The Cranes
Status Survey and Conservation Action Plan

Introduction

An understanding of the biology, ecology, and status of cranes is fundamental to the success of efforts to conserve them and the ecosystems within which they exist. Fortunately, cranes have drawn sustained attention from scientists and conservationists around the world. Walkinshaw (1973) and Johnsgard (1983) provide detailed reviews of crane biology and ecology. The species accounts in Section 2 provide summaries of recent research and conservation activities for each species, as well as additional literature sources for those seeking further information. This section focuses on the cranes at the family level, highlights contrasts among the species, and reviews the status of and threats to the family as a whole.

This section is adapted from text prepared for the Handbook of the Birds of the World: Volume 3 (del Hoyo, J. and Elliot, A., eds. In prep. Lynx Editions and the ICBP, Barcelona). Section 1.5, “Conservation Status,” was prepared based on the new categories and criteria as delineated in the IUCN Red List Categories (IUCN 1994). Section 1.8, “Captive Propagation and Reintroduction,” was prepared by Claire Mirande of the International Crane Foundation in consultation with members of the Crane Specialist Group.

Evolution and Classification

Within the order Gruiformes, cranes are closely related to the limpkins (which have similar flight patterns and loud calls), the trumpeters (which resemble Crowned Cranes in their dances and plumage), and the bustards (which are also large, long-legged, long-necked birds found in open lands). Recent studies of morphology, ethology, and DNA have shown similar patterns in the systematic relationships within this order of birds (see Archibald 1976a, 1976b; Wood 1979; Krajewski 1989; Krajewski and Fetzner 1994; Krajewski and Archibald in prep.).

The crane family (Gruidae) is divided into two subfamilies, the Crowned Cranes (Balearicinae) and the Typical Cranes (Gruinae) (Figure 1.1). Crowned Cranes date back in the fossil record to the Eocene, 37-54 million years before present. Eleven species of Crowned Cranes are known to have existed in Europe and North America over the last 50 million years. The two species of Crowned Cranes that survive are found exclusively in Africa (Urban 1987). Modern Crowned Cranes cannot withstand extreme cold, and it is conjectured that as the earth cooled these cranes died out on the northern continents and held on only in Africa, where tropical conditions persisted through the Pleistocene. The Typical Cranes, by contrast, are more cold hardy. They first appear in the fossil record in the Miocene, 5-24 million years ago. It was during this period that the thirteen surviving species of Gruinae evolved. Seven other species of Gruinae cranes are known to have gone extinct during this period (Brodkorb 1967).

Crowned Cranes are distinguished from the Typical Cranes by their lack of a coiled trachea, their loose body plumage, and their inability to withstand severe cold. They retain the ability to roost in trees, and are the only cranes able to do so. Their calls are also simpler than those of the Typical Cranes (Archibald 1976a, 1976b). There are two species: the Black Crowned Crane (Balearica pavonina) of the African Sahel Savannah from Senegal to Ethiopia, and the Grey Crowned Crane (B. regulorum) of the East African savannahs from Kenya to South Africa.

The Typical Cranes are divided into three genera: Anthropoides, Bugeranus, and Grus. The Demoiselle Crane (Anthropoides virgo) and Blue Crane (Anthropoides paradisea) have bustard-like short toes and bills, and like the bustards live in grasslands. Although the morphological features of the Anthropoides species and the larger Wattled Crane (Bugeranus carunculatus) are dramatically different, studies of their behavior and DNA indicate a close relationship between them (Archibald 1976a, 1976b; Krajewski 1989; Krajewski and Fetzner 1994). The Wattled Crane is a much more aquatic species, and undoubtedly its large size is an evolutionarily convergent feature that it shares with the Grus species that are primarily aquatic.

The species in the genus Grus are placed in four groups (Archibald 1976a, 1976b; Krajewski 1989; Krajewski and Archibald in prep.). The Sandhill Crane (Grus canadensis) stands alone, as does the Siberian Crane (Grus leucogeranus). The “Group of Three” includes the Sarus Crane (Grus antigone), the Brolga (Grus rubicundus), and the White-naped Crane (Grus vipio). The “Group of Five” consists of the Eurasian Crane (Grus grus), Whooping Crane (Grus americana), Hooded Crane (Grus monachus), Black-necked Crane (Grus nigricollis), and Red-crowned Crane (Grus japonensis).

The differences between the Siberian Crane and the other Grus species are greater than those that separate the remaining eight species. There are some morphological and ethological similarities between the Siberian and Wattled Crane, although DNA evidence suggests that these are due to convergent evolution. Many scientists hold that the Siberian Crane should be placed within its own distinct genus, Sarcogeranus. The Sandhill Crane has features in common with both the Group of Three and the Group of Five, which suggests that it might be (or might resemble) the common ancestor of the two groups. Although the Sarus Crane and Brolga are similar morphologically, DNA analysis suggests that the Brolga and White-naped Crane are actually more closely related. The Common Crane is closest to the Whooping Crane, and the Hooded Crane closest to the Black-necked Crane. Within the Group of Five, the Red-crowned Crane is the most distantly related to the other four species (Krajewski and Fetzner 1994).

Each of the two Crowned Crane species has two subspecies. The Grey Crowned Crane is divided into the South African Crowned Crane (B. r. regulorum) and the East African Crowned Crane (B. r. gibbericeps). The Black Crowned Crane is divided into the West African Crowned Crane (B. p. pavonina) and the Sudan Crowned Crane (B. p. ceciliae). The Sarus Crane has three subspecies: the Indian (G. a. antigone), Eastern (G. a. sharpii), and Australian (G. a. gilli). The Philippine Sarus Crane (G. a. luzonica), which is presumed to be extinct, may have been a discrete subspecies. Six subspecies of Sandhill Cranes are currently recognized: the Lesser (G. c. canadensis), Canadian (G. c. rowani), Greater (G. c. tabida), Mississippi (G. c. pulla), Florida (G. c. pratensis), and Cuban (G. c. nesiotes) Sandhill Cranes. In the past, the Eurasian Crane was split into two subspecies—the western (G. g. grus) and eastern (G. g. lilfordi)—and the Brolga into Northern (G. r. argentea) and Southern (G. r. rubicundus) subspecies, but these divisions have not been validated and are not widely accepted. (See the species accounts in Section 2 for further discussion of the taxonomic status and characteristics of subspecies).

Morphology

Cranes are large to very large birds with long necks and legs, streamlined bodies, and long rounded wings. In the field, they are readily recognized by their imposing size and graceful proportions. Cranes are among the world’s tallest birds, ranging in length from 90 to more than 150 cm. The smallest is the Demoiselle Crane. The Sarus Crane is the tallest. The Indian subspecies of the Sarus, which can stand as high as 175 cm, is the world’s tallest flying bird. The Red-crowned Crane is the heaviest crane, weighing up to 11 kg when fat deposits peak in the autumn. Male and female cranes of all species are identical in their external features, although males are usually somewhat larger than females (Johnsgard 1983). Compared to the other tall wetland birds, cranes generally have longer legs and hold their necks straighter than day-herons; larger bodies than egrets; and longer legs, lighter bodies, and proportionately smaller bills than storks.

Distinctive features within the family reflect the varied evolutionary history and ecological niches of the different species. The long, prehensile hind toe (hallux) of Crowned Cranes allows them to roost in trees. Demoiselle Cranes and Blue Cranes have short, bustard-like toes adapted for rapid running in their grassland habitats. The relatively short bills of these cranes allow them to forage more efficiently for seeds, insects, and other food items in upland habitats. All the other cranes display adaptations to more aquatic conditions: elongated necks and bills, long bare legs, and broader feet. Siberian Cranes, the most aquatic of all cranes, have the longest bill and toes—adaptations for probing and walking in mud. Brolgas, which use salt marshes and other saline wetlands more extensively than the other species, have specialized salt glands near their eyes, through which they are able to secrete concentrated salts.

The length and position of the trachea are critical features of crane anatomy, and shape the distinctive voices of the various cranes (Niemeier 1983). The non-Gruinae cranes have shorter tracheas that are impressed slightly against the sternum. In the Gruinae cranes, the trachea actually penetrates the sternum to varying degrees. In Siberian and Wattled Cranes the trachea makes a slight indentation on the sternum, an indentation twice as deep as that found in the Anthropoides cranes. With the exception of the Siberian Crane, the trachea of all Grus species coils on the vertical plane within the sternum. In the Brolga, Sandhill, and Sarus Cranes, the coiled trachea fills most of the anterior half of the sternum, while in the White-naped, Eurasian, Whooping, Hooded, Black-necked, and Red-crowned Cranes the trachea penetrates the entire sternum. The bony rings of the trachea fuse with the sternum to create thin plates. When cranes vocalize, the plates vibrate. This amplifies the cranes’ calls, which can carry several kilometers (Gaunt et al. 1987).

Crane eggs are ovule-pointed and in most species heavily pigmented. Cranes inhabiting tropical and subtropical areas lay either light bluish eggs (Crowned Cranes) or white eggs (Sarus, Brolga). Species inhabiting the coldest regions—Siberian, Black-necked, and Lesser Sandhill Cranes—produce darker eggs. This tendency for eggs to be light-colored in warmer climates and dark in colder climates is probably an adaptation to environmental conditions, allowing eggs to reflect heat in the former case and to absorb heat in the latter. Red-crowned Cranes lay both white and pigmented eggs, an indication that the species may have evolved under warmer climatic circumstances (G. Archibald pers. obs.).

The chicks of most crane species are predominantly brown. The exceptions are the Demoiselle, Blue, and Brolga Cranes, whose chicks are silver-grey. Chicks lose their egg tooth within a few days of hatching. The initial down is replaced by a second down that is in turn replaced by feathers (Kashentseva 1988, 1995; Kashentseva and Tsvetkova 1995). The rate of chick growth is astonishing, especially among chicks of the northernmost species. Legs grow rapidly during the first six weeks, followed by more rapid development of the wings.

Juvenile Demoiselle, Blue, Wattled, and Brolga Cranes are predominantly grey at the time of fledging (possibly affording camouflage in upland habitats). Juveniles of all the other species are russet brown, providing cryptic coloration as a defense against predation. This is of particular importance to Siberian, Whooping, and Red-crowned Crane chicks, which are destined to be primarily white as adults. During the second year of growth, adult plumage gradually replaces the juvenile plumage. By the end of their second year, many juvenile cranes are difficult to distinguish from adults.

The varied features of the heads of the fifteen species are distinctive and diagnostic (see Figure 1.2). Crowned Cranes have elaborate tawny crests, bare cheeks, and a gular wattle. Unlike any of the Typical Cranes, mated Crowned Cranes preen one another’s head plumage. Demoiselle Cranes and Blue Cranes have completely feathered heads, and during display can elongate the plumes on the sides of the head. This is especially pronounced in the Blue Crane, and gives this species its unusual “cobra-like” appearance. Wattled and Black-necked Cranes are similarly able to raise the feathers on the sides of their heads.

All cranes except for the Blue and Demoiselle have bare red skin patches on their heads. Wattled and Siberian Cranes have the red skin on the front of the face. The red skin extends down the upper mandible to the nares, and in the Wattled Crane extends further down the front of the two fleshy dewlaps suspended from its cheeks. The Siberian Crane can expand the dorsal portion of its comb backward when displaying, and the Wattled Crane can extend its wattles downward. The red comb of the White-naped Crane covers the face to a point behind the ear. In the Brolga the red skin surrounds the back of the head, and in the Sarus Crane it covers the side and back of the head and continues down the neck several centimeters. In sharp contrast, the red comb in the remaining species is on the top of the head and expands down the back of the head during display.

The cranes that dwell in vast open wetlands, where the pressure from terrestrial predators is relatively low, are either entirely white (Siberian, Whooping, Red-crowned) or partially white (White-naped, Wattled), and are generally larger in size. Their size and bright white plumage makes these cranes conspicuous to conspecifics, and presumably facilitates defense of the breeding territory. The cranes that nest in smaller and/or forested wetlands are generally smaller and colored various shades of grey. Their size and plumage color may help these cranes to hide on their nests. At the onset of the breeding season, Sandhill Cranes and Eurasian Cranes paint their feathers with mud, staining them russet brown. Cranes painted in this way are much more difficult to see on their nests than unpainted cranes. At the onset of its breeding period, the Siberian Crane paints dark mud on the base of its neck, but this behavior is part of the species’ sexual display rather than a camouflaging exercise.

Cranes have ten functional primary feathers (most species have a vestigial eleventh) and from eighteen to twenty-five secondaries. With the exception of the Red-crowned Cranes, which has white primary flight feathers, the primaries of all the cranes—including the mostly white Siberian and Whooping Cranes—are black or dark grey. The dark pigment apparently strengthens the structure of the feathers, thereby improving their effectiveness on long migrations. Red-crowned Cranes may once have been predominantly non-migratory (as they are today in northern Japan) and could “afford” to sacrifice durability for display. The inner secondaries of many species are elongated, and when the wings are folded produce the impression of a prominent “tail” or “bustle.” This is especially pronounced in the Blue, Demoiselle, and Wattled Cranes. In most species, adults molt annually during the postbreeding period. The main flight feathers are lost at this time, rendering the birds flightless. Molting patterns, however, vary among and within species. The wing molt in Brolgas, Demoiselle, and Crowned Cranes occurs gradually, so that these species do not actually experience an extended flightless period.

Cranes take flight with a running start, usually into the wind, quickly gaining speed before lifting into the air with a push of the wings. When flap-flying, cranes flick their wings with a distinctive rhythm, pushing deliberately on the downstroke and rising rapidly on the upstroke. This rhythm is especially apparent when cranes are disturbed or otherwise eager to gain altitude quickly. Cranes, like storks, flamingos, geese, and swans (and unlike the large herons) fly with their necks extended straight forward. With their long legs trailing directly behind them along a single axis with their bills, necks, and bodies, cranes in flight present an elegant silhouette, resembling perhaps most closely that of the flamingos. In cold weather, cranes sometimes pull their legs in against their bodies. When landing, cranes approach the ground with their head semi-erect, wings extended, and legs dangling. They descend with wings and tail spread out and down, and with a final flapping of the wings alight in a normal standing stance.

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.

Behavior

Cranes are isolated on their territories during the breeding season and gregarious during the non-breeding period. All cranes are basically diurnal in their habits. During the day they forage, rest, and preen, attend to their young (during the breeding season), and socialize within flocks (in the non-breeding season). At night during the breeding season, cranes stay on or near their nests, brooding their chicks and standing guard against predators and other dangers. In the non-breeding season, cranes roost at night in more or less large flocks at traditional roosting sites.

The non-breeding season pattern of feeding by day and roosting by night is universal. Roosting provides security for the flock and offers juvenile and “single” birds opportunities for pair formation. Crowned Cranes roost in trees. The other species usually roost in shallow water, but occasionally use dry ground, mudflats, or sandbars. Within roosting flocks, each crane stands about a “peck distance” away from its neighbors. Cranes rest on one leg during the night, with the head and neck tucked on or under a shoulder. They defecate at regular intervals, and may switch from one leg to the other several times during the course of a night. One unfamiliar sound or alarm call from a flock member is all that is required for the birds to become alert and prepared to fly.

At dawn the cranes awaken, stretch, preen, and drink, then begin the day’s activity. They fly off in small groups to an open upland area near the evening’s roost—the post-roosting staging area. There they land and continue to preen. Cranes from several roosting sites might join together at the staging area. From there, initially in small groups but then in larger congregations, they will move to the day’s feeding areas.

Depending on the availability of food, cranes feed for extended periods in the early morning, then move to loafing areas. There they drink, preen, and engage in social displays to facilitate the pairing of unmated birds and to establish a pecking order among families. If temperatures are unusually hot, the cranes may escape the heat by spiraling skyward on rising thermals, eventually disappearing from view. Later in the day they return to watering and/or feeding areas, where they again feed, before moving to pre-roosting staging areas. Here they may again engage in social displays before flying to the evening’s roost, where they remain silent and still through the night unless disturbed.

The behavior of individual cranes can be divided into those activities that are self-directed and those that are undertaken in response to other cranes and other external stimuli. In addition to such fundamental activities as eating, drinking, sleeping, walking, and flying, self-directed activities include preening, bathing, shaking, stretching, ruffling, scratching, and feather painting. Behavioral studies of cranes have revealed some 90 or more specific behavioral patterns within these categories (Ellis et al. 1991).

The social behaviors of cranes include a wide array of visual displays. These ritualized displays serve many intra- and interspecific functions, and are often accompanied by vocal displays (see Section 1.3.4 below). Thirteen species have bare red skin patches on their heads, this too plays an important communication role. Cranes can vary the extent of skin displayed by contracting or relaxing the subcutaneous muscles, and can change the intensity of the skin’s color by engorging it. The color and exposure of the skin changes in response to various stimuli, and often accompanies other behavioral displays.

When cranes are aggressive, they assume an upright posture with their body feathers sleeked, thighs protruding, and the head features expanded. They walk in a stilted manner that has been likened to the goose-step of parading soldiers. They will follow this threatening posture with a variety of flaps, ruffles, bows, false preenings, stomps, nasal snorts, and growls. If a crane takes to the air in this emotional state, it will fly with rigid flaps with narrow arcs, with its feet and neck arched upward.

Cranes also engage in a variety of more circumscribed threat gestures. In the “crouch threat,” the crane bends its legs, lowers itself to the ground, folds its wings loosely against the ground and body, and places its head forward with the red patch prominent. In the “ruffle threat,” the crane raises the feathers of its neck, wings, and back, partially opens and lowers its wings, ruffles them alternately, and then lowers its bill to its lower breast or leg in a preening movement, often concluding this sequence with a low growl. In a “charge,” the crane points its neck and head straight down and lifts the feathers along its neck and back, holding this stance for several seconds. In all such threat displays, the red skin patch is bright and conspicuous (Voss 1976, Nesbitt and Archibald 1981).

A crane that is filled with fear (when, for example, confronting a predator) spreads its wings, arches forward as if ready to strike, and approaches the feared animal. A submissive crane, by contrast, lowers its neck, elevates it body feathers, and diminishes the threatening display of its head features by lowering the feathers and reducing the size of its comb. In this state of accommodation, the crane walks loosely and warily.

Of all the behaviors of cranes, none is as spectacular or as well known as their elaborate and enthusiastic dancing. Cranes are not the only birds known to dance; trumpeters and egrets, for example, engage in somewhat similar displays, although not so habitually. All species of cranes dance. It is apparently an ancient and complex behavior within the family, and serves a variety of functions (Masatomi 1994). Dancing is undertaken by even very young birds as a part of their behavioral and physical development. Unpaired subadult birds probably dance more than other age groups. For these birds, dancing facilitates the processes of socialization and pair formation. Among adults, dancing can be a form of displacement activity when cranes are nervous. Among pairs, it may serve to maintain pair bonds and synchronize sexual response prior to breeding. New pairs dance during courtship. Well established pairs, on the other hand, have less need to synchronize their behavior or to ward off rivals, and hence dance less often. Cranes do not always dance in response to apparent stimuli. Within flocks, it is often a contagious activity that spreads readily among the excited birds.

The pattern and intensity of dancing vary somewhat among the crane species, but the dances of all cranes consist of long and intricate sequences of coordinated bows, leaps, runs, and short flights. In the course of dancing, cranes often pick up with their bills whatever small objects—sticks, moss, grass, feathers—happen to be in the area, randomly tossing them into the air. Dancing in the smaller species, such as the Crowned and Demoiselle, tends to be the most energetic. Crowned Cranes perhaps dance most distinctively, bobbing their heads up and down prior to bowing, spreading their wings, leaping and flapping their wings, then often landing and circling one another. The sequence of courtship dancing among Blue Cranes has been observed to last from half an hour to as long as four hours (Van Ee 1966). The dance of the Demoiselle Crane has been described as “more balletlike” than those of the Gruinae species, with fewer, less theatrical jumps (Johnsgard 1983). Among the Gruinae cranes, dancing is slightly more deliberate, and punctuated often with high, flapping leaps.

Vocalizations

Cranes have evolved elaborate vocal displays to help them communicate with one another (see Archibald 1976a, 1976b; Johnsgard 1983). From barely audible contact calls to trumpet-like notes that can carry out across their extensive territories, cranes employ a variety of calls with different meanings. The typical volume and tone likewise varies widely from species to species. The Crowned Cranes have soft honks. The voices of the Anthropoides cranes are low and raspy, and those of the Grus species high-pitched and extremely loud. The Sandhill Cranes have a distinctive low-pitched rattle. The Siberian Crane’s voice is noted for its clear, flute-like quality.

The “languages” of the various cranes develop differently, depending on the nature of the adult voice, but in all cases the “vocabulary” begins to emerge early in life. Hatching chicks emit high-pitched peeps that persist through the first year of life. Newly hatched chicks quickly acquire a low, purring “contact call” to maintain regular contact with their parents and a louder, more insistent “stress call” to draw their more immediate attention. Within a day or so of hatching, chicks develop a “food-begging call,” a soft peeping that signals the parents to provide food. Within its first year of life, the young bird also learns the “flight-intention call” and “alarm call.”

By the end of the bird’s first year, the voice deepens and gains in strength and volume. The contact, flight-intention, and alarm calls are retained, while others develop. A “guard call” is generally given as an intraspecific threat. The “location call” allows the newly mobile bird to gain its bearings if visual contact is lost. The “precopulatory call” begins to be heard at about the age of 24 months. Fully adult cranes augment these calls with an assortment of other specialized vocalizations.

The most penetrating of all the calls in the vocal repertoire of cranes, and among the most spectacular of all avian sounds, are the special duets of mated pairs. The duets, known as “unison calls,” can last from a few seconds to as long as one minute and may be repeated regularly through the course of a day, though it is most commonly heard prior to the breeding season. Unison calling begins to develop in the second or third year of a bird’s life. The call serves a variety of important functions in the individual and social lives of cranes. It plays a critical role in the initiation, development, and maintenance of pair bonds. Unison calls of very young pairs are typically loosely coordinated compared to the highly synchronous calls of well established pairs. Unison calling allows the partners to come into breeding condition at the same time, and seems to be especially important in the ovarian development of females (Archibald 1976a, 1976b). The call is also used more generally to demarcate territories, to ward off potential intruders, and to respond to other threats.

Unison calls vary among the species. During sexual displays, Crowned Cranes lower their heads to shoulder level, inflate their gular sacs, and emit a long sequence of low booming calls. The Gruinae unison calls can be used to determine the sex of the individual cranes: the female usually has the higher-pitched voice. In the case of the Siberian Crane, the pitch of the call is the only outward diagnostic feature that allows one to distinguish males from females. In the Anthropoides and Wattled Cranes, the male and female assume distinct postures during the unison call. The female Demoiselle Cranes calls with her bill pointed upward, while the male calls with the bill held horizontal. Male Blue and Wattled Cranes elevate their wings at the conclusion of the unison call. All the Grus species except the Siberian Cranes have sexually distinct voices during the unison call, with the female emitting two or three calls for every call produced by the male. Male Sarus, Brolga, and White-naped Cranes always elevate their wings over their back and droop their primaries during the unison call. In the Eurasian, Whooping, Hooded, Black-necked, and Red-crowned Cranes, the amount of wing-posturing depends on the intensity of the aggression associated with the display.

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.

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.

Breeding

Cranes are generally monogamous. Mated birds stay together throughout the year, and typically remain paired until one bird dies. The age of sexual maturity has seldom been studied in wild cranes, but individuals in most species probably begin to establish pairs in their second or third years. Pair bonds form within flocks of non-breeding birds, or outside of the breeding season within mixed flocks. Many, if not most, pairs fail to breed successfully in their initial attempts. Among Sandhill Cranes, whose breeding biology has been most extensively studied, it has been shown that pairs that are unsuccessful in their first attempts to breed often dissolve, while successful pairs remain together (Nesbitt 1989). A strong pair bond is maintained as long as the pair successfully reproduces. However, if breeding efforts continually fail, the pair bond weakens and new mates are eventually taken. Most studies indicate that individuals do not successfully reproduce until they are between four and eight years old (Drewien 1973, Kuyt and Goossen 1987). Other species may share this general pattern.

Securing a breeding territory is a prerequisite of reproduction, and in areas where all available territories are occupied, young birds may need to wait to breed. Cranes of the northern temperate and arctic zones begin to establish breeding territories soon after their arrival from the wintering grounds, usually between mid-April and mid-June. The breeding seasons of cranes in the tropical and subtropical zones are much more variable, but generally coincide (and vary) with local rainy seasons. The breeding seasons of the Brolga and Sarus Cranes are closely associated with the distinct monsoons of southeast Asia and Australia. By contrast, Sarus Cranes in India and Wattled and Grey Crowned Cranes in southern Africa may breed throughout the year, although breeding usually peaks in response to localized conditions. Such variability is evident even within species. Sandhill Cranes breeding in Alaska produce almost all of their eggs in June. The breeding season for Florida Sandhill Cranes extends from December to June, with most eggs produced from February to April (Johnsgard 1983).

Breeding densities and territory sizes are poorly known for most cranes, but in some species are apparently quite variable in response to local conditions. In India, for example, nesting territories as small as one hectare are sufficient for Sarus Cranes if the quality of the water and vegetation is adequate and human disturbance is minimized (Gole 1989b, 1991b). In Cambodia, by contrast, Eastern Sarus Cranes establish extensive nesting territories in remote and isolated wetlands (Barzen 1994). Similarly, Eurasian and Sandhill Cranes have both adapted to the intensification of human settlement by establishing breeding territories in smaller, less natural wetlands. Once territories are established, pairs defend them through unison calls, threat postures, and attacks. The male is primarily responsible for defense, while the female is more involved in domestic affairs.

New pairs engage in long bouts of dancing before attempting copulation, whereas established pairs copulate with facility and without tension. The copulatory sequence can be initiated by either sex. One member of the pair will elevate its bill, arch slightly forward, and emit a low purr-like call. If the mate reciprocates with similar behavior, one (usually the male) will circle the other with exaggerated steps. The female then spreads her wings and the male approaches. With wings flapping he jumps on her back, and crouches. The female elevates her tail as the males lowers his, and their cloaca meet. The male then jumps forward over his mate’s head and performs threat displays for a few seconds. Both members of the pair then engage in a long sequence of preening. Cranes copulate for several weeks in advance of laying, usually before sunrise, although copulation can occur at any time during the daylight hours.

Both sexes participate in nest building. They select a secluded spot within their territory and unison call from that spot. Walking away from that selected spot, they toss nesting materials (mainly the stems and leaves of sedges, cattails, and other wetland plants) behind them over their shoulders. They return to the nest site and pull in the materials within their reach before walking slowly away from the nest and throwing additional materials behind them. As they repeat this sequence many times, large quantities of nesting material accumulate at the low platform nest, while a “moat” of water forms around the platform.

This nest-building behavior holds for those species that nest within wetlands. Two species—the Blue and Demoiselle Cranes—nest on dry ground. In both cases, eggs are usually laid directly on the ground. The pair may gather together some small stones or vegetation to provide protection and camouflage, but otherwise the nests show little if any preparation. In some portions of their range, Sandhill Cranes also nest on dry sites. On rare occasion, Grey Crowned Cranes will nest in trees (and have even been observed using the abandoned nests of other large tree-nesting species).

Cranes almost invariably lay two eggs. Exceptions are the Crowned Cranes, which regularly lay three and sometimes four eggs, and the Wattled Crane, which usually lays only one egg. In the Crowned Cranes, incubation begins after the clutch is complete. In the Gruinae species, incubation begins after the first egg is laid. Incubation in cranes averages between 28 and 32 days in most species (Johnsgard 1983). Wattled Cranes, at 33-36 days, have the longest incubation period. Species breeding in higher latitudes and at higher elevations tend to have the shortest incubation periods (<30 days). The female usually incubates at night; during the day the sexes exchange incubation duties several times. The non-incubating member of the pair usually flies to a favorite feeding area far from the nest. Crowned Crane chicks hatch synchronously, while Gruinae chicks hatch asynchronously. Wattled and Siberian Cranes have been observed to leave the nest after only the first egg has hatched, and typically only a single chick is raised in these species. In other species, the parents frequently rear two chicks, but one of these soon becomes dominant. If food is scarce, the weaker chick often dies. The extent to which multiple clutching can or does occur in cranes is little known. Repeat clutches have, however, been reported for Grey Crowned, Blue, Wattled, Sandhill, Eurasian, White-naped, and Red-crowned Cranes. Florida Sandhill Cranes have been observed laying third, and in one case fourth, clutches (Mirande et al. in press b). Cranes of the northern latitudes, including the Whooping and Siberian Cranes, experience such short growing seasons that even if they did produce second clutches, it would be difficult to fledge the young in time to undertake migration. In captivity, however, females of these and other species have been induced to lay repeatedly through the removal of the eggs, either one at a time or as clutches. In this manner, females have regularly produced up to ten or more eggs in a single breeding season. Adults care for their chicks continuously through the pre-fledging period. The length of the fledging periods varies widely among the cranes (Johnsgard 1983). Fledging periods are shortest in species that inhabit upland areas (Grey Crowned, Black Crowned, Demoiselle, Blue) and that nest in the high arctic (Siberian and Lesser Sandhills). In general, chicks of these species fledge at between 50 and 90 days. On average, the Demoiselle Crane has the shortest fledging period, usually between 55 and 60 days. Cranes that inhabit permanent wetlands in warmer climates (Wattled, Sarus, Brolga) have the longest prefledging periods. Chicks of these species usually fledge at between 85 and 100 or more days. The Wattled Crane has the longest fledging period at about 90-130 days.

The productivity of a given crane population can be measured in several ways, but is most easily determined by counting the number of juveniles in the flocks during the non-breeding period. In general, about 10-15% of a healthy population will consist of non-breeding juveniles.

Juvenile cranes remain with their parents throughout the non-breeding period. At the conclusion of the non-breeding period, juveniles either voluntarily leave their parents or are driven off by the adults after the family returns to the breeding territory. Unpaired juvenile birds gather in non-breeding flocks and are often nomadic throughout the breeding period. By the end of their second year, juvenile birds have usually initiated their own attempts to form pair bonds.

Movements

Cranes can be divided into two groups: migratory and non-migratory. Non-migratory cranes move relatively short distances between breeding and non-breeding areas, and gather in large flocks prior to the onset of the breeding period. Local and seasonal movements of varying lengths are typical of the lower latitude species—the Crowned Cranes, the Blue, Wattled, Brolga, and Sarus Cranes. In most cases, their breeding seasons and hence their movements are tied to, and vary with, the duration and intensity of the local rainy seasons. Local and seasonal movements are also characteristic of southern, non-migratory populations of some of the northern migratory species. This may be seen among populations of the Demoiselle Crane in northern Africa and Sandhill Cranes in Cuba, Florida, and Mississippi.

Such limited and seasonal movements are modest in comparison with the epic migrations of the northern cranes. Some of the migration routes stretch thousands of kilometers, during which the cranes must confront broad deserts, high mountain ranges, and other formidable obstacles. This achievement is even more remarkable for the northernmost species, the Siberian and Sandhill Cranes breeding in the arctic latitudes of Eurasia and North America. Among these populations, the young of the year must in one short growing season gain the size, strength, and endurance to join their adult companions on the long journey south.

Migratory cranes spend several days or weeks at premigration staging areas building up their fat reserves and integrating into life as a flock. Then they commence migration. After feeding for several hours in the early morning (often on a clear day with northwest breezes gusting) they rise into the sky, flap-flying in wide circles, lifted by thermals. After climbing as high as 2000 meters, they stop flapping, extend their wings, assume a “V” formation, and glide southward propelled by gravity and wind. After losing altitude, they repeat the cycle, again spiralling skyward and gliding south. While flying over land, they follow this pattern throughout the day. However, when forced to fly over water, where there are no thermals, they flap-fly in “V” formation. Crane chicks fly close to their parents and during their first migration south learn the migration route. While migrating, cranes call constantly. Their voices can often be heard even before the birds are spotted as tiny spots against the blue sky.

Migration has been studied closely in several species. Whooping Cranes, for example, have been shown to migrate as much as 800 km in a single day, although 300 km is more typical (Howe 1989). A review of Sandhill Crane migration data showed average flight lengths of 267 km/day, with individual flights of up to 740 km (Melvin 1982, Melvin and Temple 1982). Estimated flight speeds in Sandhill Cranes average between 23 and 83 km/h depending on wind speed and direction (Melvin 1982). This range is probably similar to that of most migratory cranes. Several crane migrations stand out as especially impressive. Eurasian Cranes from central Eurasia fly over the Himalayas at altitudes approaching 10,000 meters, while Demoiselle Cranes negotiate the passes in these highest mountains on earth. Other Demoiselles migrate across the wide deserts of the Middle East and northern Africa to wintering grounds in the upper reaches of the Nile basin. Siberian Cranes in the remnant Central population in Eurasia and Lesser Sandhill Cranes breeding in eastern Siberia undertake the longest of all crane migrations, in excess of 5000 km. The Siberian Sandhills move east across the Bering Sea into North America and continue south as far as northern Mexico.

An understanding of crane migratory patterns and behaviors is critically important in assessing the conservation status and needs of the different species. The problems cranes face during migration often constitute the “weak links” in the chain of conservation actions. Even if the cranes are secure in their breeding and wintering areas, they may be vulnerable to habitat changes at traditional staging and resting areas, and often face other dangers associated with human activity along the migration routes. Historically, for example, collisions with utility lines and accidental shooting have been important mortality factors along the Whooping Crane’s narrow migration corridor (Faanes and Johnson 1992, Lewis et al. 1992b).

Because migration is such a critical phase in the annual cycle of cranes, crane biologists have in recent years devoted much time and effort to the study of migration through banding, radio telemetry, and satellite tracking programs. Such studies have been especially important in developing recovery and reintroduction plans for the Siberian and Whooping Cranes. Because knowledge of migration routes is passed along to new generations of cranes by experienced older birds, conservation programs for these most endangered species emphasize the maintenance of existing routes and the development of new techniques for teaching migration. Perhaps most significant, the conservation needs of cranes during migration have necessitated extensive cooperation across national boundaries, sometimes among countries otherwise in conflict with one another (Lewis 1991, Shibaev 1995).

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