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.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
Although the common grackle, a member of the blackbird family, is the bane of many corn growers as well as a threat to songbirds trying to raise young (grackles eat other birds’ eggs and nestlings), it is quite a colorful bird, with its pale yellow eyes and iridescent purple plumage. Grackles have already begun nesting and defending their territory, as can be seen from the stance of the bird in this image. This “bill-up display” is a position assumed when a male is being approached on its territory by another male. It moves its head upwards so that its bill is almost vertical, signaling to the approaching grackle that it would be in its best interest to depart.
Male red-winged blackbirds have returned to Vermont, and their most notable features are the brightly-colored reddish-orange feathers on their “shoulders”, referred to as epaulettes. In the military, an epaulette is a shoulder ornament that indicates, through its position, color, length and diameter, the bearer’s rank. Some birds, including male redwings, also possess this badge, or visual cue, which indicates the social status of the bird to other birds of the same species. Studies of male red-winged blackbirds and their epaulettes indicate (through dyeing their bright orange/red shoulder patches black) that epaulettes play a significant role in the male’s defense of his territory. Over 60% of the redwings that had their epaulettes dyed black lost their territories to other males. Further research revealed that aggression by a territorial male redwing is proportional to the epaulette size of the encroaching male redwing. It also indicated that male redwings intruding into redwing-occupied territories greatly limit the exposure of their epaulettes by covering them with black feathers. (Female red-winged blackbird plumage is brown and lacks epaulettes.)
On a cold, winter day, why would any bird choose to sit down on ice? While feathers are excellent insulators, the legs and feet of most birds lack this protective covering. Because of this, legs and feet are a major source of heat loss for birds. Physical adaptations to this loss of heat include constricted blood vessels in a bird’s feet, as well as the proximity of arteries and veins to each other which aids the transfer of heat. Birds exhibit behavioral adaptations as well, such as ducks and gulls standing on one leg and tucking the other among breast feathers, reducing by half the amount of unfeathered limb surface area exposed. By sitting down and covering both legs, even on ice, heat loss from limbs is minimized. If you observe closely, you will see many of the ground-feeding finches such as sparrows and redpolls also occasionally drop down and cover their legs and feet with their breast feathers for a few seconds.
Possibly because of the importance of summer fruits in their diet, Cedar Waxwings (Bombycilla cedrorum) are late nesters, but by late August adults have begun their migration to the southern states and Central America. This year’s young are beginning this (roughly) 900-mile flight now, a month after their parents have left. You can often find waxwings feeding in crab apple and other fruit trees where they stop over during their flight to refuel. Juvenile birds lack the sleek look of adults — the red wax-like feather tips for which this bird is named have not developed, and the color of their plumage is much duller than that of the adults.
Green herons are typically solitary and secretive birds, but if you find one, you often have an extended period of time to observe it, as they often slowly stalk their prey, or pose statue-like, sometimes for minutes at a time, while waiting to strike at a fish, frog or invertebrate. Three characteristics tell you that the green heron in the photograph is a juvenile: the tufts of down that remain on its head, its streaked neck (adults have solid rufous necks) and its yellow legs (adults have orange legs).
The Red-tailed Hawk nest that produced two fledglings last year is in use again this spring. In the past month the nestlings have gone from tiny white powder puffs to nearly equaling their parents in size. Down is still visible, especially on their heads, but contour feathers are quickly replacing them on other parts of their body. Soon there will be wing stretches and flapping, as well as hopping about on nearby branches in preparation for fledging.
American Bitterns have returned to New England from their southern wintering grounds, and are announcing their presence with a unique song that Sibley describes as a “deep, gulping, pounding BLOONK-Adoonk” that they repeat over and over. These secret, well-camouflaged marsh birds are almost invisible as they slowly walk through marsh grasses. When they stand still and point their bill skyward, they are easily mistaken for the reeds they inhabit.
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?)