Cranes: Gruidae

Many cranes are migratory, meaning they travel from breeding (summer) areas to wintering areas each year. Some species travel thousands of miles during their migration. In many species, breeding occurs during the wet season. During the non-breeding dry season, cranes may gather in large flocks, or groups of birds. This flocking behavior is believed to allow individuals to find mates.

Cranes have loud, trumpeting calls. These calls are used to communicate a wide variety of messages to individuals of the same species. A contact call is given between individuals that know each other, such as a crane and its mate or a parent and its chicks. Other calls used by cranes signal aggression, an intention to fly, pain, or a warning of danger. The unison call is made simultaneously by a male and female pair and is intended to warn other cranes away from their territory.

In addition to calls, cranes also have elaborate displays, characteristic motions used in communicating with others of the same species. These displays can involve raising feathers around the head, unique motions of the bills, and exposing and/or changing the size of red skin patches on the heads that are normally covered by gray feathers. Displays are often used to threaten other cranes or to express submission to a more dominant crane. Conflicts that are not resolved by a threat display proceed to a ritualized fight that will not seriously injure either crane. The ritualized fight involves leaping up with the legs folded, and then using the legs to push at the other bird's breast. Conflicts between cranes are particularly common during flocking, when large numbers of birds are gathered together.

Cranes are monogamous (muh-NAH-guh-mus), a single male breeds with a single female. Cranes often mate for life. They are also territorial; a pair of cranes will defend their area of land, or territory, against other cranes of the same species. Nests are built within the wetland or grassland habitat. Females generally lay two eggs at a time and both parents incubate, sit on and warm the eggs for chick development. Eggs hatch after about a month, and offspring are able to fly after about two or three months. However, young cranes usually remain with the parents until about nine months of age. If both eggs hatch, one of the crane offspring is generally dominant to the other, that is, it has higher rank and receives more food from the parents. In the majority of cases, only the dominant offspring survives from each nest.