Strong winds from opposing directions, with heavy rain, provide evidence of vigorous convergence, consistent with the deep depression shown by the Daily Weather Report as centred in this area on the morning of the 6th.The same author, writing of Heligoland ( Lockley 1938), describes 20 October 1936, when 752 birds were ringed, as--
. . . a good day for birds. The day before (i.e. 6th May, 1929) . . . sharp gale from SE. . . . five hours' heavy rain . . . roaring wind from NW., and ending with a fresh south-wester. This rude boxing of the compass had upset migrating birds. They had come down on the island in their hundreds, bewildered and weary. Swallows and willow-warblers had predominated. . . .
A deep depression was again involved.A final example comes from Canada, where at Delta in Manitoba, in April 1954, one of the biggest goose migrations on record at the station took place on the day following the worst blizzard of the year ( Hochbaum, 1955; I am indebted to Dr. G. V. T. Matthews for this reference). It is suggested that all four of these examples may be interpreted as accumulation of migrating birds in the vicinity of zones of convergent wind-flow.Following the work of Williamson ( 1955, etc.), considerable evidence of the part played by day-to-day changes of wind and weather in the varying manifestations of bird migration has accumulated in recent years; and the final suggestion arising from the consideration of this series of model 'locusts' and 'birds' is that perhaps the same processes of synoptic meteorology, which appear to dominate and largely to determine the whole pattern of 'migration' of the Desert Locust, may also account for some of the details of the day-by- day embroidery of the basic pattern of the migration of birds.
. . the best day of the year . . . due to a sudden change in the wind, northerly airs having been replaced suddenly by a whole Sale from the SW.
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