Birds: The Ultimate Guide. Amazing Bird Facts, Pictures & Information

Birds: What Is A Bird? Information, Pictures & Video. Part one of our ‘Ultimate Guide to Birds’. On this page you’ll find out what makes a bird a bird. You’ll also discover some amazing facts about birds and the lives that they lead.

If you didn’t know about the link between birds and dinosaurs, prepare to have your mind blown!

Active Wild Bird Articles

Once you've finished this page, check out the pages below for more amazing bird facts!

The Ultimate Guide To Birds: What Is A Bird?

On this page you’ll discover incredible facts about one of the most widespread and familiar types of animal in the world: birds.

snowy owl
Birds are found in many different environments. This snowy owl has adaptations that allow it to live and hunt in the Arctic.

  • Random bird fact: There are around 10,000 species of bird.

Birds are found on every continent and in many different habitats. From penguins that live on the frozen coastline of Antarctica, to ostriches found in the Sahara Desert: birds are (almost) everywhere!

Birds also play a big part in our own lives. If you look out of the window, the first animal that you’re likely to see will be a bird... or an insect... but probably a bird! Even if you can’t actually see a bird, you’ll probably be able to hear one.

Nearly everyone–even those who aren't interested in wildlife–can identify several species of bird.

On this page you’ll find out all about birds, including how they evolved and what makes a bird a bird.

  • Random bird fact: the world’s most common wild bird is the red-billed quelea. This sparrow-sized bird is found in Sub-Saharan Africa, where it forms flocks of over a million individuals. There are thought to be around 1.5 billion red-billed queleas alive today!

How many different types of bird can you name!

You may know more species of bird than you realize!

You may not be able to name all 10,000 species of bird, but you probably know more than you think you do. Grab a sheet of paper and write down all of the different types of bird that you know; you may surprise yourself!

  • Random bird fact: The world’s fastest animal is the peregrine falcon. This amazing bird can reach speeds of over 320 km/h (200 mph) when it dives!


Ornithology is the scientific study of birds, and people who study birds are known as ornithologists. For the rest of the page, you can consider yourself to be an ornithologist as you find out about bird evolution, bird characteristics, and what makes a bird a bird.


Birds are members of the class* Aves. At the time of writing, Aves contains 46 Orders, 248 families and around 10,000 species. (These figures are likely to change; animal classification never stays the same for long!)

Examples of well-known bird families include Passeridae and Accipitridae.

  • The family Passeridae comprises the true sparrows (including the house sparrow Passer domesticus, which is the world's most widely-distributed bird).
  • Accipitridae includes many species of birds of prey, including hawks, eagles, kites, harriers and some vultures.

*If you want to know more about classes, orders and other animal groups, check out our Animal Classification page.

Birds Are Reptiles (Sort Of)!

In the past, Aves was considered to be a group in its own right. Today, some scientists consider Aves to be part of the class Reptilia (the reptiles).

That’s right: birds are now considered (by some) to be reptiles! If you hear a scientist talking about avian reptiles, then he’s talking about birds!

This is because the ancestors of birds are reptiles. In fact, the crocodilians (reptiles such as crocodiles, alligators, and related animals) are more closely related to birds than they are to other reptiles such as snakes and lizards.

In modern animal classification, scientists prefer animal groups such as Reptilia to include all of the descendants of an ancestral species.

Because a bird's ancestors were reptilian, the class Reptilia would be incomplete without the birds. Therefore, Aves is seen as a sub-group of Reptilia.

The first person to recognize the link between reptiles and birds was English biologist Thomas Henry Huxley (1825 – 1895) (Wikipedia). In the 1860's he described birds as being 'glorified reptiles'.

Birds Are Dinosaurs!

Birds are the only remaining dinosaurs

As if birds weren’t already amazing enough, they take on a whole new level of awesomeness when you consider that they’re actually the direct descendants of dinosaurs. In fact, most scientists today consider birds to be dinosaurs!

So you can quite correctly tell people that you’ve seen a real, living dinosaur!

  • Random bird fact: Britain’s most common species of bird is the wren. The wren is also one of the smallest British birds: only the goldcrest and the firecrest are smaller! In fact, the goldcrest is Europe’s smallest bird.

Bird Evolution

Millions of years ago (at least 247.2 million years ago, maybe even more) a group of reptiles called archosaurs split away from other reptiles. The archosaurs themselves then split into two main groups: Pseudosuchia and Avemetatarsalia.

Pseudosuchia are the ancestors of modern day crocodilians (animals such as crocodiles and alligators).

Avemetatarsalia includes the dinosaurs, an incredibly successful group of reptiles that first appeared between 243 and 231 million years ago, during the Triassic Period.

Dinosaurs rose to dominance during the Jurassic Period. Their reign continued all the way up to the Cretaceous–Paleogene Extinction Event, which occurred around 66 million years ago.

Long before this catastrophic event, which wiped out all of the large dinosaurs, members of a group of dinosaurs known as theropods began to develop bird-like qualities. These feathered dinosaurs would be the ancestors of all living birds.

True birds first appeared around 120 million years ago, during the Cretaceous period. Birds are the only dinosaurs to have survived the Cretaceous–Paleogene Extinction Event.

A Bird’s Closest Living Relatives

Saltwater Crocodile
The group of animals most closely-related to birds are the Crocodilians.

The closest living relatives of birds are the crocodilians; members of the order Crocodilia. Crocodilia is the group of animals that contains all crocodiles, alligators and gharials.

What Makes a Bird a Bird?

Biggest and Smallest Birds

Bird facts: ostriches are the world's biggest birds.

Birds are extremely varied. An ostrich (the world’s biggest bird) is, on the surface, very different to a bee hummingbird (the world’s smallest bird).

However, despite the external differences, there are certain things that all birds have in common: characteristics that all members of Aves share.

If asked ‘what makes a bird a bird?’ the first answer that many people come up with is that birds are flying animals. If they want to be more precise, they’ll say ‘flying vertebrates’.

They would only be partly right. Although all birds are vertebrates (i.e. they have backbones), not all birds can fly (think of ostriches and penguins). In addition, there are flying vertebrates that aren’t birds, namely bats. So this isn’t how scientists define a bird.

Adelie Penguin
Not all birds can fly! (This Adelie Penguin looks like it might be trying!)

Characteristics Of Birds

There are a number of characteristics that make a bird a bird. Some, such as feathers, are only found in birds. Others, such as being warm-blooded and laying eggs, are shared by other types of animal. It’s having the right combination of these characteristics that makes a bird a bird!

What Is A Bird?

Here is a list of bird characteristics:

  • Birds are vertebrates (i.e. they have backbones)
  • Birds have feathers
  • Birds don’t have teeth
  • Birds have beaks
  • Birds have limbs that are modified for flight (wings)
  • Birds lay eggs
  • Birds are endothermic (i.e. they’re warm-blooded)
  • Birds have hollow bones & skeletons that are adapted for flight

Let’s look at these in more detail:

Birds Are Vertebrates

As we’ve already found, all birds are vertebrates (i.e. they have backbones), just like you and I! Most familiar animals, such as mammals, reptiles and amphibians, are vertebrates, but vertebrates actually only make up a very small part of the animal kingdom.

(In fact, around 97% of all animals are invertebrates – animals without backbones!)

Birds Have Feathers

Resplendent Quetzal
All birds have feathers. (But not all have feathers as long or as brightly-colored than those of this resplendent quetzal!)

Birds are the only living animals to have feathers. Feathers, as well as being necessary for flight, also serve a number of other purposes. These include: helping to keep the bird’s body at the right temperature; communication and display; camouflage; protection; and waterproofing.

Some feathers, known as filoplumes, provide sensory information.

  • Random bird fact: the bird with the largest wingspan is the wandering albatross (Diomedea exulans). Its huge wings can span 3.65 m (12.0 ft.).

Birds Have Beaks (and don’t have teeth)

As birds evolved they lost their teeth and gained beaks instead. Beaks come in all shapes and sizes, and have many uses. Beaks are mainly used for eating, but they also come in handy for preening (feather cleaning), fighting, and for picking things up (e.g. sticks, to make a nest).

Beaks are strong but lightweight, unlike teeth, which may be strong, but which are also very heavy. Having a beak is therefore the ideal solution for a flying animal.

The shape of a bird’s beak is related to what it eats. You may be surprised to learn that parts of a bird’s beak contain touch receptors, making it very sensitive.

The bird with the world’s largest beak is the Australian pelican. Its beak can be up to 50cm (20 in.) long!

The bird with the longest beak in relation to body size is the sword-billed hummingbird. Its bill can be over 10 cm (4 in.) long.

Birds Have Wings

kestrel hovering
A kestrel's specially adapted wings enable it to hover.

A bird’s wings are its modified forelimbs (front limbs, or arms). These wide, specially shaped limbs enable (most) birds to launch themselves from the ground and power themselves through the air.

Even flightless birds have wings. This is because the ancestors of all birds – including flightless birds – could fly.

The shape of a bird’s wing depends on the lifestyle it leads. Birds such as albatrosses have long, narrow wings. This helps them to glide for long distances using very little energy.

Short, narrow wings, such as those of a hawk, provide speed and maneuverability. Large, wide wings provide ‘lift’ for birds such as eagles to gain height and soar.

A penguin’s short, strong wings act as flippers, enabling it to ‘fly’ through the water.

Birds Lay Eggs

Birds develop outside of their parent’s body, protected by the hard shell of an egg. Birds aren’t the only animals to lay eggs (many reptiles and amphibians also lay eggs).

Birds are endothermic (Warm Blooded)

Birds, like mammals, are warm blooded. A warm-blooded animal’s body is able to keep itself at the ideal temperature. Unlike a lizard, for example, a bird doesn’t have to bask in the sun in order to get warm enough to hunt. Its body takes care of that automatically!

Hollow Bones & Special Skeletons

Many of a bird’s bones are hollow. This is another weight-saving adaptation for flight. The bones of diving birds are often more solidly constructed than those of other types of bird. This makes them heavier and less buoyant, helping the bird to dive deeper and for longer.

A bird’s sternum (breastbone) extends outwards to form what is known as a keel. The bird’s wing muscles attach to the keel. This arrangement gives the wing muscles additional leverage. This provides the necessary power and efficiency for flight.

The members of a group of large, flightless birds known as Ratites don’t have a keel. This group includes birds such as ostriches and cassowaries.

Air Sacs & A Special Breathing System

A bird’s skeleton has spaces for air sacs. These inflate and deflate as the bird breathes. Birds have a special breathing system that is more efficient than that of mammals.

A bird’s lungs extract oxygen both when air is breathed in and when it is breathed out. Some of the air that is breathed in is stored in the air sacs before being passed through the lungs when the bird breathes out.

This is yet another modification for flight.

  • Random bird fact: the Arctic tern travels further than any other animal in a year, covering an incredible 90,000 km (56,000 mi) during its annual migration.

Four-Chambered Heart

Like crocodilians (and mammals), birds have four-chambered hearts. Birds have higher heart rates than mammals, and their hearts are usually bigger in relation to body size.

Now you’re up to speed on bird characteristics, let’s discover more about bird biology…

Birds: Designed For Flight

Bald Eagle
A bird's body has many adaptations for flying. This bald eagle's broad wings allow it to glide and soar.

Although not all birds can fly, they all share the same ancestors, all of which could fly. This means that a bird’s body is designed around being able to fly.

In order to fly, a bird’s body must be light yet strong. Flight requires a large amount of oxygen and energy. Therefore a bird’s respiratory system (how oxygen is extracted from air) and circulatory system (how blood is moved around the body) both need to be extremely efficient.

If you’re a bit of an extrovert, stand up and try to flap your arms fast enough to take off. Try as you might, you’ll never leave the ground (sorry to break it to you like this).

Even if you only ‘flap’ for a few seconds, you’ll probably be left feeling out of breath; it’s extremely strenuous. Obviously you haven’t got feathers, but even if you did you’d find it too tiring to be able to fly.

Just imagine how much energy it would take to actually lift your body off of the ground (even if you had feathers). Now consider that some birds fly all round the world several times in their lifetimes, and that some hummingbirds flap their wings 50 times per second!

A bird’s body needs to be pretty efficient!

Birds have a higher metabolism (how fast their bodies use energy) than other land vertebrates. Their hearts beat faster, and their body temperatures are higher.

There is a trade-off to being both warm blooded and able to fly. Birds need a lot of energy to stay alive. This means that they need to eat a lot of food. Birds can’t just laze around like cold-blooded animals such as snakes and crocodiles – they need to be constantly on the lookout for the next meal!

Flying requires a great deal of energy. Hummingbirds have the highest metabolisms of all animals apart from insects.

Bird Facts: The Ultimate Guide To Birds: Conclusion

If you’ve come this far then you’re well on your way to becoming a bird expert!

Birds are very common, and it’s easy to take them for granted. A world without birds would be a very miserable place. Just imagine walking in the woods with no birdsong, or going to the park without any ducks to feed! Even going to the beach and being ‘bombed’ by a seagull is a small price to pay for the color and joy that birds bring into our lives.

Bird Articles On Active Wild

Other Pages

You can learn more about other members of the animal kingdom on the following pages: