Have you ever wondered why hen’s teeth are so rare? Close inspection of a bird's bill and digestive system might reveal some surprises, but it won’t reveal any teeth. Instead, birds have evolved complex bills, digestive systems, and behaviors to make feeding possible.
Birds do not have true teeth, but there was a time in their evolutionary history when they did. Since then, the birds' bill has evolved into a staggering array of different shapes and sizes, unique to each species of bird. Amazingly, the gene for tooth growth is still present in modern birds. Scientists have proven this by manipulating chicken genes, producing a mutant fowl with a beak full of teeth.
We don’t know exactly why modern birds lost their teeth, but it probably had something to do with shaving off weight and reducing incubation times. The loss of their teeth clearly worked for birds that are now able to thrive thanks to their specialized bills and digestive systems. This is proven by the abundance and diversity of birds seen today.
Some modern birds do have structures in their bills that look very much like teeth. Geese, for example, have sharp serrations on their teeth and tongue that are used for cutting grass and plant matter. These structures are known as tomia and they do perform some of the functions of teeth. Tomia are not classified as teeth, however, because they lack dentin, enamel, and the other tissues of true teeth.
Read along as we learn more about why birds don't have teeth, and how they survive without them.
Close up of a goose beak, where you can see the tomia
Birds are believed to have evolved from dinosaurs about 150 million years ago. At the time, dinosaurs had teeth, and this was passed on to the early birds.
Research shows that birds had lost their teeth by about 100 million years ago, however. We don’t know exactly why birds lost their teeth all those millions of years ago, but some interesting theories have been put forward.
Keep reading to learn some of the possible causes of teeth loss in evolving birds.
One of the most obvious reasons for birds to lose their teeth is to minimize weight. Birds show many other weight-saving strategies which are very important for flight. Teeth are heavy, and the strengthened skull and powerful muscles required for chewing are equally significant.
This theory could be partially true, but it certainly is not the whole story. We know this because many of the early birds had both teeth and the power of flight.
Another interesting theory on why birds lost their teeth concerns the development of baby birds. The idea is that since teeth take a long time to grow and develop, they increase the amount of time that eggs need to be protected and incubated by the parents.
By forfeiting teeth, birds may have increased the survival rate of both eggs, and the parent birds.
Red-breasted Merganser - ducks also have have tomia, which are helpful for cutting grass and plant matter
Birds have bills that are often highly specialized for their diets and behaviors. There are a staggering array of different bill shapes, including some rather remarkable shapes and sizes. Some bird bills have structures on them that resemble teeth, and these are known as tomia.
Geese, for example, have serrated tomia that run the length of their bills and help them cut the grass and plants they feed on. Falcons have a pair of tomia on their upper mandible, which is used to kill their prey.
Hatchling birds also have a structure on their bills that is known as an egg tooth. The egg tooth is not a real tooth at all but rather a sharp hardened point that the hatching bird uses to break free from its shell.
Close up of a American Robin fledgling, with visible egg tooth
We chew our food to begin the process of digestion and make our food much easier to swallow. Birds lack teeth and strong jaw muscles, so how do they chew their food? To answer this question, we first have to look inside the body of the bird, instead of its mouth.
Birds that feed on hard foods like seeds must have some way to break their food down and make it more digestible. This process begins in the crop, a sort of food storage organ.
Food is not digested in the crop, but it does soften up a little while it is stored. The food passes from the crop into the stomach where highly acidic digestive juices begin to break down the food. This softened food then moves into the gizzard, where it is ‘chewed’.
The bird gizzard is a powerful organ that is lined with a tough, coarse tissue known as koilin. Food is crushed in the gizzard with the help of small stones and grit that birds swallow.
Close up of a house wren eating a bug
Birds use their bills, tongues, and gravity to collect food and manipulate it into their digestive systems. They do not have hands like we do, so their specialized bills are used with amazing dexterity.
How birds swallow whole food items can be very important for preventing choking. Fish-eating birds like kingfishers, for example, usually swallow their prey head first for this reason.
Birds typically pick up a morsel of food and throw their head back to swallow it. Most birds swallow their food whole, but seeds often need to be crushed, and large animal prey needs to be torn into strips.
Male American Goldfinch eating seeds
Birds feed on a huge variety of different food sources, from liquid nectar to tiny seeds, large fruits, and animals even larger than themselves. Each of these diets requires a different strategy for animals without any teeth!
Most birds get by without teeth by focusing on food sources that can be swallowed whole. Some birds, like parrots and raptors, are able to crush and tear their food into manageable portions that can be swallowed, however.
This ability is really important for birds that feed on large prey, but the ability to tear food is equally important to birds that eat grass or feed from large fruits.
Bald Eagle tearing up salmon
Birds require a surprisingly large amount of food each day. Smaller birds tend to require more food than larger birds, often as much as thirty percent of their body weight each day!
Birds need so much food because they have naturally high body temperatures and require a large amount of energy to fuel their flight. Birds will not pass up a meal without eating their fill and will store excess food in their crop before being digested.
A male and female western bluebird pair feeding on seeds
Chickens have relatively unspecialized bills designed for picking up seeds, insects, and other small morsels. Chickens do not have any teeth. They use their powerful gizzards instead to grind up their food.
Crows do not have teeth. These intelligent birds have large ‘general purpose’ bills that they are able to use in a variety of ways. In fact, research on New Caledonian crows (Corvus moneduloides) suggests that their bills are at least partially adapted to tool use.
Parrots have sharp and powerful bills that make up for their lack of dentition. Their bills are highly specialized and designed for crushing and manipulating food, as well as helping the birds climb.
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