Question

How do birds keep their eggs warm in order that they're going to develop?

Answer 1

Hint: During the primary stage of embryonic development, the egg shell develops; pigments are added last. Ovulation and laying take about 24 hours, so female birds typically produce at the most one egg per day.

Complete answer:
Body temperature of birds is quite large. To stay warm birds incubate eggs with body heat.
Therefore, the temperature of the human body is 37.5 degrees Celsius. The temperature of birds is around 40 degrees Celsius. The bird eggs only incubated between 39 to 40 degrees.
To keep sufficient temperature for incubation, female birds actually sit over the egg. This keeps eggs warm. Many times eggs are incubated by both parent birds.
If rugs aren't incubated the chick won't develop.
Birds need to sit on their eggs to stay them warm. It is a bit like baking a cake - the heat from the parent bird makes sure that the chicks inside develop properly. This is often called 'incubation'.
To keep the eggs warm, a special warm patch grows on the parent birds' tummies. a number of their feathers drop out in order that the nice and cozy skin touches the eggs. This is often called a 'brood patch'.
Different birds sit on their eggs for various lengths of your time. Bigger birds lay bigger eggs which take longer to hatch. Blue tits incubate their eggs for 2 weeks but swans sit on theirs for nearly six weeks.

Note:
Most birds lay one egg each day until the eggs are all laid. Some birds disable fifteen eggs but others lay just one . But the parent birds don't start to incubate the eggs until they're all laid. In some birds, only the mother sits on the eggs. Others take it in turns to share with the daddy.