BIRDS
Scientific Classification:
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Unranked: Archosauria Class: Aves (Linnaeus 1758) Depending on the taxonomic viewpoint, there are about 8,800–10,200 living bird species (and about 120–130 that have become extinct in the span of human history) in the world, making them the most diverse class of terrestrial vertebrates Birds are one of the four classes of vertebrates which is distinguished by being:
Birds are categorized as a biological class, Aves. The earliest known species of this class is Archaeopteryx lithographica, from the Late Jurassic period. Modern phylogenies place birds in the dinosaur clade Theropoda According to the current consensus, Aves and a sister group, the order Crocodilia; together are the sole living members of an unranked "reptile" clade, the Archosauria Distribution:
Birds are distributed all over the earth’s surface, but a few species are cosmopolitan. Some waders and gulls are found on every shore and sea, and some species of ducks, owls and swallows are present in every continent. On the other hand, most oceanic islands have extremely restricted populations, each with endemic species which are tending towards extinction. Distributions are rarely static for ecological reasons. Birds choose the habitat which suits them for feeding, breeding and shelter. If the habitat changes, the species moves elsewhere (migration), or at worst, dies out. Anatomical Characteristics:
The fore-limbs have modified into wings which has enabled birds to distribute themselves by flight, to every part of the world. The wing is structurally a normal fore-limb, with a humerus, radius and ulna, carpus, metacarpus and digits. The main flight feathers, known as primaries, grow from the second digit or index, usually ten in number. The first digit, or pollux, is separate and moveable, bearing a few feathers used in controlling flight, and is known as the alula. To the ulna are attached ten to twenty secondary feathers, which act as the main supporting surface in flight. The humerus, which is not normally seen because it is under the body covering, is the lever for actuating the wing: pectoral muscles are attached to it and to the sternum or breast bone. In strong fliers the sternum is enlarged to form a keel or carina because of bigger pectoral muscles; in flightless birds the carina is reduced or absent.
The leg of a bird is composed of a femur, tibia and fibula, and a group of tarsal bones connected to toes. The tarsal bones are covered in scales. The toes are modified in different species for walking or running, gripping a branch or a prey, or for swimming (webbed toes). Birds mainly rely on vision as their main sense, with a wide angle of view, colour detection and are very capable of detecting small objects from a distance. Bird’s lungs are very small, but greatly prolonged into nine air-sacs placed among other organs and into the larger bones which are hollow. Having a rigid ribcage, birds use abdominal breathing. The avian ear lacks external pinnae but is covered by feathers. Most birds have a poor sense of smell except for the kiwis and vultures. Sound production is achieved using the syrinx, a muscular chamber with several tympanic membranes, situated at the lower end of the trachea where it bifurcates. The digestive system of the bird is unique and has a crop for storage and a gizzard for grinding food. Most are highly adapted for rapid digestion, an adaptation to flight. Migratory birds have the additional ability to reduce parts of the intestines prior to migration. The nervous system, relative to the bird's size, is actually quite large. The most developed part of the brain is the one that controls the flight related function while the cerebellum coordinates movement and the cerebrum controls behavior patterns, navigation, mating and nest building. A bird’s eyes are developed for taking off, spotting landmarks, hunting and feeding. Birds with eyes on the side of their head have a wide visual field while birds with eyes on the front of their heads like owls have binocular vision and can measure depth. The visual system is highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water. Some species also have dual fovea. The bird retina has a fan shaped blood supply system called the pecten. The inner ear has a cochlea but it is not spiral as in mammals.
Most birds are diurnal, or active during the day, but some birds, such as many species of owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night. Many birds migrate long distances to utilise optimum habitats, like the American Robin, while others spend almost all their time at sea (e.g. the Wandering Albatross). Some, such as Common Swifts, stay aloft for days at a time, even sleeping on the wing. The three mating systems that predominate among birds are monogamy (seen in approximately 91% of bird species), polygyny (2%) and polyandry (< 1%). Monogamous species of males and females pair for the breeding season. In some cases, the individuals may pair for life. One reason for the high rate of monogamy among birds is the fact that male birds are just as adept at parental care as females. In most groups of animals, male parental care is rare, but in birds it is quite common; in fact, it is more extensive in birds than in any other vertebrate class. In birds, male care can be seen as important or essential to female fitness. "In one form of monogamy such as with obligate monogamy a female cannot rear a litter without the aid of a male". The parental behavior most closely associated with monogamy is male incubation. Interestingly, male incubation is the most confining male parental behavior. It takes time and also may require physiological changes that interfere with continued mating. This extreme loss of mating opportunities leads to a reduction in reproductive success among incubating males. "This information then suggests that sexual selection may be less intense in taxa where males incubate, hypothetically because males allocate more effort to parental care and less to mating". In other words, in bird species in which male incubation is common, females tend to select mates on the basis of parental behaviors rather than physical appearance. Finally, it is important to note the growing concern amongst the bird-keeping community for the welfare of “only birds”. Almost all pet-quality birds are species that are “flock birds,” living in large social groups in the wild. It can be cruel to keep them as solitary avian members of a family which can spend only a few hours per day truly interacting with them, while leaving them alone for hours upon hours, day after day. So if you want to be a bird-keeper, please make plans to have more than one. Discover How To Stop Your Bird Biting, Screaming And Feather Plucking. And How To Take Proper Care Of Your Feathered Friend- -helping Bird Owners Solve Their Desperate Problems:Click Here! |
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The whole body is almost entirely covered in feathers to act as a heat insulator. Feathers also act as camouflage, for recognition, for display or for threat. Birds clean and trim their feathers and make them water-proof by using the secretion of oil from the uropygial gland situated near the base of the tail.