ROOK AND JACKDAW MIGRATIONS OBSERVED IN GERMANY, 1942–1945

Summary. Observations were made on Rook and Jackdaw migrations by a number of British ornithologists in Germany during the years 1942‐45, chiefly at Dössel, Westphalia; Sagan, Silesia; and Eichstätt, Bavaria. The two species were found to migrate jointly, flocks being either mixed or of Rooks alone. Rooks outnumbered Jackdaws by about nine to one, except in the opening days at both seasons. Comparative statements are given of the dates, duration and peaks of some spring and autumn passages, and of recorded numbers. Two main waves of migrants were usually apparent. Two principal kinds of passage were noticed–“high passage”, in which flocks flew above 600 ft. and in good formation, and “low passage”, in which birds straggled below 100 ft., often in long “processional streams”. The highest flocks flew at 3000 ft. at least. Both kinds of passage were interrupted by halts on the ground, and the diving method of descent for this purpose and the methods of departure after halts are characteristic. The most interesting behaviour was “gyration”, in which the birds flew round and round collectively in slowly ascending spirals before setting course. The several activities of descent, take‐off and direct passage fluctuated considerably throughout daylight, and the pattern of these fluctuations in spring at Dossel corresponded approximately with the pattern in autumn at Eichstatt. Marked intensity of descent in early morning suggests the possibility of night flying, of which, however, there was no direct evidence. The call of migrants was distinct from that of residents. It is suggested that “gyration” enables birds which have temporarily lost sense of direction to recover it.