Birds are one of versatile species that build their own home with innovative structured nests using different raw materials, stones, or sticks in various shapes and sizes. Some birds lay eggs that differ in pigments, shape, size, and markings. These traits help to identify birds even if the species is not present in the nest.
The fun fact is that birds’ eggshells can be a rainbow hue, ranging colors from pure white, cream, tan, and buff shades to yellow, mint green, orange, pale, lavender, and blue. The Eggs might be straight or have markings in green, black, gray, deep purple, or red-brown colors.
Some birds even lay eggs with spots, blemishes, specks, imperfections, and some markings with color variations. Eggshell pigmentation and patterns disclose much information about birds’ nesting habits and the evolutionary changes they face during their incubation period.
Do we wonder why the eggshell’s pigmentation varies in nature? Why do birds lay bright or intense blue colored or easy to spot eggs? The foremost reason for earthy shaded eggshells is due to camouflage or protection from sunlight.
The dull and mottled eggshells may be of camouflage, but the critical driving factor of eggshells patterns and the pigmentation is that birds lay eggs on scrape nests or directly on the open ground.
Related Read: Colors Of Birds | Interesting Things To Know
Why some birds have eggshells blue?
You may come across blue color egg remnants on the ground in your garden or the woods and think how scientifically eggshells are in blue. Generally, eggshells’ default pigment is cream white, composed of calcium carbonate.
Birds that lay eggs on the ground or open-cup nests depend on camouflage and produce speckled or brownish earthly shaded eggs.
Biliverdin is a color-related molecule present in green or blue eggshells is the science behind the blue jeweled toned gems. Compared to non-blue eggshells, blue eggs have a higher concentration of biliverdin molecules.
Birds have only two pigment molecules responsible for their egg coloring-
- Biliverdin pigment molecule (blueish-green eggs), and
- protoporphyrin (reddish-brown earthy shades eggs).
Biliverdin is an antioxidant and is broken down from the hemoglobin in the blood. The vibrant color eggs signal to the mate that the mother is healthy. The paler eggs indicate that the mother birds might be infected with any disease, low diet, or a challenged immune system.
Protoporphyrin is the color molecule responsible for visible spots and specks on eggshells and produces red or brown eggs.
In the female bird’s reproductive system, both Biliverdin and Protoporphyrin act as ink cartridges like in a printer. The freshly formed calcium carbonate eggshells are made to combine with these color pigments in the last few hours of the bird’s ovum.
Interestingly, the multiple egg-laying cycles of birds cause the color variations from being vibrant to dull shade colors at a time.
The eggs’ blue color protects the developing embryo from the damaging ultraviolet sunlight and infrared radiation rays that can make them feel overheated.
What birds lay blue eggs?
Bluebird and American robin species are famous for their blue eggs in North America. Birds that build nests on shrubs and trees lay greenish or blue eggs with either spotted or spotted outer shells.
Hole-nesting birds lay eggs usually in pale blue or white so that the parents can locate them quickly and avoid breaking them by mistake.
Some of the well-known bird’s species that lay eggs in colors vibrant blue, pale baby blue to turquoise tones include:
- Bluebirds – Bluebirds are cavity nesters and rarely lay their eggs outside the cavity. About 5% of bluebirds lay white eggs.
- American Robin
- House Finches eggs are in bluish-green pigment and use a nestbox.
- Starlings – Starlings lay blue eggs that are bigger than bluebird eggs.
- Red-winged, Tricolored, and Rusty Blackbird
- Gray Catbird
- Blue Mockingbird, Blue Grosbeak, Blue-gray Gnatcatcher, Bluethroat, and Blue-footed Boobies
- Snowy Egret
- Blue Jays
- American, Hawaiian, Fish, and Tamaulipas Crow
- Eastern, Mountain, and Western Bluebirds
- Little Blue Heron, Great Blue Heron
- Common Myna
- Cassin’s Finch, Oriental Greenfinch, and House Finch
- Wood Thrush, Dusky, Varied, Swainson’s, Bicknell’s, Aztec, Clay-colored and White-throated
- Yellow Warbler, Olive and Bay-breasted
- American, Lesser, and Lawrence’s Goldfinch
- Eurasian Jackdaw
- Eurasian Bullfinch
Mostly, 10% of the calcium in the eggshells comes from the mother bird. If she gets proper nutrients and calcium, the eggs will vary in shades.
Most of the birds need egg pigmentation for camouflage, protection from sunlight, and anti-microbial defense. Their Blue shells are a source of protection before they come into the outside world. Apart from their parents’ incubation and care, the shells keep them safe and warm away from predators.