A Robin's nest with two blue eggs.

How Do Blue Eggs Get Their Color? Discover the Reason!

How Do Blue Eggs Get Their Color? It’s a question that might have crossed your mind while admiring a robin’s nest. The short answer is: it’s all about chemistry! But why are some eggs blue and others not?

In this article, we’ll dive into the fascinating world of avian reproduction and explore the surprising factors that determine the color of bird eggs.

Get ready for a journey that involves everything from genetics to predator deterrence, and discover why the color of a bird’s egg is much more than just a cosmetic detail.

Table of Contents

How Do Blue Eggs Get Their Color?

Birds lay blue eggs by depositing pigments such as biliverdin and protoporphyrin during the egg formation process. The shade of blue is determined by the amount of pigments present and the eggshell’s structural components.

Different bird species have varying levels of pigments and structural components, resulting in eggs of different shades of blue.

Most Common Birds That Lay Blue Eggs

Bird SpeciesEgg Frequency Ranking
Eastern BluebirdMost common
American RobinSecond most common
Mountain BluebirdThird most common
Tree SwallowFourth most common
Indigo BuntingFifth most common
Blue GrosbeakSixth most common

Read more: What Bird Lays Blue Eggs? Uncover the 40 Species Now!

The Science of Blue Eggshell Color

Bird eggs come in a variety of colors, including white, brown, green, and blue. The color of an eggshell is determined by both biological and environmental factors. In the case of blue eggshells, the color is a result of a combination of pigmentation and structural factors.

The pigments that give blue eggshells their color are called biliverdin and protoporphyrin. These pigments are produced in the shell gland of the female bird’s reproductive system and are deposited on the surface of the developing eggshell.

The concentration of these pigments determines the intensity of the blue color. In addition to pigmentation, the structure of the eggshell also plays a role in the color of the shell.

The thickness and texture of the eggshell can affect how light is reflected and absorbed, which can influence the color perception of the eggshell.

Environmental factors such as temperature can also affect the color of the eggshell. For example, research has shown that eggs laid at higher temperatures tend to have lighter and less intense blue coloration.

This is because higher temperatures can affect the expression of genes responsible for eggshell pigmentation.

It is important to note that the color of an eggshell does not necessarily indicate the health or quality of the egg or the bird that laid it.

Rather, it is an indication of the specific pigments and structural characteristics that make up the eggshell.

FactorInfluence on Blue Eggshell Color
PigmentsDetermines intensity of blue color
StructureAffects light reflection and absorption
TemperatureHigher temperatures can make blue color lighter and less intense

How do the colors protect the eggs from the sun?

The colors of a bird’s egg can help protect it from the sun by regulating the amount of light and heat that penetrate the eggshell.

A study determined that darker pigments, such as those found in speckled or blotchy eggs, can help absorb more light and heat, reducing the amount that reaches the developing embryo.

Lighter pigments, such as those found in blue or white eggs, can reflect more light and heat, helping to keep the egg cool.

By regulating the amount of light and heat that penetrate the eggshell, the colors of bird eggs can help ensure the survival of the developing embryo.

A couple of blue eggs in a nest.
Photo by Landon Martin on Unsplash

Camouflage and Eggshell Color

Eggshell color is an important aspect of bird biology that serves various purposes, including camouflage. Birds with blue eggs have evolved this trait to blend into their natural surroundings, making it more difficult for predators to locate their nests.

Matching Nest Colors

Blue eggshell color provides camouflage in a variety of habitats, from woodland forests to open grasslands.

Birds such as the American Robin, Eastern Bluebird, and Mountain Bluebird lay blue eggs that perfectly match the colors of their nests, whether they are made of mud, grass, or other materials.

This allows them to hide their eggs from predators that may be lurking nearby.

In addition to providing camouflage, research conducted at the University of Oxford has revealed that blotches on eggs serve another purpose: to strengthen the eggshell.

Mimicking the Sky

In addition to matching the color of their nests, the blue color of these eggs can also help to mimic the color of the sky, making it harder for predators to detect them from above. This is especially useful for birds that build their nests in exposed areas.

Signaling Genetic Quality

Furthermore, the blue color of the eggshell may also serve as a signal of fitness to potential mates. Studies have shown that birds with brighter and more intense blue eggshell color are more likely to attract mates and produce healthy offspring.

This suggests that the ability to produce blue pigments in eggshells may be a sign of good genetic quality.

Overall, the blue eggshell color of certain bird species serves as an effective camouflage mechanism that helps protect their nests and eggs from predators.

Its presence may also indicate the genetic quality of the bird, which can have important implications for their reproductive success.

Blotches on Eggs: More Than Just Camouflage?

Recent research conducted at the University of Oxford has uncovered a surprising additional purpose of eggshell coloration, particularly the blotches found on some bird eggs.

Contrary to popular belief that blotches are primarily for camouflage, the study suggests that they may actually play a crucial role in strengthening the eggshell.

Dual Function of Eggshell Pigmentation

The study found that birds that laid eggs with darker and more pigmented blotches tended to have thicker and stronger eggshells.

This is because the pigments found in the blotches contain specific compounds that make the eggshell more resistant to cracking or breaking.

The eggshell of a bird egg is a thin and delicate protective layer that must withstand various challenges, including predators, incubation, and hatching.

The presence of pigments in the blotches may provide additional structural support, increasing the eggshell’s resilience and overall durability.

Factors Affecting Eggshell Strength

It’s worth noting that the strength and thickness of an eggshell can also be influenced by various environmental factors, including the mother bird’s diet and the conditions in which the egg is laid and incubated.

Nevertheless, the findings of this study suggest that the pigmented blotches on eggshells may have an important and previously unrecognized function beyond providing camouflage.

Revising Traditional Views

In conclusion, the traditional view of blotches on bird eggs as solely serving a camouflage purpose may need to be revised in light of this new research.

Instead, pigmented blotches may serve a dual purpose of not only providing camouflage, but also strengthening the eggshell to better protect developing embryos.

Three blue eggs in a nest.
Photo by Solen Feyissa on Unsplash

Eggshell Color and the Health of Mother Bird and Chicks

Did you know that the color of a bird’s eggshell can provide important clues about the health and nutrition of both the mother bird and her developing chicks? It’s true! In fact, the color of the eggshell is directly linked to the bird’s diet and overall health.

How Eggshell Color Indicates Health Status

The pigments that give eggshells their color are actually derived from the food that the mother bird eats. For example, if a bird’s diet is high in carotenoids, which are found in colorful fruits and vegetables, the eggshells will tend to have a brighter, more vibrant color.

On the other hand, if a bird’s diet is deficient in certain nutrients, the eggshells may appear paler or have a different hue altogether.

Importance of Eggshell Color for Developing Chicks

Eggshell color can also provide valuable information about the health and development of the chicks inside the egg.

Studies have found that eggshells with a brighter, more vibrant color were associated with a higher rate of hatching success, as well as better overall health and growth of the chicks.

In addition, the thickness and texture of the eggshell can also affect the survival of the developing chicks. If the eggshell is too thin or brittle, it may break during incubation or be more vulnerable to predators.

On the other hand, if the eggshell is too thick, it may make it more difficult for the chick to hatch out of the egg.

Factors Affecting Eggshell Color

Several factors can affect the color and quality of eggshells, including the mother bird’s age, health, and nesting habits. For example, if a bird is stressed or malnourished, her eggshells may appear paler or have a more irregular shape.

Similarly, if a bird lays her eggs in an area with poor environmental conditions, such as a polluted or toxic environment, the eggshells may be affected.

Nesting Habits and Eggshell Color

Birds’ nesting habits and behaviors can have a significant impact on the color of their eggs. Here’s how:

Nesting Location and Eggshell Color

The location where birds build their nests can have a direct impact on the color of their eggs. Birds that nest in exposed areas, such as on the ground or in open tree branches, may produce eggs with darker and more speckled shells.

This is because these eggs need to blend in with their surroundings to protect them from predators.

Nesting Materials and Eggshell Color

Birds that use different materials for their nests may also produce eggs with different colors and patterns. This is because the pigments found in the nesting materials can sometimes transfer to the eggs, creating unique and interesting patterns.

For example, birds that use grass as nesting material may produce eggs with greenish hues, while those that use twigs may produce eggs with more speckled patterns.

Nesting Habits and Eggshell Thickness

Birds’ nesting habits can also influence the thickness and durability of their eggshells. For instance, birds that build their nests in open areas may produce eggs with thicker shells to protect them from the elements and potential predators.

Similarly, birds that lay their eggs in communal nests may produce eggs with thinner shells, as they are less vulnerable to attack.

Four blue eggs in a nest.
Photo by Dean Ward on Unsplash

Sibling Rivalry and Blue Eggs: The Truth About Mismatched Siblings

When it comes to bird eggs, blue is certainly a standout color. But did you know that blue eggs can sometimes lead to sibling rivalry and mismatches within a single brood? Let’s delve into the fascinating world of blue eggs and how they can affect sibling dynamics.

The Science Behind Eggshell Color

First, it’s important to understand the science behind eggshell color. Eggshells get their color from pigments that are deposited as the egg passes through the oviduct.

These pigments are influenced by a number of factors, including the bird’s diet and genetics. For birds that lay blue eggs, the pigment responsible is called biliverdin, which gives the egg a blue-green color.

The Role of Genetics in Eggshell Color

Genetics also play a role in determining eggshell color, and not all siblings within a single brood will necessarily have the same eggshell color. In fact, it’s not uncommon for blue eggs to result in siblings with mismatched eggshell colors, including brown or white.

Sibling Rivalry and the Survival of Chicks

This is where things get interesting. In some bird species, chicks with different eggshell colors may be treated differently by their parents, leading to what’s known as sibling rivalry.

For example, a parent bird may favor chicks with blue eggshells over those with brown or white eggshells, leading to unequal distribution of food and attention.

This can have serious implications for the survival of the chicks. Chicks that are neglected or underfed may not survive to adulthood, leading to a decrease in population numbers.

The Importance of Preserving Bird Habitats

Understanding the dynamics of sibling rivalry and eggshell color is just one piece of the puzzle when it comes to preserving bird populations.

Protecting and preserving bird habitats is crucial to ensuring that these amazing creatures can thrive and continue to lay their beautiful blue eggs for generations to come.

Blue Eggshell Patterns and Characteristics

Blue eggshells are a fascinating feature of certain bird species. In this section, we’ll explore the different patterns and characteristics found on blue eggshells.

Thickness and Strength

Compared to other eggshell colors, blue eggshells are generally thicker and stronger. This provides added protection to the developing chick inside, and can make them more difficult to crack or damage.

Smoothness and Uniformity

Blue eggshells are often smoother and more uniform than other eggshell colors. This can also contribute to their strength and durability.

Variation in Patterns

One of the most notable features of blue eggshells is their range of patterns and markings. Some blue eggs have small spots or speckles, while others have larger blotches or streaks.

The patterns on blue eggshells can vary greatly between different bird species, and even between individual eggs laid by the same bird.

Influence of Pigments

The variation in blue eggshell patterns can be attributed to the presence of pigments. While blue is the primary color of the eggshell, other pigments can mix in to create unique patterns and hues.

For example, some blue eggs may have greenish undertones, while others may have purplish hues.

Influence of Genetics, Environment, and Diet

The patterns on blue eggshells can also be affected by the bird’s genetics, environment, and diet. Factors such as the mother bird’s age, stress levels, and exposure to certain toxins can all influence the appearance of the eggshells she produces.

Four blue eggs in a nest in a tree between leaves.
Photo by Ian Baldwin on Unsplash

Observing Blue Eggs in Nests: Tips for Safe and Ethical Viewing

For bird enthusiasts, observing blue eggs in their natural habitats can be an exciting and rewarding experience. However, it’s important to do so safely and ethically, without causing harm to the birds or their eggs. Here are some tips for observing blue eggs in nests:

  • Keep a safe distance: When observing blue eggs in a nest, it’s essential to maintain a safe distance from the birds. The general rule of thumb is to stay at least 100 feet away from the nest, using binoculars or a camera with a telephoto lens to view the eggs.
  • Minimize disturbance: Birds can be easily startled and agitated, which can cause them to abandon their eggs. Therefore, it’s essential to avoid making any sudden movements, loud noises, or disturbing the surrounding vegetation. It’s also important to keep pets and other animals away from the area.
  • Observe from a concealed location: If possible, observe blue eggs from a concealed location, such as a hide or blind. This will minimize the chances of being seen by the birds, reducing the risk of disturbance.
  • Timing is key: To minimize disturbance and increase the chances of observing blue eggs, choose a time when the birds are least likely to be present. Early morning or late evening is usually the best time for observation, as birds are typically less active during these times.
  • Respect the birds’ privacy: Remember that observing blue eggs in a nest is a privilege, not a right. It’s essential to respect the birds’ privacy and not disturb them or their eggs in any way. If the birds show signs of agitation or distress, it’s time to move on and observe from a different location.

Comparison of Blue Eggs and Other Eggshell Colors

When it comes to eggshell color, blue eggs are undoubtedly some of the most eye-catching and distinct of all bird egg varieties. But how do blue eggs compare to other eggshell colors, and what makes them stand out?

Unique Pigmentation

One of the main factors that make blue eggs stand out is their pigmentation. Blue eggshells are colored by a pigment called biliverdin, which is produced during the breakdown of red blood cells in the mother bird’s body.

This pigmentation process is somewhat rare, which is why blue eggs are less common than other eggshell colors.

Distinct Appearance

Another factor that sets blue eggs apart is their appearance in the nest. Because blue is a bright and distinctive color, blue eggs are much easier to spot in a nest than eggs with white or brown eggshells.

This makes them particularly vulnerable to predators, which is why many bird species that lay blue eggs have evolved to build their nests in concealed or hard-to-reach locations.

Comparison to Other Colors

In terms of comparison to other eggshell colors, blue eggs are more similar to green eggs than to white or brown eggs.

This is because the biliverdin pigment that colors blue eggshells can also produce green hues. In fact, some bird species, such as the common murre, lay eggs that are a mix of blue and green.

Functional Similarities

Despite their unique appearance, blue eggs are functionally no different from other eggshell colors. The thickness and strength of the eggshell are the same, and the eggs provide the same nutritional benefits to developing chicks.

Bird egg color is a significant trait that reveals valuable insights into a bird’s diet, habitat, and characteristics.

It is influenced by pigmentation, temperature, and the mother bird’s health. We’ll explore how eggshell color helps us better understand bird species in this section.

Blue eggs in a nest.
Photo by Ginger Jordan on Unsplash

The Role of Eggshell Color in Bird Species

Eggshell color is an important characteristic that varies between different bird species. The color of the eggshell can provide insights into the bird’s diet, habitat, and other characteristics.

For example, birds that primarily feed on plant-based diets tend to have lighter-colored eggs, while birds that eat a lot of insects or meat tend to have darker-colored eggs.

Eggshell Color and Habitat

The color of the eggshell can also give us information about the bird species’ habitat. Birds that lay eggs in open nests or exposed areas tend to have lighter-colored eggs that provide better camouflage.

In contrast, birds that nest in shaded or covered areas tend to have darker-colored eggs that provide better protection from predators.

Eggshell Color and Incubation

Eggshell color can also provide insights into the bird species’ incubation habits. For example, some bird species that lay blue eggs tend to incubate their eggs for shorter periods than those with darker-colored eggs.

Additionally, some bird species may modify the color of their eggs during incubation to regulate temperature and protect the developing embryos.

Eggshell Color and Parental Care

The color of the eggshell can also provide information about the parent bird’s care habits. Birds that provide more parental care tend to have lighter-colored eggs, while birds that provide less parental care tend to have darker-colored eggs.

This is because lighter-colored eggs tend to hatch faster and require more attention from the parents.

Time of Laying Eggs and Blue Eggshell Color

Seasonal Variations

The timing of blue egg laying can vary depending on the bird species and their specific habitat. Generally, most birds that lay blue eggs tend to do so during the spring months, when food sources are abundant and the weather is mild.

However, exceptions exist, and some birds may lay blue eggs at other times of the year.

Daily Variations

The time of day can also play a role in the color of blue eggs. Some birds lay their eggs early in the morning, while others prefer to lay them in the afternoon or evening.

This can affect the temperature of the egg and the pigmentation process, which can impact the final color of the eggshell.

Geographic Differences

In addition to seasonal and daily variations, there are also geographic differences in blue egg laying.

Birds that live in cooler regions may lay their eggs earlier in the year to take advantage of the milder weather, while birds in warmer regions may lay their eggs later in the year when temperatures are cooler.

Insights and Implications

Understanding the time of laying eggs and blue eggshell color can provide valuable insights into the behavior and biology of bird species that lay blue eggs.

Researchers can learn more about how birds adapt to their environments and the factors that contribute to the health and survival of their offspring.

By studying these patterns, we can also gain a better understanding


In conclusion, the color of a bird’s egg is a complex and fascinating topic that involves a variety of factors. From genetics to predator deterrence, there are many reasons why some birds lay blue eggs and others do not.

By exploring the science behind this phenomenon, we gain a deeper understanding of the incredible adaptations that birds have developed to survive and thrive in their environments.

So the next time you come across a blue bird egg, you’ll have a newfound appreciation for the tiny marvels of nature.

Related Post: Amazing Chickens That Lay Blue Eggs: The Ultimate Guide!