Birth is the act or process of bearing or bringing forth offspring , also referred to in technical contexts as parturition . In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.
60-482: In some species, the offspring is precocial and can move around almost immediately after birth but in others, it is altricial and completely dependent on parenting. In marsupials , the fetus is born at a very immature stage after a short gestation and develops further in its mother's womb pouch . It is not only mammals that give birth. Some reptiles, amphibians, fish and invertebrates carry their developing young inside them. Some of these are ovoviviparous , with
120-574: A continuum, without distinct gaps between them. In fish , this often refers to the presence or absence of a stomach : precocial larvae have one at the onset of first feeding whereas altricial fish do not. Depending on the species, the larvae may develop a functional stomach during metamorphosis (gastric) or remain stomachless (agastric). Precocial young have open eyes, hair or down, large brains, and are immediately mobile and somewhat able to flee from or defend themselves against predators. For example, with ground-nesting birds such as ducks or turkeys ,
180-432: A glistening grey balloon, with a puppy inside, is propelled through the vulva . After further contractions, the sac is expelled and the bitch breaks the membranes, releasing clear fluid and exposing the puppy. The mother chews at the umbilical cord and licks the puppy vigorously, which stimulates it to breathe. If the puppy has not taken its first breath within about six minutes, it is likely to die. Further puppies follow in
240-471: A length of time. Altricial birds include hawks , herons , woodpeckers , owls , cuckoos and most passerines . Among mammals, marsupials and most rodents are altricial. Domestic cats , dogs , and primates , such as humans , are some of the best-known altricial organisms. For example, newborn domestic cats cannot see, hear, maintain their own body temperature, or gag , and require external stimulation in order to defecate and urinate. The giant panda
300-471: A length of time. Altricial birds include hawks , herons , woodpeckers , owls , cuckoos and most passerines . Among mammals, marsupials and most rodents are altricial. Domestic cats , dogs , and primates , such as humans , are some of the best-known altricial organisms. For example, newborn domestic cats cannot see, hear, maintain their own body temperature, or gag , and require external stimulation in order to defecate and urinate. The giant panda
360-430: A multiple birth) signifies the end of stage two. The cow scrambles to her feet (if lying down at this stage), turns round and starts vigorously licking the calf. The calf takes its first few breaths and within minutes is struggling to rise to its feet. The third and final stage of labor is the delivery of the placenta , which is usually expelled within a few hours and is often eaten by the normally herbivorous cow. Birth
420-461: A similar way one by one usually with less straining than the first usually at 15-60-minute intervals. If a pup has not been passed in 2 hours a veterinarian should be contacted. Stage three is the passing of the placentas. This often occurs in conjunction with stage two with the passing of each offspring. The mother will then usually eat the afterbirth. This is an adaption to keep the den clean and prevent its detection by predators. An infant marsupial
480-405: A time, although they may have twin or multiple births on occasion. In these large animals, the birth process is similar to that of a human, though in most the offspring is precocial . This means that it is born in a more advanced state than a human baby and is able to stand, walk and run (or swim in the case of an aquatic mammal) shortly after birth. In the case of whales, dolphins and porpoises,
540-541: A very few give birth to offspring that are miniature versions of the adult. The aphid has a complex life cycle and during the summer months is able to multiply with great rapidity. Its reproduction is typically parthenogenetic and viviparous and females produce unfertilized eggs which they retain within their bodies. The embryos develop within their mothers' ovarioles and the offspring are clones of their mothers. Female nymphs are born which grow rapidly and soon produce more female offspring themselves. In some instances,
600-452: Is born in a very immature state. The gestation period is usually shorter than the intervals between oestrus periods. The first sign that a birth is imminent is the mother cleaning out her pouch . When it is born, the infant is pink, blind, furless and a few centimetres long. It has nostrils in order to breathe and forelegs to cling onto its mother's hairs but its hind legs are undeveloped. It crawls through its mother's fur and makes its way into
660-407: Is external protrusion of the amniotic sac through the vulva, closely followed by the appearance of the calf's front hooves and head in a front presentation (or occasionally the calf's tail and rear end in a posterior presentation). During the second stage, the cow will usually lie down on her side to push and the calf progresses through the birth canal. The complete delivery of the calf (or calves in
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#1732772632155720-559: Is hypothesized to occur so that exposure to predators during the nestling stage of development can be minimized. In the case of mammals, it has been suggested that large, hearty adult body sizes favor the production of large, precocious young, which develop with a longer gestation period. Large young may be associated with migratory behavior, extended reproductive period, and reduced litter size. It may be that altricial strategies in mammals, in contrast, develop in species with less migratory and more territorial lifestyles, such as Carnivorans ,
780-559: Is hypothesized to occur so that exposure to predators during the nestling stage of development can be minimized. In the case of mammals, it has been suggested that large, hearty adult body sizes favor the production of large, precocious young, which develop with a longer gestation period. Large young may be associated with migratory behavior, extended reproductive period, and reduced litter size. It may be that altricial strategies in mammals, in contrast, develop in species with less migratory and more territorial lifestyles, such as Carnivorans ,
840-411: Is notably the largest placental mammal to have altricial, hairless young upon birth. The larval stage of insect development is considered by some to be a form of altricial development, but it more accurately depicts, especially amongst eusocial animals, an independent phase of development, as the larvae of bees, ants, and many arachnids are completely physically different from their developed forms, and
900-411: Is notably the largest placental mammal to have altricial, hairless young upon birth. The larval stage of insect development is considered by some to be a form of altricial development, but it more accurately depicts, especially amongst eusocial animals, an independent phase of development, as the larvae of bees, ants, and many arachnids are completely physically different from their developed forms, and
960-461: Is only brief amongst primates; their offspring soon develop stronger bones, grow in spurts, and quickly mature in features. This unique growth pattern allows for the hasty adaptivity of most simians, as anything learned by children in between their infancy and adolescence is memorized as instinct; this pattern is also in contrast to more prominently altricial mammals, such as many rodents , which remain largely immobile and undeveloped until grown to near
1020-461: Is only brief amongst primates; their offspring soon develop stronger bones, grow in spurts, and quickly mature in features. This unique growth pattern allows for the hasty adaptivity of most simians, as anything learned by children in between their infancy and adolescence is memorized as instinct; this pattern is also in contrast to more prominently altricial mammals, such as many rodents , which remain largely immobile and undeveloped until grown to near
1080-413: Is termed whelping in dogs. Among dogs , as whelping approaches, contractions become more frequent. Labour in the bitch can be divided into 3 stages. The first stage is when the cervix dilates, causing discomfort and restlessness in the dog. Common signs of this stage are panting, fasting, and/or vomiting. This may last up to 12 hours. Stage two is the passage of the offspring. The amniotic sac looking like
1140-542: The Serengeti ecosystem than hartebeests , their closest taxonomic relative. Hartebeest calves are not as precocial as wildebeest calves and take up to thirty minutes or more before they stand, and as long as forty-five minutes before they can follow their mothers for short distances. They are unable to keep up with their mothers until they are more than a week old. Black mambas are highly precocial; as hatchlings, they are fully independent, and are capable of hunting prey
1200-486: The Serengeti ecosystem than hartebeests , their closest taxonomic relative. Hartebeest calves are not as precocial as wildebeest calves and take up to thirty minutes or more before they stand, and as long as forty-five minutes before they can follow their mothers for short distances. They are unable to keep up with their mothers until they are more than a week old. Black mambas are highly precocial; as hatchlings, they are fully independent, and are capable of hunting prey
1260-424: The right ventricle starts to flow to the lungs for gaseous exchange and oxygenated blood returns to the left atrium , which is pumped into the left ventricle , and then pumped into the main arterial system. As a result of these changes, the blood pressure in the left atrium exceeds the pressure in the right atrium, and this pressure difference forces the foramen ovale to close separating the left and right sides of
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#17327726321551320-429: The uterus are not obvious externally, but the cow may be restless. She may appear agitated, alternating between standing and lying down, with her tail slightly raised and her back arched. The fetus is pushed toward the birth canal by each contraction and the cow's cervix gradually begins to dilate. Stage one may last several hours, and ends when the cervix is fully dilated. Stage two can be seen to be underway when there
1380-550: The Tarangire National Park of Tanzania, estimated to have been born in August 2017. Birthing in cattle is typical of a larger mammal. A cow goes through three stages of labor during normal delivery of a calf. During stage one, the animal seeks a quiet place away from the rest of the herd. Hormone changes cause soft tissues of the birth canal to relax as the mother's body prepares for birth. The contractions of
1440-400: The buttocks in a breech birth ) of the baby is pushed against the cervix , which gradually dilates until it is fully dilated at 10 cm diameter. At some time, the amniotic sac bursts and the amniotic fluid escapes (also known as rupture of membranes or breaking the water). In stage two, starting when the cervix is fully dilated, strong contractions of the uterus and active pushing by
1500-637: The domestic chicken , many species of ducks and geese , waders , rails , and the hoatzin . Precocial birds can provide protein-rich eggs and thus their young hatch in the fledgling stage – able to protect themselves from predators and the females have less post-natal involvement. Altricial birds are less able to contribute nutrients in the pre-natal stage; their eggs are smaller and their young are still in need of much attention and protection from predators. This may be related to r/K selection ; however, this association fails in some cases. In birds, altricial young usually grow faster than precocial young. This
1560-637: The domestic chicken , many species of ducks and geese , waders , rails , and the hoatzin . Precocial birds can provide protein-rich eggs and thus their young hatch in the fledgling stage – able to protect themselves from predators and the females have less post-natal involvement. Altricial birds are less able to contribute nutrients in the pre-natal stage; their eggs are smaller and their young are still in need of much attention and protection from predators. This may be related to r/K selection ; however, this association fails in some cases. In birds, altricial young usually grow faster than precocial young. This
1620-454: The eggs being hatched inside the mother's body, and others are viviparous , with the embryo developing inside their body, as in the case of mammals. Humans usually produce a single offspring at a time. The mother's body is prepared for birth by hormones produced by the pituitary gland , the ovary and the placenta . The total gestation period from fertilization to birth is normally about 38 weeks (birth usually occurring 40 weeks after
1680-437: The expectation that a small number may survive to become mature individuals. Terrestrial invertebrates may also produce large numbers of eggs, a few of which may avoid predation and carry on the species. Some fish, reptiles, and amphibians have adopted a different strategy and invest their effort in producing a small number of young at a more advanced stage which are more likely to survive to adulthood. Birds care for their young in
1740-518: The genera Tiliqua and Corucia , give birth to live young that develop internally, deriving their nourishment from a mammal-like placenta attached to the inside of the mother's uterus. In a recently described example, an African species, Trachylepis ivensi , has developed a purely reptilian placenta directly comparable in structure and function to a mammalian placenta. Vivipary is rare in snakes , but boas and vipers are viviparous, giving birth to live young. The majority of insects lay eggs but
1800-460: The genus Nectophrynoides are ovoviviparous, developing through the larval stage inside the mother's oviduct and eventually emerging as fully formed juveniles. A more developed form of viviparity called placental viviparity is adopted by some species of scorpions and cockroaches, certain genera of sharks , snakes and velvet worms . In these, the developing embryo is nourished by some form of placental structure. The earliest known placenta
1860-422: The heart. The umbilical vein , umbilical arteries , ductus venosus and ductus arteriosus are not needed for life in air and in time these vessels become ligaments (embryonic remnants). Large mammals , such as primates , cattle , horses , some antelopes , giraffes , hippopotamuses , rhinoceroses , elephants , seals , whales , dolphins , and porpoises , generally are pregnant with one offspring at
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1920-422: The last menstrual period ). The normal process of childbirth takes several hours and has three stages. The first stage starts with a series of involuntary contractions of the muscular walls of the uterus and gradual dilation of the cervix. The active phase of the first stage starts when the cervix is dilated more than about 4 cm in diameter and is when the contractions become stronger and regular. The head (or
1980-422: The mother expels the baby out through the vagina , which during this stage of labour is called a birth canal as this passage contains a baby, and the baby is born with umbilical cord attached. In stage three, which begins after the birth of the baby, further contractions expel the placenta , amniotic sac, and the remaining portion of the umbilical cord usually within a few minutes. Enormous changes take place in
2040-559: The mothers of which are capable of bearing a fetus in the early stages of development and focusing closely and personally upon its raising, as opposed to precocial animals which provide their youths with a bare minimum of aid and otherwise leave them to instinct. Human children, and those of other primates, exemplify a unique combination of altricial and precocial development. Infants are born with minimal eyesight, compact and fleshy bodies, and "fresh" features (thinner skin, small noses and ears, and scarce hair if any). However, this stage
2100-559: The mothers of which are capable of bearing a fetus in the early stages of development and focusing closely and personally upon its raising, as opposed to precocial animals which provide their youths with a bare minimum of aid and otherwise leave them to instinct. Human children, and those of other primates, exemplify a unique combination of altricial and precocial development. Infants are born with minimal eyesight, compact and fleshy bodies, and "fresh" features (thinner skin, small noses and ears, and scarce hair if any). However, this stage
2160-411: The nest and provide for their needs after hatching and it is perhaps unsurprising that internal development does not occur in birds, given their need to fly. Ovoviviparity is a mode of reproduction in which embryos develop inside eggs that remain in the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in that there is internal fertilization and
2220-403: The nest in a short period of time following hatching (e.g. 24 hours). Many precocial chicks are not independent in thermoregulation (the ability to regulate their body temperatures), and they depend on the attending parent(s) to brood them with body heat for a short time. Precocial birds find their own food, sometimes with help or instruction from their parents. Examples of precocial birds include
2280-403: The nest in a short period of time following hatching (e.g. 24 hours). Many precocial chicks are not independent in thermoregulation (the ability to regulate their body temperatures), and they depend on the attending parent(s) to brood them with body heat for a short time. Precocial birds find their own food, sometimes with help or instruction from their parents. Examples of precocial birds include
2340-456: The nest, respectively. Precocial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous , meaning that they leave the nest shortly after birth or hatching. Altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. These categories form
2400-401: The newborn nymphs already have developing embryos inside them. Precocial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous , meaning that they leave the nest shortly after birth or hatching. Altricial species are those in which the young are underdeveloped at
2460-444: The newborn's circulation to enable breathing in air. In the uterus, the fetus is dependent on circulation of blood through the placenta for sustenance including gaseous exchange and the unborn baby's blood bypasses the lungs by flowing through the foramen ovale , which is a hole in the septum dividing the right atrium and left atrium . After birth the umbilical cord is clamped and cut, the baby starts to breathe air, and blood from
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2520-415: The pouch. Here it fixes onto a teat which swells inside its mouth. It stays attached to the teat for several months until it is sufficiently developed to emerge. Joeys are born with "oral shields"; in species without pouches or with rudimentary pouches these are more developed than in forms with well-developed pouches, implying a role in maintaining the young attached to the mother's nipple. Many reptiles and
2580-737: The pre-pupal stages of insect life might be regarded as equivalent to vertebrate embryonic development. The word “altriciality” is derived from the Latin root alere , meaning "to nurse, to rear, or to nourish", and indicates the need for young to be fed and taken care of for a long duration. The span between precocial and altricial species is particularly broad in the biology of birds . Precocial birds hatch with their eyes open and are covered with downy feathers that are soon replaced by adult-type feathers. Birds of this kind can also swim and run much sooner after hatching than altricial young, such as songbirds. Very precocial birds can be ready to leave
2640-686: The pre-pupal stages of insect life might be regarded as equivalent to vertebrate embryonic development. The word “altriciality” is derived from the Latin root alere , meaning "to nurse, to rear, or to nourish", and indicates the need for young to be fed and taken care of for a long duration. The span between precocial and altricial species is particularly broad in the biology of birds . Precocial birds hatch with their eyes open and are covered with downy feathers that are soon replaced by adult-type feathers. Birds of this kind can also swim and run much sooner after hatching than altricial young, such as songbirds. Very precocial birds can be ready to leave
2700-399: The same day. Enantiornithes and pterosaurs were also capable of flight soon after hatching. Another example is the blue wildebeest , the calves of which can stand within an average of six minutes from birth and walk within thirty minutes; they can outrun a hyena within a day. Such behavior gives them an advantage over other herbivore species and they are 100 times more abundant in
2760-399: The same day. Enantiornithes and pterosaurs were also capable of flight soon after hatching. Another example is the blue wildebeest , the calves of which can stand within an average of six minutes from birth and walk within thirty minutes; they can outrun a hyena within a day. Such behavior gives them an advantage over other herbivore species and they are 100 times more abundant in
2820-401: The single calf is normally born tail first which minimizes the risk of drowning. The mother encourages the newborn calf to rise to the surface of the water to breathe. Large mammals which give birth to twins is much more rare, but it does occur occasionally even for mammals as large as elephants. In April 2018, approximately 8-month old elephant twins were sighted joining their mother's herd in
2880-802: The size of a small rat . Precociality is thought to be ancestral in birds. Thus, altricial birds tend to be found in the most derived groups. There is some evidence for precociality in protobirds and troodontids . Enantiornithes at least were superprecocial in a way similar to that of megapodes, being able to fly soon after birth. It has been speculated that superprecociality prevented enantiornithines from acquiring specialized toe anatomy seen in modern altricial birds. In birds and mammals altricial species are those whose newly hatched or born young are relatively immobile, lack hair or down , are not able to obtain food on their own, and must be cared for by adults; closed eyes are common, though not ubiquitous. Altricial young are born helpless and require care for
2940-802: The size of a small rat . Precociality is thought to be ancestral in birds. Thus, altricial birds tend to be found in the most derived groups. There is some evidence for precociality in protobirds and troodontids . Enantiornithes at least were superprecocial in a way similar to that of megapodes, being able to fly soon after birth. It has been speculated that superprecociality prevented enantiornithines from acquiring specialized toe anatomy seen in modern altricial birds. In birds and mammals altricial species are those whose newly hatched or born young are relatively immobile, lack hair or down , are not able to obtain food on their own, and must be cared for by adults; closed eyes are common, though not ubiquitous. Altricial young are born helpless and require care for
3000-450: The stature of their parents. In birds, the terms Aves altrices and Aves precoces were introduced by Carl Jakob Sundevall (1836), and the terms nidifugous and nidicolous by Lorenz Oken in 1816. The two classifications were considered identical in early times, but the meanings are slightly different, in that "altricial" and "precocial" refer to developmental stages, while "nidifugous" and "nidicolous" refer to leaving or staying at
3060-450: The stature of their parents. In birds, the terms Aves altrices and Aves precoces were introduced by Carl Jakob Sundevall (1836), and the terms nidifugous and nidicolous by Lorenz Oken in 1816. The two classifications were considered identical in early times, but the meanings are slightly different, in that "altricial" and "precocial" refer to developmental stages, while "nidifugous" and "nidicolous" refer to leaving or staying at
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#17327726321553120-669: The time of birth, but with the aid of their parents mature after birth. These categories form a continuum, without distinct gaps between them. In fish , this often refers to the presence or absence of a stomach : precocial larvae have one at the onset of first feeding whereas altricial fish do not. Depending on the species, the larvae may develop a functional stomach during metamorphosis (gastric) or remain stomachless (agastric). Precocial young have open eyes, hair or down, large brains, and are immediately mobile and somewhat able to flee from or defend themselves against predators. For example, with ground-nesting birds such as ducks or turkeys ,
3180-440: The vast majority of invertebrates, most fish, amphibians and all birds are oviparous , that is, they lay eggs with little or no embryonic development taking place within the mother. In aquatic organisms, fertilization is nearly always external with sperm and eggs being liberated into the water (an exception is sharks and rays, which have internal fertilization). Millions of eggs may be produced with no further parental involvement, in
3240-419: The walls of the oviduct. The Lamniforme sharks practice oophagy , where the first embryos to hatch consume the remaining eggs and sand tiger shark pups cannibalistically consume neighbouring embryos. The requiem sharks maintain a placental link to the developing young, this practice is known as viviparity . This is more analogous to mammalian gestation than to that of other fishes. In all these cases,
3300-410: The young are born alive and fully functional. The majority of caecilians are ovoviviparous and give birth to already developed offspring. When the young have finished their yolk sacs they feed on nutrients secreted by cells lining the oviduct and even the cells themselves which they eat with specialist scraping teeth. The Alpine salamander ( Salamandra atra ) and several species of Tanzanian toad in
3360-415: The young are born in an advanced state, but differ in that there is no placental connection and the unborn young are nourished by egg yolk . The mother's body provides gas exchange (respiration), but that is largely necessary for oviparous animals as well. In many sharks the eggs hatch in the oviduct within the mother's body and the embryos are nourished by the egg's yolk and fluids secreted by glands in
3420-459: The young are ready to leave the nest in one or two days. Among mammals, most ungulates are precocial, being able to walk almost immediately after birth. The word "precocial" is derived from the Latin root praecox, the same root as in precocious , meaning early maturity. Extremely precocial species are called "superprecocial". Examples are the megapode birds, which have full-flight feathers at hatching and which, in some species, can fly on
3480-459: The young are ready to leave the nest in one or two days. Among mammals, most ungulates are precocial, being able to walk almost immediately after birth. The word "precocial" is derived from the Latin root praecox, the same root as in precocious , meaning early maturity. Extremely precocial species are called "superprecocial". Examples are the megapode birds, which have full-flight feathers at hatching and which, in some species, can fly on
3540-642: Was found recently in a group of extinct fishes called placoderms . A fossil from Australia's Gogo Formation , laid down in the Devonian period, 380 million years ago, was found with an embryo inside it connected by an umbilical cord to a yolk sac . The find confirmed the hypothesis that a sub-group of placoderms, called ptyctodontids , fertilized their eggs internally. Some fishes that fertilize their eggs internally also give birth to live young, as seen here. This discovery moved our knowledge of live birth back 200 million years. The fossil of another genus
3600-516: Was found with three embryos in the same position. Placoderms are a sister group of the ancestor of all living jawed fishes ( Gnathostomata ), including both chondrichthyans , the sharks & rays, and Osteichthyes , the bony fishes. Among lizards, the viviparous lizard Zootoca vivipara , the Jackson's chameleon , slow worms and many species of skink are viviparous, giving birth to live young. Some are ovoviviparous but others such as members of
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