How do Tree Swallows add heat to their eggs?
Females cover eggs with their bodies, conducting heat from themselves to the eggs and keeping them warm enough long enough for the embryos to grow. This type of heat transfer and temperature regulation is called “incubation”. However, females still need to find food and maintain their own bodies, so having to incubate eggs places an extra energy demand on females. During the time females are away the eggs cool down. They must be reheated upon the females’ return before embryonic development can begin again. So incubating female Tree Swallows must strike a balance between their own self-maintenance and the growth of the embryos within their eggs.
