Molting, the replacement of all or some of a bird’s feathers, occurs in response to a mixture of hormonal changes brought about by seasonal changes. This process serves to replace worn feathers (they cannot repair themselves) and can play a part in seasonal camouflage as well as attracting a mate.
All of our small songbirds have a complete molt, replacing all of their feathers in late summer. In addition, many species have a partial molt (replacing body feathers but not wing or tail feathers) in the spring.
According to David Sibley, American Goldfinches begin to molt all of their (alternate/breeding plumage) feathers in September, with the males replacing their brilliant gold feathers with much duller feathers by November. Come spring and the breeding season, male goldfinches replace their dull (basic/non-breeding) body feathers (but not the wing or tail feathers) with new, bright feathers.
Imagine my surprise when I spied a brilliantly colored American Goldfinch at my feeder this week. According to ornithologist George Clark, it’s usually March before one starts to see an American Goldfinch in breeding plumage. One can only wonder what prevented this individual from molting its breeding plumage in the fall. (Photo: male American Goldfinch, winter plumage; inset – male American Goldfinch in breeding plumage in January)
With birds, molting refers to the loss of old, worn feathers and the growth of new ones. A molt can involve all of the bird’s feathers (complete molt), or just some of them (such as wing or tail feathers – a partial molt). Most birds have a complete molt once a year (chickadees, hummingbirds, owls, etc.), or one complete molt and a partial molt before the breeding season (buntings, tanagers, warblers, etc.), or two complete molts per year (Bobolinks, Marsh Wrens).
Complete molts often occur in late summer and early fall, after the breeding season is over. When you think about it, the timing of this “prebasic” or “postnuptial” molt makes a great deal of sense. Growing new feathers takes an inordinate amount of energy; food is plentiful now, the demands of breeding are over and for many birds, migration isn’t quite under way. It is the perfect time to look for molted feathers on the ground. (Photo: molted Red-tailed Hawk tail feather)
New England has two small weasels: Long-tailed and Short-tailed. Both of these predators molt twice a year, from brown to white in the fall, and white to brown in the spring. The name “Ermine” can refer to either of these two species, but it is most commonly used when referring to the Short-tailed Weasel.
Telling the two species apart can be challenging. Long-tailed Weasels are the larger of the two (head to tail = 12-14 inches), while Ermine are slightly smaller (head to tail = 7-13 inches). Unless you have both species in front of you, however, their size is hard to assess. A more helpful distinguishing characteristic is the length of their tail relative to their body length. Long-tailed Weasels have a tail longer than half their body length with a black tip. Ermine have a tail length which is around a third of their body length — it also has a black tip. (Photo: Ermine (Short-tailed Weasel). Thanks to Sharon and Chad Tribou for photo op.)
In much of New England Green-winged Teals, our smallest dabbling (feed mainly on the surface rather than diving) ducks, are present either during the breeding season, or over the winter, but most of Vermont and New Hampshire have to settle for glimpses during spring and fall migration. Often these ducks stop to rest and refuel on shallow ponds, marshes and flooded fields. While occasionally one or two are spotted amongst a group of mallards, typically they are found in small groups that often congregate in large flocks.
The pictured male is soon to complete its fall “prealternate molt,” in which all body feathers except the innermost feathers of wing are replaced. When finished, he will sport brilliant cinnamon and green head feathers as part of his alternate, or breeding, plumage. Next July he will molt these feathers and acquire a duller basic, or non-breeding, plumage. (Photo by Jeannie Killam)
Like other arthropods, spiders have a protective hard exoskeleton that is flexible enough for movement, but can’t expand like human skin. Thus, they have to shed, or molt, this exoskeleton periodically throughout their lives as they grow, and replace it with a new, larger exoskeleton. Molting occurs frequently when a spider is young, and some spiders may continue to molt throughout their life.
At the appropriate time, hormones tell the spider’s body to absorb some of the lower cuticle layer in the exoskeleton and begin secreting cuticle material to form the new exoskeleton. During the time that leads up to the molt (pre-molt period), a new, slightly larger, inner exoskeleton develops and is folded up under the existing exoskeleton. This new soft exoskeleton is separated from the existing one by a thin layer called the endocuticle. During the pre-molt period the spider secretes fluid that contains digestive enzymes between the new inner and old outer exoskeletons. This fluid digests the endocuticle that separates the two exoskeletons, making it easier for them to separate.
Once the endocuticle is completely digested the spider is ready to complete the molt. At this point a spider pumps hemolymph (spider blood) from its abdomen into its cephalothorax in order to split its carapace, or headpiece, open. The spider then slowly pulls itself out of the old exoskeleton through this opening.
Typically, the spider does most of its growing immediately after losing the old exoskeleton, while the new exoskeleton is highly flexible. The new exoskeleton is very soft, and until it hardens, the spider is particularly vulnerable to attack.
Within 24 hours of hatching, downy Canada Goose goslings leave their nest and are capable of walking, swimming, diving and feeding themselves. Like many species of waterfowl, their growth is rapid. Contour feathers on their wings and tail begin to emerge in about three weeks (note wing feathers of gosling in photo). Feathers on a gosling’s head, neck and back are the last to appear. Just before a gosling develops the ability to fly, the last fluff of down, which is on top of its head, disappears.
There was no fooling the vast majority of Naturally Curious readers! As unpopular as the European Starling may be, its plumage is impressive, especially at this time of year. The starling’s summer, or breeding, plumage shows purple and greenish iridescence, especially on the head, back, and breast. Following the annual mid-summer/fall molt, most head and body feathers have whitish or buff terminal spots. Through the winter, most of these light spots gradually wear away to produce a glossy black appearance in the spring.
Most creative Mystery Photo response (from Steve Adams): “ This one’s easy. The bird is Hazel Hainsworth. She was sweet but insane. Hazel had a huge hat made of all different kinds of feathers, and because she liked her scotch, her navigation skills were somewhat dull, and she always made a point of telling people she’d been lost in every state in the nation, including Alaska.”
There is a marked seasonal difference in the Red Squirrel’s appearance due to its two annual molts (spring and fall). In the winter, a broad rusty-red band extends along its back, from its ears to the tip of its tail. The Red Squirrel’s thicker winter coat also includes ear tufts, which no other species of squirrel in the Northeast possesses. Come spring, when the squirrel sheds again, it loses its ear tufts and its new coat is closer to an olive-green color than red.
Loons begin a full body molt (minus their wings) in the late summer and early fall, prior to migration. The black and white breeding plumage of adult loons in summer is replaced by the gray-brown of winter. This process typically begins at the base of the bill and spreads across the head and over the upper back. The process of molting can extend through migration on into December.
All North American birds replace their old, worn plumage with new feathers at least once a year, a process known as molting. Most birds have what is called a “sequential molt,” in which their flight feathers are lost one at a time (from each wing). This allows many birds to continue flying while molting. However, during their annual molt, waterfowl undergo a “simultaneous wing molt,” losing all of their primary wing feathers at once, preventing them from being able to fly for a month or more while their new primaries are growing in. During this period, they are extremely vulnerable, as this photograph testifies to. If you look closely at the remains of the Canada Goose’s wing on the right in the photograph (dark feathers), you’ll see that the new primaries have almost, but not quite, grown out of their sheaths, making them not yet functional. It’s apparent that this bird was unable to take flight during its molt in order to escape its predator.
Two species of weasels (smaller relatives of mink and otters) are found throughout New England – the long-tailed weasel (pictured) and the short-tailed weasel (also known as an ermine). Both are roughly the same size (somewhere between 9 and 16 inches), with long thin bodies and short legs. Visually telling these two species apart can be challenging unless you get a good look at both the tail and the body, and even then, it can be difficult. A short-tailed weasel’s tail is about 40% of the head and body length, whereas the long-tailed weasel’s tail is more than 45% of the head and body length. In the northeast, in November, both of these carnivores usually start shedding their brown summer coat for a white winter coat, and then molt and start growing in a brown coat again beginning in March. Further south, in Pennsylvania, less than half of the long-tailed weasels turn white, and none do south of the Pennsylvania/Maryland border. (Thanks to Tom Kennedy for photo op.)
Many mammals have two molts a year, producing a winter and summer coat. Moose only have one annual molt, and it occurs in early spring. Their winter coat consists of long (up to six inches on neck and shoulders), hollow guard hairs and a thick undercoat. In early spring the faded and ragged winter hairs are shed and replaced with short, dark, shiny hairs. Molting starts on the shoulders and proceeds along the sides of the neck and back over the moose’s body. Adult bulls molt first, the cows and yearlings shortly after. Pictured is a beaver-cut tree which was used by a moose to scratch off loose winter hair.
Unlike their greenish-black iridescent parents, this year’s young European Starlings had a drab gray-brown plumage through the summer. During late summer and fall all starlings molt and black speckled feathers grow in. There is a brief period of time when juveniles still have a pale tan head, before it, too, becomes speckled. Even though both juvenile and adult European Starlings resemble each other by late fall, it is possible to tell this year’s young from adult birds. First-year starlings have more white speckles than adults, and their speckles are heart-shaped, as opposed to the V-shaped speckles of their parents.
For the first month or so of their lives, red fox kits remain in their den. They are born with a coat of dark gray fur, which is replaced when they are about a month old and starting to emerge from their den. Their second coat is sandy-colored and blends in well with the soil surrounding the den entrance, where the kits spend most of their time. By late June they will have acquired the red coat we associate with adult red foxes. Meanwhile, if you know the whereabouts of an active den, there is no better or more fun time of year to watch the antics of young kits than right now – they entertain themselves while their parents are out hunting by pouncing on each other, having mock fights, playing tag and chewing on all kinds of things from sticks to feathers – all of which is interspersed with frequent naps.
Snow Buntings begin arriving in the northern half of the United States from their summer home on the northern tundra by the end of October, and remain here until March, when they begin migrating back to their breeding grounds. Although both males’ and females’ backs and heads are brownish, their bellies and a good portion of their wings are white, and when they take to the air, a flock of snow buntings bears a strong resemblance to a massive snow storm. By the time their breeding season arrives, the male has a totally white head and belly, and a jet black back. This is not because of a second molt – snow buntings only molt their feathers once a year in the late summer – the change in appearance is due to the fact that underneath the colored feather tips, the back feathers are pure black and the body feathers all are white. The male wears off all of the feather tips by actively rubbing them on snow, which produces his black and white breeding plumage. (There is one male snow bunting in this photograph that is close to having breeding plumage — can you find it?)