Pigeon Genetics Newsletter
July 1973, pages 27-29.
WHAT DO WE KNOW ABOUT THE “DIRTY” COLORATION?
by: Robert J. Mangile
When one observes a flock of Homing Pigeons it is evident that some of the blue pigeons are of a much more “dirty” appearing coloration (not “smoky”) as compared to the other lighter blues, of both barred or checkered patterns. For years it has been felt that whatever genetic basis is involved, it is probably dominant to the usually accepted standard “Wild type”.
Wendell Levi (1) very briefly mentions “dirty” in the chapter on “Genetics–Variation and Inheritance and cites Bol (2) as a researcher who considered “dirty” to have some dominance to ordinary blue. However, there is no mention of foot and bill coloration of squabs.
With reference to “wild type”, there seems to have been much confusion among taxonomic authorities when classifying Columba livia. The wild populations inhabiting India and vicinity pose a difficult problem with regards to the true phenotypic expression of “Wild type” of Columba livia. Derek Goodwin (3) states “In parts of the Middle East and northern India grey-rumped and white-rumped Rock Pigeons intergrade.” And later he states “The Rock Pigeons of Peninsular India and Ceylon C. livia intermedia are darker blue-grey with no white on lower back. Very probable the intermedia subspecies is of the “dirty” type, but more careful study is desirable.
Columba livia livia wild type of Europe
A typical blue-barred pigeon but adult plumage showing light rather than dark overall. Lower back is particularly light (almost white) and outer-tail vane is also light (almost white). Where light back and tail merge directly over the oil gland (uropygial) there is a very sharp line of demarcation that separates the coloration of the back from the tail. The underwings are very light, leaving the impression that they are white. The plumage is generally without any completely white feathers in the rump, vent or on head. Feet, of squabs are brownish but sometimes are of a dark rather than a light brown. Squabs to 24 hours old have a very distinct upper bill-ring near the tip of their upper mandible. (It should be noted that this description is one taken from domesticated stock and not from actual wild Rock Pigeons.)
Near the color of “wild type” but of a very ” dirty” appearance. Plumage shows a definite darkening in generally all areas. Lower back is dark blue and is not sharply demarcated at oil gland (uropygial) from coloration of tail. Under-wings are dark to the degree of dark-grey. Some white feathers often occur in plumage in rump, vent, and on head near eyes. Feet of squabs are black, not dark brown, and can be noticed when 24 hours old in most squabs. Squabs to 24 hours old have a diffused bill-ring on upper mandible, that is diffused back toward the base of the bill. Outer-tail vane sometimes is about half-tone with lightness usually toward the base and darker towards the extremity, or it may be totally dark, especially in juvenile plumage.
It is of particular importance that when squabs are under 24 hours old that the “dirty” trait can be recognized with great accuracy, particularly in blue-black phenotypes. Bill-rings tend to diffuse into totally black bills by the 4th. or 5th. day of life and if the bill-ring is not classified early, squabs of “wild type” and “dirty” in the same nest may be unidentifiable by the 4th. day. Feet, are much the opposite. Two-day old squabs usually can be identified as to the black-footed trait, some showing only tiny spots of black at the bases of the toenails. However, with age the feet of “dirty” squabs become darker, and in some specimens are intense jet-black as compared to the dark brown extreme of the “wild type” foot color. This black-footed appearance usually lingers on until the molt.
I decided to try to test the inheritance of the “dirty” type. For best classification I decided to use only blues (with the exception of a single “black” (S) in one mating). And all the matings were among birds of Racing Homer lineage.
Although I have not found evidence to indicate that the “smoky” factor (a recessive gene that blurs the plumage pattern — symbolized “sy”) has made classification of squabs unreliable by expressing itself with the “dirty” plumage, there is a slight possibility that “smoky” in the heterozygous state may make classification difficult, i.e., that it is not totally recessive and sometimes produces effects almost comparable to homozygous smoky? However, not one single squab raised from tests showed the typical smoky phenotypic expression and therefore, I feel strongly that misclassification due to other genetic units did not cause classification problems with regards to test birds, and is minor to the overall picture, but acknowledge that possible interactions of various genetic units may cause classification problems. There are several alternative choices to classify “dirty” squabs, i.e., bill-ring, foot coloration, rump coloration, under-wings, and white ticking usually presents itself in many adult plumages. Rarely has a bird presented itself that posed problems, but they occasionally occur.
In six (6) matings of non-dirty parents, nineteen (19) squabs produced were all non-dirty, none of which were recorded to possess, without question, any typical “dirty” traits.
In eight (8) matings of dirty parents, of unknown genotypes with reference to “dirty”, twenty-eight (28) squabs were produced, twenty-three (23) were dirty and five (5) were non-dirty. One of these matings was a brother X sister mating that was produced by a dirty X non-dirty mating. This pair produced nine (9) squabs of which eight (8) were dirty and one (1) was a non-dirty. The overall ratio of 23:5 is not very close to 3:1, but some consideration must be given to the likely possibilities that some matings had parents that were homozygous for “dirty”.
In twelve (12) matings of non-dirty mated to a dirty of unknown genotypes, forty-one (41) squabs were produced of which twenty-six (26) were dirty and fifteen (15) were non-dirty. In two of these cases the dirty parent was known to have been produced from a dirty X non-dirty matings, and is probably justifiable considering them heterozygotes for “dirty”. These two matings produced twelve (12) squabs of which five (5) were dirty and seven (7) were non-dirty. Again the overall ratio of 26:15 is a bit high on the dirty side for a 1:1 ratio, but like the dirty X dirty matings consideration must be given to possibilities of some homozygous dirty parents being involved. However, the 5:7 ratio of the two selected matings mentioned, does appear to be significant in approaching a 1:1 ratio.
| (6)Non-dirty cock
. | (dirty total 26) | (non-dirty total 15) |
CONCLUSIONS AND DISCUSSION
It is with some caution that I submit the following but there seems to be fair evidence that “dirty” is an autosomal dominant gene. In keeping with scientific tradition it seems best to credit Bol for using the symbol “V ” in his 1926 publication in Dutch. The word for dirty in Dutch is “vuile”, therefore, giving rise to the symbol “V”. Bol also used the Dutch word “vet”.
From the evidence presented in the tabulations of matings, it appears absolutely clear that no evidence of “sex-linkage” exists with “dirty”. Particularly, in the nine (9) matings of non-dirty cocks X dirty hens, where if sex-linkage were operating only “dirty” cocks would have been produced. On the contrary, near equal numbers of “dirty” hens were also produced.
The data support the idea that dirty is a simple dominant in relation to European wild type. However, there is too little information available to make substantial claims. There is more information in my records, but it is in association with other powerful modifying genes, such as Faded (StF), Almond (St), Ash-Red (BA), Indigo (In), etc. Possibly classification with “spread” (S) and Indigo (In) can be pretty accurate, but with Ash-Red, recessive red, dilution, brown, smoky, and others there will always be difficulty.
(1) Levi, Wendell M. (1967) revised edition of “The Pigeon”, 667 pages – 1,127
(2) Bol, C. J. A. C. “(1926) “Genetische analyse van kleuren, veerpatronen, tinten,
en afteekeningen bij postduiven”. Genetica 8: 45-154.
(3) Goodwin, Derek (1970) second edition “Pigeons and Doves of the World” … The
British Museum (Natural History) Publication No. 663; 446 pages, well illustrated.