In many animal documentaries, we often see such scenes: parent birds incubate eggs in their nests and feed newly hatched chicks until they can move independently; turtles simply lay their eggs in the mud near water and bury them. After a period of time, the baby turtles will peck through the shell and start their own lives. Why do only birds need to incubate eggs while turtles don't?
The basic structure of bird eggs and turtle eggs is similar, but their shapes are slightly different. Bird eggs are mostly oval or spherical, while turtle eggs are mostly cylindrical (among which sea turtle eggs resemble table tennis balls). The outer layer of the egg is covered with a hard calcareous shell and amniotic membrane, which encloses the embryo and the nutrients needed for embryo development, namely albumen and yolk. Embryo development is a complex physiological process that requires a suitable environmental temperature. Birds are warm-blooded animals that can generate heat through metabolism. During the breeding season, birds form a bare incubation patch on their abdomens, through which they transfer heat to the eggs to maintain their temperature within a suitable range. Turtles, on the other hand, are cold-blooded animals with extremely limited heat generated by metabolism. Therefore, turtles cannot incubate eggs and instead bury the eggs in mud or sand to provide a more stable external environment for the embryos.
In fact, it's not just turtles that don't incubate eggs. Incubating eggs is a reproductive method unique to warm-blooded animals, or more specifically, ectothermic animals.