Northern Prairie Wildlife Research Center
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.