Are Robins' Eggs Blue? - Bird Spot

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The answer to this question depends on which continent you are asking from.

If you are in North America, then yes, American robins’ eggs are blue. However, if you are asking from Europe, then the European robin lays pale cream or buff eggs with reddish speckles.

Robin egg blue, also known as eggshell blue was first recorded as a colour name in 1873. It is recorded on the ISCC–NBS System of Color Designation denoted by the Hex triplet #96DED1 and a CMYK value of (38, 0, 23, 0).

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Tiffany Blue is a paler variation of robin egg blue that was first used on the cover of Tiffany’s Blue Book published in 1845. The New York City jewellery company has since then patented the colour and uses it extensively on packaging and promotional materials.

Because of the popularity of robin egg blue as a colour both in the USA and UK, many people mistakenly believe that the European robin lays blue eggs. Some birds in the UK, such as blackbirds, dunnocks and song thrushes do lay blue eggs that closer resemble the American robin’s eggs which can on occasion lead to misidentification.

Why are robins’ eggs blue?

American robins’ eggs are blue due to a pigment called biliverdin, which is deposited on the eggshell when the eggs are laid. Biliverdin is a green bile pigment and is the same pigment that causes some bruises to initially look bluey-green.

Depending on the concentration of biliverdin, robins’ eggs can range in a variety of blue shades from a pale or even icy blue-green to a bright, bold blue. Smaller eggs and those laid first in a clutch tend to be a more intense blue than larger eggs or those laid later.

There are several hypotheses that explain why birds’ eggs may be brightly coloured, particularly when it puts them at risk of predators who would find them very easy to spot. The most widely accepted is that it helps them survive exposure to the sun.

Although intensely coloured eggshells protect the egg’s interior from dangerous UV radiation, they also allow the egg to absorb more light and therefore heat up more quickly.

For species like the American robin which typically lays its eggs in forests with moderate light levels, blue-coloured eggs are a compromise. They have evolved to protect the embryo from the sun’s radiation, while absorbing enough heat for optimal embryo development. Birds that lay their eggs in bright, open areas tend to produce eggs with lighter shells where dangerous overheating carries a greater risk than the potential damage caused by radiation.

Research has also shown that male robins feed chicks that hatch from the brightest eggs the most. Evidence suggests that high levels of biliverdin are found in the healthiest females, and as healthy mates produce better offspring, male robins are more invested in ensuring the survival of chicks produced from the bluest eggs.