Seeing actual birds with its eggs is probably the most satisfying moment for ornithologists.
Bird eggs come in different sizes and are often colorful. There are at least 18,000 extant species of birds in the world today, and all of those have a different pattern and color for their eggs. Bird patterns and color have become a unique natural spectacle that people use it for identifying birds in the area.
Not just for camouflage
For years, some ornithologists and evolutionary biologists dedicated their time to figure out why bird eggs would have a different color and patterns. Many suggest that these are genetic adaptations as a response to the environmental conditions a certain bird faces and what climate is it adaptable to. It was discovered that putting pigments on eggs is a trait that was passed down from the birds' direct ancestor—the dinosaurs.
But why? That question is still unanswered until recently. A study published in Nature provided an answer to the age-old question regarding bird eggs and their color, and it is closely linked to the present climate condition to where the bird naturally occurs.
To summarize, the colder the climate, the darker the egg pigment. The paper explains that the key to the bird embryo's survival is its ability to stay "within strict thermal limits." Birds in colder regions always lay darker eggs, and it is because darker pigments tend to reflect sunlight less, which helps regulate heat.
An additional characteristic of eggs with darker pigments is its ability to filter harmful ultraviolet radiation and sometimes contain anti-microbial properties to avoid fungal attacks.
Collection is the Key to Discovery
Coming to this conclusion is no easy task for the researchers behind the study. Different analyses were done by Phillip Wisocki and his colleagues in Long Island University Post using different bird eggs from 634 species under 36 of 40 orders of birds. These eggs are collected from natural habitats and museums while meticulously noting the differences in its pigments alongside the geographical distribution of the birds. Through this experiment, they concluded that eggs are darker when the species thrives in areas where solar radiation and the temperature are low. The same thing happened with birds' eggs from species that dwell in open areas, most probably to provide camouflage.
The team did an experiment with chicken, duck, and quail eggs—all in different colors—exposing them to solar radiation, which helped them prove their theory on the egg's thermoregulation process. Those who have darker eggs were able to maintain incubation temperatures for longer times.
Adaptation Anecdotes
Although the researchers found out that this can be the primary factor for the coloration and patterns on bird eggs, they know this isn't the sole reason. It will always come down to the environmental condition that the bird is facing. Pigments are developed mostly for camouflage to avoid being eaten by predators. In an interview with Discover, behavior ecologist and co-author of the paper Daniel Hanley explains: "There are a lot of pressures that influence the way you make a life as a bird."
