Australian ornithologists believed they might be at least a step closer to answering one of their field’s more enduring questions to why “do birds lay colorful eggs?
In a study unveiled on Thursday, Macquarie University wildlife biology doctoral candidate Kiara L’Herpiniere and her colleagues have found a link between eggshell colours and the way nest constructions have evolved.
A relevant paper was published in the latest edition of the journal Evolution.
Until about 40 million years ago, songbirds built complex dome-shaped nests with insulated “walls” and “roofs”.
Over time, however, they developed the ability to create the now-familiar “open-cup” nests.
L’Herpiniere said their study has revealed that egg colors, like the nests, have evolved over the ages.
During the dome-nest era, eggs were mainly white or dark brown, whereas in modern nests they can be a variety of colors such as white, pink, olive, blue, pink, and brown.
“Any role the shell pigment is playing is inevitably going to be for the ultimate survival of that bird embryo,’’ she told Xinhua.
She said that understanding this part of the evolutionary process can lead to important scientific insights.
Many researchers believed the various colours helped to protect exposed eggs from environmental factors such as extreme cold or rain.
Eggs with darker pigments, for instance, heat up faster and maintain heat longer than white eggs, which can be crucial in colder climates.
Cup nests, however, pose particular risks for eggs such as being exposed to the weather and predators whenever the incubating parents were away foraging.
The eggs can also be vulnerable to breeds such as cuckoos which opportunistically lay their eggs in other birds’ nests.
A hypothesis raised by L’Herpiniere’s team is that the colorful eggs are an evolutionary tactic to make it harder for cuckoos to surreptitiously include their eggs among an already existing clutch in a nest.
Whatever the answer, there still remain unsolved questions about colorful eggs.
How, for instance, do the different colors and complex patterns develop while the egg was still inside the female? Such questions continue to intrigue L’Herpiniere who is fascinated by the “astonishing variation in eggshell colour.’’
“It’s all very special and it’s why I have focused my research on understanding the mechanisms of colour in nature,’’ she said.
