Crows

Crows

Crows are highly specialized insectivores that eat only some fruit. In the latter, longer billed species, the bill of the female is larger in most species. This is noteworthy as many birds of paradise appear to suffer from limited resources in no breeding seasons when the females move lower down the mountains than the males to limit intraspecific competition.

The incredible displays of promiscuous male birds are to impress females or, in birds such as the typical or plumed birds (Paradis-aea species), which congregate on breeding grounds (leks) to establish a male dominance hierarchy. The six-wired birds (Parotid species), like many promiscuous species, display as solitary males at traditional courts or perches which young males eagerly wait to occupy at the first opportunity. Meantime, like young male bowerbirds. They must spend years.

Perhaps as many as seven, in immature female-like plumage. This situation, with adult males mating pro-viscously with many females, means that there are few breeding males in the population relative to females or immature males. Pressure by the latter, in addition to that from rival adult males, ensures that only the fittest males can maintain their place in the breeding community and that only the most vigorous immature “inherit” dies-play areas or places in leks.

Interestingly, captive young male birds of paradise have been noted to breed at a relatively early again in the absence of adult plumage males. Suggesting hormonal activity may be restricted by the presence of dominant adult males. No such inhibition however acts on females, which are capable of breeding at two to three years old.

While a breeding system in which females fertilize many females has brought about evolutionary rapid divergence in the appearance of the males of the various birds of paradise, they remain genetically close. Thus species markedly different in male appearance are nevertheless not genetically isolated and as a result, hybrids are a com-moon phenomenon.

Not only do species within a genus hybridize, but species of many different genera do so; in which the males of the two parent species are utterly different in appearance. In the case of male offspring from such hybridization, the characters of the two contributing species mingle to produce different-looking birds, many of which were described as new species to science before our understanding of the hybrid situation.

The fact that some birds of paradise, and bowerbirds, are monogamous and territorial, and that some of the polygamous species have displaying areas (leks) where males congregate while others display solitarily, raises the question: how did these different systems arise? It seems that the predominance of tropical forest fruits in the diet is important to the development of poly-gamy in these bird groups and that the quality of fruit and/or its dispersion in the forest in space and time may dictate the kind of breeding system and/or how males disperse and display.

Several distribution ally restricted species may be threatened by habitat destruction but, unfortunately, some species populations, such as several in Irian Jaya (Indonesian New Guinea), are still unknown and urgently require objective assessment. Perhaps the most striking of all species, the Bluebird of paradise, is presently considered too threatened because themed-mountain forests vital to it have been reduced by encroaching agriculture. It may be further threatened by potential competition from the Regina bird of paradise. Which tolerates a wider range of habitats and abuts the lower distributional limits of the Bluebird?

Black crows resemble each other rather closely in structure and appearance but dif-far in their voices. Thus the American crow, Fish crow, Sinaloa crow, and Mexican crow are more readily separable by voice than appearance, and in Australia, the Australian crow, little crow, Australian raven, and others are difficult to identify except by their calls. The genus Corves has been more successful than others of the family in colonizing remote islands, resulting in the development of species with local distributions in the West Indies, Indonesia, the southwest Pacific, and Hawaii.

The chough. And Alpine chough resemble Corvus in their glossy all-black plumage but differ in having more slender downcurved bills colored red or yellow. They are mainly mountain birds, extending to elevations of nearly 9,000m (2 7,000ft) in the Himalayas, but also occurring near rocky sea cliffs income regions.

Two species of nutcracker inhabit Eurasia and North America, respectively. The European nutcracker is mainly chestnut with white streaks, whereas the American Clark’s nutcracker is mainly gray. Both feed largely on seeds of nuts and rely on hidden supplies during the winter.

The magpies include not only the familiar piebald magpie of Europe, Asia, and North America but also several more brightly colored species from southern Asia such as the Green magpie and Red-billed blue magi-pie. They all have short strong bills and very long graduated tails. The dividing line between Asian magpies and jays relies mainly on the length of the tail. But the American jays include both short-tailed and rather long-tailed forms. Among the American jays, there is a large proportion of species of rather small size. Some of them are no bigger than large thrushes, and also a large proportion with many blues in the plumage.

Among several atypical groups placed in the crow family, the ground jays of central Asia are unusual in being predominantly ground-dwelling. They inhabit dry semi-desert and steppe regions and usually run from danger rather than taking to the air. Hume’s ground jay is particularly small and lark-like and there is uncertainty about whether this species rightfully belongs in the crow family.

However, allowing for this and very few other exceptions, the Crow family is fairly well-defined. The combination of large to very large size, robust build, a strong bill with the external nostrils covered by bristle-like feathers, and strong legs, serves to distinguish most crows from other songbirds, although certain starlings, drongoss, and birds-of-paradise share some features.

The adaptability and versatility of crows show most clearly in their diets and feeding behavior. Most species take both animal and plant foods. And many are quick to exploit new and artificial food sources. The manipulation of food is made easier by the robust. Generalized bill is widespread in the family and most species also by the use of the feet to hold food while it is dismembered.

Many species have been recorded as “dunk-in” or washing food. And this may be an adaptation to counter stickiness. Food hiding is also prevalent in the family. It has often been suggested that crows can survive on almost any food, but the poor physical condition of many cap-tie birds strongly implies that their nutritional requirements are similar to those of most other birds.

The longevity of crows has probably been overestimated by casual observers because of the tendency for them to persist from generation • to generation in suitable territories. Thus we have the old folk saying that “a crow lives three times as long as a man and a raven lives three times as long as a crow.”

However, the maximum age recorded in captivity for a raven was 2 9 years, and that bird died of senile decay, suggesting that wild birds do not often live alone. Recoveries of ringed birds of several crow species show that one-third to one-half of young birds may die in the first year and that few adults live to be older than voyeurs. Nevertheless, some of the larger crows would thus appear by passerine standards to be long-lived.

Several studies of marked birds have shown that individuals do not start to breed until they are two years old, although, in the Carrion crow and magpie, they may be paired and holding territories during the second year of life. This deferment of sexual maturity may allow the young birds to gain additional experience before attempting to breed.

A majority of members of the Crow family defend exclusive breeding territories in which they nest. For example, the raven, jay, and Blue jay all defend territories from which both birds of the pair threaten intruders. A few species nest colonially, notably the jackdaw, which has rather loosely spaced colonies nesting in holes, and the rook which nests in denser colonies in
The tops of trees. The colonial nesters are gregarious throughout the year, and many of the species that hold breeding territories flock outside the breeding season, some of them occupying large communal roosts. Studies of marked birds of several species have shown that the same territories are occupied year after year and that the pair bond often lasts for life.

Several different species of crows are known to have breeding seasons that are timed to take advantage of peak food supplies for the nestlings. Thus, in England, the rook lies in March to take advantage of the peak in earthworm abundance in April, whereas the jay lies in late April or May to take advantage of the late May and early June peak in abundance of defoliating caterpillars on trees.

Incubation is carried out by the female alone in most species (by both sexes in nut-crackers), and the female is usually fed on the nest by the male. Because incubation Often starts when the first egg of the clutches is laid, the nestlings differ in size as they hatch over several days. When food is short the smallest of the brood often dies. Both parents feed the young food that is mostly carried to the nest concealed in the throat of the adult bird.  Nest, and in at least some species they may remain in the parents’ territory for many months after they become independent. Florida Scrub jay young may stay for a year or more. This species is known to breed cooperatively.

Several species of crows are significant pests in agriculture. The rook makes severe inroads as a pest because of its depredation son cereal sowings in winter and early spring. During World War II it was est.-mated that rooks in Britain caused damage costing £3 million per annum, but no recent estimates of this damage are available