sheath of scales falls away and the beak becomes duller and lighter.
An extra hand
Parrots have immensely strong beaks, adapted to crushing hard seeds and nuts. This strength also allows them to grip branches, acting like a hand to help them clamber through the canopy.
How birds use their beaks
The shape of a bird's beak tells you what it eats. A sparrow crushes seeds with its short thick beak; a robin catches insects with its short thin beak; a snipe probes for worms with its long straight beak; and a sparrowhawk tears meat with its sharp hooked beak. Some birds' beaks have weird adaptations to suit their diets. Here are just few:
A crossbill feeds on the seeds of pine trees, hidden deep inside pinecones. Its name comes from the fact that its beak crosses over at the tip. It uses these ends of its beak to prise out the seeds, just like a pair of tweezers.
Getting a grip
The goosander belongs to a family of ducks called sawbills, which feed on fish. The edges of its beak have fine serrations, like a saw. This helps them to cling onto their slippery, wriggling catch.
Sword of nectar
The sword-billed hummingbird, from Ecuador, has a bill longer than its entire body. It uses it to probe deep into flowers for nectar, as it hovers beside them.
Taking the strain
The beaks of flamingos have a special lining that filters the plankton they eat from the water, acting like a sieve. They first take in a beakful of water, then pump it out again with their tongue to leave the tiny food trapped inside.
Skimming the surface
The skimmer is a tropical water bird and the lower half of its beak is larger than the upper half. It flies low over the water, trailing the bottom half of its beak along the surface. As soon as it feels a fish, it flips it up and swallows it.