Birds’ eggs come not only in many different sizes and shapes, but some species also lay coloured eggs. You may have seen blue or green eggs and wondered which birds lay them and why they are different colours.
Bird egg colouration, also known as cryptic pigmentation, plays a critical role in developing a solid defence mechanism. Different colours allow the eggs to stay hidden in their nest away from predators. Different colours depend on the nest’s location and the surrounding habitat.
Birds are the only vertebrates on earth that lay colourful eggs. Although more research is needed, the most common theory speculating among scientists is the different colours camouflage eggs from potential enemies.
Numerous environmental factors affect the shell’s colour, such as the bird’s location, habitat, and the nest’s exposure to predators. Many birds that lay eggs that are vulnerable to predators have elaborate colours. Likewise, coloured eggs are common in ground-nesting birds.
The nests of ground-nesting bird species are scraped in the soil. Birds that are ground-nesting lay eggs in a small depression and use surrounding debris, such as twigs, stones, or animal dung, to hide them. The purpose is to protect the eggs from potential predators.
Although scientists and researchers are making substantial efforts to find the reason behind various colours, there is no solid evidence explaining the causes.
Birds with different coloured eggs
Although there are many species that lay eggs of different colours, here are a few with some of the most exotic colours
- Cetti Warbler – Chestnut colour
- Emu – Deep green and bluish specks
- Peregrine Falcon – Cream to brick red
- Great Tinamou – Glossy and irridiscent
- Golden Plover – Sandy brown with black spots
- Red-Winged Blackbird – Greenish-blue with red-brown freckles
- Common Murre – Deep blue to pale beige
What is the Importance of Colourful Eggs?
Although scientists do not have solid research evidence for why birds lay eggs with varied colours, some researchers believe that the colours protect their eggs from predators and harsh environmental conditions, such as rain, snow, and storms.
Birds that lay darker coloured eggs can maintain heat longer than species that lay white eggs. Generally, the darker the colour of the egg, the stronger the eggshell.
Eggshells are made up of calcium deposits, but low calcium in eggs can cause problems. The lack of calcium content is a primary reason eggshells become thin faster.
Thin eggshells are a problem common among bird species with ground-nesting characteristics. Pesticides, insecticides, and other chemicals used for agricultural purposes can fade the egg’s colour and make the shell thinner and vulnerable to environmental pathogens.
How are coloured eggs produced?
Female birds produce egg colours or pigments in the uterus. The process occurs during the formation of the egg’s shell. Depending on the species, a bird develops different colours and patterns during the shell’s construction, but birds carry out this process while the egg is inside the uterus.
Female bird species deposit more pigments in areas where the shell is more prone to thinning or breaking. The purpose is to cover the spots and protect the egg from breaking. That way, birds reinforce the eggshells, ensuring they are structurally stable and produce young.
Some scientists believe that different pigments, colours and patterns give birds a survival advantage. For example, birds camouflage their eggs against parasites and predators.
Likewise, an egg’s colour is a signal to a male bird, known that the female bird has good reproductive fitness. While most coloured eggs are blue, others are brown, beige, yellow, or green.
Why do bird eggs have different patterns?
Ground-nesting birds or species residing in exposed locations have developed a natural mechanism to lay eggs with different patterns. On the other hand, cavity-nesting birds have pure-white eggs.
Pigeons and ducks cover their eggs when flying away from their nests because they lack patterns and colours. The primary purpose behind covering or camouflaging the eggs is to prevent predators from attacking them.
Some species have coloured eggs for other purposes, such as maintaining structural integrity. For example, many species of tits are cavity-nesting birds with unique egg patterns, such as red-brown markings that provide extra structural stability for the shell.
Do nests affect egg color?
A growing body of research evidence shows that birds started to develop dome-shaped nests about 40 million years ago. These nests had walls and roofs with excellent insulation features.
Over time, birds made substantial changes to their nesting abilities. Today, most bird species create open-cupped nests through their beak and feet using natural materials. Although colours and patterns are due to their unique genetic makeup, some scientists believe environmental factors also play a critical role.
The eggshell colour changes due to exposure to environmental conditions, including the nest construction. For example, birds with dome-shaped nests lay white or dark brown eggs. On the other hand, birds that create open-cup nests have a wide range of eggshell colours, including brown, blue, olive, pink, and white.
Open-cup nests usually have different coloured eggs, which is simply explained. When a bird creates a cup nest, the eggs become more exposed to environmental conditions and predators.
The colours also help protect the egg from extreme temperatures, allowing it to survive, especially if fertilised.
Which birds lay different colour eggs
Bird eggs come in a wide range of colours and patterns beautifully maculated with scrawls, blotches, and spots. Numerous bird species lay different coloured eggs, particularly blue eggs. Black tinamous, House finches, Dunnocks, and Red-winged blackbirds all lay blue eggs.
The American robin is a common species found in North America. They lay bright blue or blue-green eggs in their mud-lined nests during the spring season. American robins also make nests on the ground, especially in areas where trees are sparse. The eggshell may appear slightly darker than the regular bright blue in these cases.
Eggs usually avoid hatching due to predators, such as crows, snakes, and squirrels. Many of these predators look for eggs and will try to rob them quickly. Many species, including the American robin, use debris to cover the eggs when they are not at the nest.
Many bird species, such as Flycatchers and Thrushes, lay multiple eggs and change their colours throughout the laying cycle. Changing colours prevents predators from recognising and attacking the eggs and are not because the mother ran out of pigment.
Eggs in the same nest with different sizes, shapes, and colours could also be due to brood parasites. Species like cowbirds and cuckoos lay their eggs in other birds nests allowing them to look after them and raise them.