The Cranes
Status Survey and Conservation Action Plan
An Overview of Crane Biology: Distribution and Habitat
Cranes are cosmopolitan in their distribution, occurring from the North American and Asian tundra to the Asian, Australian, and African tropics. East Asia, with seven species occurring on a regular basis, has the highest level of species diversity. Five species occur during the year in the Indian subcontinent. Africa has four species year-round, resident and wintering populations of a fifth (the Demoiselle), and wintering populations of a sixth (the Eurasian)1. Why cranes never colonized South America remains a biogeographic mystery.
Most of the cranes prefer relatively open spaces and require territories with a wide range of visibility. Space and solitude are especially important requirements during the breeding season. Most species nest in shallow wetlands, where the cranes meet both their feeding and nest-building needs. The Crowned Cranes roost in trees, nest in wetlands, and forage predominantly in grasslands. The two Anthropoides species usually nest, and almost invariably feed, in open grasslands and roost in wetlands. In central Asia, the Demoiselle Crane will nest in arid grasslands, and even true deserts, as long as water is available.
The degree to which cranes use and require wetlands varies widely among, and within, species. The Cuban Sandhill Crane lives in pine-palmetto savannas and nests and rears its young on dry ground. Other Sandhill Cranes and the Sarus, Brolga, White-naped, Eurasian and Black-necked Cranes nest in wetlands; however, soon after the chicks hatch they are led to neighboring uplands to forage, returning to wetlands for the night. Wattled Cranes in the enormous floodplains of south-central Africa nest when water levels peak during the annual floods, but remain in the wetlands throughout much of the year. Wattled Cranes in the montane wetlands of South Africa, Zimbabwe, and Ethiopia nest at the end of the dry season on small wetlands bordered by grasslands. The large white cranes (Siberian, Whooping, and Red-crowned), and perhaps also the Hooded Crane (which nests in isolated tamarack swamps), remain in wetlands throughout the nesting and rearing period.
In the migratory species, family groups join together into flocks at premigration staging areas soon after the chicks fledge. A staging area usually contains safe roosting sites as well as a dependable source of food. The number of cranes using a staging area continues to increase until inclement weather forces the cranes to move south to join even larger prestaging congregations. The major portion of the migration flight then commences. Along the way there may be several stopover points. Most species of migratory cranes remain in large flocks throughout the winter non-breeding period, roosting at night in shallow wetlands and foraging during the day in wetlands and upland areas, including agricultural fields. Species that feed primarily on sedge tubers and other aquatic vegetation (Siberian, Sandhill, White-naped, Brolga) forage in flocks, while those that feed more on animals (Whooping, Red-crowned) are more territorial and often forage in family groups.
Non-migratory cranes also gather in groups during the non-breeding season. They are somewhat opportunistic and nomadic in choosing habitats, moving from area to area in search of food and security. Although the availability of food is always of paramount importance during these times, social needs such as pairing and the introduction of juveniles to flocks also contribute to habitat choice and flocking behavior in the non-migratory cranes.
Cranes generally try to maintain a distance of at least several kilometers between themselves and areas of human activity. If, however, they are not harmed or disturbed, cranes can acclimate to the presence of people. Thus, Sarus Cranes in India have adapted to the high human population density in that country, and commonly nest and roost in small village ponds and jheels (Gole 1989b, 1991b, 1993a). In recent decades recovering populations of Sandhill Cranes in North America and Eurasian Cranes in Europe have taken to using smaller, less isolated, and lower quality wetlands closer to human settlements (Gluesing 1974, Mewes 1994). In parts of Kazakhstan and Ukraine, the Demoiselle Crane has been able to continue breeding in steppes that have been converted to agriculture as long as farming operations are timed so as to minimize disturbance (Winter 1991, Kovshar et al. 1995).
Agricultural development has had varying impacts on cranes and their habitats. The drainage of wetlands for agriculture has deprived most cranes of habitat to one degree or another, with the more wetland-dependent species—the Wattled, Siberian, Whooping, and Red-crowned—being most profoundly affected. Other species have adapted to and even benefitted from agriculture. For some cranes, wetlands bordered by agricultural fields often provide more favorable breeding habitat than do pristine regions where wetlands are surrounded by forests or other wetland types. In general, the species that can subsist on gleanings of waste grain in agricultural fields during migration and on their wintering grounds are faring better than those that depend exclusively upon wetlands throughout the year.
1In this document, "population" refers to a group of interbreeding cranes of the same species that occupies a distinct geographic area or region. In most cases this area or region is within the species' breeding range (the term "breeding population" is also sometimes used). If the area is within the species' winter range, the term "wintering sub-population" is used (since birds from different wintering areas may breed in the same area). When used in reference to the species as a whole or to subspecies, "population" refers to the total number of individuals in the taxon.
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