As the mating season draws near, female owls begin acting as if they are brooding even before there are eggs. After an egg is fertilized (usually within a day or 2), it goes through several stages of development. The developing egg, which is known as the yolk, initially picks up several coatings of albumen (egg white). It then gets two coatings of a material that forms the familiar (calcareous shell) hard shell. As soon as the first egg forms a shell, another egg begins to develop. The first egg may be ready to lay as early as one day after copulation.
Initially, eggs are laid individually every 1 to 2 days.
During the incubation process, female owls rarely leave the nest except to defecate and get water. To help with incubation, female owls have a sparsely feathered brood patch on their bellies that has a higher percentage of blood vessels than other parts of the skin. Blood flow through these vessels creates a good source of heat (in the range 101-103)for the eggs.
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