N E A R L Y A L L OF 2,546 Swifts Apus apus caught at Rye Meads Sewage Purification Works, Hertfordshire, in the late spring and summer of 1962 (845) and 1963 (1,701) were weighed and examined before being ringed and released. The pattern of the weights was then determined. In 1962 large numbers were trapped during particularly unseasonable weather. Analysis of these weights revealed significant l...

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