Question

How do birds keep their eggs warm so that they will develop?

Answer 1

Body temperature of birds is more than mammals. To keep eggs warm birds incubate eggs with body heat.

Explanation:

Temperature of human is 37.5 degrees Celsius. While temperature of birds is around 40 degrees Celsius. The bird eggs develop only when incubated between 39 to 40 degrees.
To keep sufficient temperature for incubation female bird actually sit over the egg. This keeps eggs warm. Many a times eggs are incubated by both parent birds.
If rugs are not incubated the chick will not develop.