The gathering in late summer
Beginning in August, the native breeding pairs and their offspring meet at so-called gathering places, which are distributed at a distance of 20 to 50 kilometers across the distribution area.
First non-breeders and couples without breeding success arrive, then couples with their young. As from September onwards they mix with cranes from northern and eastern breeding grounds which take a rest in Germany.
Autumnal rest as a stopover before the migration to the wintering grounds
From mid-September the numbers of resting cranes in Germany pick up significantly because of the influx of cranes from Scandinavia and Eastern Europe. The cranes then concentrate in specific resting areas, which have attractive feeding grounds, and most important provide sleeping places for large numbers of resting cranes.
Suitable roost sites with surrounding feeding grounds are the basic requirement for the use of resting areas by cranes. The birds need large undisturbed shallow waters to spend the night. Waters with shallow water zones with a depth of 20-30 cm in which the cranes sleep at night standing on one leg and protected from predators are preferred.
Cranes react quite sensitively towards disturbances in the sleeping areas which is why many roost sites can be found in protected areas where durable undisturbed conditions are ensured. Disturbances unsettle the birds, separating parents from their young and causing additional energy use, which must be compensated for by an increased food intake. If stronger disturbances occur, roost sites might be abandoned completely.
The types of roost sites are quite varied, ranging from shallow lagoons and wind tidal flats on the Baltic Sea coast, natural and artificial lakes and reservoirs (lakes, ponds, reservoirs, flooded former mining areas, gravel pits, former peat-cutting areas), roost sites at flowing waters (old river arms, shallow littoral zones of rivers) and rewetted peatland and flooded meadows.
A fixed daily routine exists in the resting areas. The morning departure begins with dawn after the birds have made contacts by calling and have shaken their plumage. It often takes place much faster than the evening landing, which can last for one to two hours. The arrival and departure to and from the roost sites is carried out simultaneously in small groups, but also in large flocks of hundreds or thousands of cranes in large roost sites. The flights to and from the feeding areas take place in large energy saving chains or in wedge formation.
Large autumn resting populations and internationally important resting sites in Germany
Through regular simultaneous counts at all major roost sites the autumnal resting populations in Germany are annually determined. Thereby autumn resting populations of more than 350,000 birds in Germany have been determined in recent years. This number represents more than 90 % of the Western European flyway population which is why Germany has a huge international responsibility to protect the Eurasian cranes in Europe.
In autumn many cranes are concentrated in relatively few large roost sites. In around 20 of these places regular concentrations of up to 10,000 resting cranes have been determined.
Although there are more than 200 roost sites in Germany, especially in eastern Germany and in Lower Saxony, most cranes concentrate in three particularly significant resting regions in Brandenburg (Rhin - Havelluch) , Mecklenburg-West Pomerania (Darß - Zingst Bodden chain and island Rügen ) and Lower Saxony (Diepholzer Moorniederung).
Beside birds of the native breeding population mainly Eastern European (Poland and Baltic) and Finnish cranes use roost sites in Rhin - Havelluch northwest of Berlin. The main roost site are the Linum fish ponds and flooded meadows east of the ponds, where more than 70,000 cranes regularly rest at the same time in recent years. In the autumn of 2014 a record number of 123,000 cranes were recorded here. Linum is thus to be regarded as the most important inland resting place in Central Europe. Other important roost sites are located in close proximity to Linum in waste-water ponds near Nauen and in flooded grassland areas of Rhin - Havelluch, for example in Jahnberge and Senzke.
On the other hand up to 70,000 birds from Scandinavia (Sweden, Norway) can be observed at the same time in the resting region of the Darß - Zingst Bodden chain and island Rügen, which are increasingly joined by cranes from Eastern Europe and Finland. Shallow lagoons, wind tidal flats and islands mainly serve as roost sites here, whereas most cranes use the wind mudflats in the area of Pramort/Werder islands, the island of Kirr and Udarser Wiek overnight.
Only in the course of extensive rewetting in former peat cutting areas in the Diepholzer Moorniederung between Osnabrück and Bremen has the area developed into an internationally significant resting region, in which more than 100,000 simultaneously resting cranes have been regularly observed in recent years. Interestingly, many previously on the Baltic Sea coast of Mecklenburg-West Pomerania and in inland of Mecklenburg resting cranes use the Diepholzer Moorniederung as a further intermediate resting area before flying to wintering areas in France and Spain.
Energy reserves for the flight to the wintering grounds
For the partially several thousand kilometers long migration to the winter grounds, the cranes need large energy reserves, which are applied in form of fat deposits during the rest by high-energy food.
Daily flights to feeding areas will be made in the surrounding area of the roost sites. Stubble fields (in early autumn cereals, later in autumn and winter especially maize stubble) are specifically approached. In case of lack of appropriate stubble fields, foraging partly takes place on newly sown fields which then partially causes conflicts with agricultural interests.
Although the cranes prefer feeding areas near their sleeping grounds, they also accept distances up to 30 km if especially worthwhile feeding grounds exist there. In areas with a good food supply, hundreds to thousands of cranes gather on the site. A crane consumes 200 to 300 grams of grain daily.
Spring migration on the journey to the breeding grounds
In the course of February and March the cranes return from the wintering areas in France and Spain and take an in-between rest in Germany of up to several weeks before moving to their breeding grounds in Scandinavia and Eastern Europe. The most southerly based cranes, including birds of the native breeding population, usually reach Germany first. Subsequently the southern Scandinavian and finally at the end of March the mid-, Northern Scandinavian and north-eastern European breeding birds follow. This migratory behavior determines various migratory waves in Central Europe and is also referred to as leap-frog migration of the different populations.
The areas of the autumn rest are often also sought out for spring rest. In addition however there are also numerous special springtime rest areas, which are often located in river valleys and large peatlands with temporarily flooded meadows.
When the cranes withdraw from the wintering areas they don’t know which resting conditions to expect in Germany. Therefore it may happen that the birds come upon a late onset of winter with snowy fields and frozen waters. Only in rare cases do the cranes dodge back to the west or southwest. They usually try to persevere in the intermediate resting places, even if the conditions are difficult.
Cranes during their second or third year of life are not yet ready for breeding. Many of them even do not return to their breeding area, but spend the summer months at specific gathering places for non-breeders. Several of such places exist in Germany, well distributed over the whole breeding range. At such places, up to a few hundred non-breeders spend the breeding season. Many of these birds can be recognized by head coloration, which is not yet developed like in adult cranes. Especially the red cap on top of the head is often missing.
Although most non-breeders come from surrounding breeding areas, even some birds of breeding origin in Scandinavia and Eastern Europe join these flocks. The real origin can be only achieved by reading their coloring combinations.
Non-breeding adult cranes also gather at special moulting sites, where they replace their wing feathers (primaries and secondaries) and are therefore flightless for a few weeks. In opposite to most of the other bird species, crane change their flight feathers only every 3-4 years.
Help for resting cranes and affected farmers
Under particular circumstances cranes can cause damage on freshly sown agricultural fields. For this reason some farmers try to chase the birds away from their fields. As a result the cranes use up a lot of energy which is actually needed for the onward flight to the wintering grounds.
To help both farmers and cranes, government agencies (Ministry of Environment, Schwerin; State office of Environment, Nature conservation and Geology, Güstrow; Government Office for Environment and Nature, Stralsund) work in close cooperation with the affected farmers, with Crane Conservation Germany and the registered Association for the Protection and Preservation of the Crane resting area Rügen-Bock-Region and have established a system of special feeding sites.
In 1999 the Ministry of Environment financed 17 distraction areas with a size of around 350 hectares. For financial reasons only two to four special feeding sites in the Rügen-Bock-Region can be maintained nowadays. Crane Conservation Germany has additionally been operating different special feedings in the region since 1998 and supports similar projects e.g. in Linum area.
In order to reduce the disturbances and for visitor information during the resting season the use of crane rangers has been found to be very helpful (in the years 1999 to 2005 partly supported by the Ministry of Environment of Mecklenburg-West Pomerania and the Bingo Lottery, north German fund for environment and development). Nowadays the project is partly supported by the Schneider-Menden-foundation and the Elisabeth and Bernhard Weik fund.