How and Why Birds Molt

Different Plumage for Different Seasons

Dunnock Bird Feather Molt

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Birds have thousands of feathers, and each one is subject to wear and tear that leads to molting. Birders who understand the molting process can recognize how birds change their appearances and why those changes are a necessary and vital part of bird biology. Understanding the molting process will lead to easier identification no matter what stage a bird's plumage may be in.

What Is Molting?

Molting is the process of a bird shedding old, worn feathers to replace them with fresh plumage. A molt may be partial and replace just some of a bird's feathers or complete when all the feathers are replaced at once. The time it takes to complete a molt varies for different species, but may last as little as two weeks or as long as several years. Some birds molt only once per year, while others may molt several times.

About the Molting Process

Feathers are composed of keratin, the same protein that makes hair and fingernails, and they are under constant stress and subject to a great deal of damage. Daily activities such as rubbing against bushes or trees, preening, flying, and dust bathing all subject feathers to friction that causes wear, and the keratin weakens as the feathers age.

Fun Fact

Unlike hair and fingernails that continually regenerate and grow, a feather is a complete structure and no longer grows once it reaches full size.

As damage accumulates, the feather's aerodynamic and insulating properties are compromised, and the feather must be shed so a new one can take its place.

There are four general types of molting in a bird's life cycle:

  • Juvenile to Adult: Young birds have down feathers or subadult plumages that must be shed as the birds reach maturity and develop their adult coloration. In larger species, such as gulls and raptors, there may be several molt cycles to reach adult plumage.
  • Breeding to Non-Breeding: Many birds with bright breeding plumage molt into more camouflaged colors after the breeding season ends, and non-breeding plumage may also feature more feathers for better insulation during the winter.
  • Non-Breeding to Breeding: After a winter in dull plumage, fresh, brightly colored feathers are part of many birds' preparation for attracting a mate. Studies have shown that many birds with brighter plumage have better breeding success.
  • General Feather Replacement: Even if feathers do not change color for breeding and non-breeding plumages, general replacement of worn feathers is an essential molt that birds must undergo to maintain healthy plumage.

Not all birds undergo all types of molting, but those that do may spend significant parts of the year experiencing various feather changes.

How Birds Molt

The exact cycles, frequency, and timing of molts vary for different species, but every bird shares some similarities when molting. In general, feathers are molted in a symmetrical pattern across the bird's wings, tail, and body so it retains its balance for flight. The entire cycle typically takes 5-12 weeks, though ducks often molt in as little as two weeks with a brief flightless period during the accelerated molting. Pelicans and parrots have some of the longest molt cycles and may take up to two years to replace all their feathers.

As feathers age, the quills loosen in their shafts and it is not until they are ready to fall out that new feathers begin to grow. The new feathers then create visible gaps in a bird's plumage, particularly in the wings and tail where shorter feathers are more noticeable. Nearby feathers on the body overlap the bare space so the bird's skin is not exposed, but the bird may look scruffy and its markings will be indistinct until the molt is complete.

Molting requires a tremendous amount of energy, and birds do not molt during the breeding season or migration periods when that energy is needed for nesting or traveling. The most common molting period is just after the breeding season when food sources are still abundant but chicks are no longer so demanding, when birds can focus their energy on refreshing their plumage just before migration. The second most common period is just before the breeding season when food sources are increasing but there are not yet any chicks to care for; this is the time when many birds develop their attractive breeding plumage.

The Dangers of Molting

Molting can be a dangerous period for birds if there are not sufficient resources for them to molt properly. Flying may be difficult if not impossible while molting, which makes birds more susceptible to predators, and while feathers are missing, a bird's insulation and protection from poor weather are compromised. If a bird does not get proper nutrition while molting, its feathers may be thinner or poorly formed, creating difficulties that can last for months or years.

Backyard birders can help ease the dangers of molting by providing a rich, reliable food source for birds to take advantage of, along with safe, secure shelter for birds that become more elusive and shy while molting. If birds trust their habitat to meet their molting needs, they will stay around during this uncertain period, giving birders the opportunity to witness molting firsthand and enjoy ever more intimate knowledge of their favorite feathered friends.