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Animals make use of a variety of modes of reproduction to produce their young. Traditionally this variety was classified into three modes, oviparity (embryos in eggs), viviparity (young born live), and ovoviviparity (intermediate between the first two).
[9] [23] Most birds, including passerines (perching birds), have their young born blind, naked and helpless (altricial), totally dependent for their survival on parental care. The young are typically raised in a nest; the parents catch food and regurgitate it for the young.
Goat kids will stay with their mother until they are weaned. Most mammals are viviparous, giving birth to live young. [1] However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. [2]
Vertebrate maternal behavior is a form of parental care that is specifically given to young animals by their mother in order to ensure the survival of the young. [1] Parental care is a form of altruism, which means that the behaviors involved often require a sacrifice that could put their own survival at risk. [1]
Brood parasitism: this is where the genetic parent will leave their young in either the care of a conspecific or heterospecific alloparent who commonly has a brood of their own. [28] Cuckoldry: this occurs in many colonially breeding bird species where extra-pair copulations may take place and the males end up caring for unrelated offspring. [29]
In the English language, many animals have different names depending on whether they are male, female, young, domesticated, or in groups. The best-known source of many English words used for collective groupings of animals is The Book of Saint Albans , an essay on hunting published in 1486 and attributed to Juliana Berners . [ 1 ]
The traditional modes of reproduction include oviparity, taken to be the ancestral condition, traditionally where either unfertilised oocytes or fertilised eggs are spawned, and viviparity traditionally including any mechanism where young are born live, or where the development of the young is supported by either parent in or on any part of their body.
In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5]