Bird Eggs Are Darker In Cold Climates Than Warm Ones

Bird eggs come in a stunning array of colors, but from a global perspective, this diversity follows a simple pattern. Cooler climates and darker bird eggs support the new research. According to the study published online October 28 in the journal Nature Ecology and Evolution, bird eggs… Darker eggs absorb more heat than lighter eggs, which may help the embryos develop inside the nest and keep them warm while their parents search for food.

Biologists have long tried to tease out the selective forces that shape and color certain types of bird eggs. These forces include keeping the eggs hidden from predators, protecting them from bacteria, signaling the quality of bird eggs, and keeping the eggs warm, says Philip Wysocki, who worked on the research during the study. Biology at Long Island University College in Brookville, New York All of these hypotheses have some level of support, but scientists aren’t sure whether any of these factors are important in determining the diversity of bird eggs globally, says Daniel Hanley, Wysocki’s biologist advisor, if If your focus is too narrow you can miss a lot of what is happening.

Using collections of bird eggs held in some museums, Hanley Wysocki and his colleagues collected data on eggs from 634 bird species for about 36 of the 40 living orders of birds. They then analyzed the data against a global map, and found that the brightness and gloss of bird eggshells and their color are closely related. temperature even after correcting for similarities in color between closely related species.

Birds farther north, which tend toward cooler weather, had darker, brown eggs, Hanley says, and birds’ eggs became relatively light and dull for birds living closer to the equator, although bird egg colors were generally more variable in the regions. Tropical.

The researchers suggest that the trend may reflect adaptation to the cold. Dark bird eggs, such as a dark car parked in the sun, absorb more heat rays from the sun than light eggs. To test the theory, the researchers exposed white, brown, and blue chicken eggs to direct sunlight and retain traces of heat. Brown ones warm up faster and cool more slowly than light eggs, and Hanley says in the Arctic parents must go out to forage and return to their eggs quickly to warm them.

Biologist Mary Caswell Stoddard welcomed the study’s interest in the role of bird egg color in thermoregulation. Stoddard of Princeton University says, “This study, along with the discovery that birds living in cold habitats tend to lay darker eggs, is very exciting, but there is no doubt that there are other selective factors at work.” the study.