Blue-Egg Chickens: The Araucana, the Ameraucana and the Blue-Egg Gene

The blue egg is the most fascinating subject in poultry keeping — and the story behind it is stranger than you'd guess: chickens lay blue eggs because of a virus.

In this guide we cover the blue-egg breeds (the Araucana, the Ameraucana and the "Easter Egger"), how the blue gene works, how blue plus brown makes a green egg, and the lethal genetic problem the Araucana causes in the incubator. That last point is the single most important thing to know before you hatch from this breed.

How Is a Blue Egg Made? (And Where Does the Virus Come In?)

As we explained in our Marans guide, brown pigment (protoporphyrin) is applied to the outside of the shell after it has formed — scratch it and the shell is white underneath.

Blue works entirely differently. The blue pigment is oocyanin, derived from the bile pigment biliverdin, and it is laid down through the whole thickness of the shell as it forms. Scratch a blue egg and it is still blue inside.

Now the strange part. The O gene that produces this does not naturally belong to the chicken genome. Research has shown that a retrovirus called EAV-HP inserted itself into chicken DNA and switched the gene on. In other words, a viral infection long ago is the reason for the blue egg in your hand today — one of geneticists' favourite stories.

The O gene is dominant: a single copy is enough to make a hen lay blue. That has important consequences when crossbreeding.

The Colour Mixing Rule: Blue + Brown = Green

Know this rule and you can predict what colours will end up in your basket:

Shell base	Brown coat applied	Result
White	None	White (Leghorn)
White	A little	Cream / light brown (Sussex)
White	A lot	Dark chocolate (Marans)
Blue	None	Blue (Araucana, Ameraucana)
Blue	A little	Green (Easter Egger)
Blue	A lot	Olive (Olive Egger)

An Olive Egger is exactly that: a bird carrying the blue-egg gene crossed with a dark-brown layer such as the Marans. A thick brown coat over a blue shell gives a deep olive egg. You can easily breed this cross in your own flock.

Three Different Birds: Araucana, Ameraucana, Easter Egger

All three are often sold simply as "blue-egg chickens". They are not the same thing:

	Araucana	Ameraucana	Easter Egger
Origin	Chile (Mapuche people)	USA, 1970s	A cross (not a breed)
Tail	None (rumpless)	Yes	Yes
Head	Ear tufts	Beard and muffs	Varies
Egg	Blue	Blue	Blue, green, pink…
Hatching risk	Lethal gene	None	None

The Ameraucana was developed in 1970s America precisely to clean up the Araucana's genetic problems: it has a tail, it has a beard instead of ear tufts, and it carries no lethal gene.

The Easter Egger is not a breed at all but any crossbred bird carrying the blue-egg gene. Most birds sold as "blue-egg layers" are these. Their eggs can be blue, green or even pink — a surprise box. They are cheap, hardy and free of hatching risk; you just can't guarantee the colour.

Critical Warning: The Araucana's Lethal Gene

This is the most important thing to know before hatching from a blue-egg breed.

The gene that produces the Araucana's ear tufts is lethal when homozygous. That is:

• A chick that inherits one copy → is tufted and healthy
• A chick that inherits two copies (one from each parent) → dies in the shell, usually in the last days before hatch

The result: in a tufted × tufted mating, about 25% of fertile eggs never hatch. That is not a fault in your incubator; it is genetics. It's why Araucana breeders are used to poor hatch rates.

The fix: mate a tufted bird with a non-tufted one. The lethal combination then never arises and your hatch rate returns to normal (half the chicks come out tufted).

The rumpless gene creates a second problem: with no tail structure, mating is physically harder and fertility drops. If you see a poor hatch, the fault may lie with your breeders rather than the machine — see our guide on how to improve egg fertility.

The Ameraucana and the Easter Egger have none of these problems. If you just want blue eggs and intend to hatch, those two are far safer choices.

Output and General Traits

Trait	Araucana	Ameraucana
Cock	~3.0 kg	2.7 – 3.5 kg
Hen	~2.5 kg	2.0 – 2.6 kg
Eggs per year	150-180	180-200
Egg colour	Blue / blue-green	Blue
Comb	Pea comb	Pea comb

Both have a pea comb — which, as the comb table in our Wyandotte guide shows, is a big advantage in the cold: a small comb doesn't get frostbite. Both are calm and curious, active and good foragers. Broodiness is moderate.

Care and Housing

• Coop space: 0.3-0.4 m² per hen (a medium body)
• Run: 2-3 m²; active birds and good foragers
• Flying: being light, they fly well — the fence must be high, or the run covered
• Cold: the pea comb makes them cold-hardy
• Nest boxes: one per 4 hens

For coop dimensions see how to build a chicken coop, and for vaccination and hygiene our coop biosecurity guide.

Hatching

The period is standard: 21 days, 37.5-37.8 °C, 45-55% humidity, lockdown on day 18. Unlike the Marans' dark shell, a blue shell lets light through — so candling works comfortably, which is a real advantage.

We set out the process step by step in our 21-day incubation guide; to keep the days straight, the Kuluçka Takip app builds the calendar and reminds you of turning and hatch days. You can check out the app here.

A breeding note: because the blue-egg gene (O) is dominant, crossing a blue-egg bird with any other breed still gives you daughters that lay blue or green. That is the exact opposite of the Marans, whose dark colour needs many genes and is easily lost — blue survives crossbreeding easily.

Pros and Cons

• + Blue and green eggs — unmatched visual appeal in the basket
• + The blue gene is dominant: it survives crossing, and you can breed Olive Eggers
• + Pea comb → cold-hardy
• + Active, curious, good foragers
• + A blue shell candles well (unlike the Marans)
• − Araucana: the tuft gene is lethal when homozygous → a 25% hatch loss
• − Araucana: rumplessness lowers fertility
• − Moderate egg output (150-200)
• − They fly well; a high fence or covered run is needed
• − Most birds sold as "Araucana" are really Easter Eggers

Who Is It For?

It suits you if: you want a basket of coloured eggs; you keep birds as a hobby or a collection; your children will enjoy collecting blue eggs; you live somewhere cold; you like the idea of breeding crosses such as the Olive Egger.

Which one should you buy?

• If you're going to hatch → the Ameraucana (no lethal gene, guaranteed blue eggs)
• If you just want eggs and don't mind a colour surprise → the Easter Egger (cheap, hardy, trouble-free)
• If you're after show birds and pure stock → the Araucana (but stick to the tufted × non-tufted breeding rule)

It is not for you if: you want maximum eggs → the Lohmann or the Leghorn; you want meat too → the Sussex or the Plymouth Rock.

To compare all the breeds side by side, see our guide to choosing a laying or meat breed.