Uropygial gland

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Position of the uropygial gland, indicated on a budgerigar
Uropygial gland of a blue jay

The uropygial gland, informally known as the preen gland or the oil gland, is a bilobed

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).[1]

Etymology

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

Distribution amongst species

The gland is invariably present during

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
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.

Gland secretion

preening
. The bird on the left is pushing its head towards its uropygial gland.
White-winged crossbill
(Loxia leucoptera) extracting preen oil from its uropygial gland.

The uropygial gland secretes an oil (preen oil) through the dorsal surface of the skin via a

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.[4] 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[7] and Corynebacterium uropygiale[8]
). Some of those bacteria add to the antimicrobial properties of preen wax.

A bird will typically transfer preen oil to its body during preening by rubbing its

budgerigars, use the feet to apply the oil to feathers around the vent.[9]

History

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.[10]

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.[1] Many ornithologists believe the function of the uropygial gland differs among various species of birds.[11]

Feather and body integrity

Preen oil is believed to help maintain the integrity of

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

lipids with female pheromone activity.[1]

Waterproofing effect

The uropygial gland is strongly developed in many waterbirds, such as

electrostatic charge to the oiled feather through the mechanical action of preening[12] are not supported by scientific studies.[10]

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

symbiotic bacteria whose excretions reduce the activity of feather-degrading bacteria and thus help to preserve the plumage.[14]

In vitro studies suggest that the preen oils of

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.[5] 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).[15]

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".[16]

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. [17]

See also

References

  1. ^
    PMID 19675950
    .
  2. ^
    doi:10.1111/bij.12139
    .
  3. ^ "BirdChannel.com". Retrieved August 10, 2012.
  4. ^ a b c Montalti, Diego & Salibian, Alfredo (2000). "Uropygial gland size and avian habitat". Ornitologia Neotropical. 11 (4): 297–306.
  5. ^
    S2CID 38680397
    .
  6. ^ "The Grey Roost". Archived from the original on March 24, 2015. Retrieved August 10, 2012.
  7. PMID 12807187
    .
  8. PMID 26776107
    .
  9. ^ "Everything About Budgies". Retrieved August 10, 2012.
  10. ^ a b Elder, William H. (1954). "The oil gland of birds". Wilson Bulletin. 66 (1): 6–31.
  11. ^ "Encyclopædia Britannica – Uropygial gland". Retrieved August 10, 2012.
  12. ^ Schauer, E (1877). "Elektrische Eigenschaft der Bürzeldrüse" (PDF). Mittheilungen des Ornithologischen Vereins in Wien. 1: 55–56.
  13. S2CID 11433594
    .
  14. PMID 19812087
    .
  15. S2CID 12856821
    .
  16. S2CID 30299643.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  17. doi:10.1071/AN16268
    .

External links

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