will destroy the homing instinct of the racing pigeon, but experiments 

 in the form of delicate operations, or closing the ears with wax, prove 

 such a serious shock to the sensitive nervous system of the bird that 

 they cannot be considered as affording conclusive evidence. Several 

 years ago careful studies were made of the homing instinct of the sooty 

 and noddy terns, tropical species that in the Atlantic region reach their 

 most northern breeding point on the Dry Tortugas Islands, off the 

 southwest coast of Florida. They are not known to wander regularly 

 any appreciable distance farther north. It was found that some were 

 able to return to their nests on the Tortugas after they had been taken 

 on board ship, confined in cages below decks, and carried northward 

 to distances varying from 400 to 800 miles before being released. Land- 

 marks of all kinds were entirely lacking, and the birds certainly were 

 liberated in a region in which they had had no previous experience. 



Possibly the "homing instinct" as shown by these terns, by the man- 

 of-war birds that are trained and used as message carriers in the Tua- 

 motu, Gilbert, and Marshall Islands, and by the homing pigeon, is not 

 identical with the sense of perceptive orientation that figures in the 

 flights of migratory birds. Nevertheless, it seems closely akin and is 

 probably caused by the same impulses, whatever they may be and 

 however they may be received. It should be remembered, however, 

 that while homing may involve flight from a point that the bird has 

 never before visited, the flight is always to a known point — that is, 

 the bird's nest — while, on the other hand, the first migratory flight 

 is always from the region of the bird's birth to a region it has never 

 before visited. The spring migration might, of course, be more nearly 

 considered as true "homing." 



Some students have leaned strongly toward the possible existence 

 of a "magnetic sense" as being the important factor in the power of 

 geographical orientation. The theory that migratory birds might 

 be responsive to the magnetic field of the earth was conceived as early 

 as 1855, when some experimental work was done in Russia, and nearly 

 60 years later in France. Recently investigations in this field have 

 been conducted by Yeagley (1947) and by Gordon (1948) with dia- 

 metrically opposite results. The idea carries with it the implication 

 that contained in the bird's body is an organ that is sensitive to the 

 effect of its motion through the vertical component of the magnetic 

 field and to other related factors. In the tests by Dr. Yeagley, 20 young 

 homing pigeons were given training flights to their home loft from 



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