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Molts

Birds Molting Old Feathers And Growing In New Ones

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)

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Distinguishing Small Weasels

12-21-18 ermine_U1A8001New 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.)

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Green-winged Teals Molting & Migrating

11-2-16-male-green-winged-teal-by-jeannie-male-moltingIn 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)

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Spiders Molting Exoskeletons

shed spider skin 052Like 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.

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Canada Goose Goslings: Contour Feathers Replacing Down

Canada goose gosling 207Within 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.

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European Starling

European starling IMG_8398There 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.”

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Caterpillars Molting

6-25-14 caterpillar molting 044A caterpillar is the larval stage of a moth or butterfly. It is the only stage that has chewing mouthparts, and therefore a caterpillar spends most of its waking hours eating. This consumption of food results in massive growth, making its skin/exoskeleton very tight. When this happens, a hormone called ecdysone is produced, prompting the caterpillar to molt, losing its old exoskeleton (to left of caterpillar in photo) under which is a new and larger exoskeleton. After the molt, while the new exoskeleton is still soft, the caterpillar swallows a lot of air, which expands its body. Then, when the exoskeleton hardens, it lets the air out and has room for growth. Caterpillars molt four or five times as they grow. Each different caterpillar stage is called an instar. (Photo: Forest Tent Caterpillar)

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