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Moulting

life science Maturity 9-11 Next article →

Moulting is a biological process where an animal casts off parts of its body for a beneficial purpose. This shedding can happen at specific times of the year or at certain stages in a life cycle. Animals may shed their epidermis, which is their skin, or their pelage, which includes hair, feathers, or fur. In many invertebrates, this process is known as ecdysis.

Rat Snake moulted skin
Rat Snake moulted skin

Historically, this was called "mewing," a term derived from the French verb "muer." This term is the reason for the name of Britain's Royal Mews, a place once used for keeping hawks during their moulting period.

In birds, moulting is the periodic replacement of feathers. Because feathers are dead structures once they reach maturity, they gradually wear down and must be replaced. This is a cyclical process involving several phases. First, the bird sheds some old feathers. Next, pin feathers grow in to replace them. As these pin feathers develop into full feathers, more old feathers are shed.

Loggerhead Shrike molting
Loggerhead Shrike molting

This process is usually symmetrical, meaning feather loss is equal on both sides of the body. Because feathers account for 4% to 12% of a bird's body weight, replacing them requires a large amount of energy. Consequently, birds often moult after the breeding season when food is still abundant.

Different types of birds exhibit different moulting patterns. Some birds produce postnuptial plumage, which is the plumage produced after the breeding season. In contrast, red-collared widowbirds undergo prenuptial moulting, where males replace nonbreeding plumage with breeding plumage. Some species may even undergo a "wing moult," where they become temporarily flightless. During this time, they must stay in protected habitats with reliable food.

Lanius ludovicianus1
Lanius ludovicianus1

For mallards, moulting flight feathers occurs in mid-summer to early fall. This allows males to replace brightly colored breeding plumage with eclipse plumage, which helps them hide from predators.

Reptiles and amphibians have their own unique methods for shedding. Squamates, such as snakes, have scaly skin that they must periodically shed. A snake often rubs its head against a hard object like a rock or wood to split its stretched skin. The snake then continues to rub until the skin peels back, allowing the animal to crawl out of it.

Black-bearded Gliding Lizard Shedding 18 24 23 285000
Black-bearded Gliding Lizard Shedding 18 24 23 285000

This process is similar to pulling a sock off a foot. Often, the snake leaves the skin in one piece, including the brille, which is the ocular scale. This helps maintain the animal's vision. Lizards, however, generally shed their skin in pieces. Amphibians like frogs and salamanders also moult regularly and often consume their shed skin for nutrients.

In the world of arthropods, moulting is essential for growth and transformation. This process, ecdysis, involves shedding the exoskeleton, or the hard outer shell. The old exoskeleton left behind is called an exuviae.

Dragonfly metamorphosis
Dragonfly metamorphosis

This process allows for metamorphosis, which is the radical change in body shape between different life stages. For example, a soft-bodied larva can transform into a winged, reproductive adult. In some species like mayflies, a winged subimago undergoes one last moult to become a winged adult. Some crustaceans, such as the Ovalipes catharus, must moult before they are able to mate.

Mammals also experience moulting, often driven by seasonal changes. Cats typically moult their fur during spring and summer to replace thick winter coats with thinner summer ones. Dogs and other canids often moult semi-annually in the spring and fall. This is not caused by temperature, but by fluctuations in melatonin secreted by the pineal gland in response to sunlight.

SGI-2016-South Georgia (Fortuna Bay)–King penguin (Aptenodytes patagonicus) 05
SGI-2016-South Georgia (Fortuna Bay)–King penguin (Aptenodytes patagonicus) 05

Arctic dog breeds are notable because they shed twice every year. Other small mammals, like guinea pigs, may moult constantly, while hamsters shed less frequently.

Scientists use various methods to study these biological cycles. Researchers can use field photography as a non-invasive way to observe bird moulting. They can also use stable hydrogen isotope analysis to investigate the evolutionary and ecological forces driving the process. A 2023 paleontological analysis suggested that moulting likely evolved late in the evolutionary lineage of birds. In commercial farming, some hens are "force-moulted" to increase egg production. This is done by withdrawing food for 7 to 28 days, causing a body weight loss of 25% to 35%. This process stimulates the hen to lose feathers and reinvigorates egg-laying.

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🖼️ Images & Media (7)
File:Dragonfly metamorphosis.jpg
Dragonfly metamorphosis.jpg
File:Loggerhead Shrike molting.jpg
Loggerhead Shrike molting.jpg
File:Lanius ludovicianus1.jpg
Lanius ludovicianus1.jpg
File:SGI-2016-South Georgia (Fortuna Bay)–King penguin (Aptenodytes patagonicus) 05.jpg
SGI-2016-South Georgia (Fortuna Bay)–King...
File:Mediterranean house gecko1.jpg
Mediterranean house gecko1.jpg
File:Rat Snake moulted skin.JPG
Rat Snake moulted skin.JPG
File:Black-bearded Gliding Lizard Shedding 18 24 23 285000.jpeg
Black-bearded Gliding Lizard Shedding 18...
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