Bird

Birds are a fascinating group of warm-blooded vertebrate animals known as the class Aves. They are special because they have feathers, beaks without teeth, and lay hard-shelled eggs. Birds live all around the world and come in many sizes, from the tiny 5.5 cm bee hummingbird to the large 2.8 m common ostrich. There are many different kinds of birds, and most of them can fly with their wings.

Birds evolved from earlier theropod dinosaurs and are considered the only living dinosaurs today. They first appeared during the Late Jurassic period and became more diverse after the Cretaceous–Paleogene extinction event. Many birds are social and talk to each other using calls and songs. They often work together to find food and stay safe.

Birds are important to humans in many ways. Some birds are raised for their meat and eggs, while others, like songbirds and parrots, make great pets. Birdwatching is a fun activity that helps people enjoy and protect birds. Sadly, some birds have disappeared because of human activity, and many are in danger. People all over the world are working to help protect bird populations.

Evolution and classification

Main article: Evolution of birds

Birds are warm-blooded animals that evolved from dinosaurs. They have feathers, lay hard-shelled eggs, and have strong but light skeletons. Scientists first classified birds in the 1600s. Today, we use a system made by Carl Linnaeus in 1758 to group them.

Birds belong to a group called Theropoda, which includes some dinosaurs. Over time, scientists found dinosaurs that looked a lot like birds, especially in how they flew or glided. One famous example is Archaeopteryx. It lived about 150 million years ago and had features of both birds and reptiles.

Modern birds have evolved many traits that help them fly, such as special bones and feathers. They come from different lineages. Some early groups like Enantiornithes went extinct, while others, like Euornithes, led to today’s birds. Today, there are many species of birds, grouped into different orders. Scientists study their DNA to learn more about how they evolved and are related.

Distribution

Birds live almost everywhere, from the cold Antarctica to warm rainforests. You can find them in forests, deserts, mountains, and even far out at sea. Many birds fly very long distances each year when they migrate, traveling across lands and oceans.

Some birds now live in new places because humans moved them there, either on purpose or by mistake. For example, the ring-necked pheasant was brought to many areas as a game bird, and monk parakeets escaped from cages and now live in cities. Other birds, like the cattle egret, spread to new areas naturally as farms grew around the world.

Anatomy and physiology

See also: Egg tooth

Birds have special features that help them fly. Their bones are light and have air spaces connected to their breathing system. Their skulls are fused together, and they have large eye sockets separated by a bony wall. Birds have flexible necks but stiffer backs, and their wings are modified forelimbs.

Birds excrete waste as uric acid, which is passed along with feces through a single opening called the cloaca. Female birds typically have one ovary and oviduct. Birds have a four-chambered heart and a complex respiratory system that allows for efficient oxygen intake during both breathing in and out.

The nervous system of birds is large relative to their size. Their brains are well-developed for flight, movement coordination, and behavior. Birds generally have a poor sense of smell, except for some like kiwis and vultures. Their vision is usually excellent, with many able to see ultraviolet light. Birds also have special adaptations for hearing and protecting their eyes.

Behaviour

Most birds are awake during the day, but some, like owls and nightjars, are awake at night or during twilight. Coastal birds often find food depending on the tides.

Birds eat many different things, like nectar, fruit, plants, seeds, small animals, and sometimes other birds. Their bodies have special parts to help with eating. They have a crop to store food and a gizzard to grind it. Some birds, like pigeons, do not have a gallbladder. Most birds eat fast to help them fly. Birds that fly long distances use extra fat for energy.

Birds find food in many ways. Some look for insects, while others chase or take food from other birds. Some birds, like hummingbirds, have long tongues to drink nectar. Others, like shorebirds, look for food in mud. Seabirds dive into water to catch fish, and some, like flamingos, feed by filtering water.

Ecology

Birds live in many different places and eat many kinds of food. Some birds in forests eat insects, fruit, or nectar from flowers. Birds near water may fish or eat plants. Some birds hunt other animals, and others eat animals that have already died.

Birds help plants by spreading seeds and pollen. For example, some birds that drink nectar help flowers by moving pollen from one flower to another. On islands, birds can be very important to the environment. Birds build nests, which can create homes for tiny creatures and change the land around them. Scientists study birds by counting them and watching their nests.

Main articles: Niche, Forest canopy, Insectivore, Frugivore, Nectarivore, Kleptoparasitism, Scavenger, Avivorous, Coevolution, Moa, Kererū, Kōkako, Ecosystem engineer, Seabird, Guano, Avian ecology

Relationship with humans

Main article: Human uses of birds

Birds have been important to humans for thousands of years. Sometimes birds help us, like honeyguides that help people find honey. Other times, birds benefit from us, like house sparrows that live in towns and cities. Some birds, like the Sarus Crane and woolly-necked storks, do well in farming areas.

Birds are also important for food, with poultry providing protein. Chickens are the most common, but turkeys, ducks, and geese are also raised for meat and eggs. Birds are also hunted for sport, with waterfowl, pheasants, and doves being popular. Birds give us useful products too, like feathers for clothing and guano as fertilizer. Many birds are kept as pets, and some, like falcons, are used for hunting. Birdwatching is a popular hobby, with many people enjoying feeding birds in their gardens.

Threats and conservation

See also: Late Quaternary prehistoric birds, List of extinct birds, and Raptor conservation

People have made life harder for birds in many places. Over a hundred kinds of birds have gone away since people started writing things down, and many more are in trouble. One big reason is that birds lose where they live and build nests because people change those places. Other troubles come from birds hitting buildings or cars, getting stuck in fishing lines, pollution, and weather changes.

People and groups work to help birds by making rules to keep their homes safe and by raising birds in special places to put them back in the wild later. These efforts have helped some birds that were almost gone.