Moulting

Emily White
2010-10-27

Moulting
The replacement of all or part of the feathers is called a moult. Moults produce feathers that match the age and sex of the bird, and sometimes the season.
Moulting occurs in response to a mixture of hormonal changes brought about by seasonal changes. The entire process is complex and many questions remain regarding how the process is controlled. A basic understanding of moulting patterns can, however, be a useful aid in identifying many species and in determining their age.
There are two kinds of moults with different degrees of feather replacement. In a complete moult all feathers are replaced. In a partial moult only some feathers are replaced. Damaged feathers are replaced during a moult, but a feather that has been lost completely is replaced immediately.
Timing:
It takes a lot of energy to build new feathers. Moulting is, therefore, often timed to coincide with periods of less strenuous demands, such as after nesting or before migration. Late summer is a common time for moulting and many backyard birds will benefit from a good protein source now. Peanuts are very high in protein. Offer them alone in any of a variety of peanut feeders, or provide a high-quality birdseed blend like our Featherfields’ Feast or Chickadee Picnic which are both high in peanut content. Offering our peanut suet by Mill Creek Seed is also a great choice.
Moult stage nomenclature:
There are three commonly used systems for identifying different plumage stages.
The most common way to identify different plumage stages in North America is to distinguish between a winter (non-breeding) plumage and a summer (breeding) plumage. This approach works in most cases but there are always exceptions to the rule. Species that look the same way on a year-round basis are always in basic plumage.
Moult Cycles:
How often do birds moult? This varies by species, but almost all birds fall into one of the following three categories.
One moult per year:
Many species have one complete moult per year and maintain the same appearance throughout the year. These include chickadees, jays, hummingbirds, swallows, hawks and owls.

One complete moult and one pre-breeding partial moult:
Some species have a complete moult after nesting, moulting into their basic plumage.
These species then have a pre-breeding moult of body feathers that results in their bright breeding plumage. Species with this moult pattern include warblers, buntings, and tanagers.
Two complete moults per year:
Only a few species undergo two full moults per year. Most of these live in areas where the environment causes significant feather wear and tear. Marsh Wrens and Bobolinks, two species that move through abrasive vegetation, are representative examples.
Young birds of certain species acquire their adult plumage in a single year. Others require up to five years (eagles) to reach full adult plumage. Gulls are often broken into categories such as a "three-year gull" or "four year gull," based on how long it takes the bird to reach full adult plumage.
A good field guide is a must for identifying birds in different plumages. Featherfields’ stocks many excellent field guides including Sibley, Peterson, Kaufman, National Geographic, Smithsonian and more. Our expert staff would be happy to help you choose the right one for you.

(Adapted from the Cornell Lab of Ornithology website)
Emily White, B.Sc.
Featherfields



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