1950, British Ecological Society, The Journal of Animal Ecology, Blackwell Science, page 66,While the migrations of many butterflies now appear to be twice-yearly movements away from and back to the same areas, they differ from those of birds in ...
1992, Rigas Doganis, The Airport Business, Routledge, ISBN 0415078776, page 101,At the twice-yearly IATA timetable co-ordination meetings, airlines from ...
