By Gail Cochrane

Liberty Wildlife Volunteer

Feathers, those remarkable instruments of flight, insulation and beauty, do not last forever.  They fray and break down, wearing with use and exposure to the elements. So, birds must replace them and do so with annual or biannual molts.

Molting happens when hormonal changes are brought on by the seasons, and allows birds to exchange worn feathers for shiny new ones that offer greater performance. This happens gradually over several weeks as birds must continue to stay warm and find food while also expending the energy to grow in a new supply of feathers. The frequency and timing of molting varies by species and by the climate of their habitat, but some generalizations can be made.

The Cornell Lab of Ornithology identifies several categories of molting behavior. Species including hawks, owls, woodpeckers, hummingbirds, flycatchers and thrushes have one complete molt per year, when they replace all of their feathers. These birds’ appearance are the same year around.

Birds such as warblers and tanagers have one complete molt, plus one “pre-nuptial” molt where only body feathers are exchanged. Males in particular don brighter, bolder colors for breeding season. The complete molt takes place after breeding season and before migration. Gambel’s quails fall into this group, although quails only exchange a limited number of body feathers in the early spring prenuptial molt.

Birds that live in areas where their plumage takes a lot of wear and tear have two complete molts per year.  Marsh wrens and bobolinks encounter harsh vegetation as they forage, and require two molts.

Young birds are identifiable by their immature feathers. Passerines, or perching birds, hatch naked and grown their first feathers or juvenal plumage in their first few weeks. Nonpasserines hatch with a natal down covering their bodies. These downs are replaced by juvenal plumage in what’s termed a postnatal molt. Most passerines come into their adult plumage or definitive plumage around one year of age.

Larger birds do not reach plumage maturity for two years or more. Gulls and eagles take the longest, with complex stages of molting and plumage coloration. Gulls generally acquire definitive plumage at four years and bald eagles at five to six years.

The American Kestrel is one of the only birds of prey that exhibits sexual dimorphism, and is unique in that nearly adult-like plumage is attained prior to fledging. Thus, the males and females of this species can be identified early on, due to the coloration of their feathers.  Kestrels have an incomplete molt in the fall of their first year, but retain feathers in their wings and tail and parts of their bodies until the second and complete molt the following year.  By winter of their second year, the young falcons have attained their definitive plumage.

(female kestrel)                                                                                                                     (male kestrel)