Editing Common crane (section)

===Breeding===
[[File:PSM V09 D158 Crane throat structure.jpg|thumb|The long coiled [[Vertebrate trachea|trachea]] (TR) penetrating the [[Keel (bird anatomy)|sternum]] (S, K, A) produces the trumpeting calls of the crane. L on the left - [[Lung#Avian_lungs#Avian lungs|lungs]], LA - [[larynx]], L on the right - [[tongue]].]]
This species usually lays eggs in May, though seldom will do so earlier or later. Like most cranes, this species displays indefinite monogamous pair bonds. If one mate dies, a crane may attempt to court a new mate the following year. Although a pair may be together for many years, the courtship rituals of the species are enacted by every pair each spring. The dancing of common cranes has complex, social meanings and may occur at almost any time of year. Dancing may include bobs, bows, pirouettes, and stops, as in various crane species. Aggressive displays may include ruffled wing feathers, throwing vegetation in the air and pointing the bare red patch on their heads at each other. Courtship displays begin with a male following the female in a stately, march-like walk. The unison call, consists of the female holding her head up and gradually lowering down as she calls out. The female calls out a high note and then the male follows with a longer scream in a similar posture. Copulation consists of a similar, dramatic display.

<gallery mode="packed" heights="150px">
File:Baltsende en parende kraanvogels-Stichting Natuurbeelden-170687.webm|pair showing the mating behavior
Grus grus egg - Niitvälja bog.jpg|Egg on nest
Common crane chick swimming alone on the Tidan River, Sweden.jpg|Chick on the [[Tidan|Tidan River]], Sweden
Common crane (Grus grus) juvenile Oppdal.jpg|Juvenile in [[Norway]], showing developing adult plumage
</gallery>

The nesting territory of common cranes is variable and is based on the local habitat. It can range in size from variously {{convert|2|to|500|ha|acre|abbr=on}}. In common with sandhill cranes (and no other crane species), common cranes "paint" their bodies with mud or decaying vegetation, apparently in order to blend into their nesting environment. The nest is either in or very near shallow water, often with dense shore vegetation nearby, and may be used over several years. The size and placement of the nest varies considerably over the range, with Arctic birds building relatively small nests. In Sweden, an average nest is around {{convert|90|cm|in|abbr=on}} across.

The clutch of the common crane usually contains two eggs, with seldom one laid and, even more rarely, 3 or 4. If a clutch is lost early in incubation, the cranes may be able to lay another one within a couple of weeks. The incubation period is around 30 days and is done primarily by the female but occasionally by both sexes. If humans approach the nest both parents may engage in a [[distraction display]] but known ground predators (including [[Dog|domestic dogs]] (''Canis lupus familiaris'')) are physically attacked almost immediately.

New hatchlings are generally quite helpless but are able to crawl away from danger within a few hours, can swim soon after hatching and can run with their parents at 24 hours old. Chicks respond to danger by freezing, using their camouflaged brownish down to defend them beyond their fierce parents. Young chicks use their wings to stabilise them while running, while by 9 weeks of age they can fly short distances. The adult birds go through their postbreeding moult while caring for their young, rendering them flightless for about 5 to 6 weeks around the time the young also can't fly yet. According to figures of cranes wintering in Spain, around 48% birds have surviving young by the time they winter and around 18% are leading two young by winter. By the next breeding season, the previous years young often flock together. The age of sexual maturity in wild birds has been estimated at variously from 3 to 6 years of age.