question: What is it called when birds keep their eggs warm while the embryos inside develop?
distractor3: fertilization
distractor1: insulation
distractor2: spawning
correct_answer: incubation
support: After birds lay their eggs, they generally keep the eggs warm with their body heat while the embryos inside continue to develop. This is called incubation, or brooding . In most species, parents stay together for at least the length of the breeding season. In some species, they stay together for life. By staying together, the males as well as females can incubate the eggs and later care for the hatchlings . Birds are the only nonhuman vertebrates with this level of male parental involvement.