Moulting

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A dragonfly in its radical final moult, metamorphosing from an aquatic nymph to a winged adult. Dragonfly metamorphosis.jpg
A dragonfly in its radical final moult, metamorphosing from an aquatic nymph to a winged adult.

In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis , is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer layer or covering), either at specific times of the year, or at specific points in its life cycle.

Contents

Moulting can involve shedding the epidermis (skin), pelage (hair, feathers, fur, wool), or other external layer. In some groups, other body parts may be shed, for example, wings in some insects or the entire exoskeleton in arthropods.

Examples

GroupItem shedTimingNotes
Cats Fur Usually around spring-summer timeCats moult fur around spring-summer time to get rid of their "winter coat". Cats have thicker fur during the colder winter months to keep them warm, then around spring and summer they shed some of their fur to get a thinner coat for the warmer summer months. Some cats need brushing during moulting, since dead hairs can get trapped in the cat's fur.
Chicken Feathers Usually autumn (non-commercial hens).Chickens generally stop laying eggs when their moulting begins and recommence laying when their new feathers have re-grown.
Dogs and other canids Fur Semi-annually, spring and fall (autumn).Moulting or shedding in canids, as in all mammals, [1] is due to fluctuations in the amount of melatonin secreted by their pineal gland in response to seasonal sunlight variations rather than temperature variations. This seasonality in moulting is most preserved in Arctic breeds of dogs which shed twice each year whereas most other breeds moult once each year.
Snakes Skin Regularly, when old skin is outgrown.Snakes rub against rough surfaces to assist removal of their shed skin.[ citation needed ]
Lizards Skin Regularly, when old skin is outgrown.Lizards, like snakes, rub against objects to help remove their shed skin and then consume the shed skin for calcium and other nutrients.
Hermit crabs Exoskeleton Regularly, when the carapace is outgrown.Land hermit crabs bury themselves for many weeks while they moult and then consume their exoskeleton.[ citation needed ]
Amphibians Skin Regularly.Salamanders and frogs shed their skins regularly, then often eat it.
Arachnids Exoskeleton Regularly, when the exoskeleton is outgrown.Arachnids moult regularly to grow, often becoming reclusive and fasting for long periods prior to a moult.[ citation needed ]
Insects Exoskeleton Regularly in larvae, when the exoskeleton is outgrown.In species with a "complete" metamorphosis, the final moult transforms the body, typically from a soft-bodied larva to a reproductive, winged and sometimes colourful adult. In mayflies, a winged subimago moults one last time to a winged adult.

In birds

Loggerhead Shrike molting.jpg Lanius ludovicianus1.jpg
A loggerhead shrike in mid-moult (left) and with regular plumage (right).
A king penguin with developing replacement feathers, sometimes called pin feathers SGI-2016-South Georgia (Fortuna Bay)-King penguin (Aptenodytes patagonicus) 05.jpg
A king penguin with developing replacement feathers, sometimes called pin feathers

In birds, moulting is the periodic replacement of feathers by shedding old feathers while producing new ones. Feathers are dead structures at maturity which are gradually abraded and need to be replaced. Adult birds moult at least once a year, although many moult twice and a few three times each year. [2] It is generally a slow process as birds rarely shed all their feathers at any one time; the bird must retain sufficient feathers to regulate its body temperature and repel moisture. The number and area of feathers that are shed varies. In some moulting periods, a bird may renew only the feathers on the head and body, shedding the wing and tail feathers during a later moulting period. [2] Some species of bird become flightless during an annual "wing moult" and must seek a protected habitat with a reliable food supply during that time. While the plumage may appear thin or uneven during the moult, the bird's general shape is maintained despite the loss of apparently many feathers; bald spots are typically signs of unrelated illnesses, such as gross injuries, parasites, feather pecking (especially in commercial poultry), or (in pet birds) feather plucking. Some birds will drop feathers, especially tail feathers, in what is called a "fright moult". [3]

The process of moulting in birds is as follows: First, the bird begins to shed some old feathers, then pin feathers grow in to replace the old feathers. As the pin feathers become full feathers, other feathers are shed. This is a cyclical process that occurs in many phases. It is usually symmetrical, with feather loss equal on each side of the body. [2] Because feathers make up 4–12% of a bird's body weight, it takes a large amount of energy to replace them. For this reason, moults often occur immediately after the breeding season, but while food is still abundant. The plumage produced during this time is called postnuptial plumage. [2] Prenuptial moulting occurs in red-collared widowbirds where the males replace their nonbreeding plumage with breeding plumage. It is thought that large birds can advance the moult of severely damaged feathers. [4]

Determining the process birds go through during moult can be useful in understanding breeding, migration and foraging strategies. [5] One non-invasive method of studying moult in birds is through using field photography. [6] The evolutionary and ecological forces driving moult can also be investigated using intrinsic markers such as stable hydrogen isotope (δ2H) analysis. [7] In some tropical birds, such as the common bulbul, breeding seasonality is weak at the population level, instead moult can show high seasonality with individuals probably under strong selection to match moult with peak environmental conditions. [8]

Forced moulting

In some countries, flocks of commercial layer hens are force-moulted to reinvigorate egg-laying. This usually involves complete withdrawal of their food and sometimes water for 7–14 days or up to 28 days under experimental conditions, [9] which presumably reflect standard farming practice in some countries. This causes a body weight loss of 25 to 35%, [10] which stimulates the hen to lose her feathers, but also reinvigorates egg-production. Some flocks may be force-moulted several times. In 2003, more than 75% of all flocks were force-moulted in the US. [11] Other methods of inducing a moult include low-density diets (e.g. grape pomace, cotton seed meal, alfalfa meal) [12] or dietary manipulation to create an imbalance of a particular nutrient(s). The most important among these include manipulation of minerals including sodium (Na), calcium (Ca), iodine (I) and zinc (Zn), with full or partially reduced dietary intakes. [13]

In reptiles

A young Mediterranean House Gecko in the process of moulting. Mediterranean house gecko1.jpg
A young Mediterranean House Gecko in the process of moulting.
Rat Snake moulted skin.JPG Black-bearded Gliding Lizard Shedding 18 24 23 285000.jpeg
Close up view of snake's moulted skin (left) and a black-bearded gliding lizard moulting (right).

The most familiar example of moulting in reptiles is when snakes "shed their skin". This is usually achieved by the snake rubbing its head against a hard object, such as a rock (or between two rocks) or piece of wood, causing the already stretched skin to split. At this point, the snake continues to rub its skin on objects, causing the end nearest the head to peel back on itself, until the snake is able to crawl out of its skin, effectively turning the moulted skin inside-out. This is similar to how one might remove a sock from one's foot by grabbing the open end and pulling it over itself. The snake's skin is often left in one piece after the moulting process, including the discarded brille (ocular scale), so that the moult is vital for maintaining the animal's quality of vision. The skins of lizards, in contrast, generally fall off in pieces.

In arthropods

In arthropods, such as insects, arachnids and crustaceans, moulting is the shedding of the exoskeleton (which is often called its shell), typically to let the organism grow. This process is called ecdysis. It is commonly said that ecdysis is necessary because the exoskeleton is rigid and cannot grow like skin, but this is simplistic, ignoring the fact that most Arthropoda with soft, flexible skins also undergo ecdysis. Among other things, ecdysis permits metamorphosis, the sometimes radical difference between the morphology of successive instars, and the fact that a new skin can replace structures, such as by providing new external lenses for eyes. The new exoskeleton is initially soft but hardens after the moulting of the old exoskeleton. The old exoskeleton is called an exuviae. While moulting, insects can't breathe. [14]

Aeshna cyanea freshly slipped L2.jpg
Moulting phase of a southern hawker

In dogs

Most dogs moult twice each year, in the spring and autumn, depending on the breed, environment and temperature. Dogs shedding much more than usual are known as "blow coats" or "blowing coats". [15] [16]

In amphibians

Both frogs and salamanders moult regularly and consume the skin, with some species moulting in pieces and others in one piece. [17]

See Also

Related Research Articles

Ecdysis

Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remnants of the old, empty exoskeleton are called exuviae.

Whinchat Species of bird

The whinchat is a small migratory passerine bird breeding in Europe and western Asia and wintering in central Africa. At one time considered to be in the thrush family, Turdidae, it is now placed in the Old World flycatcher family, Muscicapidae. Both sexes have a strong supercilium, brownish upper parts mottled darker, a pale throat and breast, a pale buff to whitish belly, and a blackish tail with white bases to the outer tail feathers, but in the breeding season, the male has an orange-buff throat and breast.

European nightjar Migratory bird found in Eurasia and Africa

The European nightjar, common goatsucker, Eurasian nightjar or just nightjar, is a crepuscular and nocturnal bird in the nightjar family that breeds across most of Europe and the Palearctic to Mongolia and Northwestern China. The Latin generic name refers to the old myth that the nocturnal nightjar suckled goats, causing them to cease to give milk. The six subspecies differ clinally, the birds becoming smaller and paler towards the east of the range. All populations are migratory, wintering in sub-Saharan Africa. Their densely patterned grey and brown plumage makes individuals difficult to see in the daytime when they rest on the ground or perch motionless along a branch, although the male shows white patches in the wings and tail as he flies at night.

Red-winged blackbird Species of bird in North and Central America

The red-winged blackbird is a passerine bird of the family Icteridae found in most of North America and much of Central America. It breeds from Alaska and Newfoundland south to Florida, the Gulf of Mexico, Mexico, and Guatemala, with isolated populations in western El Salvador, northwestern Honduras, and northwestern Costa Rica. It may winter as far north as Pennsylvania and British Columbia, but northern populations are generally migratory, moving south to Mexico and the southern United States. Claims have been made that it is the most abundant living land bird in North America, as bird-counting censuses of wintering red-winged blackbirds sometimes show that loose flocks can number in excess of a million birds per flock and the full number of breeding pairs across North and Central America may exceed 250 million in peak years. It also ranks among the best-studied wild bird species in the world. The red-winged blackbird is sexually dimorphic; the male is all black with a red shoulder and yellow wing bar, while the female is a nondescript dark brown. Seeds and insects make up the bulk of the red-winged blackbird's diet.

Eurasian teal Species of bird (duck)

The Eurasian teal, common teal, or Eurasian green-winged teal is a common and widespread duck which breeds in temperate Eurosiberia and migrates south in winter. The Eurasian teal is often called simply the teal due to being the only one of these small dabbling ducks in much of its range. The bird gives its name to the blue-green colour teal.

American white ibis Bird in the ibis family

The American white ibis is a species of bird in the ibis family, Threskiornithidae. It is found from Virginia via the Gulf Coast of the United States south through most of the coastal New World tropics. This particular ibis is a medium-sized bird with an overall white plumage, bright red-orange down-curved bill and long legs, and black wing tips that are usually only visible in flight. Males are larger and have longer bills than females. The breeding range runs along the Gulf and Atlantic Coast, and the coasts of Mexico and Central America. Outside the breeding period, the range extends further inland in North America and also includes the Caribbean. It is also found along the northwestern South American coastline in Colombia and Venezuela. Populations in central Venezuela overlap and interbreed with the scarlet ibis. The two have been classified by some authorities as a single species.

Common tern Migratory seabird in the family Laridae with circumpolar distribution

The common tern is a seabird in the family Laridae. This bird has a circumpolar distribution, its four subspecies breeding in temperate and subarctic regions of Europe, Asia and North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. Breeding adults have light grey upperparts, white to very light grey underparts, a black cap, orange-red legs, and a narrow pointed bill. Depending on the subspecies, the bill may be mostly red with a black tip or all black. There are a number of similar species, including the partly sympatric Arctic tern, which can be separated on plumage details, leg and bill colour, or vocalisations.

Wood sandpiper Species of bird

The wood sandpiper is a small wader. This Eurasian species is the smallest of the shanks, which are mid-sized long-legged waders of the family Scolopacidae. The genus name Tringa is the New Latin name given to the green sandpiper by Aldrovandus in 1599 based on Ancient Greek trungas, a thrush-sized, white-rumped, tail-bobbing wading bird mentioned by Aristotle. The specific glareola is from Latin glarea, " gravel".

Common murre Species of bird

The common murre or common guillemot is a large auk. It is also known as the thin-billed murre in North America. It has a circumpolar distribution, occurring in low-Arctic and boreal waters in the North Atlantic and North Pacific. It spends most of its time at sea, only coming to land to breed on rocky cliff shores or islands.

Ruff (bird) A medium-sized migratory wading bird that breeds in northern [[Palearctic|Eurasia]]

The ruff is a medium-sized wading bird that breeds in marshes and wet meadows across northern Eurasia. This highly gregarious sandpiper is migratory and sometimes forms huge flocks in its winter grounds, which include southern and western Europe, Africa, southern Asia and Australia.

Instar Developmental stage of arthropods between moults

An instar is a developmental stage of arthropods, such as insects, between each moult (ecdysis), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, changes in the number of body segments or head width. After moulting, i.e. shedding their exoskeleton, the juvenile arthropods continue in their life cycle until they either pupate or moult again. The instar period of growth is fixed; however, in some insects, like the salvinia stem-borer moth, the number of instars depends on early larval nutrition. Some arthropods can continue to moult after sexual maturity, but the stages between these subsequent moults are generally not called instars.

White-tailed ptarmigan Species of bird

The white-tailed ptarmigan, also known as the snow quail, is the smallest bird in the grouse family. It is a permanent resident of high altitudes on or above the tree line and is native to Alaska and the mountainous parts of Canada and the western United States. Its plumage is cryptic and varies at different times of the year. In the summer it is speckled in gray, brown and white whereas in winter it is wholly white. At all times of year the wings, belly and tail are white. The white-tailed ptarmigan has a diet of buds, leaves, flowers and seeds. The nest is a simple depression in the ground in which up to eight eggs are laid. After hatching, the chicks soon leave the nest. At first they eat insects but later move on to an adult diet, their mother using vocalisations to help them find suitable plant food. The population seems to be stable and the IUCN lists this species as being of "Least Concern".

Plumage Layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers

Plumage is a layer of feathers that cover 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 be different colour morphs. The placement of feathers on a bird is not haphazard, but rather emerge in organized, overlapping rows and groups, and these feather tracts are known by standardized names.

Forced molting Practice of artificially provoking a flock to molt simultaneously

Forced molting, sometimes known as induced molting, is the practice by some poultry industries of artificially provoking a flock to molt simultaneously, typically by withdrawing food for 7–14 days and sometimes also withdrawing water for an extended period. Forced molting is usually implemented when egg-production is naturally decreasing toward the end of the first egg-laying phase. During the forced molt, the birds cease producing eggs for at least two weeks, which allows the bird's reproductive tracts to regress and rejuvenate. After the molt, the hen's egg production rate usually peaks slightly lower than the previous peak, but egg quality is improved. The purpose of forced molting is therefore to increase egg production, egg quality, and profitability of flocks in their second or subsequent laying phases, by not allowing the hen's body the necessary time to rejuvenate during the natural cycle of feather replenishment.

Moulting is the manner in which an animal routinely casts off a part of its body.

White-plumed antbird Species of bird

The white-plumed antbird is a small species of insectivorous bird found in the understories of rainforests. It is smaller than most species of its family (Thamnophilidae), weighing 26 grams on average. The family Thamnophilidae is known commonly as the antbirds, as they use the presence of ants to locate food. This species is largely solitary except during the breeding season, and different individuals will follow individual ant swarms.

Black-chested prinia Species of bird

The black-chested prinia is a species of bird in the family Cisticolidae. It is found in Angola, Botswana, Lesotho, Namibia, South Africa, Zambia, and Zimbabwe. Its natural habitat is dry savanna.

Arthropod exoskeleton

Arthropods are covered with a tough, resilient integument or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization. The crystals and fibres interpenetrate and reinforce each other, the minerals supplying the hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs mainly in crustaceans; in insects and Arachnids the main reinforcing materials are various proteins hardened by linking the fibres in processes called sclerotisation and the hardened proteins are called sclerotin. Four sclerites form a ring around each segment: a dorsal tergite, lateral sternites and a ventral pleurite.

Arthropod cuticle

The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda.

Glossary of bird terms Glossary of common English language terms used in the description of birds

The following is a glossary of common English language terms used in the description of birds—warm-blooded vertebrates of the class Aves and the only living dinosaurs, characterized by feathers, the ability to fly in all but the approximately 60 extant species of flightless birds, toothless, beakedjaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart and a strong yet lightweight skeleton.

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