"There is recent evidence that many birds find their way 

 not by relying on a special 'sense of direction or other 

 unique sensory mechanism, but rather by an ability to 

 perceive environmental cues which are within the scope 

 of the receptors common to all higher vertebrates." Don- 

 ald R. Griffin and Raymond J. Hock (1949) 



14 



Magnetic and Radio Fields 



Since the twelfth century man has depended so on 

 the compass that some students quite naturally have attempted to explain 

 the homing of birds as a biological awareness of the magnetic pole ( Viguier, 

 1882). Thomson (1942:176) points out that "no evidence of any magnetic 

 sense has ever been obtained, however, despite a good deal of experiment." 

 Rowan (1931:84) remarks that 'magnetic sensibility is an intriguing hy- 

 pothesis, but the best we can say for it is that it never has been disproved. 

 There is no evidence in its favor." Griffin's attempts (1944:25) "to train 

 three homing pigeons to respond to a magnetic field were entirely negative, 

 although the field was of considerably greater intensity than the earth's 

 field." Henderson (1948) serving on a Canadian minesweeper during the 

 last war, had abundant opportunity critically to observe the behavior of 

 gulls, ducks, and other migratory birds exposed to intense magnetic fields 

 set up by the vessel, and he found that "birds appeared to be supremely 

 indifferent to magnetic field, even at the sudden beginning of magnetic 

 pulsing." Yeagley ( 1947, 1951 ) conducted experiments testing the homing 

 ability of pigeons wearing small wing magnets but found no "indication 

 that the experimentally induced pulsing magnetic field moving across the 

 birds' bodies in flight confused them insofar as navigation was concerned." 

 Van Riper and Kalmbach (1952), in a meticulously planned experiment, 

 found homing pigeons unaffected by wing magnets. Matthews (1951a) 

 and Kramer (1949, 1950) likewise had negative results with magnetic tests, 

 as did Gordon (1948) in his earlier studies. 



Besides the lack of evidence in favor of a magnetic awareness, there is 



186 



