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The birds in this genus are infamous for laying their eggs in other birds' nests. The female cowbird notes when a potential host bird lays its eggs, and when the nest is left momentarily unattended, the cowbird lays its own egg in it. The female cowbird may continue to observe this nest after laying eggs.
Holoblastic cleavage occurs in animals with little yolk in their eggs, [10] such as humans and other mammals who receive nourishment as embryos from the mother, via the placenta or milk, such as might be secreted from a marsupium. Meroblastic cleavage occurs in animals whose eggs have more yolk (i.e. birds and reptiles).
These mostly relate to its habit of following cattle and other large animals, and it is known variously as cow crane, cow bird or cow heron, or even elephant bird or rhinoceros egret. [23] Its Arabic name, abu qerdan , means "father of ticks", a name derived from the huge number of parasites such as avian ticks found in its breeding colonies.
In comparison, a group of eggs and the offspring that hatch from them are frequently called a clutch, while young birds are often called a brood. Animals from the same litter are referred to as littermates.
Oviparous animals laying eggs with thick calcium shells, such as chickens, or thick leathery shells generally reproduce via internal fertilisation so that the sperm fertilises the egg without having to pass through the thick, protective, tertiary layer of the egg. Ovoviviparous and viviparous animals also use internal fertilisation.
Some species, such as cats, cows and domestic pigs, are polyestrous, meaning that they can go into heat several times per year. Seasonally polyestrous animals or seasonal breeders have more than one estrous cycle during a specific time of the year and can be divided into short-day and long-day breeders:
The U.S. Department of Agriculture said this week that cow-to-cow transmission is a factor in the spread of bird flu in dairy herds, but it still does not know exactly how the virus is being moved ...
Reptile eggs, bird eggs, and monotreme eggs are laid out of water and are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are usually kept within a warm and favorable temperature range while the embryo grows. When the embryo is adequately developed it hatches, i.e., breaks out of the egg's shell.