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SMOKY BLUE AND DIRTY BLUE IN DOMESTIC PIGEONS
The genetic factors Smoky and Dirty have long been recognized in the
blue coloration of domestic pigeons. Typical characteristics of
Smoky include, at least in the juvenile stage, a light beak, a
solid-colored back, and solid-colored outer tail feathers. In
contrast, Dirty has dark beaks and, in juveniles, initially dark
legs. The outer corner feathers of the tail are lighter on the
sides, like the wild type. Smoky and Dirty are both usually darker
in blue than the wild type.
Dirty
The variations in both groups are less well known. Dirty was studied
in 1926 by the Dutchman Bol and found to be dominant over the wild
type. He examined racing pigeons with a typical dark blue variant,
similar to that found in high-flying pigeon breeds.
Dirty (Vetblauw) and wild-type at Racing Homers. Source: Bol 1926
However, there are also very light dirty blues in racing pigeons,
where the dirty factor is only noticeable in the adult plumage of
the offspring, who have dark legs. Very dark dirty blues are typical
of some high-flying breeds. A regional term for these is 'stock
blue’, means deep or strong dark blue. Even within the breeds, there
are still different color shades.
Dirty at Racing Homers. At the left a common variation with the
typical dark feet a youngsters. At the right a light variation. As
adult only to identify as dity by progeny with dark feet.
Dirty at highflyer breeds with different darkening effect
Smoky
Smoky was studied as a recessive by W.F. Hollander (1938) in racing
pigeons and Gimpel Pigeons. Photos were not included in the report.
The most common variant in racing pigeons shows a somewhat darker
blue with a cloudy wing shield. The light beak is only clearly
present in juveniles; it turns gray in adults. Some high-flying
pigeon breeds have smoky colors similar to those of racing pigeons.
However, there are also very dark blues and, in contrast, very light
blues, both with light beaks even in adults.
 
Smoky-Blue at Racing Homere and a dark blue Memel Highflyer
 
Smoky-Blue at Pomeranian Eye-Crested Highflyers, at the left light
blue with clear wing shield, at the right smoky-blue with cloudy
wing shield
Allelic Relationships of Dirty and Smoky
In 2020, Krishnan/Cryberg surprised the reader with the finding that
Dirty and Smoky were alleles, alternative genes at the same gene
locus. Pigeons could thus be homozygous Smoky, homozygous Dirty, or
heterozygous Smoky/Dirty. If the wild type is included, in addition
to purebred wild type, there are also heterozygous Smoky/Wild type
and heterozygous Dirty/Wild type. This makes investigations complex.
For Dirty, the dark variant was tested, and for Smoky, a variant
with a dark blue color was tested, not the 'racing pigeon variant'
or the light Smoky variant.
Dirty, Smoky and Wild-Typ (from left) in the investigation of
Krishnan/Cryberg 2020. Source. Krishnan/Cryberg 2020
The question of whether there are additional alleles for Dirty and
Smoky, or whether the color variations within the groups are due to
modifying factors, remains open.
Literature
Bol, C.J.A.C., Genetische analyse van kleuren, veerpatronen, tinten,
en afteenkenigen bij postduiven.
Genetica 8: S. 45-154.
Hollander, W.F., Inheritance of Certain “Blue-Black’ Patterns and
“Bleached” Colorations in the Domestics Pigeon. Genetics 23 (1938),
S. 12-27.
Krishnan, Shreyas and Richard L. Cryberg, Department of Biology,
University of Texas at Arlington, Arlington, Texas, 76019, Effects
of mutations in pigeon Mc1r implicate an expanded plumage
color patterning regulatory network,
bioRxiv preprint doi: https://doi.org/10.1101/792945,
2020
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