Revealed: 7 Birds That Lay Stunning Blue Eggs and the Fascinating Science Behind Their Color

Key Takeaways

• Several bird species including American Robins and Blackbirds lay blue eggs due to the presence of a molecule called biliverdin in their reproductive systems.
• The intensity of blue color in eggs depends on the concentration of biliverdin—higher concentration produces bluer eggs.
• Unlike brown eggs which provide camouflage, blue eggs often have distinct patterns or speckles that serve as identification markers for parent birds.
• Blue eggs come in various sizes and textures, ranging from the small eggs of Dunnocks (19mm) to the larger eggs of Magpies (35mm).
• Birds like Song Thrush and House Finch lay blue-green eggs with distinctive spots or speckles that help strengthen the shell and protect against predators.

Have you ever come across a nest having beautiful blue eggs of different sizes and textures in them? If yes, then you may wonder what kinds of birds must have laid those blue eggs. You must also think about the reason why these birds lay blue eggs and even come up with “camouflage” as a possible explanation. But it should be noted here that camouflage is the reason for the brown color of earthly shades like green. So why do birds lay blue eggs and what birds lay them? Let’s find out.

What birds lay blue eggs?

American Robin is widely known for laying blue eggs. However, they are not the only ones to do that. Here is a list of birds that lay blue eggs with varying patterns on them.

1.   American Robin

American Robin is known to sing the most beautiful songs, especially in North America. They appear in the regions during the early winter and build their round nest in trees. The female American Robins lay around 3 to 5 light blue colored eggs having no patterns on them. The size of these eggs ranges from 28 to 30 mm in length and 20 mm in width (check also our post: Do Robins Reuse Their Nests?).

2.   Blackbird

Blackbirds are known for their strong beaks that they use to pull insects and food dug in the soil. They lay 3-5 bluish-green colored eggs between March and July. They have red speckles on them. The blackbird’s eggs are generally 29 mm in length and 22 mm in width.

3.   Song Thrush

Song thrushes are brown-colored birds that sing repetitive notes. These birds lay clear and glossy blue-colored eggs having purple or black spots on them. The eggs are laid in a cluster of 4 or 5. The size of the eggs is usually 21 mm in width and 27 mm lengthwise.

4.   Dunnock

Dunnocks are popular for the distinctive multifunctional sound that they use as a contact call, display, and alarm call. These birds resemble the normal house-sparrows. Their eggs are small with a width of 14 mm and a length of 19 mm. Dunnocks lay their eggs in a group of 4 to 5. The eggs are smooth and shiny, having reddish spots on them.

5.   Starlings

These birds are highly recognized for their aerial dances and their sparkling feathers with dots on them. Starlings lay white or pale blue or green colored eggs in a clutch of 2 to 9. The size ranges from 21 mm in width and 30 mm in length. They lay their eggs over a few days.

6.   Magpies

They are intelligent birds and rank among the smartest birds in the world. Their tales make about half of their body length. Magpies’ eggs look very similar to blackbirds. They are bluish-green in color with red speckles on them. However, they are bigger than those of blackbirds with a width of 24 mm and length of 35 mm.

7.   House Finch

House finches lay their eggs from the end of March to late July. Their eggs are light bluish-green with speckles on them. They lay eggs in a group of 4 to 5. The size of these eggs varies from 16-21mm in length and 13-15 mm in width.

Why do birds lay blue eggs?

All the female birds have two types of molecules namely biliverdin and protoporphyrin in their reproductive systems that are responsible for the egg color. But only a few species of birds use these ink molecules and produce different colored eggs. The birds that use biliverdin lay blue or green colored eggs whereas those using protoporphyrin lay red or brown colored eggs. The higher the concentration of biliverdin in the eggshells, the bluer the egg will be. The concentration of calcium and the number of eggs laid at a time also affect the color of the eggs.

What about the patterns and spots on the blue eggs?

The patterns, spots, and blotches on the eggs are formed as a part of the camouflage. This protects the eggs against predators. Another important function of patterns on the eggs is to strengthen the shell, especially on the inner side. The pattern on the eggs also acts as identification marks for birds who lay their eggs in the nests of other birds. This helps them identify their own eggs from those of the others. 

Exploring Robin’s Egg Blue: Nature’s Distinctive Color

The iconic “robin’s egg blue” has fascinated bird enthusiasts and artists alike for centuries. This distinctive shade—a soft, pale blue with slight greenish undertones—is most famously associated with American Robin eggs, though several other bird species produce similarly colored eggs. Many wonder why robin eggs are blue instead of brown or white like most other bird eggs found in nature. Scientists have discovered that this vibrant coloration serves multiple evolutionary purposes beyond simple aesthetics.

The Science Behind Blue Bird Eggs

When comparing blue bird eggs from different species, subtle variations become apparent. A robin’s egg blue differs slightly from the turquoise hue of starling eggs or the blue-green of dunnock eggs. Research indicates that exposure to sunlight may help regulate embryonic development in these blue-shelled eggs. The pigment allows some sunlight to penetrate while blocking harmful UV rays—essentially functioning as natural sunscreen for developing chicks. Additionally, male birds may be more attentive to bright blue eggs, as the color intensity can signal the female’s health and genetic quality.

Identifying Blue Eggs in Your Backyard

If you discover little blue eggs in a nest in your yard, you might wonder what kind of bird has made your property home. In North America, American Robins are the most likely culprits, while in the UK, blackbirds and song thrushes commonly lay blue eggs with distinctive speckles. The size of the eggs provides additional clues—smaller blue eggs (around 1-2 cm) might belong to bluebirds or house finches, while slightly larger ones are typical of robins. When watching birds that lay blue eggs, you might notice interesting behaviors like the spectacular aerial displays of starlings forming murmurations at dusk, adding another dimension to your bird-watching experience.

Conclusion

Some birds like American Robin, house finches, and blackbirds lay blue eggs due to the use of biliverdin molecules present in their reproductive systems. The blue eggs may have patterns in the forms of spots, speckles, or blotches to serve as identification marks for birds that use other bird’s nests.

FAQ

Why are some bird eggs blue in color?

Bird eggs appear blue due to a pigment called biliverdin that’s deposited during shell formation. This natural compound is the same molecule responsible for bruise coloration in humans. Higher concentrations of biliverdin result in deeper blue hues, while lesser amounts create lighter blue or blue-green tints.

Do blue eggs have any evolutionary advantage?

Blue eggs offer several evolutionary benefits. The pigmentation helps filter harmful UV radiation while allowing beneficial wavelengths to reach the embryo. Blue coloration may also signal female health quality to males and might be more visible against nest materials, helping parent birds identify their own eggs.

Which backyard birds typically lay blue eggs?

Common backyard birds that lay blue eggs include American Robins, Eastern Bluebirds, Starlings, and House Finches. In the UK, gardeners might find blue eggs from Blackbirds and Dunnocks. The exact shade varies by species, with some laying pure blue eggs and others producing blue eggs with speckles.

How can I identify different species’ blue eggs?

Identify blue eggs by examining size, shade, and markings. Robin eggs are medium-sized (20-25mm) and unmistakably sky-blue. Bluebird eggs are smaller with a paler blue. Blackbird eggs feature distinctive brown speckles on a blue background, while Starling eggs are more elongated with a slightly greenish-blue tint.

Is the blue egg color consistent throughout the shell?

The blue coloration penetrates the entire eggshell, unlike brown pigments that are often only on the surface. If you look inside a cracked blue eggshell, you’ll notice the interior also appears blue. This occurs because biliverdin is incorporated throughout the calcium carbonate shell during formation.

Can diet affect the intensity of blue in bird eggs?

A bird’s diet can influence egg color intensity. Females with superior nutrition can produce more vibrant blue eggs as they have more resources to create biliverdin pigment. Studies show that birds with calcium-rich and diverse diets typically lay eggs with stronger, more intensely colored shells.

Are blue eggs more fragile than other colored eggs?

Blue eggs are not inherently more fragile than brown or white eggs. Shell strength depends primarily on thickness and calcium content rather than color. However, some blue-egg layers like Song Thrushes add speckled patterns that can provide additional structural reinforcement to certain areas of the shell.