Gru della Manciuria

Identificazione

Adult red-crowned cranes are named for a patch of red bare skin on the crown, which becomes brighter during the mating season. Overall, they are snow white in color with black on the wing secondaries, which can appear almost like a black tail when the birds are standing, but the real tail feathers are actually white. Males are black on the cheeks, throat, and neck, while females are pearly gray in these spots. The bill is olive green to a greenish horn, the legs are slate to grayish black, and the iris is dark brown. <p>Juveniles are a combination of white, partly tawny, cinnamon brown, and rusty or grayish. The neck collar is grayish to coffee brown, the secondaries are dull black and brown, and the crown and forehead are covered with gray and tawny feathers. The primaries are white, tipped with black, as are the upper primary coverts. The legs and bill are similar to those of adults but lighter in color.This species is among the largest and heaviest cranes, typically measuring about 150 to 158 cm (4 ft 11 in to 5 ft 2 in) tall and 101.2–150 cm (3 ft 4 in – 4 ft 11 in) in length (from bill to tail tip). Across the large wingspan, the red-crowned crane measures 220–250 cm (7 ft 3 in – 8 ft 2 in). Typical body weight can range from 4.8 to 10.5 kg (11 to 23 lb), with males being slightly larger and heavier than females and weight ranging higher just prior to migration. On average, it is the heaviest crane species, although both the sarus and wattled crane can grow taller and exceed this species in linear measurements.<p>On average, adult males from Hokkaidō weighed around 8.2 kg (18 lb) and adult females there averaged around 7.3 kg (16 lb), while a Russian study found males averaged 10 kg (22 lb) and females averaged 8.6 kg (19 lb); in some cases, females could outweigh their mates despite the males' slightly larger average body weight. Another study found the average weight of the species to be 8.9 kg (20 lb). The maximum known weight of the red-crowned crane is 15 kg (33 lb). Among standard measurements, the wing chord measures 50.2–74 cm (19.8–29.1 in), the exposed culmen measures 13.5–17.7 cm (5.3–7.0 in), tail length is 21.5–30 cm (8.5–11.8 in), and the tarsus measures 23.7–31.9 cm (9.3–12.6 in).

Tassonomia

Nome scientifico

Grus japonensis

Autorità

(Müller, PLS, 1776)

Ordine

Gruiformi

Famiglia

Gruidae

Genere

Grus

Areale e habitat

In the spring and summer, the migratory populations of the red-crowned crane breed in Siberia (far eastern Russia), Northeast China and occasionally in north-eastern Mongolia (i.e., Mongol Daguur Strictly Protected Area). The breeding range centers in Lake Khanka, on the border of China and Russia. Later, in the fall, they migrate in flocks to the Korean Peninsula and east-central China to spend the winter. Vagrants have also been recorded in Taiwan. In addition to the migratory populations, a resident population is found in eastern Hokkaidō, Japan. This species nests in wetlands, marshes and rivers. In the wintering range, their habitat consists mainly of paddy fields, grassy tidal flats, and mudflats. In the flats, the birds feed on aquatic invertebrates, and, in cold, snowy conditions, the birds switch to mainly living on rice gleanings from the paddy fields.

Migrazione

Complete migrants

Comportamento

Red-crowned cranes have a highly omnivorous diet, though the dietary preferences have not been fully studied. They eat rice, parsley, carrots, redbuds, acorns, buckwheat, and a variety of water plants. The animal matter in their diet consists of fish, including carp and goldfish, amphibians, especially salamanders, snails, crabs, dragonflies, small reptiles, shrimp and small birds. The daily food requirement of adult red-crowned cranes is 750 g.<p>They seem to prefer a carnivorous diet, although rice is now essential to survival for wintering birds in Japan and grass seeds are another important food source. While all cranes are omnivorous, per Johnsgard, the two most common crane species today (the sandhill and common cranes) are among the most herbivorous species while the two rarest species (the red-crowned and whooping cranes) are perhaps the most carnivorous species. When feeding on plants, red-crowned cranes exhibit a preference for plants with a high content of crude protein and low content of crude fiber. In Hokkaido, fish such as Tribolodon, Pungitius, Sculpin and flatfish was major prey of adults, while chicks mostly feed on various insects. In Zhalong Nature Reserve, small fish less than 10cm, such as common carps, pond loach, and Chinese sleeper was mainly taken as well as aquatic invertebreas like pond snails, dragonflies, water beetles and large amount of plant matter. Elsewhere, mudflat crabs are locally important food source in Yellow River Delta.<p>They typically forage by keeping their heads close to the ground, jabbing their beaks into mud when they encounter something edible. When capturing fish or other slippery prey, they strike rapidly by extending their necks outward, a feeding style similar to that of the heron. Although animal prey can be swallowed whole, red-crowned cranes more often tear up large prey by grasping with their beaks and shaking it vigorously, eating pieces as they fall apart. Most foraging occurs in wet grasslands, cultivated fields, shallow rivers, or on the shores of lakes.<p>The population of red-crowned cranes in Japan is mostly non-migratory, with the race in Hokkaidō moving only 150 km (93 mi) to its wintering grounds. Only the mainland population experiences a long-distance migration. They leave their wintering grounds in spring by February and are established on territories by April. In fall, they leave their breeding territories in October and November, with the migration fully over by mid-December.<p>Flock sizes are affected by the small numbers of the red-crowned crane, and given their largely carnivorous diet, some feeding dispersal is needed in natural conditions. Wintering cranes have been observed foraging, variously, in family groups, pairs, and singly, although all roosting is in larger groups (up to 80 individuals) with unrelated cranes. By the early spring, pairs begin to spend more time together, with nonbreeding birds and juveniles dispersing separately. Even while not nesting, red-crowned cranes tend to be aggressive towards conspecifics and maintain a minimum distance of 2 to 3 m (6.6 to 9.8 ft) to keep out of pecking range of other cranes while roosting nocturnally during winter. In circumstances where a crane violates these boundaries, it may be violently attacked.<p>The red-crowned crane is monogamous and long-lived, with stable pair-bonding both within and between years, and believed to mate for life. The breeding maturity is thought to be reached at 3–4 years of age. All mating and egg-laying are largely restricted to April and early May. A red-crowned crane pair duets in various situations, helping to establish the formation and maintenance of the pair bond, as well as territorial advertisement and agonistic signaling. Both males and females may start a duet with the production of a start call, but the main part of the duet always began with a long male call. The pair moves rhythmically until they are standing close, throwing their heads back and letting out a fluting call in unison, often triggering other pairs to start duetting, as well. As it occurs year-round, the social implications of dancing are complex in meaning. However, dancing behavior is generally thought to show excitement in the species. Also, the performance of duet displays increased the probability of staying in a favorable area, supporting the hypothesis that duet displays function as a signal of joint resource defense in the flock.<p>Pairs are territorial during the breeding season. Nesting territories range from 1 to 7 km2 (0.39 to 2.70 sq mi) and are often the same year after year. Most nesting territories are characterized by flat terrain, access to wetland habitat, and tall grasses. Nest sites are selected by females, but built by both sexes and are frequently in a small clearing made by the cranes, either on wet ground or shallow water over waters no more than 20 to 50 cm (7.9 to 19.7 in) deep. Sometimes, nests are built on the frozen surface of water, as frigid temperatures may persist well into nesting season. Nest building takes about a week. A majority of nests contains two eggs, though one to three have been recorded. <p>Both sexes incubate the eggs for at least 30 days. They also both feed the young when they hatch. Staying in the nest for the first few weeks, the young start to follow their parents as they forage in marshes by around 3 months of age. New hatchlings weigh about 150 g (5.3 oz) and are covered in yellow natal down for two weeks. By early fall, about 95 days after hatching, the young are fledged and are assured fliers by migration time. Although they can fly well, crane young remain together with their parents for around 9 months. Young cranes maintain a higher-pitched voice that may serve to distinguish them from outwardly similar mature birds, this stage lasting until the leave parental care. The average adult lifespan is around 30 to 40 years, with some specimens living to 75 years of age in captivity. It is one of the longest-living species of bird.<p>The red-crowned crane is a big-sized bird and there are no natural predators within their wintering ground. With their height averaging 1.5 m (5 ft), their large size deters most predators. As a result, red-crowned cranes often react indifferently to the presence of other birds such as small raptors; with harriers, falcons, owls, and usually buzzards being allowed to hunt small prey near a crane nest without any of these parties harassing each other. However, birds more likely to be egg or nest predators, such as corvids, some buzzards, and various eagles, are treated aggressively and are threatened until they leave the crane's territory. Mammalian carnivores, including small Siberian weasels (Mustela sibirica) to large red foxes (Vulpes vulpes), Asian badgers (Meles leucurus), common raccoon dogs (Nyctereutes viverrinus), and domestic dogs (Canis familiaris) which pose a threat to eggs and chicks, are attacked immediately, with the parent cranes attempting to jab them in the flanks until the predators leave the vicinity. These predators generally do not present any danger to chicks in the presence of adults and are chased away by the crane without difficulty. Larger predators such as gray wolves (Canis lupus) and large dogs can be repelled by aggressive crane pairs.<p>Occasionally, losses at the nest occur to some of the above predators. Introduced American mink on Hokkaidō are one of the most successful predators of eggs and nestlings. Also, immature and unwary subadult or even adult cranes may be ambushed killed by red foxes in Japan and leopard cats in South Korea, though this is rare reports, especially with adults. More often, these birds can easily defend themselves by using sharp beak or just fly away from danger.<p>Smaller white-naped cranes often nest near red-crowned cranes, but competition between these species for food in a common nesting area is lessened due to the greater portion of vegetation in the white-naped crane's diet. In cases where interactions turn aggressive between white-naped and red-crowned cranes, red-crowned cranes are dominant, as expected due to their considerably larger size. As reported researchers trying to band or examine the cranes or their nest, this powerful species is considered mildly hazardous and prone to respond quickly with considerable aggression to being approached or handled by humans and are able to inflict painful injuries using both its kicking feet and dagger-like beak.

Conservazione

Tendenza della popolazione

declining