Many flock owners keep several chicken breeds that lay a diversity of shell colors ranging from light to dark brown, blue/green, white, and virtually every shade in between.
Some shells are smooth and glossy, while others are more textured. When arranged in an egg carton they are a delight to the eye and a striking contrast to the sameness of supermarket eggs.
Many wonder why eggs are so diverse. The answer is simple. Chickens are genetically complex. They have between 20,000 and 23,000 genes in about one billion DNA base pairs. This compares with the 20,000-25,000 human genes in 2.8 billion DNA base pairs.
Enormous genetic complexity results in much individual variation. Just as people come in many shapes, sizes, and colors because of genetic diversity, so do chickens. This explains why chickens range in size from the tiny Serama bantam breed to immense Jersey Giants.
Chicken feathers come in dozens of color shades and marking patterns.
Chicken breeds were developed over centuries by human selection for certain traits, like egg production, shell color, fast growth, pleasant demeanor, and attractive feathers.
As a rule breeds developed around the Mediterranean Sea, such as Leghorns and Anconas, are relatively small in body size, are nervous and active, and lay many white shelled eggs. Some more northern European breeds, like Hamburgs, also lay white eggs.
In contrast, most breeds developed in England, the United States, and Australia are large bodied and lay brown shelled eggs. Marans, a French breed, lays exceptionally dark shelled brown eggs.
Araucanas from South America are oddballs that lay eggs with shells ranging from greenish to blueish. No matter how diverse chickens are, they are all of the same species.
When breeds are crossbred, egg shell color is usually (but not always) a blend of what the parent breed lays.
Genetics get complicated but modern poultry breeds generally understand the key to traits and have created hybrid broilers that grow astonishingly fast and also hyper laying strains.
Eggs of all birds are amazing far beyond their color. Shape varies with species and within a species. Generally, wild birds that make sparse nests on rocky cliffs lay pointy, oblong eggs that roll in a circle, keeping them in the nest. Birds that nest in tree cavities, where it’s impossible for eggs to roll out, tend to lay more round eggs.
Chickens fall somewhere in between. In the wild they nest on the ground, so eggs are mildly asymmetric, although some are nearly round. Usually during laying, the blunt end emerges from the hen’s body first, followed by the tapered skinny end.
Individual hens usually lay similar eggs that may vary in shape from another hen of the same breed. For example, a Barred Rock hen in a small flock may lay eggs that are unusually round while another Barred Rock may lay much more oblong ones. Each will continue laying eggs of that shape throughout her life.
One hen may also lay darker brown eggs than a sister of the same breed, and this characteristic will persist through her life. Generally, brown eggs get somewhat lighter in shell color as a hen ages.
According to Pat Leonard, who wrote an extensive article on egg color for the Summer 2017 issue of Living Bird magazine, egg pigments are complex molecules synthesized in the shell glad. A pigment called protoporphyrin produces reddish-brown colors while biliverdin produces blue and green shades.
Varied amounts of each explains the intensity of shell color and when pigments are absent the shell is white.
The article lists several other interesting egg facts. For example, eggshells can have from a few hundred to tens of thousands of pores and eggs that hatch into chicks able to walk and feed shortly after hatching, like chickens, have larger yolks than species that hatch naked and helpless, like baby robins.
People who tend small flocks enjoy the delightful diversity of eggs of many shapes, sizes, and hues. A carton full is a delight to the eye.