Researchers have found that the color of bird eggs has a lot to do with temperature
The great cuckoo lodges its eggs in the nests of more than 100 species of birds. In order to prevent the eggs from being driven away by the owners of the nest, they can produce more than 20 colored eggs.
 The results show that dark eggs are more common in areas where the intensity of sunlight is lower, while eggs are generally lighter in areas where the intensity of sunlight is higher and warmer, and the team believes that darker-colored eggshells mean that they can absorb more calories and thus have an advantage in a colder environment because the embryo in the egg needs a stable environmental temperature, but it does not have the ability to regulate the temperature itself