Want to learn about birds? Here is a simple explanation to understand our feathered friends.

Birds (Aves) are a group of endothermic vertebrates, characterized by feathers, beaks, the laying of eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton.

Birds are warm-blooded vertebrates that have wings, feathers and beak/bill. They have a skeleton in which multiple bones are fused together – strong hollow bones with powerful flight muscles. They are classified under the kingdom of Animalia and further under the class of Aves. This class of Aves has an estimated 9,000+ species ranging in size from a thumb-sized humming bird to ostriches which are larger than humans. Most of the species fall somewhere in between these two extremes.


Based on the best evidences accumulated, it is found that birds evolved from dinosaurs. Of course, the early types of birds had teeth unlike the modern birds which have beaks/bills. The theory comes from one of the most famous fossils ever found of a small animal with clawed toes, scaly legs, teeth and feathered wings. The scientists call it is Archaeopteryx. It was found in rocks dating from the Jurassic period i.e. 150 million years ago. Many scientists classify Archaeopteryx as a bird while on the other hand few made a note that if the feathers were to be taken out, this fossil would look just like a small theropod dinosaur. They all agree to the fact that Archaeopteryx wasn’t able to fly, partly because it had a flat sternum (breastbone) while modern birds have a keeled sternum to which flight muscles are attached. Yet Archaeopteryx clearly had feathers. So the question still prevails – was this fossil a dinosaur or a bird? This is only one of the many questions paleontologists struggle with when they study the evolution of birds.


The classification or the taxonomy is a system which was penned down by Carl Linnaeus who was a Swedish botanist, physician and a zoologist. He is also referred to as the father of modern taxonomy who normalised the modern system of naming organisams.

Let’s look at an example of House Sparrow to understand the modern taxonomy:

    • Kingdom: Animalia
    • Phylum: Chordata
    • Class: Aves
    • Order: Passeriformes
    • Family: Passeridae
    • Genus: Passer
    • Species: Passer domesticus

Let’s break this down further to understand the importance of each classification:

      • Kingdom: The first division of classification is into kingdom. Birds are classified into the kingdom of Animalia (Animals).
      • Phylum: The kingdom is further divided into the Phylum and birds are in the Phylum of Chordata (Animals with a backbone).
      • Class: The class is next and the class of birds is Aves. This also means that the top order for birds is the class Aves and all birds fall under this class.
      • Order: The class Aves is further split in to 24 orders. Orders are where birds share a very similar characteristic and the order is then further divided in to family.
      • Family: There are in all about 146 families and it generally ends with a “dae”.
      • Genus: Within families, falls the genus which are about 2000+ and the next smallest unit is the species under it.
      • Species: There are about 9000+ species of birds and they may be further divided in to subspecies if the birds of the same species are living in different geographical area and have a slightly different characteristic or behaviour.

The genus and species name is used when quoting a bird by its scientific name where the genus starts with a capital letter and the species with a lower case.

So in our example of a House Sparrow, the family is Passeridae and the genus is Passer. There are about 20 species and the related species are grouped together as they have many characteristics in common.

Flight & Feathers

Most birds can fly while some can run too and some can swim. There are others who do a combination of these while there are some which simply cannot fly. But almost all birds have feathers. Different types of feathers and each has different use. Feathers are useful for flying which we normally call as flight feathers and they grow in the wings and tails. Then there are feathers which are useful for thermal insulation and these are soft feathers that grow close to the skin. Feathers play an important role in courtship and mating display’s too and vary from species to species.


Now we all know that modern birds do not have teeth. Instead they have a bill/beak which has aptly evolved to help the bird consume the diet that it prefers. Some birds are carnivores (meat-eaters), some birds are herbivores (plant-eaters), some are omnivores (plant and meat-eaters), while some birds are fructivore (fruit-eaters), but they all swallow food without chewing. They do have a tounge but unlike us, they have a bone in it.


Many birds are migratory, nesting and raising their young in temperate or higher latitudes during the warm months and spending the winter in tropical or sub-tropical areas. Some of the species make long journeys of thousands of kilometers twice a year. Some birds migrate over 70,000 kilometers! It is unknown exactly how birds are able to navigate accurately, but many scientists are studying this mystery and believe that some birds have Magnetite (mineral) above their nostrils which helps them to use the Earth’s magnetic field to navigate. Some birds navigate using the landscape such as coastline, mountains or even motorways while some birds use the position of the sun and stars to navigate.

Nests & Eggs

Nests provide a safe place for eggs and young birds to develop. Bird nests are extremely diverse, although each species typically has a characteristic nest style. Some birds do not make nests at all and instead lay their eggs in a simple scrape in the ground. Other birds construct nests from natural materials, such as grass, leaves, mud, lichen, and fur, or from man-made materials like paper, plastic, and yarn. The total number of eggs that a female can lay in one nesting is called a clutch. Clutch size can also vary widely among individuals of the same species depending on food and calcium availability, latitude, age of the female, weather, and time of year. The size, shape, color, and texture of bird eggs are also extremely variable both within and among species.