On migrations of Hemianax ephippiger (Burmeister) and Tramea basilaris (P. de Beauvois) in West and North-West Africa in the winter of 1975/1976 (Anisoptera: Aeshnidae, Libellulidae)

H. ephippiger migrated along the Atlantic coast of Senegal and Mauretania in January 1976. An analysis of the movement is made, and its causes and consequences are discussed. It is suggested that specimens found in Iceland and the British Isles are more likely to have come from West Africa, moving with the air current between the Agores and Iceland, than from the Mediterranean. Swarms seen in Italy, because of the period of their appearance, must, conversely, have come from the steppes of North Africa. T. basilaris was seen in high numbers in Dakar, Senegal in January 1976, and a dense migratory swarm was observed in March 1976 along the River Niger near Segou, Mali. Possible relations with the migratory behaviour of Libellula quadrimaculata L. are discussed.