Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Rydzewski W. (1956) The nomadic movements and migrations of the European Common Heron, Ardea cinerea L. ARDEA 44 (1-3): 71-188
This study is based on 4,187 selected recoveries of Herons ringed by all the European ringing schemes. The 'Heron Year' is divided into three periods: nomadic, migratory, and returning, and each population is discussed accordingly. Particular emphasis has been laid on the directions taken and the distances covered by the birds. The following populations have been discussed in detail: Swedish, Norwegian, Danish, North British, South British, French, Belgian, Dutch, NW German, NE German, Central German, South German, Swiss, North Polish, 'Central' Polish, E Prussian, and Hungarian. In the general discussion the following problems have been examined: the nomadic period, the migration, the winter quarters, the homeward migration, the return & resettlement, the migratory habit in Herons. The following conclusions have been drawn. 1. The nomadic period begins as soon as the young birds can fly and lasts to the middle of September. Topographical obstacles influence the movements. The open sea, even as narrow as the English Channel, is a serious obstacle for the western continental Herons. The mountain chain of an altitude of over 1.000 metres seems to be an insuperable obstacle. Almost any direction may be attempted but contrary to previous statements the SW direction predominates. The areas covered increase steadily: June-150 kms radius, July-200 kms, August-250 kms, and September-300 kms. The search for food and the tendency to reduce the density of birds in the vicinity of a heronry would appear sufficient causes to account for the nomadic movements of the Herons. 2. The migratory period extends from mid September to mid winter. Only the Atlantic coastline is a barrier. The standard direction is the SW. It is used by the Swedish and Danish birds in over 70% of cases, by the 'coastal' populations in 50%-60%, and by the 'inland' populations in 25%-45%. The Norwegian and British Herons are exceptional (below 20%). The migration proceeds on a broad front, without leading lines. The causal factor of the migration is an internal, inherited migratory urge independent of external factors. 3. The wintering area comprises the Iberian Peninsula, central and southern France, Italy, the Mediterranean islands, and southern part of the Balkan Peninsula, as well as the northern part of Africa from Morocco to Libya. Subsidiary areas lie in West Africa. The author supposes that the winter quarters south of the Sahara are the original and the North African ones would be the later or secondary ones. Many birds winter at home or in intermediate areas. 4. Homeward migration proceeds on a broad front towards NE. It is possible that some western Herons return from Africa through a changed route via Italy. Some birds do not return but remain either in their winter quarters or en route. 5. Return to the natal heronries is proved by many birds. The older birds are more attached to home than the juvenile. The resettlement of Herons in strange colonies is proved in several instances. The distances vary from 27 km's to 490 km's. 6. The European populations may be divided into Continental, British, and Norwegian ones. Among the continental populations the Swedish, Danish, and 'coastal' ones are the greatest migrants, in the 'inland' populations the migratory habit is weaker. The sedentary habit is most marked in British Herons. The Norwegian population takes an intermediate place. The migratory urge reveals itself in the SW direction of migration and in the distances covered by birds. The migratory habit in European Herons seems to be a primary one while the sedentary habit is a later consequence of adaptation to climatic changes. Both habits, i.e. the migratory and the nomadic one, are equally ancient but their present status is different. The migratory one is in course of weakening and it is possible that in the distant future the Heron will be a sedentary species. The nomadic habit will be apparently maintained and will replace the long migration.


[close window] [previous abstract] [next abstract]