Page:The Migration of Birds - Thomas A Coward - 1912.pdf/113

Rh the letters indicate the direction of the wind, the figures its speed in miles per hour. The last one in the table, observations made at Brighton on September 20th, is particularly useful. The conditions on this date were anticyclonic, and favourable to migration. At 400 feet above the sea the wind was blowing at 5 miles an hour; at between 5000 and 6000 feet its force was 20 miles per hour. What then would happen to a bird leaving Brighton for say the Spanish Peninsula? If it flew at 20 miles an hour towards the French coast about Dieppe, it would meet the wind blowing at 5 miles an hour, and take between five and six hours to reach the coast, head to wind. If it rose to the height of 3000 feet it would meet» a wind blowing at the some speed as it was flying, and it could make no headway. If, however, it flew in a south-westerly direction the more it turned westerly the farther it would drift down channel towards Normandy or Brittany, and be carried out to sea! But this is exactly what would not have happened, for on this date a feeble cyclonic system was approaching from the Atlantic and extending its area of influence over southern England. In the Channel the bird would meet westerly winds which would bring it safely to the Brittany shores, or if it missed them, to the western shores of the Bay, where the wind was actually from the north. I mention this