A Tough Call; Feathered Shanks

I realized early on that the first chicken had rather unusual feather appendages, but I would have missed this next one except for a translated excerpt from early writings by Professor Alexander Sergeevich Serebrovsky (1892-1948), a prominent Russian geneticist.

I knew about feathered shanks and toes in modern breeds of pigeons as well as in chickens, hardly a natural trait, more like a modification of the foot in the direction of a wing as Darwin observed in his description of the Trumpeter Pigeon, "Their feet are so heavily feathered, that they almost appear like little wings.", not quite as prescient as I remembered it.

Feather footed chickens are much the same in the development of useless quill-like flight feathers growing laterally from the sides of the shank and the middle and outer toes. The genetics is complex, more than one dominant gene being suggested along with inhibitors to leg feathering noted in some stock. Most likely the common concurrence of brachydactyly (shortening) of the outer toe and the quill-like foot feathering and the frequent syndactyly (webbing) found between the middle and outer toes is an indication of some malfunctioning developmental or hox controlled gene. The foot is literally being modified into a wing.

This foot of a Brahma chick illustrates both brachydactyly and syndactyly. The outer toe on the right in this picture is normally slightly longer that the inner toe. In this case it is slightly shorter and the webbing between outer and middle toes more pronounced than usual.


What Serebrovsky discovered and what made me take a closer look was a recessive form of foot feathering that enveloped the tarsus and was largely confined to the shank, not the toes, resembling the shank feathering found on many grouse species.

Serebrovsky calls this the Pavloff type of foot feathering after an extinct Russian breed of fowl. The feathering is more symmetrical on the shank or tarsus as compared with the "Cochin type", the wing-foot, and the feathers are soft and downy, not quill-like. I see this as a natural trait in the flightless Malayoid, the shank covered with small soft feathers except for the rear or ventral side and the toes completely bare.

This recessive trait commonly occurs with and is obscured by the wing-foot. It can be recognized in these cases by feathering on the medial or inner surface of the shank that stops abruptly at the toes.

Here I have managed to isolate the grouse-foot type of feathering to a reasonable degree.

There is one other factor to consider, another recessive character known as the vulture hock, which can be seen in Serebrovsky's illustration above in a reduced form. These are stiff contour feathers in line with the lower leg segment known as the tibiotarsus in birds and projecting beyond the hock joint where the tibiotarsus meets the metatarsus, the shank. Interestingly, these vulture hocks appear to have had a functional purpose in the Malayoid in that they project rearward when the bird squats down enveloping somewhat the rear of the bird.

Thus....

See what I mean?


There has to be a connection between the grouse-foot/vulture hock complex attributable to the Malayoid and the inappropriate wing-foot, perhaps something to do with the transition from scales to feathers.


References:
Darwin, Charles. 1875? The Variation of Plants and Animals under Domestication, Volume 1, Chapter 1.V. Domestic Pigeons, pg 123.

Serebrovsky, A. S. The Genetics of the Domestic Fowl. Part II. The Genetics of Leg Feathering. Memoirs of the Anikowo Genetical Station, 1926.
Abstracted by L. C. Dunn from the translation of B. F. Glessing (The Journal of Heredity, 20:111-118)