Bird

Bird Diversity 2013

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Archaeopteryx lithographica (Berlin specimen)

Birds and dinosaurs

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Anchiornis feathers

Confuciusornis male

Birds are a group of warm-blooded vertebrates constituting the class Aves, characterized by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich. They rank as the class of tetrapods with the most living species, with approximately ten thousand different species.

Evolution

Birds are descendants of the primitive Avialans which first appeared about 160 million years ago (mya) in China. Modern birds are considered to have evolved from theropod dinosaurs during the Mesozoic Era. The first known bird, the Archaeopteryx, lived during the Late Jurassic period about 150 mya. Despite its small size, it shared many anatomical features with the non-avian dinosaurs.

Anatomy and Physiology

Birds' bodies are adapted for flight, with a lightweight skeleton and large pectoral muscles. The bones are hollow and contain air sacs which contribute to this lightness. Birds also have a unique respiratory system that allows for a high rate of oxygen exchange necessary for flight. Their feathers serve multiple functions, including insulation, display, and aiding in flight. Birds are the only living animals with feathers.

Reproduction

Birds are generally oviparous, with the female laying eggs that are then incubated. The duration of incubation and the level of parental care after hatching vary widely among different species. Most birds build some form of nest for their eggs and young.

Diet and Feeding

The diet of birds is diverse, ranging from nectar to carnivorous diets. The structure of their beaks is highly adapted to their feeding habits. Birds of prey, such as eagles and falcons, have sharp, hooked beaks for tearing flesh, while hummingbirds have long, slender beaks for extracting nectar from flowers.

Migration

Many bird species undertake long-distance annual migrations, often triggered by the change of seasons. These migrations can cover thousands of miles and are driven by the availability of food and suitable breeding sites. Birds navigate during migration using various methods, including the sun, stars, and Earth's magnetic field.

Conservation

Bird populations are facing threats from habitat destruction, pollution, hunting, and climate change. Numerous species are endangered or have become extinct in recent times. Conservation efforts include habitat protection, legal protection, and the establishment of wildlife reserves.

In Human Culture

Birds have been significant in human culture for thousands of years. They have been used as symbols, in art, literature, and as pets. The study of birds, ornithology, has helped develop key concepts in biology, including the understanding of species, the process of speciation, and the principle of evolution by natural selection.