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with considerable accuracy. After release at Harviala in Finland, the birds correctly headed south until they arrived at the Gulf of Finland. They then seemed completely baffled by the wide stretch of sea, and promptly returned to the place where they were released. This snowed the same queer attachment to an entirely new locality. Many experiments have been carried out on storks, which are particularly suitable birds for this type of investigation, being large migrant birds, easily identified, and associating with man in their nesting areas. Polish scientists have shown that storks nesting near Lwow, in central Poland, could get back from Warsaw 187 miles north-west, Bukharest 415 miles south, and Palestine 1420 miles south. All the birds had young in the nest and were ringed, and colour-marked by dyed feathers, for identification. A recovery of 75 per cent was obtained of the total of released birds. The rate of return varied from 103 miles a day for the Bukharest birds, to 116 miles a day for the Palestine birds. The behaviour of the birds on release was identical in all cases ; they took time to clean and preen their feathers, then took wing, circled, and headed straight for home. The sense of direction seemed unerring, but we cannot yet tell through what part of a bird's physiological or psychological make-up this sense is operated. There have been many suggestions to explain it, the most persistent one being the " terrestrial magnetism " theory. This theory suggests, that birds are able to sense, in some way, the direction of the lines of force of the earth's magnetic field, some people even suggesting that each part of the earth's surface, having as it has a characteristic of terrestrial magnetism known as the " dip " at that place, can be pin-pointed by a magnetic recording mechanism somewhere in the bird's body. The theory was supported by nebulous reports of homing pigeons which, released near large broadcasting stations, were said to be unable to orientate themselves in the neighbourhood of the aerials. Once again, the theories have failed to stand the hard facts of controlled experiments, Thus, the same Polish scientists tested the homing abilities of storks which had magnetised iron bars fixed to their heads, of such a strength that they would completely over-ride any effect of the earth's magnetic |
