Vijayadurga arumugam

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Crows

Bird

Family: Corvidae link=|வலது|thumb link=|வலது|thumb Kingdom: Animalia

Scientific name: Corvus

Class: Aves

Lifespan: Common raven: 10 – 15 years, American crow: 7 – 8 years, Australian raven: 22 years

Did you know: Baby crows stay in the nest up to 2 months before leaving

life style

Crows are found all over the world. A group of crows is called a murder. Crows are black birds known for their intelligence and adaptability, and for their loud, harsh "caw." They also have a reputation for damaging crops; however, their impact may be less than previously thought.

fact about crow

Crows are black birds known for their intelligence and adaptability, and for their loud, harsh "caw." They also have a reputation for damaging crops; however, their impact may be less than previously thought.

The genus Corvuscomprises crows, ravens and rooks. These birds are all part of the Corvidaefamily, which includes jays, magpies and nutcrackers.

Size

There are about 40 species of crow, according to PBS, so there are many different sizes of crows. The American crow measures around 17.5 inches (45 centimeters). The fish crow measures around 19 inches (48 cm). The common raven is much larger and measures around 27 inches (69 cm). Crows can weigh anywhere from 12 to 57 ounces (337 to 1,625 grams). Rooks are smaller than crows and have distinct wedge-shaped tails and light-colored bills. They average 18 inches (47 cm) long.

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GENERAL APPEARANCE

The American crow is a fairly large bird, 17 to 21 inches from bill to tail (43-53 cm), with the mean weight for males 458 grams and for females, 438 grams. Its plumage appears black at a casual look, though it contains various other colors as described below. Bill, legs, and feet are black, though very young birds may have yellow areas on the bill. Eyes in adults are dark brown, while young birds have blue eyes. In flight the crow has what is described as a "fan shaped tail", as distinct from the "wedge shaped tail" of the larger common raven.

PLUMAGE

"In color, the Common (American) Crow is rather distinctive when it comes to a comparison with other North American and Caribbean species. The occiput and crown is lightly flecked with violet blue on a background of black, this area contrasting fairly sharply with the nape, which is a uniform dull black. This flecking on the head is more apparent on some specimens than on others. The upper back, scapular, central and lower back feathers are metalic violet and show the scale-like appearance alluded to by several authors. In some lights, there is a gloss of reddish violet to the primary coverts, scapulars, and secondaries, or there might be a slight greenish cast to the primaries. Ventrally, by way of contrast, the throat and neck are generally black with a wash of metalic violet. The chest and flanks are also washed with violet on a black background, and usually give a mottled appearance. The central abdomen and belly feathers are dull black without any violet luster." (Johnston, 1961)

Of all the above characteristics, the scale-like appearance of the feathers on the upper back are the most obvious and distinctive.

NESTS:

One of the more common misconceptions about birds is that they actually live in nests like humans live in houses or, at the very least, sleep in them at night. In reality, birds use nests only to incubate eggs and to hold the young birds until they are ready, or almost read to fly (fledge). After the young have fledged, the nest is generally abandoned, either permanently or until the next breeding period.Crows nests are quite large, measuring up to two feet or more in diameter and nine or more inches high. The outer portion of the nest, which comprises the major portion of the structure, is composed primarily of dead branches, although many other materials may be used if sufficient branches of the proper size are not available. Within this large outer structure is an interior “cup” composed of softer materials in which the eggs are laid and incubated and the young reared. This interior cup is much smaller than the outer nest with a diameter of six or seven inches and a depth of four or five inches.

Both male and female crows work in constructing the nest sometimes aided by one or more “helpers”, generally their offspring from previous years. When possible, nests are located well hidden in crotches high up in tall trees. If no suitable trees are available, crows may nest in shrubs, man-made structures, and rarely on the ground. Crows tend to build new nests each year, seldom reusing a nest from a previous year. The new nests, however, will generally be located close to the old nests within the area claimed as the territory of a particular pair, or family, of crows.

EGGS:

Crows generally lay from 3 to 7 eggs, with 4 or 5 being the most common number. The coloration and pigment pattern of the eggs can vary widely even within a single clutch with eggs being bluish-green to pale olive and variously marked with brown and gray and can vary from almost unmarked sky blue to very heavily blotched or spotted dark green. In size they average about 1.15 inches (29.13 mm) by 1.6 inches (41.40 mm) and about .0.6 ounce (17.0 g).

Eggs may be laid as soon as the nest is finished but some crows may wait two weeks or more between completion of the nest and laying of the first egg. Eggs are usually laid one a day, generally in the late morning, with occasionally a day or two skipped between eggs. The female will generally begin incubation of the eggs before all of them have been laid, usually beginning to sit continuously after the laying of the third egg. This results in an interval between the hatching of the first and last bird of about 3 days. The female commonly is the only one of the pair that incubates the eggs, which hatch after about 18 days.

NESTLINGS:

When crows hatch they are blind and helpless covered with a small amount of down, and weigh a bit over an half ounce (15.5 g). The mother will brood the young birds more or less continuously for up to two weeks, with rare breaks to collect food. After two weeks the breaks become more frequent and of longer duration until, somewhere between 30 and 40 days after hatching the young are ready to leave the nest. While the female is brooding the young the male, and frequently one or more helper crows, will collect food and carry it to the nest in their throats and/or “sublingual pouches”. They may feed the young birds directly or pass some of the food to the brooding female who may eat some of it or pass it along to the nestlings.

FLEDGLINGS:

When young crows leave the nest, their flight feathers are not fully developed and they may not be capable of taking to the air for at least several more days. Ideally they will hop about in the nest tree while they gain the full ability to fly, but sometimes they fall to the earth where they may spend several days on the ground or in low vegetation . Even when they are on the ground, the parent birds will look after them and feed them if possible and as long as they are not taken by predators or “rescued” by helpful humans, they will eventually rejoin their family.

Young crows will be completely dependent upon their parents for food for a couple of weeks after leaving the nest and it may be three or four months before they are completely able to obtain all of their food themselves.

The fledgling in the photo shows the characteristics that distinguish these young birds from adult crows and from other species. The fledgling differs from an adult crow in that it has yellow coloration on its bill, eyes that appear gray or blue rather than dark brown, and poorly developed tail feathers. Its large size, along with its black legs and feet, distinguish it from any species other than the raven or other varieties of crow.