Rumplessness, pygostyles and more

January 8, 2024
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coloured illustration of a cock and hen with no tail feathers
Illustration from the Geflügel-Album of Jean Bungartz, 1885

Rumpless chickens are characterised by caudal dysplasia, the absence of the pygostyle or caudal appendage – the “parson’s nose”. This is the result of inheritance of an autosomal dominant trait. The mutation which causes it is unknown; two candidates have been proposed.

Caudal regression syndrome, or sacral agenesis (or hypoplasia of the sacrum), is a rare birth defect. It is a congenital disorder in which the fetal development of the lower spine—the caudal partition of the spine—is abnormal. It occurs at a rate of approximately one per 60,000 live births. Currarino syndrome is an inherited congenital disorder where either the sacrum (the fused vertebrae forming the back of the pelvis) is not formed properly, or there is a mass in the presacral space in front of the sacrum, and there are malformations of the anus or rectum. It occurs in approximately 1 in 100,000 people. Mutations in the MNX1 gene are associated with Currarino syndrome.  In 2000, the first large series of Currarino cases was genetically screened for HLXB9 mutations. It was shown that the gene is specifically causative for Currarino syndrome, but not for other forms of sacral agenesis. The study was published in the American Journal of Human Genetics. There is reportedly a connection to spina bifida.

See also

History

Rumplessness in chickens has been documented for centuries. An early description is that of the Bolognese ornithologist Ulisse Aldrovandi in his Ornithologiae Tomus Alter of 1600.

Rumpless breeds

black-and-white illustration of a cock with no tail feathers
“Gallus ex Persia”, illustration from the Ornithologiae Tomus Alter of Ulisse Aldrovandi, 1600

Rumpless breeds of chicken include: the Araucana or Rumpless Araucana of South America, both large fowl and bantam;  the Belgian Barbu de Boitsfort, Barbu de Grubbe and Barbu d’Uccle bantams;  the Japanese Uzurao, a rumpless equivalent of the Tosa-Kojidori bantam, and Ingie (large fowl) from Kagoshima Prefecture; the Rumpless Game of the United Kingdom (both large fowl and bantam), sometimes called the Manx Rumpy or Persian Rumpless; and the German Ruhlaer Zwerg-Kaulhühner or Rumpless Booted Bantam.

Pigeon skeleton with “plowshare”-type pygostyle (number 17) A stylised bird skeleton 1. Skull, 2. Cervical vertebrae, 3. Furcula, 4. Coracoid, 5. Uncinate process, 6. Keel, 7. Patella, 8. Tarsometatarsus, 9. Digits, 10. Tibiotarsus (10 and 11), 11. Tibiotarsus (10 and 11), 12. Femur, 13. Pubis (innominate bone), 14. Ischium (innominate bone), 15. Illium (innominate bone), 16. Caudal vertebrae, 17. Pygostyle, 18. Synsacrum, 19. Scapula, 20. Lumbar vertebrae, 21. Humerus, 22. Ulna, 23. Radius, 24. Carpus, 25. 3rd digit, 26. 2nd digit, 27. Alula (1st digit). Note: identification of bird digits as 1, 2, 3 or 2, 3, 4 is an unclear long-standing question (see, for example, doi:10.1002/dvdy.22595)

Pygostyle

“Pope’s nose” redirects here. It may also refer to the licence plate light on early Volkswagen Beetles.

Pygostyle describes a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main component of the uropygium, a structure colloquially known as the bishop’s nose, parson’s nose, pope’s nose, or sultan’s nose. This is the fleshy protuberance visible at the posterior end of a bird (most commonly a chicken or turkey) that has been dressed for cooking. It has a swollen appearance because it also contains the uropygial gland that produces preen oil.

Rectrices (singular rectrix) from the Latin word for “helmsman”, help the bird to brake and steer in flight. These feathers lie in a single horizontal row on the rear margin of the anatomic tail. Only the central pair are attached (via ligaments) to the tail bones; the remaining rectrices are embedded into the rectricial bulbs, complex structures of fat and muscle that surround those bones. Rectrices are always paired, with a vast majority of species having six pairs. They are absent in grebes and some ratites, and greatly reduced in size in penguins. Many grouse species have more than 12 rectrices. In some species (including ruffed grouse, hazel grouse and common snipe), the number varies among individuals. Domestic pigeons have a highly variable number as a result of changes brought about over centuries of selective breeding.

Pygostyle Etymology

Look up pygostyle in Wiktionary, the free dictionary.

“Pygostyle” is formed from Ancient Greek words, literally meaning “rump pillar”.

The insulting equation of the pygostyle with the noses of dignitaries dates back to 18th century Britain where pope’s nose first appears (in 1786). The form parson’s nose appears much later, dated to 1839. The usage is somewhat dependent on either a Catholic or Protestant viewpoint.

The forms bishop’s nose and sultan’s nose are 20th century variants.

The uropygial gland, informally known as the preen gland or the oil gland, is a bilobed sebaceous gland possessed by the majority of birds used to distribute the gland’s oil through the plumage by means of preening. It is located dorsally at the base of the tail (between the fourth caudal vertebra and the pygostyle) and is greatly variable in both shape and size. In some species, the opening of the gland has a small tuft of feathers to provide a wick for the preen oil (see below). It is a holocrine gland enclosed in a connective tissue capsule made up of glandular acini that deposit their oil secretion into a common collector tube ending in a variable number of pores (openings), most typically two. Each lobe has a central cavity that collects the secretion from tubules arranged radially around the cavity. The gland secretion is conveyed to the surface via ducts that, in most species, open at the top of a papilla (nipple-like structure).

Uropygial Etymology

From uropygium: Medieval Latin, from Ancient Greek οὐροπύγιον (ouropugion), from οὐρά (oura) ‘tail’ and πυγή (puge) ‘rump’.

History

Emperor Frederick II, in his thirteenth-century treatise on falconry, was seemingly the first to discuss the function of the uropygial gland of birds. He believed that its product not only oiled the plumage but also provided a poison which was introduced by the claws of hawks and owls thus bringing quicker death to their prey. However, studies in 1678 on the question of the toxic nature of the uropygial gland secretion found no evidence to support Frederick’s contention.

The preen gland is invariably present during embryonic development, whereas it can be vestigial in adults of certain orders, families, genera and species. Some or all species in at least nine families of birds lack a uropygial gland, mostly the ones unable to fly or the ones that produce powder down for feather maintenance. These include kiwis (Apterygidae), emu (Dromaiidae), ostriches (Struthionidae), rheas (Rheidae), cassowaries (Casuariidae), mesites (Mesitornithidae), bustards (Otididae), pigeons and doves (Columbidae), amazon parrots (Psittacidae), frogmouths (Podargidae), and woodpeckers (Picidae). These birds typically find other means to stay clean and dry, such as taking a dust bath. Researchers have been unable to correlate the presence or absence of the uropygial gland with factors such as distribution, climate, ecology, or flightlessness.

Preen Gland secretion

European herring gull (Larus argentatus): The bird on the right is uncovering its uropygial gland to distribute the gland’s oil through the plumage by means of preening. The bird on the left is pushing its head towards its uropygial gland.

The uropygial gland secretes an oil (preen oil) through the dorsal surface of the skin via a grease nipple-like nub or papilla. The oil contains a complex and variable mixture of substances formed greatly of aliphatic monoester waxes, formed of fatty acids and monohydroxy wax-alcohols. However, some types of diester waxes called uropygiols and containing hydroxyfatty acids and/or alkane-diols exist in the secretions of the uropygial gland of some groups of birds. Preen gland secretion of some, but not all, birds have shown to be antimicrobial. Some birds harbor bacteria in their preen gland, which to date, have (exclusively) been isolated from preen glands (e.g. Enterococcus phoeniculicola and Corynebacterium uropygiale). Some of those bacteria add to the antimicrobial properties of preen wax.

  • Montalti, Diego & Salibian, Alfredo (2000). “Uropygial gland size and avian habitat”. Ornitologia Neotropical. 11 (4): 297–306.
  • “The Grey Roost”. Archived from the original on March 24, 2015. Retrieved August 10, 2012.
  • Law-Brown, Janette; Meyers, Paul R. (2003). “Enterococcus phoeniculicola sp. nov., a novel member of the enterococci isolated from the uropygial gland of the Red-billed Woodhoopoe, Phoeniculus purpureus”. International Journal of Systematic and Evolutionary Microbiology. 53 (3): 683–685. doi:10.1099/ijs.0.02334-0. PMID 12807187.
  • Braun, Markus Santhosh; Zimmermann, Stefan; Danner, Maria; Rashid, Harun-or; Wink, Michael (2016). “Corynebacterium uropygiale sp. nov., isolated from the preen gland of Turkeys (Meleagris gallopavo)”. Systematic and Applied Microbiology. 39 (2): 88–92. doi:10.1016/j.syapm.2015.12.001. PMID 26776107.

A bird will typically transfer preen oil to its body during preening by rubbing its beak and head against the gland opening and then rubbing the accumulated oil on the feathers of the body and wings, and on the skin of the feet and legs. Tailward areas are usually preened utilizing the beak, although some species, such as budgerigars, use the feet to apply the oil to feathers around the vent.

White-winged crossbill (Loxia leucoptera) extracting preen oil from its uropygial gland.

Function

Several researchers have reported differences in the relative gland weights attributing them to factors like seasonal changes, habitat, body weight, inter-individual variations, and sex. Significant differences are found in the relative gland size between males and females in most species, however, no coherent explanation has as yet been found for these results. Many ornithologists believe the function of the uropygial gland differs among various species of birds.

Feather and body integrity

Preen oil is believed to help maintain the integrity of feathers. In waterbirds, preen oil maintains the flexibility of feathers and keeps feather barbules from breaking. The interlocking barbules, when in good condition, form a barrier that helps repel water (see below). In some species, preen oil is also believed to maintain the integrity of the horny beak and the scaly skin of the legs and feet. It has also been speculated that in some species, preen oil contains a precursor of vitamin D; this precursor is converted to vitamin D by the action of sunlight and then absorbed through the skin.

Courtship and pheromone production

Some researchers have postulated that the change in preen oil viscosity may be related to the formation of the more brilliant plumage required for courtship, although later research did not find support for this idea. The results of other studies suggest that the gland in females may be involved in the production and secretion of lipids with female pheromone activity.

Waterproofing effect

The uropygial gland is strongly developed in many waterbirds, such as ducks, petrels, pelicans and in the osprey and the oilbird. A study examining the gland’s mass relative to body weight in 126 bird species showed the absence of a clear-cut correlation between the gland’s mass and the degree of birds’ contact with water. Anecdotal reports indicating that the waterproofing effect of the hydrophobic uropygiols might be increased by electrostatic charge to the oiled feather through the mechanical action of preening are not supported by scientific studies.

Antiparasitic effect

Hoopoes host symbiotic bacteria in their uropygial glands whose secretions act against feather-degrading bacteria.

The taxonomic richness of avian louse burdens covaries positively with uropygial gland size (relative to body size) across avian taxa, suggesting coevolution between gland size and parasite biodiversity. The hoopoe (Upupa epops) uropygial gland harbours symbiotic bacteria whose excretions reduce the activity of feather-degrading bacteria and thus help to preserve the plumage.

In vitro studies suggest that the preen oils of rock doves (Columba livia) are effective against lice, however in vivo studies which removed the preen gland from captive birds had no significant effect on louse loads over the course of four months (but did reduce plumage quality), suggesting that preen oil may not be an important defense against lice in this species. Similarly, there was no evidence to support a role of the gland secretion in attracting biting midges and black flies in blue tits (Cyanistes caeruleus) and feral pigeons (Columba livia).

Cosmetic effect

Secretions of the uropygial gland of greater flamingos (Phoenicopterus roseus) contain carotenoids, organic pigments which give flamingos their pink colour. During the breeding season, greater flamingos increase the frequency of their spreading uropygial secretions over their feathers and thereby enhance their colour. This cosmetic use of uropygial secretions has been described as applying “make-up”.

  • Amat, J.A., Rendón, M.A., Garrido-Fernández, J., Garrido, A., Rendón-Martos, M. and Pérez-Gálvez, A. (2011). “Greater flamingos Phoenicopterus roseus use uropygial secretions as make-up”. Behavioral Ecology and Sociobiology. 65 (4): 665–673. doi:10.1007/s00265-010-1068-z. S2CID 30299643.

The chemical composition

The biochemical composition of preen oil has been reported to significantly vary among birds in several ways: for example, the qualitative and quantitative content of the volatile compounds, chain length of diols, lipid concentration, ester saturation, type of fatty acids and their percentage composition. This variation is due to a range of factors, including species, age, sex and season. In chickens, a limited number of studies have investigated the specific effect of diet on the fatty acid composition of preen oil in meat chickens. The preen oil of meat chickens is dominated by saturated fatty acids, which make up to 97% of the total fatty acids, with 13 different medium to long chain saturated fatty acids (C8:0 to C22:0) detected. The preen oil contained several odd-chain fatty acids, which suggests they may be derived from lipolysis by the uropygial gland and/or its microbiome. Diet and gender had small but significant effects on levels of specific saturated fatty acid in the preen oil. The fatty acid composition of the preen oil did not reflect the more diverse fatty acid compositions of the diet or whole blood. Therefore, this clearly indicate that measuring the fatty acid profile of preen oil is not a suitable alternative approach for predicting the fatty acid composition of the blood of meat chickens. 

  • Kanakri, K.; Muhlhausler, B.; Carragher, J.; Gibson, R.; Barekatain, R.; Dekoning, C.; Drake, K.; Hughes, R. (2016). “Relationship between the fatty acid composition of uropygial gland secretion and blood of meat chickens receiving different dietary fats”. Animal Production Science. 58 (5): 828. doi:10.1071/AN16268.

See also

Pygostyle As food

Turkey tail or turkey butt has an international exportation market in places such as Micronesia, Samoa, and Ghana. The turkey tail is commonly exported from America because it is considered unhealthy and cut off the normal turkey. After World War II, cheap imported turkey tails became popular in Samoa. Because the cut has a very high fat content, it was banned from 2007 to 2013 to combat obesity, only allowed back when Samoa joined the World Trade Organization. The meat is otherwise used in pet food.

Pygostyle Evolution

There are two main types of pygostyle:[citation needed] one, found in Confuciusornithidae, Enantiornithes, and some other Mesozoic birds, as well as in some oviraptorosaurs like Nomingia, is long and rod- or dagger blade-like. None of the known fossils with such pygostyles show traces of well-developed rectrices. The tail feathers in these animals consisted of downy fuzz and sometimes 2–4 central “streamers” such as those found in some specimens of Confuciusornis or in Paraprotopteryx.

By contrast, the function of the pygostyle in the terrestrial Nomingia is not known. It is notable however that its older relative Caudipteryx had no pygostyle but a “fan” of symmetrical feathers which were probably used in social display. Perhaps such ornaments were widespread in Caenagnathoidea and their relatives, and ultimately the oviraptorosaurian pygostyle evolved to help support them. The related Similicaudipteryx, described in 2008, also had a rod-like pygostyle, associated with a fan of tail feathers.

Yixianornis grabaui, one of the oldest known species with a pygostyle like that in living birds

The other pygostyle type is plowshare-shaped. It is found in Ornithurae (living birds and their closest relatives), and in almost all flying species is associated with an array of well-developed rectrices used in maneuvering. The central pair of these attach directly to the pygostyle, just as in Confuciusornis. The other rectrices of Ornithurae are held in place and moved by structures called bulbi rectricium (rectricial bulbs), a complex feature of fat and muscles located on either side of the pygostyle. The oldest known species with such a pygostyle is Hongshanornis longicresta.

As evidenced by the oviraptorosaurian cases, the pygostyle evolved at least twice, and rod-shaped pygostyles seem to have evolved several times, in association with shortening of the tail but not necessarily with a retractable fan of tail feathers. In other words, the pygostyles of oviraptorosaurs and Confuciusornis were likely weight-saving measures, and the specialized “true” pygostyles of ornithurans were adapted from these later to improve flight performance.

The bird clade Pygostylia was named in 1996, by Luis Chiappe, for the presence of this feature and roughly corresponds to its appearance in the bird family tree, though the feature itself is not included in its definition. In 2001, Jacques Gauthier and Kevin de Queiroz (2001) re-defined Pygostylia to refer specifically to the apomorphy of a short tail bearing an avian pygostyle.

This set of notes was inspired by an article which turned up in a biotin search of older articles.. actually the Insulin-induced abnormalities article showed up as an article that cited the Effect of biotin deficiency article. Both articles are from the 40s.

Cravens, W.W., W., & Sebesta, M.A. (1944). Effect of biotin deficiency on embryonic development in the domestic fowl. The Anatomical Record, 90. Cited by LANDAUER W. Insulin-induced abnormalities of beak, extremities and eyes in chickens. J Exp Zool. 1947 Jul;105(2):145-72. doi: 10.1002/jez.1401050202. PMID: 20251299.

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