Bird Classification: What are birds?

Birds are warm-blooded vertebrates that evolved from dinosaurs. They’re identifiable by feathers, toothless beaked jaws, and laying of hard-shelled eggs. They also have a high metabolic rate, a four-chambered heart, and strong but light skeletons.

Birds have wings that are more or less developed between species. The only known species of wingless birds are moa and elephant birds – both of which are now extinct. While wings allow most birds to fly, species like ratites and penguins cannot travel in the air.

Birds like crows and parrots are intelligent, and several species can make and use tools. In addition, they’re social – migrating great distances together- and communicate with signals, calls, and songs. Some birds also cooperate when breeding and hunting, while mobbing predators as a group is common too.

How many species of birds are there?

Around 10,000 living species of birds make up a worldwide population of about 100 billion!

Bird habitat information

A bird’s habitat can vary between species, and birds occupy many different environments worldwide. They’re found in deserts, forests, mountains, tundras, grasslands, oceans, urban areas, and more. Some birds never leave their habitat, while others migrate incredible distances when the weather changes.

Tropical regions exhibit an impressive diversity of species, and birds have adapted to life in and around the world’s oceans. For example, penguins have been recorded diving down to 300 meters, and some seabirds only come onshore to breed.

What does a bird habitat require?

  • Food, such as berries, worms, and small insects.
  • Camouflage so that they are less visible to predators.
  • Materials for nest-building, such as twigs and leaves.
  • Water to drink and bathe in.
  • Shelter from the elements.
  • Nesting sites like hollow trees or snags.

Bird habitats for different species:

  • Shore and sea birds inhabit beaches, estuaries, and other coastal habitats. These birds tend to be able to dive or sift for food with beaks adapted to the task. Examples include auks and fulmars.
  • Forest birds are found in tropical regions and temperate and cold climates. Examples include parrots, owls, and pheasants.
  • Wetland birds inhabit rivers and lakes and include species like ducks, geese, and herons.
  • Birds of the plains live in grassland and even desert environments of different temperatures. Examples include rheas, seriema, and parakeets.
  • Urban birds live in cities and towns and can be found under bridges and on buildings, among other places. Birds that live in these environments include pigeons, sparrows, and starlings.

Habitats for garden birds

Garden birds include robins, collared doves, blackbirds, and house sparrows. Good bird habitats in the garden feature:

  • Trees provide shelter, nesting sites, and a variety of insects and fruits to eat.
  • Shrubs also provide shelter and nesting sites, while the berries they produce are a great food source for birds.
  • Lawns are a feeding ground for lots of birds.
  • Climbers, which provide cover, nesting sites, and food.
  • Hedges, which are ideal nesting sites.

How does habitat loss affect birds?

Lots of species of birds are threatened by habitat loss and fragmentation. Harmful activities include:

  • Agricultural use, such as clearing habitats for fields.
  • Logging and forest harvesting.
  • Expanding urban areas for housing or industry.
  • Building dams, canals, or other structures that interfere with waterways.
  • Infrastructure that fractures habitats, like roads or electrical lines.

These activities are detrimental to the birds’ chances of survival and impact the population. These human changes can have drastic consequences, causing the numbers of a species to plummet.

Quick-fire Questions!

What is the circulatory system of birds like?

The four-chambered heart means that birds’ systemic and pulmonary circulation are separate. This means arterial and venous blood don’t mix, making them warm-blooded. As a result, their average body temperature is between 41 and 42 °C.

What country has the most species of birds?

Colombia has more birds than any other country, with around 2000 species.

How do birds breathe?

Birds have air sacs and lungs to compensate for the amount of oxygen in flying. Air passes through the lungs in one direction to ensure maximum blood oxygenation.

What senses do birds use most?

Birds’ organs of senses aren’t developed evenly. For example, they have great vision and depend upon this more than any other sense. They also have good hearing, but their senses of taste and smell are poor.

Are birds warm-blooded?

Much like mammals, birds are warm-blooded. This is a pretty common fact, but what does it mean? Because birds are warm-blooded, they can generate their body heat instead of relying on the weather to warm them up. Cold-blooded animals, like reptiles, do not have this ability. The ability to regulate their body temperature means that birds can survive in extremely cold environments. This is why birds like the yellow lion, peregrine falcon, and snow goose can live in the arctic tundra. One of the best examples of birds withstanding freezing temperatures can be seen in Emperor penguins. During the arctic winter, these penguins can sit in temperatures as low as -50ºC.

How do birds’ legs and feet not get cold?

Most of a bird’s body is covered in thick feathers, which help keep them warm. The legs and feet, however, are left uncovered, leaving us to question whether or not they get cold. Birds have adapted over time to overcome this issue through their circulation system. The arteries within birds that carry warm blood from their heart travel alongside the veins carrying cold blood from the legs, heating them. This system also works in hotter weather to help birds cool down. The warm blood flow to the legs increases in hot temperatures, allowing birds to lose any unwanted heat and stay cool.

Do feathers keep birds warm?

Birds are warm-blooded animals and have many different systems in place to keep them warm. These systems have been adapted to help birds survive in cold, challenging environments. For instance, the feathers on a bird’s body can fluff out to trap warm air. These feathers also provide a place for birds to tuck their heads when cold. Birds also have a layer of fat that builds up under their skin as cold weather approaches, which helps keep them warm.

Why do birds migrate?

One of the main reasons why birds migrate to different places is to source better weather conditions. Millions of birds migrate every single year from cold environments to warmer ones. Migration allows birds to find the best place to breed during the summer and the best place to feed during winter.

Bird Classification: Taxonomic Hierarchy

There are estimated to be around 8.7 million species on earth, which are greatly varied. To better understand the vast species of animals, we categorize them into different groups known as taxa. The taxonomic hierarchy is the process through which taxonomic groups and categories are organized into successive levels.

The taxonomic hierarchy is as follows:

  1. Kingdom: Animalia
  2. Phylum: Chordata
  3. Subphylum: Vertebrata
  4. Class: Aves

The hierarchy following from the class Aves is categorized like this: the orders are split up into families, the families are split up into genera (singular: genus), and the genera are made up of distinct species.


There are around 29 orders of birds. However, this statistic is under review as more research is done in bird biology. For instance, the order of birds called Struthioniformes used to include the Ostrich, the Rheas, Cassowaries, Emus, and Kiwis. However, this has recently been revised, and now Struthioniformes only consists of the Ostrich, the Rheas are in the order Rheiformes, the Cassowaries and Emus are in the order Casuariformes, and the Kiwis are in the order Dinornithiformes.

The driving force behind these changes in the classification of birds is new research that has been done using DNA analysis. This research is more effective at determining how closely two species are related than the previous methods, which focused on the morphology and anatomy of the birds.


The 29 orders of birds are divided into 233 families. As the number of orders of birds, the number of families is ever-changing as more and more research is being carried out. For instance, the family Laridae used to include all species of Gulls, Terns, Skuas, Jaegers, and Skimmers. However, this family has recently been split into four different families: Gulls are Laridae, Terns are Sternidae, Skuas and Jaegers are Stercorariidae, and Skimmers are Rynchopidae.


The genus is the primary taxonomic division between the family group and individual species.


All other categories in the taxonomic hierarchy are based on species groupings, making it a very important level in this system. A species comprises related organisms with common characteristics and can breed with other similar organisms. Currently, there are around 9700 to 9800 separate species of birds on earth. However, as with all the categories in this hierarchy, this number changes as scientists find new species, etc.

Bird Classification: Characteristics

Birds are fascinating creatures, which is clear from the number of people that spend their time bird-watching. There are around 10,000 species of birds today, all with different features and characteristics, but there are certain similarities that all birds share.

All birds are classified as members of the Kingdom Animalia, Phylum Chordata, and Class Aves.

The characteristics that all birds share are:

  • Vertebrates: All birds have a backbone, making them an animal of the Phylum Chordata. However, the vertebrates in birds are very different from those found in other animals; for example, birds have a unique, light skeletal structure filled with hollows, gaps, and air sacs. This is so birds can be lightweight and, thus, able to fly more efficiently.
  • Feathers: All birds have feathers, which are made up of a range of proteins, including keratin, as well as light-reflecting pigments which act as body insulation. Types of feathers vary greatly between different types of birds. For instance, some feathers are purely decorative, like plumes and streamers, while others are designed to help birds control their flight or for insulation.
  • Wings: One thing that all birds have in common, of course, is wings. Even birds that cannot fly have adapted wings or flippers they use for things like swimming, displays of confrontation, and courtship dances. In addition, the size and shape of birds’ wings vary depending on how they fly. Therefore, wing markings are a really useful way to identify species of birds.
  • Bill: Bills are bony, keratin-covered projections that form the mouths of all birds. While all birds have them, bills are constantly evolving for different bird species as they are used for many things. For example, birds use their bills for eating, carrying items, drumming, drilling, preening, regulating body temperature, attacking opponents, and much more.
  • Warm-blooded: Birds are endothermic creatures that can generate their internal body heat. This allows them not to rely on their environment to maintain their body temperature. However, a lot of birds still sit in the sun frequently, but this has many purposes, as well as body temperature maintenance.
  • High metabolism: All birds have a very high metabolism, allowing them to turn food into energy quickly. They also have a four-chambered heart and increased respiratory rate, enabling them to be efficient fliers and helping them maintain their high body temperatures.
  • Bipedal: All birds are bipedal, which means they have two legs that they use for walking, hopping, perching, and running. Different birds have developed different leg shapes and sizes over time to fit their specific needs. For instance, flamingoes have long, thin legs that can wade through deep water.
  • Furcula: A furcula is a wishbone that all birds have, and it is designed to protect their chest cavity during wing beats. The furcula guards the organs in a bird’s chest from the extreme pressure that builds up as its wings move and change altitudes.
  • Laying Eggs: As part of their reproductive cycle, all birds lay amniotic eggs. Bird eggs have a hard shell that needs to be incubated to develop before they hatch. The size, shape, and markings of bird eggs vary between species. The number of eggs laid is also different for each bird species and how they need to be incubated.
  • Communication: Birds are fantastic communicators. A lot of species of birds can communicate verbally with one another through songs and calls. They can also share non-verbally. Birds share for many reasons, notably as part of their courtship process, confrontations, and parenting.
  • Navigation: Excellent navigational skills are a key characteristic for all birds, both those who migrate and those who don’t. These navigational skills enable migratory birds to travel extremely long distances through many different climates and conditions and arrive at the same places every year. Non-migratory birds, on the other hand, use their navigational skills to repeatedly source the same spots for food and nest.
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