Some birds can fly, some can swim, and some can run super-fast.
Through evolution, birds have developed hollow bones, feathers, and wings. They also have warm blood, a unique respiratory system, and large hearts. All species of birds have these special characteristics.
9 Major Characteristics That Define Birds
Birds are called glorified reptiles. They have evolved from bipedal reptiles and still share many characteristics in common. There are proofs showing birds are direct descendants of dinosaurs.
Most of these characteristics are universal to all known bird species of the world. Others have few exceptions.
- Use of Feathers
Having feathers is a unique feature of birds. All birds flying or flightless have feathers. But no other animals have feathers. Bird feathers are made of keratin. Keratin is also found in the hair and nails of other animals.
Scientists believe it was one of the most needed evolutions for birds. Millions of years ago, the environment of the earth changed. The temperature dropped. So, the ancestors of birds evolved to get feathers to control their body heat.
Later, feathers turned out to be convenient for flying. Although feathers look soft and vulnerable, they actually protect birds in many ways. It protects birds from rain and bad weather. Many birds naturally produce oil from a special gland under the feathers. They apply this oil to their feathers to make them waterproof.
Different birds have different types of feathers. They have various shapes and sizes. For example, Contour feathers and flight feathers assist birds to fly. These kinds of feathers are common in hawks, falcons, and even pigeons.
Besides, many male birds of different species use their feathers to attract female birds. For instance, male peacocks have more beautiful and colorful feathers than female peacocks.
Birds shred their old wings once or twice a year. It depends on the species of the bird. This way, they can recover from any external damages on feathers.
- Warm Blood
Birds are endothermic. It means they can produce their own heat to keep their body warm. Feather help birds to adjust their body temperature. The feathers entrap warm air under the feathers when they feel cold. The high metabolism system and complex respiratory system also take part in warming blood.
The muscles of the wings give the birds ability to fluff and trap more heat. Again, when birds feel hot, they compress their feathers. Therefore, heat cannot pass through the feathers.
- Flying Ability and Wings
All species of birds have wings. Unfortunately, not all of them can use their wings to fly. They may not use wings for flying, but there are other uses of wings.
Similar to feathers, wings also have various shapes depending on the bird species. The shape of the wings is defined by their use. Thus, the feathers on the wings are arranged in different ways. Apart from flying, birds also use wings for swimming, attracting opposite sexes, and threat displays. They puff and ruffle their wings to look larger and scarier.
The shape of the wings is crucial for the flight capability of birds. For example, hunting birds like falcons or hawks have developed sharp-tipped wings. These narrow wings allow them to gain more speed while flying. Then, there are penguins. They use their flipper-like wings to swim in the water. But they cannot use the wings for flying.
The size of the wings is crucial for flying. Birds like owls and hawks have much larger wingers compared to their bodies. These large wings let them fly swiftly. The feathers of their wings are designed to make very little sound.
On the other hand, birds with small wings and large bodies cannot fly. Their wings fail to carry their body weight. Ostrich and emu have a heavy body with thick feet. Their wings are small and weak. Even tiny birds like Kiwi cannot fly due to wings being smaller than its body.
Birds like penguins use their wings to swim. Even though they are quite pathetic on land. They are excellent swimmers and can swim at a speed of 4 to 22 mph depending on the species.
- Beaks or Bills
This is another unique feature of birds. All birds have a bony beak. It is covered with a keratin layer. This keratin is much stronger. So, the beak of a bird is quite strong. Different species of birds have developed their beaks based on the environment they live in. The food they eat shapes the structure of their beak.
Seed-eating birds like the chicken have a cone-shaped beak. On the other hand, hawks and falcons have sharp and hooked beaks. They need it to tear the meat of their prey. Then, there are ducks that use their flat beaks to catch fish. A pelican has a large bill. So, it can carry a lot of fish inside its beak at once.
Again, some birds have developed beaks with tomia. These are tooth-like sharp serrations on the edges of the beak. It helps them to grab on to their food. They even use the beak to feed hatchlings. Swans have tomia. They can get aggressive sometimes and bit people.
Birds also use their beaks to build their houses. They catch tree branches and twigs to build their nest. Woodpeckers use their strong beaks to dig holes in trees. Moreover, birds use it to fight against threats.
- Laying Eggs
All kinds of birds lay eggs. But the shapes, sizes, and colors of the eggs vary from species to species. Some birds lay multiple eggs. Others lay only one or two eggs. However, all eggs have a shell made of calcium similar to the ones found in bones. Inside of the egg, there is the egg white and the yellow yolk.
The shell is strong enough for the embryo, but they are still fragile. The eggs also need different incubation times. Female birds build a nest far from prying eyes to incubate the eggs. They sit on the eggs to maintain the temperature essential for hatching the babies. The bigger the bird species is, the longer it takes to incubate.
Laying eggs is a very common trait that birds still share with their reptile ancestors. But the eggs have also become smaller like the birds.
- Respiratory System
Birds have a very complex respiratory system. This system enables them to fly thousands of kilometers without taking a break. It provides them with the necessary oxygen required for such long flights.
Birds have very special and efficient one-way air passageways. It has only one lung. They take air through the external nares. Nares are near the beak. The air goes through the Trachea and directly fills the posteriors sacs with air. The posterior sacs then push the air towards the lung.
This way, birds can hold in more oxygen. The air sacs or pockets surround the lungs. They are also the reason why birds are so light. So, for this system, birds can get more oxygen as well as physical support to fly thousands of miles.
- High metabolism
Birds need a lot of energy to travel long distances. So, with a high supply of oxygen, they also need food to produce energy. To turn the food into energy, they have a high metabolism system.
Birds have large hearts compared to their body size. It is also muscular. There are four chambers inside the heart. The chambers keep the oxygenated and deoxygenated blood separate. The heart pumps oxygenated blood through the body and pushes the deoxygenated blood towards the internal sacs. Thus, it keeps producing energy by supplying oxygen.
Both the respiratory system and the heart of the birds work together to give birds the agility they need. Hence, birds are capable of flying all day with ease.
All kinds of birds have backbones. Thus, they are under the phylum Chordata. They are bipedal. It means they use two feet to walk on the ground. Most of the species have hollow and light bones. Also, the bones are fewer in number compared to other animals. Consequently, they cannot move all their limbs freely.
However, the light bone structure is necessary for flying. They developed this kind of bone to adjust their flying skills. At one point, it became essential for their survival. Birds have sturdy feet, and so they can add momentum when they take flight.
Then again, some birds cannot fly. So, they had to evolve to grow stronger and rigid bones. The ostrich has strong leg bones to fight and run from its predators. Penguins have a rigid bone structure. It has marrow in the bone joints to survive in the cold environment. If you have noticed, their heavy bones are also the reason they cannot fly.
Birds have sharp claws. They are made of protein keratin. The claws are hard and sharp. Birds use the claws and their strong feet to catch their prey and hold onto things.
All birds have large eyes. In fact, some birds have larger eyes than the eyes of humans. The eyes of birds weigh about 15% of their head. For humans, it is only 1%. The size and position of the eyes developed with their use.
Birds have bones in their eyes. It is called the sclerotic ring, and it surrounds the pupil. As a result, birds have great control of their Irish muscles. The predatory birds have eyes located on the front as they hunt a lot. Pigeons can rotate their eyes nearly 360 degrees to stay careful about dangers.
So, most of the bird species have good vision. Furthermore, they can cover a lot of areas with their large eyes when they are flying. Actually, birds have better vision than most animals. Interestingly, they see things in color, not in black and white.
Each species of bird has its own unique sound. Birds communicate with each other through their vocal sounds and beautiful singing. Some birds make screeching sounds while others have a melodious voice.
You may think the sounds are not that different, but scientists have found a difference in their voice frequency.
Birds use their voices to communicate with each other. They even make elaborate songs and tunes. Some species even use special sounds during mating season. For example, a male Bewick can sing 20 different songs. They also use sounds to call on their hatchlings, scaring off enemies, and warning.
Some species of birds are capable of communicating through non-verbal signs. In various situations, they ruffle their feathers to show interest, fear, and antagonism. For instance, roosters ruffle and puff their feathers when they go into fights.
Out of necessity, birds have evolved to become what they are now. They have abandoned their predatory instincts and adopted new ones to survive in this world.
There are about 10,000 species of birds! They live all around the world. Some are small, and some are large. They all have their unique lifestyles and habitats. However, they also have some common features as they evolved from the same ancestor.
Why Some Birds Can Not Fly?
Among the 10,000 bird species in the world, some groups of birds cannot fly. These flightless birds live all around the world. From Australia to African Savanna to Antarctica, you will see earthbound birds. They include all species of penguin, some swamp dwellers, ostriches, emus, some species of duck, and the little Kiwis.
All of them have wings, but none of them can fly. Interestingly, flying is not mandatory to fall under the class of Aves. Surprisingly, these species of birds were also flying birds millions and thousands of years ago.
The common ancestor of all birds could fly. However, some of the descendants lost the ability to fly for various reasons.
- Change of Environment
Flying is extremely beneficial. Interestingly, millions of years ago, the reptile ancestor of the birds gradually developed wings to escape predators. Flying also became essential for hunting. Thus, birds got strong wings and crossed long distances.
But, flying can also be exhausting. It requires high energy, light bone structure, and a small body. When some of the species found a secure place without many life threats, they stopped flying. After thousands of years of evolution, the birds’ bodies changed to adjust to the new environment.
- Change of Bone and Muscle Structure
The lightweight bones of earthbound birds became dense. Since they did not need to fly anymore, they needed stronger bones to survive on the ground. Their wings shrunk. In some cases, the wings completely disappeared. As a result, the flight muscles and keel also disappeared from their body.
Penguins managed to hold on to this trait. But they did not use the muscles for flying. Instead, they use their muscles for swimming.
Due to the loss of flying, many species of birds became endangered. Most flightless bird species lost their ability to fly when they traveled to remote islands with no predators to hunt them. In this environment, they not only survived but also grew in number.
As time passed by, the islands were inhabited by humans and their pet animals. The birds became the source of food for the settlers. As the birds lost the ability to fly, they became easy prey. Thus, many species of birds went extinct.
- Change of Size
Some species of flightless birds still managed to survive in harsh conditions. Again, they evolved. This evolution further stopped them from flying. To survive in a place full of predators, these species of birds become bigger and bigger. For example, ostriches can grow up to 7 to 9 feet tall.
They evolved for millions of years. The emus and Ostriches grew big. They could weigh hundreds of pounds. Moreover, their wings become smaller. Hence, the wings cannot lift the heavy body. Their legs also become thick with muscles as they use them for defense and running.
Even if flightless birds do not use their wings for flying, they still use them in other ways. They use the wings to stir their direction while running. They tuck themselves or their hatchlings under the wings to protect them from harsh weather.
What is the Earliest Bird Species?
All birds are descendants of meat-eating theropod reptiles. They were small dinosaurs. So, it is certain that these dinosaurs have to undergo extensive changes to look like today’s modern bird. The earliest species of birds is the Archaeopteryx.
Herman von Meyer first published writings on the fossils of Archaeopteryx in 1861. Archaeopteryx means “ancient wings”. The fossil was a skeleton of an animal with feathers. This bird-like animal lived nearly 150 million years ago. It has the characteristics of both theropod dinosaurs and modern birds.
Throughout the 20th century and 21st century, more fossils were found in Germany. The fossils allowed scientists to look into the past of the evolution of modern birds.
Let us see some of its features to understand how different it was compared to modern-day birds:
The fossil of Archaeopteryx, tells a lot about this early bird. It was evolving, but it still resembled a small dinosaur a lot. However, it had feathers similar to modern-day birds, which were well-developed.
It had a considerably small size like a magpie. They were probably half a meter long and weighed only 1 or 1.5 kilograms.
The small size of Archaeopteryx made them quite vulnerable in the age of large animals like dinosaurs. Hence, they might have developed wings for survival. They may not have been efficient flyers because of the lack of flight muscle and keel. Nonetheless, they were still good flyers.
They could flap their wings efficiently and gather altitude while flying. This gave them the opportunity to hunt and make nests in trees.
They also had claws on their wings. The claws were probably necessary to grab on tree branches. In the case of modern birds, these claws completely disappeared. Modern birds use their toes to hold on to things. The grip is quite strong as well.
Archaeopteryx did not develop fully reversed tows yet. So, they could not apply the same effect of taking off from the ground or trees like modern birds.
Again, their feet did not resemble dinosaur’s feet either. They had feathers on their feet. It is absent in both dinosaurs and modern birds. With time, this characteristic became unnecessary.
This reptile bird had lightweight bones. This brings it closer to modern-day birds. It had thin and light bones that allowed them to actively fly above the ground. Previously it was thought that the birds glided instead of flying. But this was not the case.
The bones of Archaeopteryx were structures in such a way that they could twist and turn while they were flying. Yet, the shoulder blade joints of the birds may not allow the animal to flap the wings like modern birds. Yet, their bone structure enabled them to fly well enough.
Archaeopteryx had a full set of teeth in their jaws. These teeth were also necessary to bite and chew food. It means Archaeopteryx was still meat-eating birds back then. The beak might not have looked the way it looks now because of the teeth.
Modern birds have lost their teeth. Even the hunting birds do not have teeth. They use their powerful beak instead. Some species of birds have sharp tomia, but they are not teeth.
As you can see, Archaeopteryx was the same as modern-day birds in a lot of ways. It took millions of years to change from a reptile. Then, modern birds appeared after 66 million years of evolution. Besides, just because Archaeopteryx might be the earliest birds, they may not be the direct ancestor of modern birds. Thus, it is natural to have some dissimilarity.
Why Bats Are Not Birds?
Some consider bats as birds. Bats can fly, they live in trees, and they are lightweight like birds. But these are all the wrong reasons to categorize bats as birds.
Even though bats have wings and they can fly, they are not birds. Wings and flight are not the only traits that define birds. So, let us consider the main reasons why bats are not birds:
Feathers are the most important features of birds. All kinds of birds have this characteristic. It does not matter whether they can fly or not. Bats do not have any feathers. On the contrary, they have fur.
Another universal feature for birds is the beak or bill. It is obvious that bats have no beaks. They have a mouth. Moreover, they have teeth. Birds have evolved not to have any teeth.
Birds have large feathered wings. On the other hand, bats have no fathers in their wings. They have membranes that stretch over their shoulders and hands. The hands of bats resemble animal hands more than bird wings.
This is the biggest difference between bats and birds. Bats do not lay eggs. They are mammals. Thus, they give birth to their babies like any other mammal. They also feed milk to their babies.
Birds have great eye-sight. Their visions are one of the best in the animal kingdom. They see things in color. On the contrary, bats have really small eyes. They do not have colorful visions like birds. Although bats have high night vision, they still rely on their hearing power to hunt.
In short, bats have more dissimilarities than similarities with a bird. The only thing birds and bats have in common is the ability to fly. That does not make bats birds in any way. To be exact, bats have more similarities with mammals. Thus, they should be considered mammals.
Birds have always fascinated people with their unique features and behavior. They are the best example of Darwin’s evolution theory.
They changed their appearance and physical abilities to survive in this world for millions of years.