The Cranes
Status Survey and Conservation Action Plan
An Overview of Crane Biology: Diet and Foraging Behavior
Although some species are more specialized than others, most cranes are generalists and opportunists, feeding on a remarkably wide variety of plant and animal foods. Among cranes that use upland areas, the diet includes seeds, leaves, acorns, nuts, berries, fruits, waste grains, worms, snails, grasshoppers, beetles, other insects, snakes, lizards, rodents and other small mammals, and even small birds. Wetland food items include the roots, bulbs, rhizomes, tubers, sprouts, stems, and seeds of submergent and emergent plants, and mollusks, aquatic insects, crustaceans, small fish, and frogs. Cranes readily shift their feeding strategies on a daily or seasonal basis to take advantage of available food items. For example, Eurasian Cranes wintering on the Iberian Peninsula subsist primarily on cereal grains in the early part of the winter, switch to acorns of the holm oak in mid-winter, and may turn again to germinating cereals and legumes in the late winter (Alonso et al. 1987, Sànchez et al. 1993).
The anatomy of cranes reveals much about their feeding preferences. Cranes with shorter bills usually feed in the dry uplands, while those with longer bills usually feed in wetlands. Crowned Cranes stamp the ground to scare up insects, which they then grasp in their short bills. These species, together with the two Anthropoides species, the Sandhill Cranes, and the Eurasian, Hooded, and Black-necked Cranes, also use their shorter bills for grazing in a goose-like manner. The taller cranes with the largest and longest bills (Wattled, Siberian, Sarus, Brolga, White-naped) are diggers, and use their powerful mandibles to excavate tubers and roots from the muddy soils of wetlands. The long-billed Whooping Cranes and Red-crowned Cranes use their bills to gently probe the bottom of shallow wetlands for crustaceans and other small aquatic animals.
The foraging behavior of cranes reflects their varied strategies, niches, and diets. The diggers usually stay in the same area for extended periods of time, excavating holes that are continually enlarged to expose the tubers that proliferate in certain types of wetland soils. Unlike herons, which stand motionless and wait to strike for prey, the hunting cranes walk slowly through the water searching and probing for prey to grab. Upland feeders usually walk with their heads lowered, hunting and pecking at the ground for insects, seeds, and other morsels. Generalist feeders use different strategies under different circumstances. Sarus Cranes, for example, often dig for tubers and other subsurface plant materials, but are effective upland foragers and hunters, and have also been observed stripping grains of rice from their stalks (Gole 1989b, 1991b).
Crane parents begin to feed their chicks almost immediately after hatching occurs. Both parents contribute to the feeding of young. Adults carry small food items to the chicks and either present the food directly to them by holding it at the tip of their bills or by dropping it before them. Chicks eventually begin to follow their parents to nearby food sources, although in some cases adults will continue to bring food until the chicks are several months old. Demoiselle Crane chicks are unusually mobile at an early age (G. Archibald pers. obs.).
Where several species of cranes occur together, the varied feeding strategies and adaptations tend to minimize the degree of niche overlap. This occurs most noticeably in wintering areas in China, where four species may coexist in the same area. Thus, at Poyang Lake in Jiangxi Province, Siberian Cranes have been observed feeding in the shallow water and mud flats, White-naped Cranes along the wetland borders, Hooded Cranes in adjacent croplands, and Eurasian Cranes in the available “spaces” in between (Zhou and Ding 1987, Chen and Wang 1991). When Sarus and Siberian Cranes have occurred together at Keoladeo National Park in India, the Siberians have foraged for sedge tubers in deeper waters while the Sarus have fed on a broader variety of plants and animals in shallower waters (Sauey 1985). A somewhat analogous situation has been observed in parts of Australia where Brolgas and Sarus Cranes are sympatric. The former tend to use larger, more open sedge marshes in the lowlands; the latter to use smaller wetlands in more forested areas as well as drier habitats (Archibald and Swengel 1987; A. Haffenden pers. comm.).
Many species of cranes benefit from the food provided by agricultural fields during the breeding and/or non-breeding phase of their annual cycle. At one time or another, most cranes forage in crop lands and pastures that border the wetlands where they nest or roost. At migration stopovers and on the wintering grounds, those species that feed on gleanings from agricultural fields usually find an abundance of food, and interfere minimally with farming operations. For example, the great congregations of migrating Sandhill Cranes that stop along the Platte River in the central United States in the spring subsist largely on waste corn gleaned from nearby fields. Crop damage can occasionally be a serious problem (e.g., Mizoguchi 1985, Parasharya 1986, McIvor and Conover 1994, Bouffard in press). This usually occurs during the fall migration or early in the winter, when crops are being harvested, or in the early spring, when new crops are germinating. During these times, not only are the field foods available, but the cranes are usually in large flocks (see Topic 1).
For several species, artificial feeding has come to play an important role not only in their annual cycle, but in their survival and recovery as species. Some three-fourths of the world’s population of Hooded Cranes, and about 40% of the White-naped Crane, are sustained by artificial feeding on the Japanese island of Izumi, a program that was initiated in the 1950s (Goto 1986; Ohsako 1987, 1994; Matano 1995). The Hokkaido population of Red-crowned Cranes, about one-third of the total population, has used feeding stations since 1952 (Archibald 1978). In both cases, artificial feeding has contributed to the rapid growth of small remnant populations. However, the success of such programs now presents its own conservation challenges (see Topic 1).
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