Moulting

moulting out its brown chick down and growing its first dark grey and white adult 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. 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. Determining the process birds go through during moult can be useful in understanding breeding, migration and foraging strategies. One non-invasive method of studying moult in birds is through using field photography. The evolutionary and ecological forces driving moult can also be investigated using intrinsic markers such as stable hydrogen isotope (δ2H) analysis. 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. A 2023 paleontological analysis concluded that moulting probably evolved late in the evolutionary lineage of birds. 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 (e.g. grape pomace, cotton seed meal, alfalfa meal) 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. ==In reptiles and amphibians==

in the process of moulting.|300px Squamates periodically engage in moulting, as their skin is scaly. The most familiar example of moulting in such 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. Both frogs and salamanders moult regularly and consume the skin, with some species moulting in pieces and others in one piece. ==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. Most Arthropoda with soft, flexible skins also undergo ecdysis. Ecdysis permits metamorphosis, the sometimes radical difference between the morphology of successive instars. 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 cannot breathe. In the crustacean Ovalipes catharus molting must occur before they mate. ==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". ==In guinea pigs, hamsters and rabbits==

Most guinea pigs moult constantly, whereas hamsters shed less frequently, and rabbits experience seasonal moulting in spring and autumn. The moulting process in small mammals is influenced by seasonality, hormones, and overall health. In hamsters, excessive shedding may indicate stress or disease. A balanced diet and regular grooming are essential for maintaining a healthy coat. ==Gallery==

File:Molting yellow-eyed penguin IMG 6073.jpg|A moulting yellow-eyed penguin File:Ranapipiensmoulting.jpg|A leopard frog moulting and eating the skin File:Extatosoma tiaratum - Crawling out of skin.jpg|Giant prickly stick insect crawling out of his moulted skin File:SnakeSkin.JPG|Moulted snake skin File:Balcan Green Lizard 2.JPG|Moulting European green lizard File:Grasshopper moult 2015-08-04.jpg|Discarded moult of a grasshopper (Caelifera) File:Cicada Final Molt and Darkening timelapse 14 2021-05-27.webm|A cicada moulting File:Shed Tiliqua rugosa skin, 5 cm scale.jpg|Moult of a Tiliqua rugosa lizard, 5 cm scale bar == See also ==