Preening is a found in
bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s that involves the use of the beak to position
feather
Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and an exa ...
s, interlock feather that have become separated, clean
plumage
Plumage () is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, there can b ...
, and keep
ectoparasites
Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...
in check. Feathers contribute significantly to a bird's insulation, waterproofing and
aerodynamic flight, and so are vital to its survival. Because of this, birds spend considerable time each day maintaining their feathers, primarily through preening. Several actions make up preening behaviour. Birds fluff up and shake their feathers, which helps to "rezip" feather barbules that have become unhooked. Using their
beak
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, grasping, and holding (in probing for food, eating, manipulating and ...
s, they gather preen oil from
a gland at the base of their tail and distribute this oil through their feathers. They draw each
contour feather through their bill, nibbling it from base to tip.
Over time, some elements of preening have
evolved
Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
to have secondary functions.
Ritualised preening has become a part of some
courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
s, for example. It is also a
displacement activity
Displacement activities occur when an animal or human experiences high motivation for two or more conflicting behaviours: the resulting displacement activity is usually unrelated to the competing motivations. Birds, for example, may peck at grass ...
that can occur when birds are subjected to two conflicting drives. Though primarily an individual function, preening can be a social activity involving two or more birds – a behaviour known as allopreening. In general, allopreening occurs either between two members of a mated pair or between flock members in a social species. Such behaviour may assist in effective grooming, in the recognition of individuals (mates or potential sexual partners), or in reducing or redirecting potential aggressive tendencies in social species. Most allopreening is confined to the head and neck, smaller efforts being directed towards other parts of the body.
Ingestion of
pollutant
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
s or disease-causing organisms during preening can lead to problems ranging from liver and kidney damage to pneumonia and disease transmission. Injury and infection can cause overpreening in caged birds, as can confining a bird with a dominant or aggressive cage mate.
Etymology
The use of the word ''preen'' to mean the tidying of a bird's feathers dates from
Late Middle English
Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman Conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old English pe ...
. It appears to be a variant of the word ''prune''; one now-obsolete definition of ''prune'' meant "anoint", based on the
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''ungere'', which had the same meaning. This usage was combined with the Scottish and northern English dialect ''preen'' meaning "pierce" or "pin", due to the "pricking" action of the bird's beak during preening.
Importance
Preening is a maintenance behaviour used by all birds to care for their feathers. It is an innate behaviour; birds are born knowing the basics, but there is a learned component. Birds that are hand-reared without access to a role model have abnormalities in their preening behaviours. Despite spending considerable time in their efforts, they do not use proper techniques to groom effectively and may do a poor job overall as a result. Displaced feathers can cause birds considerable trouble; such feathers might become damaged, could interrupt the smooth flow of air over a flying bird, or might allow the bird's body heat to escape. Preening allows a bird to reposition such displaced feathers. There is evidence that
filoplumes, specialised feathers buried under a bird's outer covering of
contour feathers, help to signal when contour feathers have been displaced.
Mechanoreceptor
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are located on sensory neurons that convert mechanical pressure into action potential, electrical signals tha ...
s at the base of the filoplumes only fire when contour feathers are displaced or the filoplume moves.
Preening enables birds to remove dirt and parasites from their plumage, and assists in the waterproofing of feathers. During
moult
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
, birds remove the sheaths from around their emerging
pin feathers while preening.
Because feathers are critical to a bird's survival – contributing to insulation, waterproofing and aerodynamic flight – birds spend a great deal of time maintaining them. When resting, birds may preen at least once an hour. Studies on multiple species have shown that they spend an average of more than 9% of each day on maintenance behaviours, preening occupying over 92% of that time, though this figure can be significantly higher.
Studies found that some
gull
Gulls, or colloquially seagulls, are seabirds of the subfamily Larinae. They are most closely related to terns and skimmers, distantly related to auks, and even more distantly related to waders. Until the 21st century, most gulls were placed ...
species spent 15% of daylight hours during the breeding season preening, while another showed that
common loon
The common loon or great northern diver (''Gavia immer'') is a large member of the loon, or diver, family (biology), family of birds. Reproduction, Breeding adults have a plumage that includes a broad black head and neck with a greenish, purpli ...
s spent upwards of 25% of their day preening.
In most of the studied species where the bird's sex could be determined in the field, males spent more time preening than females, though this was reversed in ducks.
Some
ratite
Ratites () are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal ...
s, which are not dependent on their feathers for flight, spend far less time on maintenance behaviours. One study of
ostrich
Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa.
They are the heaviest and largest living birds, w ...
es found that they spent less than 1% of their time engaged in such behaviours.
Preen oil

Fully grown feathers are essentially dead structures, so it is vital that birds have some way to protect and lubricate them. Otherwise, age and exposure cause them to become brittle. To facilitate that care, many bird species have a
preen or uropygial gland, which opens above the base of the tail feathers and secretes a substance containing fatty acids, water, and waxes. The bird gathers this substance on its bill and applies it to its feathers. The gland is generally larger (in relation to body size) in waterbirds, including
tern
Terns are seabirds in the family Laridae, subfamily Sterninae, that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated in eleven genera in a subgroup of the family Laridae, which also ...
s,
grebe
Grebes () are aquatic diving birds in the order (biology), order Podicipediformes (). Grebes are widely distributed freshwater birds, with some species also found in sea, marine habitats during Bird migration, migration and winter. Most grebes f ...
s and petrels. However, studies have found no clear correlation between the size of the gland and the amount of time a species spends in the water; it is not consistently largest in those species that spend the most time in the water.
Preen oil plays a role in reducing the presence of parasitic organisms, such as feather-degrading bacteria, lice and fungi, on a bird's feathers. One study of
Eurasian hoopoes showed that the presence of symbiotic bacteria (''
Enterococcus faecalis
''Enterococcus faecalis'' – formerly classified as part of the group D '' Streptococcus,'' is a Gram-positive, commensal bacterium naturally inhabiting the gastrointestinal tracts of humans. Like other species in the genus '' Enterococcus'', ' ...
'') in their preen oil inhibited the growth of the feather-degrading bacteria ''
Bacillus licheniformis
''Bacillus licheniformis'' is a bacterium commonly found in the soil. It is found on bird feathers, especially chest and back plumage, and most often in ground-dwelling birds (like sparrows) and aquatic species (like ducks).
It is a gram-positi ...
''. ''Enterococcus faecalis'' did this by releasing a
bacteriocin
Bacteriocins are proteinaceous or peptide, peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally ...
.
Female hoopoes transfer preen oil onto their brood patches and eggs, which results in the transfer of bacteria as well. Preen oil and bacteria are rubbed into microscopic pits on the surface of the eggs during
incubation. This alters the colour of the eggs (darkening them) but there is also evidence that the bacteria may help to protect the developing chicks.
Other studies have shown that removing or restricting access to the uropygial gland typically results in a higher bacterial parasite load on the plumage, though not necessarily of feather-degrading bacterial species. Preen oil may play a part in protecting at least some species from some internal parasites; a study of the incidence of avian malaria in house sparrow
The house sparrow (''Passer domesticus'') is a bird of the Old World sparrow, sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pa ...
s found that uninfected birds had larger uropygial glands and higher antimicrobial activity in those glands than infected birds did. There is even evidence that the foul-smelling preen oil of hoopoes and wood hoopoes may help to repel mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
ian predator
Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
s.
Preen oil helps to maintain the waterproofing of a bird's plumage. Though the oil does not provide any direct waterproofing agent, it helps to extend the life of the feather – including the microscopic structures (the barbs and barbules) which interlock to create the waterproof barrier.
While most species have a preen gland, the organ is missing in the ratites (emu
The emu (; ''Dromaius novaehollandiae'') is a species of flightless bird endemism, endemic to Australia, where it is the Tallest extant birds, tallest native bird. It is the only extant taxon, extant member of the genus ''Dromaius'' and the ...
, ostriches, cassowaries
Cassowaries (; Biak language, Biak: ''man suar'' ; ; Papuan_languages, Papuan: ''kasu weri'' ) are flightless birds of the genus ''Casuarius'', in the order Casuariiformes. They are classified as ratites, flightless birds without a keel (bird a ...
, rheas and kiwis) and some neognath birds, including bustards, woodpecker
Woodpeckers are part of the bird family (biology), family Picidae, which also includes the piculets, wrynecks and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar and the extreme ...
s, a few parrot
Parrots (Psittaciformes), also known as psittacines (), are birds with a strong curved beak, upright stance, and clawed feet. They are classified in four families that contain roughly 410 species in 101 genus (biology), genera, found mostly in ...
s and pigeon
Columbidae is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with small heads, relatively short necks and slender bills that in some species feature fleshy ceres. ...
s. Some species that lack a preen gland instead have powder down
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and p ...
feathers which continually break down into a fine dust that the birds apply to their contour feathers while preening. These powder down feathers may be scattered throughout the bird's plumage or concentrated into dense patches. As well as helping to waterproof and preserve the bird's feathers, powder down can give a metallic sheen to the plumage.
Preening action
A bird's plumage is primarily made up of two feather types: firm vaned or pennaceous feathers on the surface, with softer down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and p ...
s underneath. Both feather types have a central shaft with narrower branching from that shaft. Pennaceous feathers also have much smaller barbules branching from the entire length of each barb; these barbules have tiny hooks along their length, which interlock with the hooks of neighbouring barbules. Barbules can become unhooked as a result of a bird's daily activities – dislodged when the bird brushes up against vegetation, for instance, or when it interacts with another bird during fighting or mating. Preening may involve two kinds of bill actions: nibbling (or mandibulating) while working the feather from base to tip, or stroking with the bill either open or closed. The nibbling action is the one used most often; it is more effective than stroking for applying preen oil, removing ectoparasite
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
s, rejoining unzipped barbules, and rearranging feathers. The stroking action is typically done in the direction the feathers lie, with the bill either opened or closed. Stroking is used to apply preen oil, as well as to dry and smooth plumage. Grebes stroke more vigorously with an open bill – a behaviour known as "stropping". Penguin
Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...
s use their whole heads to stroke, in a motion referred to as "wiping". Birds regularly fluff up their plumage and repeatedly shake their bodies while preening. Experiments have shown that the shaking action can "rezip" a majority of split feather barbules.
Birds cannot use their beaks to apply preen oil to their own heads. Instead, many use their feet in an action called scratch-preening. Once they have gathered preen oil on their beak, they scrape a foot across their bill to transfer the oil, and then scratch the oil into the feathers on their head. Longer-necked birds may rub their head directly on their uropygial gland. Some species (including nightjar
Nightjars are medium-sized nocturnal or crepuscular birds in the family Caprimulgidae and order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called bugeaters, their primary source of food ...
s, heron
Herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 75 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genus ''Botaurus'' are referred to as bi ...
s, frigatebird
Frigatebirds are a Family (biology), family of seabirds called Fregatidae which are found across all tropical and subtropical oceans. The five extant species are classified in a single genus, ''Fregata''. All have predominantly black plumage, l ...
s, owls and pratincoles) have comb-like serrations on the claw (a pectinate claw) of the middle toe which may aid in scratch-preening. Some species stretch their leg over their lowered wing to reach their head (known as "indirect" scratching), while others extend their leg between their wing and their body (known as "direct" scratching). There is some evidence that the method used by a species may be related to its ecology. For instance, New World warblers that are primarily arboreal
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
tend to be overwing scratchers, while those that spend significant time on the ground are typically underwing scratchers. In general, preening takes place while the bird is perched, on the ground, or swimming, but some of the more aerial species (including swift
Swift or SWIFT most commonly refers to:
* SWIFT, an international organization facilitating transactions between banks
** SWIFT code
* Swift (programming language)
* Swift (bird), a family of birds
It may also refer to:
Organizations
* SWIF ...
s, swallow
The swallows, martins, and saw-wings, or Hirundinidae are a family of passerine songbirds found around the world on all continents, including occasionally in Antarctica. Highly adapted to aerial feeding, they have a distinctive appearance. The ...
s, terns and albatross
Albatrosses, of the biological family Diomedeidae, are large seabirds related to the procellariids, storm petrels, and diving petrels in the order Procellariiformes (the tubenoses). They range widely in the Southern Ocean and the North Paci ...
es) preen while flying. Many birds have a slight overhang at the tip of their upper mandible. Experiments suggest that this allows birds to apply shearing forces that kill the flat-bodied feather lice
A bird louse is any chewing louse (small, biting insects) of order Phthiraptera which parasitizes warm-blooded animals, especially birds. Bird lice may feed on feathers, skin, or blood. They have no wings, and their biting mouth parts distingui ...
; the removal of the bill tip caused an increase in feather lice due to ineffective preening.
Preening is often done in association with other maintenance behaviours, including bathing, dusting, sunning, oiling or anting
Anting () is a town in Jiading District, Shanghai, bordering Kunshan, Jiangsu to the west. It has 96,000 inhabitants and, after the July 2009 merger of Huangdu (), an area of . , and can either precede or follow these other behaviours. All birds typically preen after bathing. Groups of birds sometimes all groom individually at the same time. This has been seen in species ranging from herons to blackbirds.
Secondary functions
Preening may help to send sexual signals to potential mates because plumage colouration (which can be altered by the act of preening) can reliably reflect the health or "quality" of its bearer. In some species, preen oil is used to cosmetically colour the plumage. During the breeding season, the preen oil of the great white pelican
The great white pelican (''Pelecanus onocrotalus'') also known as the eastern white pelican, rosy pelican or simply white pelican is a bird in the pelican family. It breeds from southeastern Europe through Asia and Africa, in swamps and shallow ...
becomes red-orange, imparting a pink flush to the bird's plumage. The preen oil of several gull and tern species, including Ross's gull
Ross's gull (''Rhodostethia rosea'') is a small gull, the only species in its genus, although it has been suggested the genus should be merged with the closely related '' Hydrocoloeus'', which otherwise only includes the little gull.
This bird ...
, contains a pink colourant which does the same. The heads of these birds typically show little pink, because of the difficulty of reaching those areas with preen oil. The yellow feathers of the great hornbill are also cosmetically coloured during preening. The preen oil of the Bohemian waxwing increases the UV reflectance of its feathers. Ritualised preening is used in courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
s by several species, particularly ducks; such preening is typically designed to draw attention to a modified structure (such as the sail-shaped secondaries of the drake mandarin duck
The mandarin duck (''Aix galericulata'') is a perching duck species native to the East Palearctic. It is Sexual dimorphism, sexually dimorphic – the males are elaborately coloured, while the females have more subdued colours. It is a medium- ...
) or distinctive colour (such as the ) on the bird. Mallard
The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa. It has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Arge ...
s of both sexes will lift a wing so that the brightly coloured speculum is showing, then will place their bill behind the speculum as if preening it. Courtship preening is more conspicuous than is preening for feather maintenance, using more stereotypical movements.
Preening may be performed as a displacement activity
Displacement activities occur when an animal or human experiences high motivation for two or more conflicting behaviours: the resulting displacement activity is usually unrelated to the competing motivations. Birds, for example, may peck at grass ...
. In some cases, it is done in place of another activity that birds are strongly motivated, but unable, to do. In one study, black-headed gull
The black-headed gull (''Chroicocephalus ridibundus'') is a small gull that breeds in much of the Palearctic in Europe and Asia, and also locally in smaller numbers in coastal eastern Canada. Most of the population is migratory and winters fu ...
s which were prevented from incubating a full clutch
A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...
of eggs (by the removal of eggs from their nest) responded by preening and nest building – both displacement activities. When all three eggs in their regular clutch were removed, the gulls showed a significant increase in the amount of time they spent preening. The conflict between two incompatible drives, such as incubating and escape, can lead a bird to engage in displacement activities. Nesting Sandwich
A sandwich is a Dish (food), dish typically consisting variously of meat, cheese, sauces, and vegetables used as a filling between slices of bread, or placed atop a slice of bread; or, more generally, any dish in which bread serves as a ''co ...
and common tern
The common tern (''Sterna hirundo'') is a seabird in the family Laridae. This bird has a circumpolar distribution, its four subspecies breeding in Temperateness, temperate and subarctic regions of Europe, Asia and North America. It is stron ...
s preen when they have been alarmed by a potential predator or when they have had an aggressive encounter with a neighbouring bird, for instance. Fighting European starling
The common starling (''Sturnus vulgaris''), also known simply as the starling in Great Britain and Ireland, and as European starling in North America, is a medium-sized passerine bird in the starling family, Sturnidae. It is about long and ha ...
s will break off their battles to preen.
Allopreening
Although preening is primarily an individual behaviour, some species indulge in allopreening, one individual preening another. It is not particularly common among birds, though species from at least 43 families
Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...
are known to engage in the mutual activity. Most allopreening activity concentrates on the head and neck, a lesser amount being directed towards the and and an even smaller percentage applied to the . A few species are known to allopreen other areas, including the rump, tail, belly and underwing.
Several hypotheses have been advanced to explain the behaviour: that it assists in effective grooming, that it assists in recognition of individuals (mates or potential sexual partners), and that it assists in social communication, reducing or redirecting potential aggressive tendencies. These functions are not mutually exclusive. Evidence suggests that different species may participate for different reasons, and that those reasons may change depending on the season and the individuals involved. In most cases, allopreening involves members of the same species, although some cases of interspecific allopreening are known; the vast majority of these involve icterids, though at least one instance of mutual grooming between a wild black vulture
The black vulture (''Coragyps atratus''), also known as the American black vulture, Mexican vulture, zopilote, urubu, or gallinazo, is a bird in the New World vulture family whose range extends from the southeastern United States to Peru, Ce ...
and a wild crested caracara
The crested caracara (''Caracara plancus'') is a bird of prey (raptor) in the falcon Family (biology), family, Falconidae. It was formerly placed in the genus ''Polyborus'' before being given in its own genus, ''Caracara (genus), Caracara''. It i ...
has been documented. Birds seeking allopreening adopt specific, ritualised postures to signal so; they may fluff their feathers out or put their heads down. Captive birds of social species that normally live in flocks, such as parrots, will regularly solicit preening from their human owners.
There is some evidence that allopreening may help to keep in good condition those feathers that a bird cannot easily reach by itself; allopreening activities tend to focus on the head and neck. It may also help to remove ectoparasite
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
s from those hard-to-reach areas. Allopreening is most common among species that are regularly in close physical contact due to flocking or social behaviours, where such contact allows for easier transfer of ectoparasites between individuals. In one study, Macaroni penguin
The macaroni penguin (''Eudyptes chrysolophus'') is a species of penguin found from the Subantarctic to the Antarctic Peninsula. One of six species of crested penguin, it is very closely related to the royal penguin, and some authorities consid ...
s that frequently allopreened had significantly fewer tick
Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, and species, but can become larger when engorged. Ticks a ...
s on their heads and necks than those that did not. Green wood hoopoes, a flocking species with a complex hierarchy, show similar frequencies of initiating and reciprocating allopreening of the head and neck regardless of social status, time of year or group size, which suggests that such activity is primarily related to feather hygiene.
Most allopreening is done between the two members of a mated pair, and the activity appears to play an important role in strengthening and maintaining pair bond
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of young and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently ...
s. It is more common in species where both parents help to raise the offspring and correlates with an increased likelihood that partners will remain together for successive breeding seasons. Allopreening often features as part of the "greeting ceremony" between the members of a pair in species such as albatrosses and penguins, where partners may be separated for a relatively long period of time, and is far more common among sexually monomorphic species (that is, species where the sexes look outwardly similar). It appears to inhibit or redirect aggression, as it is typically the dominant bird that initiates the behaviour.
Allopreening appears to reduce the incidence of conflict between members of some colonially living or colonially nesting species. Neighbouring common guillemots that engaged in allopreening were much less likely to fight. Since fights often lead to eggs or chicks being knocked off breeding cliffs, fewer fights led to greater breeding success for allopreening neighbours. Among social flocks of green wood hoopoes, rates of body allopreening (that is, allopreening of another bird's body rather than head and neck) increase with group size. Evidence suggests this type of allopreening reduces social tension, and thus plays an important role in group cohesion. More dominant birds receive far more body allopreening services than do lower-ranked birds, and lower-ranked birds initiate far more body allopreening bouts than do their higher-ranked flock mates. Body allopreening is only reciprocal when done between members of a mated pair; otherwise, the dominant bird reciprocates in fewer than 10% of the instances.
Potential problems
If birds are exposed to some pollutant
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
s, such as leaking petroleum
Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
, they can quickly lose the preen oil from their feathers. This causes a loss of heat regulation and waterproofing, and rapidly leads to the bird becoming chilled. If waterbirds are exposed, they can lose both buoyancy and the ability to fly; this means they must swim constantly to stay warm and afloat (if they cannot reach land), and eventually die of exhaustion. While preening in an effort to clean themselves, they may ingest harmfully large amounts of the petroleum. Ingested oil can cause pneumonia
Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...
, as well as liver and kidney damage. Studies done with black guillemots showed that even small amounts of ingested oil caused the birds physiological distress. It interfered with the foraging efficiency of adults and decreased the growth rates of young birds.
Allopreening may facilitate disease transmission between infected and non-infected individuals. West Nile virus
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...
has been found in the feather pulp of several species of corvid
Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers. In colloquial English, they are known as the crow family or corvids. Curre ...
, for instance, meaning that birds that preen infected partners might become infected themselves. Even preening its own body may expose a bird to pathogens. There is evidence that water-borne avian influenza
Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A viru ...
virus is "captured" by the preen oil on feathers, providing a possible route for infection. The ingestion of parasites during preening may result in infection; the tick-borne disease louping ill virus can be transmitted to red grouse
The red grouse (''Lagopus scotica'') is a medium-sized bird of the grouse family which is found in Calluna, heather moorland in Great Britain and Ireland.
It was formerly classified as a subspecies of the willow ptarmigan (''Lagopus lagopus'') ...
if the bird consumes a tick carrying the disease.
Caged birds, particularly parrots, sometimes overpreen in response to being exposed to strong scents (such as nicotine or air fresheners) or as a result of neuropathy
Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...
. Reducing exposure to the offending odour, or treating the underlying cause of the neuropathy (such as injury, infection, or heavy metal intoxication) can help to eliminate the behaviour. Confining a bird with an incompatible or very dominant cage mate can lead to excessive allopreening, which can result in feather plucking or injury.
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External links
Barred owl preening
on YouTube
Splendid fairy-wrens preening and allopreening
on YouTube
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Bird behavior
Feathers
Hygiene
Articles containing video clips