In Sweden, lake Hornborgasjon in April becomes the main assembly site before the adults disperse to their nesting sites. The fantastic ballet show of the Cranes during their courtship at Hornborga is famous throughout Europe. This same ballet can be seen between pairs here in France when on the ground, especially so just prior to flying North, although not on such a large scale.
Map above shows main spring migratory corridors across France.
In August and September thousands of cranes gather on the Swedish island of Oland from here they can cross the Baltic sea to the Island of Rügen where around 30,000 birds gather in October with about another 15,000 on the German mainland with the birds moving through in groups with continuous arrivals and departures, birds staying perhaps two or three days, possibly longer. As with all things natural nothing is precise with much being determined by weather and temperature along with access to food on the ground that is most important both during migration the places they over winter. What we can say is that the main migration is October to December with small movements from September and possibly continuing sporadically until early Spring and that therefore the “migration” is both gradual and partial, spread out over several months with them wintering at various locations stretching from north-eastern France (Lorraine and especially Champagne) to Morocco with various locations in between, however the majority will end up in Spain with most of them in the large wintering areas of Extremadura.
The Common Crane is one of the largest birds in Europe with a wingspan of 2 meters and a weight of 4 - 6 kg. Overall plumage is a nearly uniform grey with long legs and neck. Adults are distinguished by the black and white contrast to the neck and head, marked with a bright red spot and young Cranes have a brownish plumage that they keep for a year that gradually changes to adult plumage. On the ground they appear to have a fluffy puffed up tail that is actually formed by the last wing feathers that are very elongated.
Cranes are very sociable and gregarious during their migration and wintering when they can form very large groups, especially on the ground which can be many tens of thousands. They are however extremely territorial when nesting.
Breeding grounds are situated principally in Russia, Finland, Sweden, Norway and the Baltic countries where large solitary nests using dry grass are constructed on the ground situated in large areas of marsh or swamp forests that can occupy up to several hundred hectares.
Here a couple will produce one or two eggs in May that take about 4 weeks to hatch. Shortly after hatching, the chicks are able to follow their parents and sneak into the swamp in search of insects, molluscs and small vertebrates which then make up the bulk of their food. Thereafter, they consume more plants: tender herbs, aquatic plants and berries. The young start to take to the air at around two months between mid July and August when they have to prepare for their first migration when they will stay with their parents until their return in the spring. Sexual maturity isn’t actually achieved for between 3 and 5 years when, assuming they find a partner, they pair for life.