H.J. Ruiz – Avian101

Molting (Moulting) in Birds

In birds, molting 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 molt at least once a year, although many molt 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 molting periods, a bird may renew only the feathers on the head and body, shedding the wing and tail feathers during a later molting period. Some species of bird become flightless during an annual “wing molt” and must seek a protected habitat with a reliable food supply during that time. While the plumage may appear thin or uneven during the molt, 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.

The process of molting 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, molts often occur immediately after the breeding season, but while food is still abundant. The plumage produced during this time is called postnuptial plumage. Prenuptial molting occurs in red-collared widowbirds where the males replace their non breeding plumage with breeding plumage. It is thought that large birds can advance the molt of severely damaged feathers.

Determining the process birds go through during molt can be useful in understanding breeding, migration and foraging strategies. One non-invasive method of studying molt in birds is through using field photography.

Photo Gallery

Song Sparrow

Northern Cardinal (F)

Mourning Dove

Northern Cardinal (M)

© HJ Ruiz – Avian101