Northern Prairie Wildlife Research Center
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.