Kingdom: Animalia Phylum: Chordata Class: Aves (Evolution of birds)
Birds are warm-blooded bipedal vertebrates that lay hard-shelled eggs. They are characterized by bony beaks, hollow bones, feathers and forelimbs modified as wings. In short, birds can be called Feathered Bipeds. Since birds are warm-blooded, their body is covered with insulating feathers to maintain an even temperature. Size of the birds can vary from the tiny flowerpeckers & hummingbirds, to the huge Ostrich and the Sarus Crane. In India, other than the Sarus Crane, the Himalayan Bearded Vulture or Lammergeier is the biggest bird and the tiny Tickell's Flowerpecker is hardly bigger than a human thumb. Most birds are capable of flight, but some larger birds like Penguins, Ostrich and Kiwi are flightless. Depending on different scientific classifications, as of today there are over 9000 bird species (1250 in India), with almost 150 having become extinct after the arrival of Humans. The Sibley-Ahlquist taxonomy, based on extensive DNA-DNA hybridization, has resulted in the Sibley-Monroe checklist which has revolutionized the whole system of bird classification.
Birds have a keen eyesight and good hearing but their sense of taste and smell is poor. Birds are generally diurnal (active during the day), some are nocturnal (active during the night), some crepuscular (active during twilight hours) and some nocturnal & crepuscular both. Many birds migrate long distances with change in seasons to maximize feeding hours and/or to breed in suitable habitats. Arctic Terns migrate twice every year from Arctic to Antarctica and back (over 15,000 km one way!). Some birds, like the Wandering Albatross, spend most of their time at sea. Some, such as frigatebirds, stay aloft for days at a time, even sleeping on the wing. The large variety of bird food includes honey, nectar, seeds, grains, vegetable matter, insects, larva, spiders, fish, molluscs, rodents, reptiles, small mammals, carrion or other birds.
Usefulness of birds
Birds are very useful as destroyer of pests. A big proportion of birds' diet consists of insects (and their larva), including many that are highly injurious to man. A large number of birds feed on rodents and mice, both very destructive for farmers all over the world. Vultures, Crows, Kites and Egrets feed on carrion and waste in garbage dumps. These birds play an invaluable part in keeping our environment clean and disease-free.
Birds are also an important food source for humans. The most commonly eaten species is the domestic chicken (a descendant of the Red Junglefowl and its eggs, although geese, pheasants, turkeys and ducks are also widely eaten. Other birds that are used for food include partridges, grouse, quails, pigeons, emus, ostriches and doves. Along with bees, birds such as the Purple Sunbird, are important pollinating agents. Birds as seed dispersers, play an essential for the propagation of many species of trees and plants. Other examples include Homing pigeons to carry messages, Falcons for hunting and Cormorants for fishing. Chickens and pigeons are used in experimental research in biology and comparative psychology.
Many species have become extinct through human activities like excessive hunting, logging, large scale use of insecticides and pesticides in agriculture and industrial pollution. Two birds that have become extinct in India in the not too distant past are Mountain Quail and the Pink-headed Duck.
Numerous species have come to depend on human activities for food and are widespread to the point of being pests. They have adapted well to the rapid urbanization and growth in human population. For example, the House Crow and Rock Pigeon thrive near human habitation in large parts of the world. While in addition to these two species, the Common Myna, Bank Myna and Black Kite are thriving in India; Vultures (Aegypiinae) and the House sparrow are facing an inexplicable decline in their population.