Why Are Some Bird Eggs Blue?

Bird eggs can range in color from white to mottled to dark greenish-blue. Scientists have suggested that eggshell pigmentation has something to do either with camouflage, especially for birds that nest on the ground, or protection from the effects of sunlight, especially in nests found in brightly-lit places. To clarify the interactions between eggshell color and sunlight, researchers David Lahti and Dan Ardia studied village weaverbirds, a species that produces a variety of egg colors, and found that nesting environment has a lot to do with the color of a bird’s eggs.

Blue for a reason:

• If eggs are too dark, they will absorb more light and overheat in sunlight. However, if they are too pale, the researchers found, they will not effectively shield against ultraviolet radiation.
• The researchers determined that pale blue eggs, most commonly associated with robins, may be the ideal color for protecting a developing embryo from both excess heat and UV radiation, especially in more sheltered settings.
• For nests in brighter environments, such as open land and more arid regions, the danger of overheating favors white or light-colored eggshells.

Frequently Asked Questions

What causes some bird eggs to be blue?

The blue coloration in bird eggs is primarily due to the pigment biliverdin, which is deposited on the eggshell while it is being formed in the mother's oviduct. This pigment not only provides the egg with its distinctive color but also has antioxidant properties that may help protect the embryo.

Do blue eggs have any advantages over eggs of other colors?

Blue eggs may have several advantages. The pigment biliverdin, which gives them their color, has been shown to have antioxidant properties that could protect the embryo from harmful bacteria and excessive sunlight. Additionally, the color might help in camouflage or in signaling the female's health to potential mates.

Which bird species lay blue eggs?

Several bird species lay blue eggs, with the American robin being one of the most well-known examples. Other species include the Eastern bluebird, the starling, and some thrushes. The shade of blue can vary significantly among species, from pale blue to turquoise.

Is the color of a bird's egg related to its habitat?

Yes, the color of a bird's egg can be related to its habitat. Birds that nest in open or exposed areas tend to have eggs that are camouflaged to match their surroundings, which can include various shades of blue. This helps protect the eggs from predators by making them less visible.

Can the diet of a bird affect the color of its eggs?

The diet of a bird can influence the intensity of the egg's color. Birds with a diet rich in carotenoids tend to lay eggs with deeper pigmentation. However, the blue color in eggs is less influenced by diet and more by genetic factors and the presence of biliverdin.

Are blue eggs more or less common than eggs of other colors?

Blue eggs are less common than white or brown eggs in the bird world. The production of blue pigment, biliverdin, is a metabolic process that not all bird species have evolved. Therefore, while blue eggs are relatively rare, they are a remarkable example of the diversity of avian reproductive strategies.