Food, glorious food

Young swallow calling for 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.

Fattening up

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 grammes in just 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.

Sticky spittle

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.