Because birds do not have teeth, they cannot chew their food. Birds have adapted by eating in two different ways. They either swallow their food whole or use their bills and talons to tear it into pieces.
Birds do not need teeth as they will weigh them down when flying. By using gastric juices in a specially adapted two-chambered stomach, birds can digest their food quickly, giving them the energy they need without being weighed down. Birds don’t need teeth because of their specialised bills.
Without the need for chewing, food passes from the mouth into the throat and down into the stomach. There are two parts to a birds stomach. The first part has digestive glands, while in the second part, the gizzard, the already digested food is ground by the muscles of the hard-ridged walls.
Birds have some excellent ways of catching fish. Find out more here
Birds don’t have teeth because they add extra weight, which a flying animal does not need. However, chickens have been known to be born with teeth on occasion. The saying “rare a hen’s teeth” really has meaning.
Lots of birds rely on a diet of seeds, and they can often be seen eating grit or small stones. This allows the gizzard to grind up the food faster.
Because of their small size and their need for constant energy, birds digest their food much more quickly than other types of animals.
Birds have a high metabolic rate and need an alimentary tract to digest food efficiently and quickly.
Birds have developed several adaptations to allow this. Birds have two chambers in their stomach. In this first chamber, food is finely ground down, allowing it to be rapidly ingested.
The first chamber is full of glands that make gastric digestive juice, allowing the food to be quickly digested and broken down.
Further down in the second chamber, most of the digestion takes place using enzymes. This muscular stomach is called the gizzard and is where the physical digestion takes place in many species. Birds that feed on soft fruit or fish usually let the gastric juices break down the food. The gizzard is contracted using a shunting method to crush their meal for birds that eat harder foods.
Food storage occurs in the oesophagus. This allows them to store large amounts of food due to the size, and food is swallowed in relation to its size. This is why some can eat whole fish while others only eat small insects.
As food is swallowed whole and alive, this could cause damage, but the oesophagus is lined with a protective membrane that is thick enough to withstand this.
How the crop helps
Halfway down the throat, many birds have a crop that is essentially a pouch where food that is swallowed can be temporarily stored. Because of this pouch, birds can eat much more than its stomach will hold. The crop doesn’t have digestive glands, as does the first part of the stomach, but the saliva will help soften it.
By having a crop, birds do not need to have teeth. By swallowing large amounts of food and letting the saliva soften it, birds do not need to chew their food.
Not all birds have a crop, with pigeons, parrots, some songbirds, and ducks exception. Pigeons have two sacs in their crop, which allows them to hold food and a liquid called crop milk, which they feed to their chicks.
Birds flying to their young will often hold food in their crop before regurgitating it to nestlings. When there is plenty of food around, birds will often fill their crops and their throats so full they cannot fly.
Birds don’t need teeth because of their bills
You can tell the diet of a bird by looking at the type of bill it has. There are many different types, and they are all used in different ways depending on their diet. While some birds have versatile bills that allow them to take different kinds of food, others have bills designed for a specific food.
Because birds don’t have teeth, they use their bills to get to different types of food. Birds use their bills as a replacement for having no teeth.
Thrushes have versatile bills, allowing them to pick fruit and dig worms out of the ground or take insects from leaves. A bird with a wedge-shaped bill such as a finch is designed to get to seeds. Finches fit seeds into the top mandible before pressing the lower part against it, releasing the kernel inside.
Parrots are adept at cracking nuts and have a powerful bill. They hold the nuts in their feet and use the tip to get into the nutritious centre. Toucans have a large bill to reach fruit before throwing it upwards and swallowing it whole.
Many birds feed on flying insects, and to catch them while flying, they need wide mouths and short bills. Nightjars are a perfect example of these, using their excellent agility and short bills to feed on mosquitoes, beetles, midges, blackflies, moths, flying ants, spiders, mayflies and other flying insects.
Woodpeckers use their short bills to chisel out the wood in search of insects, while nuthatches use their tweezer-like bills to get under the bark of trees.
Pelicans filter-feed, scooping up large amounts of water and food before draining the water and swallowing any remaining food.
Other birds, such as curlews, use their long bills to feed on molluscs and crabs, along with worms and insects in the mud.
As you can see, the bill on a bird specialises for catching and eating the food they live on. By utilising their different bills, birds do not need to rely on their teeth to chew food.