The electron is a subatomic particle that carries a negative electrical charge. It is an elementary particle with no known substructure and is believed to be a point particle.[2] Each electron participates in gravitational, electromagnetic and weak interactions. The mass of an electron is approximately 1⁄1836 of a proton. Like its rest mass and elementary charge, the intrinsic angular momentum (or spin) of an electron has a constant value. In the collision of an electron and a positron, the electron's antiparticle, both are annihilated. An electron–positron pair can be produced from gamma ray photons with a combined energy at least equal to the energy at rest of the particles.[8]
Electrons are identical particles that belong to the first generation of the lepton particle family. Electrons have quantum mechanical properties of both a particle and a wave, so they can collide with other particles and be diffracted like light. Each electron occupies a quantum state that describes its random behavior upon measuring a physical parameter, such as its energy or spin orientation. Because they are a type of fermion, no two electrons can occupy the same quantum state; a property known as the Pauli exclusion principle.[9]
In order to explain the chemical properties of atoms, the concept of an indivisible amount of electrical charge was theorized on several occasions, beginning in 1838 by British natural philosopher Richard Laming;[4] the name electron was introduced for this charge in 1894 by Irish physicist George Johnstone Stoney. The electron was first identified as a particle in 1897 by J. J. Thomson and his team of British physicists.[6][10] Electrons play an essential role in many physical phenomena such as electricity, magnetism, and thermal conductivity. When an electron is in motion, it both generates a magnetic field and is deflected by external magnetic fields. While an electron is undergoing acceleration, it can absorb or radiate energy in the form of photons. Electrons, together with atomic nuclei made of protons and neutrons, make up atoms. The attractive Coulomb force between an electron and a proton is what causes electrons to be bound into atoms. The exchange, sharing or interaction of the electrons in two or more atoms is the main cause of chemical bonding.[11]
Selasa, 10 Februari 2009
Meteor
Meteoroid
A meteor (possibly two) and Milky way.
The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom."[1] The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across.[2] The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids; smaller still is interplanetary dust.
Many meteoroids are formed by impacts between asteroids or left in trails behind comets. Meteoroids are also known to have been ejected by impacts on the Moon or Mars as some meteorites from these bodies have been identified (see Lunar meteorites and Mars meteorites).
The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectory and the light spectra of the resulting meteor. Their effects on radio signals also yield information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice,[3] to nickel-iron rich dense rocks. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs.
[edit] Meteor
Comet 17P/Holmes and Geminid.
A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km.[4]
For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres)[clarification needed] the visibility is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry. Since the majority of meteors are from small sand-grain size meteoroid bodies, most visible signatures are caused by electron relaxation following the individual collisions between vaporized meteor atoms and atmospheric constituents.
Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause.
A meteor (possibly two) and Milky way.
The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom."[1] The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across.[2] The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids; smaller still is interplanetary dust.
Many meteoroids are formed by impacts between asteroids or left in trails behind comets. Meteoroids are also known to have been ejected by impacts on the Moon or Mars as some meteorites from these bodies have been identified (see Lunar meteorites and Mars meteorites).
The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectory and the light spectra of the resulting meteor. Their effects on radio signals also yield information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice,[3] to nickel-iron rich dense rocks. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs.
[edit] Meteor
Comet 17P/Holmes and Geminid.
A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km.[4]
For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres)[clarification needed] the visibility is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry. Since the majority of meteors are from small sand-grain size meteoroid bodies, most visible signatures are caused by electron relaxation following the individual collisions between vaporized meteor atoms and atmospheric constituents.
Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause.
Sun
The Sun (Latin: Sol), a yellow dwarf, is the star at the center of the Solar System. The Earth and other matter (including other planets, asteroids, meteoroids, comets, and dust) orbit the Sun,[9] which by itself accounts for about 98.6% of the Solar System's mass. The mean distance of the Sun from the Earth is approximately 149,600,000 kilometers, or 92,960,000 miles, and its light travels this distance in 8.3 minutes. Energy from the Sun, in the form of sunlight, supports almost all life on Earth via photosynthesis,[10] and drives the Earth's climate and weather.
The surface of the Sun consists of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 24% of mass, 7% of volume), and trace quantities of other elements, including iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium, and chromium.[11] The Sun has a spectral class of G2V. G2 means that it has a surface temperature of approximately 5,780 K (5,500 °C) giving it a white color that often, because of atmospheric scattering, appears yellow when seen from the surface of the Earth. This is a subtractive effect, as the preferential scattering of shorter wavelength light removes enough violet and blue light, leaving a range of frequencies that is perceived by the human eye as yellow. It is this scattering of light at the blue end of the spectrum that gives the surrounding sky its color. When the Sun is low in the sky, even more light is scattered so that the Sun appears orange or even red.[12]
The Sun's spectrum contains lines of ionized and neutral metals as well as very weak hydrogen lines. The V (Roman five) in the spectral class indicates that the Sun, like most stars, is a main sequence star. This means that it generates its energy by nuclear fusion of hydrogen nuclei into helium. There are more than 100 million G2 class stars in our galaxy. Once regarded as a small and relatively insignificant star, the Sun is now known to be brighter than 85% of the stars in the galaxy, most of which are red dwarfs.[13]
The Sun orbits the center of the Milky Way galaxy at a distance of approximately 24,000 to 26,000 light years from the galactic center, moving generally in the direction of Cygnus and completing one revolution in about 225–250 million years (one Galactic year). Its orbital speed was thought to be 220±20 km/s, but a new estimate gives 251 km/s[14]. This is equivalent to about one light-year every 1,190 years, and about one AU every 7 days. These measurements of galactic distance and speed are as accurate as we can get given our current knowledge, but may change as we learn more.[15] Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.[16]
The surface of the Sun consists of hydrogen (about 74% of its mass, or 92% of its volume), helium (about 24% of mass, 7% of volume), and trace quantities of other elements, including iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium, and chromium.[11] The Sun has a spectral class of G2V. G2 means that it has a surface temperature of approximately 5,780 K (5,500 °C) giving it a white color that often, because of atmospheric scattering, appears yellow when seen from the surface of the Earth. This is a subtractive effect, as the preferential scattering of shorter wavelength light removes enough violet and blue light, leaving a range of frequencies that is perceived by the human eye as yellow. It is this scattering of light at the blue end of the spectrum that gives the surrounding sky its color. When the Sun is low in the sky, even more light is scattered so that the Sun appears orange or even red.[12]
The Sun's spectrum contains lines of ionized and neutral metals as well as very weak hydrogen lines. The V (Roman five) in the spectral class indicates that the Sun, like most stars, is a main sequence star. This means that it generates its energy by nuclear fusion of hydrogen nuclei into helium. There are more than 100 million G2 class stars in our galaxy. Once regarded as a small and relatively insignificant star, the Sun is now known to be brighter than 85% of the stars in the galaxy, most of which are red dwarfs.[13]
The Sun orbits the center of the Milky Way galaxy at a distance of approximately 24,000 to 26,000 light years from the galactic center, moving generally in the direction of Cygnus and completing one revolution in about 225–250 million years (one Galactic year). Its orbital speed was thought to be 220±20 km/s, but a new estimate gives 251 km/s[14]. This is equivalent to about one light-year every 1,190 years, and about one AU every 7 days. These measurements of galactic distance and speed are as accurate as we can get given our current knowledge, but may change as we learn more.[15] Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.[16]
Larva
A larva (Latin; plural larvae) is a young (juvenile) form of animal with indirect development, going through or undergoing metamorphosis (for example, insects, amphibians, or cnidarians).
The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly. Larvae often have special (larval) organs which do not occur in the adult form. The larvae of some species can become pubescent and not further develop into the adult form (for example, in some newts). This is a type of neoteny.
Eurosta solidaginis Goldenrod Gall Fly larva
It is a misunderstanding that the larval form always reflects the group's evolutionary history. It could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases the larval form might differ more from the group's common origin than the adult form.
The early life stages of most fish species are considerably different from juveniles and adults of their species and are called larvae.
Names of various kinds of larvae:
Insects (Class Insecta) are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the Earth, where they're most diverse at the equator and their diversity declines toward the poles. With over a million described species—more than half of all known living organisms[2][3]—with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet.[4] Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
There are approximately 2,000 praying mantis, 5,000 dragonfly species, 20,000 grasshopper, 82,000 true bug, 120,000 fly, 110,000 bee, wasp ant and sawfly, 170,000 butterfly and moth, and 360,000 beetle species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million.[2][5][6] Adult modern insects range in size from a 0.139 mm (0.00547 in) fairyfly (Dicopomorpha echmepterygis) to a 56.7 centimetres (22.3 in) long stick insect (Phobaeticus chani).[7] The heaviest documented insect was a Giant Weta of 70 g (2½ oz), but other possible candidates include the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.[8]
The study of insects (from Latin insectus, meaning "cut into sections") is called entomology, from the Greek εντομον, also meaning "cut into sections".[9]
The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly. Larvae often have special (larval) organs which do not occur in the adult form. The larvae of some species can become pubescent and not further develop into the adult form (for example, in some newts). This is a type of neoteny.
Eurosta solidaginis Goldenrod Gall Fly larva
It is a misunderstanding that the larval form always reflects the group's evolutionary history. It could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases the larval form might differ more from the group's common origin than the adult form.
The early life stages of most fish species are considerably different from juveniles and adults of their species and are called larvae.
Names of various kinds of larvae:
Insects (Class Insecta) are the biggest class of arthropods and the only ones with wings. They are the most diverse group of animals on the Earth, where they're most diverse at the equator and their diversity declines toward the poles. With over a million described species—more than half of all known living organisms[2][3]—with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet.[4] Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
There are approximately 2,000 praying mantis, 5,000 dragonfly species, 20,000 grasshopper, 82,000 true bug, 120,000 fly, 110,000 bee, wasp ant and sawfly, 170,000 butterfly and moth, and 360,000 beetle species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million.[2][5][6] Adult modern insects range in size from a 0.139 mm (0.00547 in) fairyfly (Dicopomorpha echmepterygis) to a 56.7 centimetres (22.3 in) long stick insect (Phobaeticus chani).[7] The heaviest documented insect was a Giant Weta of 70 g (2½ oz), but other possible candidates include the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.[8]
The study of insects (from Latin insectus, meaning "cut into sections") is called entomology, from the Greek εντομον, also meaning "cut into sections".[9]
Mouse
General
Mice have been known to humans since antiquity. The Romans differentiated poorly between mice and rats, calling rats Mus Maximus (big mouse) and referring to mice as Mus Minimus (little mouse). Mice can also be kept as pets as they are often sold in petshops.[1]
De-coloration in mice was supposedly first noticed in China by 900 BC, where a white mouse was discovered.The white gene is a recessive gene which arose from mutation.
The word "mouse" and the word muscle are related. Muscle stems from musculus meaning small mouse - possibly because of a similarity in shape.[2][3] The word "mouse" is a cognate of Sanskrit mus meaning 'to steal,' which is also cognate with mys in Old Greek and mus in Latin.[4]
[edit] Characteristics
Mice range in size from 12 to 21 cm (4 to 8 inches) long (including a long tail). They weigh from .25 to 2 oz (7.1 to 57 g). The coat color ranges from white to brown to gray. Most mice have a pointed snout with long whiskers, round ears, and thin tails. Many mice scurry along the ground, but some can hop or jump.
[edit] Distribution and habitat
All species of Mus are native to Eurasia and Africa, where they range from lowlands to mountaintops. The five species in the subgenus Pyromys are found in Sri Lanka, India, Pakistan, and mainland Southeast Asia. Much of their range originally consisted of open grasslands or grassy patches in forests.
[edit] Reproduction
Pups that are just a day old
Breeding onset is at about 50 days of age in both females and males, although females may have their first estrus at 25-40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating.[5]
Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the estrous cycle is known as the Whitten effect. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the Bruce effect.[5]
The average gestation period is 20 days. A fertile postpartum estrus occurs 14-24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3-10 days owing to delayed implantation. The average litter size is 10-12 during optimum production, but is highly strain dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh 0.5–1.5 g (0.018–0.053 oz) at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 10–12 g (0.35–0.42 oz). If the postpartum estrus is not utilized, the female resumes cycling 2-5 days postweaning.[5]
Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.[5]
Mice have been known to humans since antiquity. The Romans differentiated poorly between mice and rats, calling rats Mus Maximus (big mouse) and referring to mice as Mus Minimus (little mouse). Mice can also be kept as pets as they are often sold in petshops.[1]
De-coloration in mice was supposedly first noticed in China by 900 BC, where a white mouse was discovered.The white gene is a recessive gene which arose from mutation.
The word "mouse" and the word muscle are related. Muscle stems from musculus meaning small mouse - possibly because of a similarity in shape.[2][3] The word "mouse" is a cognate of Sanskrit mus meaning 'to steal,' which is also cognate with mys in Old Greek and mus in Latin.[4]
[edit] Characteristics
Mice range in size from 12 to 21 cm (4 to 8 inches) long (including a long tail). They weigh from .25 to 2 oz (7.1 to 57 g). The coat color ranges from white to brown to gray. Most mice have a pointed snout with long whiskers, round ears, and thin tails. Many mice scurry along the ground, but some can hop or jump.
[edit] Distribution and habitat
All species of Mus are native to Eurasia and Africa, where they range from lowlands to mountaintops. The five species in the subgenus Pyromys are found in Sri Lanka, India, Pakistan, and mainland Southeast Asia. Much of their range originally consisted of open grasslands or grassy patches in forests.
[edit] Reproduction
Pups that are just a day old
Breeding onset is at about 50 days of age in both females and males, although females may have their first estrus at 25-40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating.[5]
Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the estrous cycle is known as the Whitten effect. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the Bruce effect.[5]
The average gestation period is 20 days. A fertile postpartum estrus occurs 14-24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3-10 days owing to delayed implantation. The average litter size is 10-12 during optimum production, but is highly strain dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh 0.5–1.5 g (0.018–0.053 oz) at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 10–12 g (0.35–0.42 oz). If the postpartum estrus is not utilized, the female resumes cycling 2-5 days postweaning.[5]
Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perineums.[5]
Mushroom
Birds (class Aves) are bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.7 m (9 ft) Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 155–150 Ma. Most paleontologists regard birds as the only clade of dinosaurs that survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Bird
Birds (class Aves) are bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.7 m (9 ft) Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 155–150 Ma. Most paleontologists regard birds as the only clade of dinosaurs that survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Langganan:
Postingan (Atom)