In biology, moulting or molting, 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, either at specific times of the year, or at specific points
in its life cycle. Moulting can involve shedding the
epidermis, pelage, 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
In birds 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. 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. 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, 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. It is usually symmetrical, with
feather loss equal on each side of the body. 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. Prenuptial moulting occurs in red-collared
widowbirds where the males replace their nonbreeding plumage with breeding
plumage. = 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, which presumably reflect standard farming practice in some
countries. This causes a body weight loss of 25 to 35%, 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. Other methods of inducing a moult
include low-density diets or dietary manipulation to create an imbalance of a
particular nutrient(s).The most important among these include
manipulation of minerals including sodium, calcium, iodine and zinc, with
full or partially reduced dietary intakes.
In 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 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, so that the moult is vital for maintaining the animal's
quality of vision. Conversely, the skins of lizards generally fall off in pieces.
In arthropods In arthropods, such as insects,
arachnids and crustaceans, moulting is the shedding of the exoskeleton,
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 molting,
insects can't breathe. In dogs
Most dogs moult twice each year, in the spring and autumn, depending on the
breed, environment and temperature. In amphibians
Both frogs and salamanders moult regularly and consume the skin, with
some species moulting in pieces and others in one piece.
Gallery References
External links Crayfish Moulting Video on YouTube
Moulting in Chicken and other fowl