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?).
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.
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.
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.
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.
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.