We, being the animals that we are, shed hair. Dogs shed. Cats shed. You notice all the hair that builds up in your hair brush don’t you? How about a white, long haired cat that likes to get up in your lap, good luck with that. It is one of the criteria of being a mammal: having hair. Yup, animals shed. Birds also shed and this is called a molt or molting. While feathers are actually very durable, they do wear out, as with all things in life, and must be replaced. However, because feathers are necessary for flight, there are certain periods of molting, and also sequences, that are followed.
All adult birds molt at least once a year. Many birds will molt twice a year. Few birds molt three times a year and it is very rare to have four molts in a species. The prebasic (formerly postnuptual) period of molting generally occurs after breeding. This is when food is still plentiful and the demands of breeding are over. Feathers make up 4% to 12% of a bird’s body weight, and this requires the bird to use a lot of energy to replace the lost feathers.
Within the same species the sequence or progression of the molt tends to be relatively the same; in many birds the body feathers are molted progressively in “waves,” beginning on the head, face, and throat, extending backwards toward the tail. There is usually a symmetrical loss of feathers from both sides of the body, which balances feather loss, so that the bird still functions.
A good many species have a prealternate (formerly called prenuptual) molt during late winter or spring, usually it is a partial one. The prealternate molt tends to make the males have more prominent plumage than the females.
In most male ducks the full adult plumage at the end of the breeding season is replaced by a dull basic plumage (formerly called eclipse plumage), in which the males resemble the females. This period lasts for about two months.
Most birds molt wing and tail feathers, so critical for flight, symmetrically and one or two pairs at a time. As a result of the gradual, balanced loss of feathers, most birds are able to fly at all times. Before I ever started bird watching, I would see a raptor soaring and notice that a wing or tail feather was missing. I used to think that some yahoo was shooting at them. It is nice to know that I was wrong on that. One last fact; any single full feather lost between molts is replaced immediately.
These molts that birds do take some time. I don’t know if the molt lasts a full month, but it is close to that. I have been watching some of the birds here molt every summer for several years now. They look so disheveled, and I find that I really feel for them. I do have one question in my mind about being in a molt; besides looking really bad, do they feel bad? Like, is it itchy?
Your’s in Nature,