Black crane ( Aramus guarauna )
|Scientific name of the family|
|Bonaparte , 1854|
|Scientific name of the genus|
|Vieillot , 1816|
|Scientific name of the species|
|( Linnaeus , 1766)|
The black-wheeled crane ( Aramus guarauna ) is a species of bird from the order of the crane birds that lives in the tropical and subtropical areas of America and is the only member of the Aramidae family . As a food specialist, the long-legged bird mainly eats apple snails . Its name comes from its rallen similar behavior and both cranes and Rails-like anatomy . There are four subspecies . The IUCN lists the species as not endangered .
The black-legged crane is reminiscent of an ibis due to its size, long beak and neck and long legs . The body length is about 56 to 71 cm, the beak, which is only imperceptibly bent downwards, is ten to twelve centimeters long. The body weight varies depending on the subspecies, males of the northern subspecies pictus usually weigh between 1.13 and 1.37 kg, the females weigh a little less with 1.05 to 1.17 kg. The wide wings , rounded at the ends, reach a span of a little more than a meter. Noteworthy is the outermost hand swing, which is short and sickle-shaped with a club-shaped tip and, thanks to this shape, is used to generate sounds during flights to defend the territory . The rump and attached control feathers of the cranks are relatively short and wide, the twelve rounded control feathers are covered when the wings are closed and are therefore not visible when individuals are at rest or walking.
The long, slightly downward curved bill is greenish yellow and turns dark to black towards the tip. It shows some peculiarities in adaptation to the special diet of the black-wheeled crane: In the last few centimeters it is bent slightly to the right in order to allow the beak to be inserted into the right-winding casing of the main food, apple snails of the genus Pomacea . In addition, there is an almost horizontal twisting of the tip of the lower beak against that of the upper beak. The tip of the beak is constantly sharpened by friction, the resulting razor-sharp tip is used to crack the operculum of the apple snail and sever the sphincter muscle . The two types of gaping beaks proceed in a similar way, but their beaks are much more specialized. Also noticeable is the tongue , which reaches almost to the end of its beak and which is frayed at its tip into several horny strips to make it easier to pull snails out of their shells.
The iris is hazel brown. The legs are long and slender, the lower leg is feathered at the base. The toes have long, sharp claws. They are narrow and, as with jacana, very long, the middle toe reaches a length of 11 to 13 cm. The birds can therefore run around on floating vegetation as well as find support and climb around in trees.
Coloration and plumage
The basic color of the plumage is brown with a bronze sheen, depending on the subspecies and the individual, brown tones from umber to dark olive appear. The feathers on the head, neck, chest and shoulder, on the coat, as well as the shoulder feathers and arm covers, have white areas along their shaft that taper towards the tip of the feathers. The white parts of the feathers on the head and neck are very short and narrow, which gives the bird a white grained appearance. From the nape of the neck, however, the white parts of the feathers are longer and wider, the result is a coarser pattern of points, triangles and stripes.
The proportion of white feathers varies depending on the subspecies, the nominate form guarauna, for example, has hardly any white below the neck. With regard to the plumage, the species shows a low sexual dimorphism , the white markings of the males are slightly larger than those of the females , especially in the subspecies pictus . After the young birds have lost their downy plumage at the age of about five weeks, they are largely similar to the adults, only the white portion of their plumage is less. Before the breeding season , cranes moult between February and April, after the breeding season, the feathers change between August and November.
Black cranes are good swimmers and fast runners, and they can also fly. In the event of danger, the animals flee running or flying, depending on the situation, and they constantly reach high speeds over short distances. In order to take off, the birds first jump into the air. When flying over short distances, the legs are not drawn in and hang down under the body, only when flying over longer distances are they stretched backwards. The flight is similar to that of the cranes , the wings are flapped down forcefully and evenly about twice per second. During flight, the neck is stretched forward and slightly downwards, which gives the species a slightly hunched-looking silhouette in flight. The animals usually only fly short distances, for example to defend the territory, but flights that are kilometers long are occasionally undertaken, for example when open, uncovered areas have to be overcome. In these cases they fly at a height of about 15 meters and phases of flapping wings alternate with phases of sailing. For a landing, which always seems a bit abrupt, the species stretches its wings upwards after a glider flight and lets itself fall to the ground from a low height, after touching down there are often a few quick steps to lose speed. When running, the body axis is kept parallel to the ground, the neck points vertically upwards. Head and neck nodding at every step, a total remember limpkins while running on Rails . Cranes swim well, but rarely, then lie high in the water and lift wings and control feathers slightly while swimming to protect them from getting wet.
Cranes , like cranes, have a very long, winding windpipe , which lies in several turns under the breastbone . By means of this greatly enlarged resonance body , the birds produce an enormously loud call that can still be heard over three kilometers away and is often described as melodious. The call of the males sounds like a sharp, high-pitched scream and ends after about two seconds with a softening squeak or a gurgling crackle. Calls are almost always uttered several times in a row. Above all, males use the call to demarcate the territory. A second call that sounds like “ chew ” is used by unmated males in the breeding season to attract females. This call is shorter and more frequent, about once per second. The calling males show themselves to be extremely persistent, up to 80 calls are emitted one after the other, the calls often do not fall silent for hours. Females are comparatively calm, their quieter call is a seldom performed " gonn ", which is used to drive other females out of the occupied breeding territory during the breeding season. Sometimes females join in the calls of a male. Adult birds communicate with one another with various chuckling and rattling sounds and warn of predators , while young birds call their parents with a chirping “ wiiitiii ” when they approach to feed the brood.
distribution and habitat
The black-wheeled crane is common in four subspecies in the tropical and subtropical areas of America. The subspecies Aramus guarauna pictus lives as the northernmost subspecies in Florida , Cuba and Jamaica , A. g. elucus is common in Hispaniola and Puerto Rico , A. g. dolosus in southeastern Mexico to Panama , A. g. Finally, guarauna lives as the southernmost subspecies in all of South America , only in the dry west, in the Andes and in the extreme south the species is missing.
Common cranes usually live wherever they find sufficiently large numbers of their main food, the apple snails of the genus Pomacea . These are mostly inland waters that are not too deep for wading and wetlands such as the Everglades with abundant occurrences of floating aquatic and marsh plants on which the animals roam in search of food. In parts of the distribution area, however, the black-wheeled crane inhabited habitats that seem less suitable at first glance, for example in Puerto Rico wet forests on slopes or mountain rivers in Jamaica . However, due to the destruction of these habitats, such occurrences have meanwhile been completely or largely extinct. In Mexico, black cranes can also be found in dry savannahs and forests far from the nearest water point. Flooded agricultural areas are occasionally visited, but they are not permanently settled.
Grazing area and migration behavior
Males defend a territory of two to four hectares in size, depending on the food supply and nesting possibilities. The male territories defended by means of vocalizations and territorial flights are mostly adjacent to one another. Females, on the other hand, only take part in defending the territory in the breeding season, mainly by driving off invading foreign females. Territories with abundant food supply are occupied and defended by males all year round, territories of poorer quality only during the breeding season.
As birds that are relatively faithful to their location in the majority of their range, black cranes are only forced to leave their traditional territory, for example when apple snails can no longer be found due to drought or flooding. In such cases, the animals gather in large flocks in areas close to the original habitat, where they can still find food. However, between April and November, after the breeding season, some birds show an urge to dismigrate and sometimes travel a few hundred kilometers to more distant areas. Individuals of the Brazilian population are often short-range migrants who leave the drying areas after the breeding season and return when the rainy season begins . Similar behavior has also been demonstrated in some females of the best-researched population in Florida , although the water levels there do not change or change only insignificantly over the course of the year. Males stay true to their location in Florida all year round.
Way of life
Activity and comfort behavior
Elderly cranes are primarily diurnal, but the animals can also be observed in search of food after dark. At night they sleep in smaller clusters in trees and higher vegetation. To rest, cranes often stand on one leg, fold their necks in an S-shape and close their eyes. At night the head is sometimes hidden under the wing. In direct and strong sunlight, cranes occasionally spread their wings to sunbathe.
In large parts of the distribution area, the black-wheeled crane is a food specialist that feeds almost exclusively on apple snails of the genus Pomacea . To a much lesser extent, the diet consists of freshwater mussels and smaller snails. In areas further away from the water it eats land snails and small lizards , worms and insects . If there is a shortage of apple snails, crayfish , frogs and geckos are not spurned. In Florida and Jamaica in particular, it is observed that small amounts of rotting wood are ingested before and after the search for food; the reason for this behavior is unknown.
In dry areas and on land, the black-wheeled crane catches its food animals by chasing them over short distances and snapping them with its beak or, in the case of snails, eating them immediately. When looking for food in or on the water, the birds wade through the water or use their long toes to walk over floating vegetation. With the beak near-surface vegetation is searched for snails, the bottom of the water is searched with the head partly under water. Food animals are targeted with the eyes as well as found via the sense of touch.
Found snails and mussels are first held in the beak until the bird has found a place with solid ground. There, snails are arranged so that the opening of the housing faces upwards and the tip of the housing faces the bird's feet. If the operculum is closed, the crane breaks a small hole or a gap with its beak with a few targeted blows, introduces the extremely sharp and laterally bent lower beak into the winding housing and cuts the sphincter there . The snail's body is then pulled out of the shell, the orange-red vitellarium (yolk stick) is removed from female snails and the snail is finally eaten. The entire process, carried out extremely precisely by the bird, takes between 10 and 20 seconds. To open mussels, the bird breaks a hole at the point where the two halves of the shell meet, introduces the lower beak, cuts the sphincter and unfolds the mussel. Only very rarely are snails or mussels opened and eaten at the place where they were found. Individual individuals have preferred locations for opening their prey, where small clusters of empty snail shells and mussel shells often form over time.
Most broods in the northern range take place between February and June, the Jamaican population usually nests between April and November, in Cuba the birds seem to breed all year round, in Costa Rica the breeding business begins in the rainy season in July and ends with the beginning of the Dry season in December. In South America, the breeding season is usually between August and January. However, breeding can be carried out all year round in the entire range if there is sufficient food and the water level is not too high or too low.
Clawed cranes form solid partnerships for a breeding season, males and females do not leave each other during this time, while eating and sleeping the animals always keep in contact with soft, chuckling noises. The male first builds several provisional nests that it offers to the female. Immediately before completion of the nest chosen by the female, a pronounced infantilism of the female can be observed, it crouches under or next to the male and takes on snails previously caught and separated from the shell.
Nest building and nest location
Clawed cranes have no special demands on their nesting sites. Nests are created in dense reed beds as well as in tree tops and on branches, large hollows in dead trees are accepted as nesting sites , as are abandoned clumps of birds of prey . It is not uncommon for the nest to be placed directly on the water by accumulating floating plant material on the surface to form a floating island. The material used to build nests also varies greatly. Floating nests consist of aquatic plants, while nests on the bank or in trees usually consist of material that can be found in the immediate vicinity, such as dead leaves, twigs and grass. The nest is only sparsely padded with grass and down if it consists largely of twigs, floating nests are almost never padded, in these cases the nest only consists of a hollow in the vegetation piled up on the water. The nests on land vary in diameter between 40 and 60 centimeters and are around 20 centimeters high. A hollow is often only rudimentary, mostly it is nothing more than a slight depression on the nest surface.
Clutch and brood
The eggs are laid after the female has chosen one of the provisional nests made by the male and both birds have finished building the chosen nest. At intervals of one day, 4 to 7 eggs are laid, which measure approximately 60 × 44 mm and weigh 57 grams. In terms of color, even eggs in a clutch can differ considerably and can be sand-colored or gray, with spots that vary from light to dark brown. The breeding season lasts about 27 days, males and females breed in equal proportions during the day, at night only the female sits on the eggs.
All chicks hatch in a period of between 18 and 24 hours, when they flee from the nest , the cinnamon-brown chicks, which swim well and run, immediately follow the adult birds to a newly created platform on the water, consisting of accumulated aquatic plants. After about a week, another change of location is made. In the first weeks after hatching, the legs of the chicks appear oversized, the wings develop late until they are fit to fly. After about six weeks, the young birds have roughly reached the size and proportions of their parents, only the beak is even shorter and its tip is even less curved. The young birds are fed until the eighth or ninth week, and in the sixth week the offspring, which is then capable of short flights, begins to look for snails independently and at first somewhat clumsily and to learn the correct technique for opening and removing the shells.
After the adult birds have stopped feeding, the young birds leave the association and go in search of food on their own. Young males begin to defend a small territory in the territory of the adult male after just eleven weeks. Ultimately, most fledglings leave their parents' territory between 15 and 17 weeks of age and establish their own territories at some distance or migrate to areas further away. It is not uncommon for the adult pair to move on to a second brood afterwards. However, if the breeding success is low due to the high mortality of the young birds, the female often leaves the breeding territory and her partner as soon as the remaining young birds eat alone and mates with a male from neighboring territories.
The systematic position of the black-wheeled crane was and is the subject of scientific discussion. At times the crane was assigned to the hens or the herons . For a long time it was assumed that the railing crane was a link between the railing and the cranes . Some aspects of the anatomy , for example the elongated and folded windpipe, the osteology , the musculature and the fletching correspond more to the cranes. The morphology of the beak and the feet, as well as the shape and size of the wings, the structure of the digestive tract and parasitological aspects are more reminiscent of rails. Sibley et al. put the species after phylogenetic studies on the rush rushes . However, the latest results based on phylogenetic studies seem to confirm that the black-winged crane is not a close relative of the rush-claws. The species is regarded as the sister taxon of the cranes.
The oldest fossil from a member of the Aramidae family was found in a 54-million-year-old rock layer in Wyoming . Other, more recent fossils have been found in Argentina , Patagonia and Nebraska , among others , which proves that the black cranes were more widespread in earlier times. Between 1856 and 1934, the black cranes were often divided into a northern species living in North and Central America and a species living in South America, but this classification did not prevail among experts , so that the species Aramus guarauna is now divided into four subspecies A. . pictus , A. g. elucus , A. g. dolosus and A. g. guarauna is classified. These are differentiated on the basis of small differences in body size, plumage color and white proportion of the plumage. Animals of the southern subspecies generally have less white part of their plumage.
Rallied crane and human
Everywhere in the area of distribution, the black-wheeled crane is known because of its unmistakable reputation and also the tasty meat. In Cuba it is called Guareáo , in Brazil Carao or Guarauna , in Costa Rica and Puerto Rico the species is called Carrao , each based on its characteristic reputation. The English name limpkin ( to limp = to limp) is said to refer to the allegedly limping gait of the cranes, although this property is not particularly noticeable. The inhabitants of the Amazon basin believe that the water level of rising rivers does not rise any more as soon as the crane begins to call. It is remarkable how little shy the species is towards humans. Brooding females do not leave their nest even when observers are standing next to the nest. During the colonization of Florida, the birds' lack of fear was their undoing. They were often shot at close range for their tasty meat or even caught by hand.
Threat and protection
The IUCN lists the cranes as not endangered because they can be found everywhere in the distribution area, at least regionally, if suitable habitats are available. In the past, however, this has not always been the case everywhere. At the beginning of the 20th century, with the increasing settlement of Florida, a large part of the local population was wiped out. The people appreciated the tasty meat of the relatively large bird, the hobby hunting did the rest. Likewise, the deposits in Cuba, Haiti, Jamaica and in Puerto Rico were decimated by hunting. In Puerto Rico, especially the populations of the still not resettled were Highlanders affected, there also is entrained gold dust Mongoose and the destruction of upland forest for the decline of the deposit charge. Wetlands such as the Everglades were drained to a greater extent in Florida than in other parts of the range , which in the 1950s led to the loss of thousands of breeding pairs in eastern Florida alone. Although this negative trend did not continue in such a massive form, the number of breeding pairs in Florida continued to decline in the following decades, for example by 9 percent from 1966 to 1993. In 2002 there were between 3,000 and 6,000 occupied territories in Florida. Regardless of local population declines, the stock of the black crane is considered to be secure, as there are still large, inaccessible wetlands that can serve as retreats for the species. In addition to the drainage of wetlands, another potential threat is the colonization of aquatic ecosystems by plant-based neozoa, which displace the food plants of the apple snails and thus also deprive the common crane of the nutritional basis. Since pesticides are still frequently used in South America , among other things, to keep waterways free from vegetation, these also pose a threat. The toxins collect in the body of the herbivorous apple snail and ultimately also accumulate in the body of the black cranes .
Much of the information in this article is taken from:
- Josep del Hoyo , Andrew Elliot, Jordi Sargatal: Handbook of the birds of the world. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona 1996, ISBN 84-87334-20-2 .
The following sources are also cited:
- Rallenkranich releases the snail from the housing
- CG Sibley, JE Ahlquist. Distribution and Taxonomy of Birds of the World . Yale University Press, New Haven, 1990
- MG Faina, C. Krajewskib, P. Houde. Phylogeny of "core Gruiformes" (Aves: Grues) and resolution of the Limpkin-Sungrebe problem . In: Molecular Phylogenetics and Evolution 2007, Vol. 43, No. 2, pp. 515-529
- A. Wetmore, A. Thomson. Additional specimens of fossil birds from the upper tertiary deposits of Nebraska . In: American Museum Novitates 1928, 302, Weblink (PDF; 404 kB)
- DJ Nicholson: Habits of the Limpkin in Florida . In: The Auk 1928, 45, pp. 305–309, web link (PDF; 343 kB)
- US Fish & Wildlife Service, S. Delany, S. Scott, DC Bryan. Waterbird Status Assessment 2002, Weblink (PDF; 226 kB)
- Videos, photos and sound recordings of Aramus guarauna in the Internet Bird Collection
- Birdlife International 2007 factsheet; engl.
- Aramus guarauna in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- xeno-canto: sound recordings - Limpkin ( Aramus guarauna )