what’s molting for birds

When I was very young, I used to think that when birds molted their feathers it meant they dropped every feather at once and were running about looking like a plucked chicken. Thankfully, I quickly figured out that this was not the case. Feather molting in birds is a complicated process that can vary between individuals, species and years. Molting serves two purposes: to replace worn or damaged feathers, and to provide different plumage that helps indicate a bird’s age, sex, and season of the year, as many birds have differing winter and summer plumages. Most birds will molt once or twice a year, and each molt is classified as a partial molt or complete molt. Partial molt means that only some of the feathers are replaced in that cycle, and the others will be replaced in the next cycle that year or the following year. Complete molt means that every feather is replaced at some point during one cycle.

Now, even though birds do not drop every single feather they have at once, molting still can make it difficult and even impossible for some birds to fly. Most ducks and geese will molt their primary flight feathers at one time, which leaves them grounded until new feathers are grown within a few weeks. During this flightless period, the sitting ducks stick close to ponds and lakes which provide them with an easy escape from predators who won’t follow a bird into deep water. Other birds, who may have limited flight ability as well, will stay in dense shrubs and woods to hide from potential predators. This secretive behavior makes it difficult to see birds molting in the wild, but you can often witness molting firsthand here at Zoo Atlanta. Many of our colorful birds, such as the golden pheasant, molt yearly to replace their vibrant beautiful plumage each season. So next time you’re at Zoo Atlanta and see a bird that is looking a bit ruffled and bare, just remember, they may be molting and will soon be a fully feathered beauty once more!

**It is illegal to collect feathers from native migratory species due to the Migratory Bird Treaty Act. For more info visit https://www.fws.gov/lab/featheratlas/featherlaw.html ** Katherine B. Keeper I, Birds

**It is illegal to collect feathers from native migratory species due to the Migratory Bird Treaty Act. For more info visit https://www.fws.gov/lab/featheratlas/featherlaw.html ** Katherine B. Keeper I, Birds

Now, while molting does not result in a bird losing every feather at once, it can still make flying difficult or even impossible for certain birds. The majority of ducks and geese will molt their main flight feathers all at once, leaving them grounded for a few weeks while new feathers grow. The sitting ducks stay near ponds and lakes during this time when they are unable to fly, giving them a simple way to escape from predators that won’t pursue a bird into deep water. Some birds will stay in thickets and forests to hide from possible predators; these birds may also have restricted flight abilities. Because of their reticent nature, it is challenging to observe birds molting in the wild, but at Zoo Atlanta, you can frequently see it happen in person. A lot of our colorful birds undergo annual molting to replace their brilliant, gorgeous plumage every season, like the golden pheasant. The next time you’re at Zoo Atlanta and you notice a bird that appears a little disheveled and naked, don’t forget that it might be molting and will soon be back to its gorgeous full plumed state!

When I was a little child, I used to believe that when birds molted, it meant they suddenly dropped all of their feathers and started to run around looking like a plucked chicken. Fortunately, I discovered very quickly that this was untrue. Birds undergo a complex process called feather molting, which varies between individuals, species, and years. Because many birds have different winter and summer plumages, molting serves two purposes: replacing worn or damaged feathers and providing different plumage that helps indicate a bird’s age, sex, and season of the year. The majority of birds will molt once or twice a year, and there are two types of molts: partial and complete. When there is a partial molt, only a portion of the feathers are replaced during that cycle; the remaining feathers will either be replaced in the subsequent cycle that year or the year after. A complete molt occurs when all of the feathers are replaced at one time during a cycle.

How Many Molt Cycles Per Year?

The frequency of avian molting varies from species to species, but in general, birds belong to one of three groups:

  • Birds that undergo a single full molt a year include woodpeckers, hummingbirds, jays, owls, thrushes, swallows, and flycatchers.
  • Before the breeding season, these birds—which include buntings, tanagers, and warblers—molt all of their feathers after nesting and take on their basic plumage during one full and one partial molt. The males then undergo a partial molt of their body feathers prior to the next breeding season, which results in their bright alternate (breeding) plumage. Females undergo this same partial molt even though they don’t usually molt into bright plumage.
  • Merely a small number of species experience two full molts annually. The majority of these reside in regions where the environment significantly ages their feathers. Two species that travel through rough vegetation are marsh wrens and bobolinks. These birds undergo two full molts: one into their basic plumage and another into their alternate plumage. While male Bobolinks change from a basic brown and streaky plumage to a bold alternate black and cream, Marsh Wrens don’t look much different from winter to summer.

The Cornell Lab of Ornithology’s Handbook of Bird Biology provides additional molting information. If you really enjoy studying birds, careful observation and recording of molting patterns of even common species can be a valuable addition to the knowledge base of a particular species. When it comes to molting, there are a lot of “except for the exceptions.” The best resource for details on individual species can be found at Birds of the World.

whats molting for birds

Using Molt Patterns to Determine a Bird’s Age

Some species acquire their adult plumage in a single year. Others, like eagles, can take up to five years to reach their full adult plumage. Gulls are frequently divided into groups according to how long it takes them to grow into their full adult plumage, such as “3-year gulls” or “4-year gulls.”

whats molting for birds

This chart shows the Humphrey-Parkes system’s nomenclature for plumage molting. On the right is a picture of a Herring Gull’s four-year growth from juvenile to adult. Keep in mind that molting periods are unique to the Herring Gull, can last up to 4 months, and are merely estimates. Some birds will start molting earlier and others later. Since not every feather is shed at once during the molt, a bird’s appearance can vary significantly from week to week as it transitions from one set of plumage to another. The second prebasic molt in Herring Gulls can take up to six months to finish. A partial molt is indicated by a “P” in front of the molt period on the chart.

FAQ

What happens when birds molt?

Molting serves two purposes: to replace worn or damaged feathers, and to provide different plumage that helps indicate a bird’s age, sex, and season of the year, as many birds have differing winter and summer plumages.

How long does it take for birds to molt?

How often do birds moult? Moults occur once to twice a year depending on the bird species. The most common time for a moult is mid-summer, with often a second, smaller moult in early-mid winter. Most normal moults take about 6 weeks to complete.

How do I know if my bird is molting?

How do I tell if the bird is molting? If a bird is molting, it will have a lot of pin feathers around its head area, and it will look ragged, with a bunch of dropped feathers at the bottom of the cage.

Why is molting necessary for birds?

Moulting in Birds Generally it’s the periodic replacement of the feathers. This is carried out annually in most of the species, while in some it may occur twice and in a very few thrice in a year. The birds typically don’t shed all their feathers together at one time as they need them to regulate the body temperature.