The Sandhill Crane (Grus canadensis) is a species of large crane of North America and extreme northeastern Siberia. The common name of this bird references habitat like that at the Platte River, on the edge of Nebraska's Sandhills in the American Midwest. This is the most important stopover area for the nominotypical subspecies, the Lesser Sandhill Crane (Grus canadensis canadensis), with up to 450,000 of these birds migrating through annually.
Adult is gray overall; during breeding, the plumage is usually much worn and stained, particular in the migratory populations, and looks nearly ochre. The average weight of the larger male is 4.57 kg (10.1 lb), while the average weight of females is 4.02 kg (8.9 lb), with a range of 2.7 to 6.7 kg (6.0 to 15 lb) across the subspecies. The Sandhill Crane has a red forehead, white cheeks and a long dark pointed bill. Its long dark legs trail behind in flight, and the long neck is kept straight in flight. Immature birds have reddish brown upperparts and gray underparts. The sexes look alike. Size varies among the different subspecies; the average height of these birds is around 80 to 120 cm (2.6 to 3.9 ft). The standard linear measurements of the Sandhill are: the wing chord measures 41.8–60 cm (16.5–24 in), the tail is 10–26.4 cm (3.9–10.4 in), the exposed culmen is 6.9–16 cm (2.7–6.3 in) long and the tarsus measures 15.5–26.6 cm (6.1–10.5 in).
This crane frequently gives a loud trumpeting call that suggests a French-style "r" rolled in the throat, and they can be heard from a long distance. Mated pairs of cranes engage in "unison calling." The cranes stand close together, calling in a synchronized and complex duet. The female makes two calls for every single call of the male.
The sandhill crane's large wingspan, typically 1.65 to 2.1 m (5.4 to 6.9 ft), makes this a very skilled soaring bird similar in style to hawks and eagles. Utilizing thermals to obtain lift, they can stay aloft for many hours, requiring only occasional flapping of their wings and consequently expending little energy. With migratory flocks containing hundreds of birds, they can create clear outlines of the normally invisible rising columns of air (thermals) that they ride.
The Sandhill Crane flies south for the winter. In their wintering areas they form flocks of over 10,000 birds. One place to observe this is at Bosque del Apache National Wildlife Refuge, 100 miles south of Albuquerque, New Mexico. There is an annual Sandhill Crane Festival in November.
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The Sandhill Crane has one of the longest fossil histories of any bird still found today. A 10-million-year-old crane fossil from Nebraska is often cited as being of this species, but this is more likely from a prehistoric relative or the direct ancestor of the Sandhill Crane and may not belong in the genus Grus. The oldest unequivocal Sandhill Crane fossil is 2.5 million years old, over one and a half times older than the earliest remains of most living species of birds, which are primarily found from after the Pliocene/Pleistocene boundary some 1.8 million years ago. As these ancient Sandhill Cranes varied as much in size as the present-day birds, even those Pliocene fossils were sometimes described as new species. Grus haydeni on the other hand may or may not have been a prehistoric relative of the living species, or it may actually comprise material of the Sandhill Crane and its ancestor.
Subspecies and evolution
There is considerable variation in size (much of which is clinal) and in migratory habits. A female of G. c. canadensis averages 7.4 lbs (3.46 kg), 37 in (94 cm) in length and has a wingspan of 5.3 ft (1.6 m). A male of G. c. tabida averages 11 lbs (5 kg), 47 in (119 cm) in length and has a wingspan of 7 ft (2.12 m). The southern subspecies (along with G. c. rowani) are intermediate, roughly according to Bergmann's Rule.
Three subspecies are resident; pulla of the Gulf Coast of the U.S., pratensis of Florida and Georgia and nesiotes of Cuba. The northern populations exist as fragmented remains in the contiguous U.S. and a large and contiguous population from Canada to Beringia. These migrate to the southwestern United States and Mexico. This crane is a rare vagrant to China, South Korea and Japan and a very rare vagrant to western Europe.
Six subspecies have been recognized in recent times:
- Lesser Sandhill Crane, Grus canadensis canadensis
- Cuban Sandhill Crane, Grus canadensis nesiotes – ESA: Endangered
- Florida Sandhill Crane, Grus canadensis pratensis – ESA: Endangered
(The Florida Sandhill Crane was listed as EC or easily confused in order to facilitate an attempted re-introduction of the Whooping Crane (Grus americana) into Florida. The attempt failed but the listing remained. The current list of endangered subspecies includes only 2 birds, nesiotes and rowani, with pratensis no longer listed. http://ecos.fws.gov/tess_public/SpeciesReport.do)
- Mississippi Sandhill Crane, Grus canadensis pulla – ESA: Endangered
- Canadian Sandhill Crane, Grus canadensis rowani
- Greater Sandhill Crane, Grus canadensis tabida
The Canadian Sandhill Crane is morphologically not reliably distinct and was never unequivocally accepted as valid subspecies. The other can be somewhat more reliably distinguished in hand by measurements and plumage details, apart from the size differences already mentioned. Unequivocal identification often requires location information, which is often impossible in migrating birds.
Analysis of control region mtDNA haplotype data shows 2 major lineages, one including the Lesser Sandhill Crane or Little Brown Crane, the Arctic and the subarctic migratory population. The other lineages can be divided into a migratory and some indistinct clusters which can be matched to the resident subspecies. The Lesser and Greater Sandhill Cranes are quite distinct, their divergence dating roughly to some time during the Late Pliocene or Early Pleistocene, some 2.3–1.2 million years ago (mya). It seems as if glaciation fragmented off a founder population of the Lesser Sandhill Crane, because during each major ice age its present breeding range was frozen year-round. Still, Sandhill Cranes are amply documented from fossil and subfossil remains right to the modern era. Conceivably, they might be considered distinct species already, a monotypic G. canadensis and the Greater Sandhill Crane G. pratensis, which would include the other populations.
It appears as if the scant differences between southern Canadian and western U.S. populations result from genetic drift due to the recent reduction in population and range fragmentation; until the early 20th century the southern migratory birds occupied a much larger and continuous range. Thus, the subspecies rowani may well be abandoned.
The two southern U.S. resident populations are somewhat more distinct, while the Cuban population has been comparatively little studied but appears to have been established on the island for a long time. These and the migratory Greater Sandhill Crane proper form a group of lineages that diverged much more recently from a range in the southern U.S. and maybe northern Mexico, where they would have been resident. The southern migratory population would then represent a later re-expansion which (re-)evolved their migratory habits independent from the northernmost birds, the geographically separated populations expanding rapidly in numbers when more habitat was available as the last ice age ended.
Sandhill cranes are fairly social birds that are usually encountered in pairs or family groups through the year. During migration and winter, non-related cranes come together to form "survival groups" which forage and roost together. Such groups often congregate at migration and winter sites, sometimes resulting in thousands of cranes being found together.
Sandhill Cranes are quite catholic in diet but are mainly herbivorous, often eating various types of food based on availability. They often feed with their bills down to the ground as they root around for seeds and other foods in shallow wetlands with vegetation or various upland habitats. Cultivated foods such as corn, wheat and sorghum are readily eaten and may support large numbers of cranes. For example, waste corn is useful to the cranes in preparing for their migrations, providing them with nutrients for the long journey. Among northern races of Sandhill cranes, the diet is most varied especially among breeding birds. Northern cranes and their offspring may variously feed on berries, small mammals, insects, snails, reptiles and amphibians.
Sandhill cranes raise one brood per year. In non-migratory populations, egg-laying can begin as early as December or as late as August. In migratory populations, egg-laying usually begins between early April and late May. Both members of a breeding pair build the nest using plant material from the surrounding areas. Nest sites are usually in marshes, bogs, or swales, though cranes will occasionally nest on dry land. The female lays 1 to 3 (usually 2) eggs that are oval-shaped and dull brown with reddish brown markings. Both parents participate in incubation, which lasts 29 to 32 (though usually 30) days. Incubation begins with the laying of the first egg and continues until the second egg has hatched. The chicks are precocial; they hatch covered in down, with their eyes open and are able to leave the nest within 24 hours of hatching. The parents brood the chicks for up to 3 weeks after hatching. They feed the young intensively for the first few weeks, and with decreasing frequency until they reach independence at 9 or 10 months old.
The chicks remain with their parents until 1 or 2 months before the parents begin laying the next clutch of eggs. After leaving their parents, the chicks form nomadic flocks with other subadults and non-breeders. They remain with these flocks until they form breeding pairs and begin breeding between the ages of 2 and 7 years old. Sandhill cranes provide extended biparental care to their young. Both members of a breeding pair build the nest, incubate the eggs and feed and protect the chicks for up to 10 months after hatching. Sandhill cranes that reach independence are expected to live around 7 years. Sandhill cranes can live to at least 21 years of age.
As a conspicuous and ground-dwelling species, Sandhill Cranes may face a variety of predators. Mammalian predators such as foxes, raccoons, coyotes, wolves, bobcats and lynxes readily predate cranes of any age, although they are a greater threat to young cranes. Birds that may predate young cranes or crane nests include corvids such as ravens and crows and smaller raptors, including hawks. Cranes of all ages may be predated by eagles, large owls and even Peregrine Falcons. Sandhill cranes often vigorously defend themselves from predators, especially when defending offspring which are not able to avoid ambushes as easily as their parents. When attacking potential avian predators they fly up at the predator and kick with their feet. When facing mammalian predators, they move toward the predator with their wings open and their bill pointed towards it. If the predator persists, the often hissing crane will attack, stabbing with their bill (which is powerful enough to pierce the skull of a small carnivore) and kicking with their feet.
Status and conservation
Though the Sandhill Crane is not considered threatened as a species, the three southernmost subspecies are quite rare. While the migratory birds could at least choose secure breeding habitat, the resident populations could not, and many subpopulations were destroyed by hunting or habitat change. However, initially the Greater Sandhill crane proper suffered most from persecution; by 1940 probably fewer than 1,000 birds remained. They have since increased greatly again, though with nearly 100,000 individuals they are still less plentiful than the Lesser Sandhill Crane, which numbers over 400,000 individuals, making the species the most plentiful crane alive today.
In some migratory populations, Sandhill Cranes face population threats due to inter-species competition with Snow geese. Since the 1990s, snow geese have begun to eat waste corn prior to their migration, exacerbating the Sandhill crane population.
The Florida Sandhill Crane is far less common, with some 5,000 individuals remaining. They are most threatened by habitat destruction and probably depend on human management in the long run. In Florida, it is protected, and if killed, carries a very high monetary penalty. This subspecies is under protection of state and federal law at this time. Since the loss of habitat is a somewhat controllable cause of a declining population, habitat preservation is a valuable management measure. The current outlook for the Florida sandhill crane, if it can be maintained on the protected habitats, is good. Transplanting wild birds, as well as introducing captive-reared birds into suitable areas where crane numbers are low, appears to be a viable technique in the management of this threatened species. It is hoped that these management strategies, plus continued ecological research, will prevent the Florida sandhill crane from reaching a more critical status.
The Mississippi Sandhill Crane has most drastically declined in range; it used to occur along most of the northern Gulf of Mexico coast and its range was at one time nearly parapatric with that of its eastern neighbor (compare the Mottled Duck); today only 25 breeding pairs exist in an intensively managed population, but this seems at least stable in recent times. Some 300 Cuban Sandhill Cranes remain; this is the least-known of the populations.
The Mississippi Sandhill Crane has become the first bird to have a young hatched where an egg was fertilized by a sperm that was previously thawed out from a cryogenic state. This occurred at the Audubon Institute as part of this subspecies' Endangered Species Recovery Plan.
Sandhill Cranes have been used as foster parents for Whooping Crane eggs and young in reintroduction schemes for that species. This project failed as these foster-raised Whooping Cranes imprinted on their foster parents and later did not recognize other Whooping Cranes as their conspecifics – attempting instead, unsuccessfully, to pair with Sandhill Cranes.
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