Nocturnal Songbird Migration

Abstract

WE would like to comment on Evans's criticisms¹ of our recent article² concerning the influence of wind on the direction of nocturnal songbird migration. We pointed out that problems in identifying bird types from radar echoes may have contributed to the controversy about passerine nocturnal migrants compensating for wind drift. Evans claims that there is no difficulty in distinguishing between radar echoes from small land birds and those from waders and waterfowl in England. But his own radar work in Northumberland clearly demonstrates that this is not the case. In 1963 he attributed radar echoes of migrants in October and November to songbirds (wheatears, icelandic redwings, robins and song thrushes) and used these data to support his hypothesis that birds fly on fixed tracks, thus correcting completely for the drifting effects of the wind³. In a later article⁴, there is the following statement (pages 54–55): “However, records from October and November are excluded from this paper, because echoes from waders are difficult to distinguish from those from larger passerines, for example migrant thrushes, whose movements often overlap in timing, area of departure and direction with those of waders”.