Like dogs, pigeons belong to hundreds of different breeds. While there can be variation within a breed, especially in feather color and wing pattern, each breed is defined by specific characteristics. Pigeon breeds can be as different from each other as German shepherds are from miniature poodles. Yet all of these breeds are descended from one ancestral species: the wild rock dove.
The examples below describe some of the inherited characteristics that vary in pigeons.
White feather color comes not from white pigments, but from the absence of colored pigments. Genetically, there are multiple ways to make a white bird; however, most involve breaking something. White coloring can come from "broken" alleles of genes that code for proteins that help make melanin pigments. It can also come from alleles that prevent pigment-making cells from forming or migrating to the skin. Not surprisingly, white alleles tend to be epistatic to all other color genes.
Other colors and patterns
Other colors and patterns Pigeonetics describes just a handful of the genes that influence feather colors and patterns. Several other genes—including milky, almond, opal, dirty, indigo, grizzle, and various "stencil" and "bronzing" factors—affect the base and pattern colors, or the way pigments are distributed along individual feathers and across the body. Some alleles can strip the color away from certain body regions, leaving the head, tail, wings, or middle white. All of these genes work in combination to make nearly endless color and pattern variations.
No, these aren't parent and child—they're both adults. But like the Chihuahua and the Great Dane, they belong to breeds characterized by vastly different body sizes. The Runt is the largest pigeon breed, with males weighing in at 3 pounds (1.4 kg). At an average of 6 ounces (170 g), the Valencian Figurita is one of the smallest. Other breeds come in every size in between. Body size is a "continuous" trait: it's controlled by the combined action of several genes.
Pigeon breeds vary not only in size, but also their proportions. The Pouter (right) stands tall on extra-long legs. The Old Dutch Capuchin (left) has an elongated neck, accentuating its dramatic crest. Other breeds have distinctly shaped skulls, longer or shorter wings and tails, and countless other distinct proportions. The genetics of body proportion has not been studied closely, but like size, each aspect probably involves multiple genes.
If you played Pigeonetics, you saw pigeons with crests on their heads and feathers on their feet. Pigeons can have other ornaments too. These birds have "neck frills" on the front of the neck. Neck frills vary from subtle to dramatic, just like crests do. While neck frills are inherited, they seem to be the product of at least two genes.
The fantail has another type of ornament: extra tail feathers that spread out like a turkey tail. Fantail breeds tend to have up-turned tails, and some breeders have selected for puffed-out chests for added drama. Fantails can have as many as 40 tail feathers, while a typical breed has just 12. Evidence from genetic crosses suggests that a small number of genes control the size, number, and texture of the tail feathers.
The frillback breed has curly feathers, especially on the back and wings. Some evidence suggests that variations in two genes work together to make their feathers curly. In people and dogs, wavy and curly hair come from variations in genes that code for structural proteins called keratins; we don't know if this is also the case in pigeons.
Trumpeter pigeons have been bred for their special song. Interestingly, their song is not learned—it's an inherited characteristic controlled by genes (though we do not know which genes). Several sub-types of Trumpeters have been bred for additional characteristics. These English Trumpeters have muffs on the feet, a crest around the back of the head, and a tuft on the forehead.
Most breeds of Pouter pigeons are tall, with especially long legs. But their most unusual, and defining, characteristic is their tendency to swallow air and inflate their extra-large crop (food-storage pouch) like a balloon. Crop inflation is in some ways more of a behavior than a physical characteristic—but of course behaviors are rooted brain chemistry and physiology. Crop inflation is highly heritable, suggesting a strong genetic component. It appears to be controlled mainly by a partial-dominant allele of a single gene; however, male birds are more likely than females to show the behavior.
Tumbler pigeons are good flyers, but they have the habit of doing an occasional back flip in mid-flight. Pigeon fanciers say that their birds seem to enjoy these acrobatics. Interestingly, tumbling seems to be rooted not in the shape of the wings or tail, but in brain chemistry. And it's highly heritable: one allele of a single gene is enough to cause a pigeon to tumble. When pigeons are given a type of antidepressant called SSRIs (selective serotonin reuptake inhibitors), they stop tumbling. These drugs work by increasing levels of serotonin, a natural signaling molecule, in the brain. In people, serotonin is active in brain areas that control mood. In pigeons, apparently, too little serotonin makes it hard to fly straight.
The same tumbling allele, in combination with certain alleles of other genes, can cause an even more extreme behavior called "rolling." Some rollers can fly, but they somersault continually. Parlor Rollers can't fly at all—they just roll head over heels along the ground.
The Stargard Shaker pigeon has a long, curving neck. Instead of bobbing its head like most pigeons, it continually wiggles the middle of its neck back and forth. A few other breeds have the same behavior, in combination with other defining characteristics. The behavior is highly heritable, and it may be controlled primarily by a single partially dominant allele.
Pigeon breeds have dramatic differences in the overall size and shape of the beak. Owl breeds have the teeniest hint of a beak, while the Scandaroon has an enormous, curving beak. Other beaks are short and thick or long and pointy. The "wild type" beak is somewhere in between all of these. Beaks also vary in their color (from colorless to black), as well as in the size, texture, and color of the wattle, the fleshy bit that sits at the top.
Pigeon eyes come in many colors, often with rings of different shades. Like feather color, eye color is the product of several genes working together. "Wild type" eye color comes from orange pigment, which looks darker orange or red where it's covered in layers of fine blood vessels. "Pearl" irises are filled with shiny, white pigment. Orange and pearl color come from two alleles of the same gene: orange is dominant to pearl. White-feathered birds often have solid black "bull" eyes or pink "albino" eyes. Bull eyes have completely transparent irises; their color comes from dark pigment inside the back of the eye. Albino birds make no pigment at all; their light pink eye color comes from fine blood vessels. Albino is epistatic to bull, which is epistatic to pearl and orange. We know little about the genetic basis of the less common eye colors, including brown, green, blue, and lilac. The flesh around the eye, called the cere, can also vary—in size, shape, color, and texture.