Moult

In biology, moulting (or molting,^[1] also known as shedding or for some species, ecdysis) signifies 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 year, or at specific points in its life-cycle.

Moulting can involve the epidermis (skin), hair or fur, or other external layer. In some species, other body parts may be shed, for example, wings in some insects. Examples include old feathers in birds, old hairs in mammals (especially dogs and other canidae), old skin in reptiles, and the entire exoskeleton in arthropods.

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Examples

Specific species notes

Birds

In birds, moulting is the periodic replacement of feathers by shedding old feathers while producing new ones. Feathers are dead structures at maturity, and they become gradually worn down and need to be replaced. Adult birds moult at least once a year, though many moult twice, and a few three times.^[2] It is a comparatively slow process, as a bird never sheds all its feathers at once; it must keep enough of its feathers to regulate its body temperature and repel moisture. The amount of shed feathers 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 wild bird become flightless during an annual "wing moult" and must seek protected habitat with a reliable food supply during that time. A moulting bird should never have any bald spots. If a pet bird has any bald spots, the bird should be taken to an avian veterinarian to search for possible causes for the baldness, which may include giardiasis, mites, or feather-plucking.

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. In general, a moult begins at a bird's head, progresses down the body to its wings and torso, and finishes with the tail feathers. It is usually symmetrical, with feather loss equal on each side of the body.^[2] Because feathers make up 4-12 percent of a bird's body weight, it takes a large amount of energy to replace them. For this reason, moults are frequently timed to occur right after the breeding season, but while food is still abundant. The plumage produced during this time is called postnuptial plumage.^[2]

Canidae

Main article: Coat (dog)

Dogs and other canids routinely shed their fur twice a year, in the spring and fall.

Seasonal temperature variations influence shedding; some shed all year, some shed specifically twice a year.

Reptiles

  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 molted skin inside-out. This is similar to how you might remove a sock from your 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. Conversely, lizards' skins fall off in pieces.

Arthropods

Main article: Ecdysis

  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. Ecdysis is necessary because the exoskeleton is rigid and cannot grow like skin. The new exoskeleton is initially soft but hardens after the moulting of the old exoskeleton.

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