HISTORICAL AND EXPERIMENTAL STUDY OF HOMING. 59 



BEARING OF THE PRESENT STUDIES UPON THE GENERAL PROBLEM 

 OF HOMING. 



We shall not here attempt to summarize our results in detail, but in the 

 present volume there are two other papers (see p. 61 and y>. 87) which throw 

 some light upon the problem of distant orientation. We shall incorporate the 

 main results of these papers with the results obtained from the present study 

 and trace the bearing of the whole series upon the general problem of homing. 



(1) Lashley (p. 61) has shown that the problems of pro.ximate orientation 

 are relatively simple and straightforward. On the island of Bird Key the 

 terns make their adjustment to the nest, mate, young, etc., on the basis largely 

 of visual habits. Kinaesthetic habits are involved, but to a less e.xtent. 

 There is no evidence of any remarkable or unusual sensitivity, nor of the 

 functioning of any hypothetical sense-organ. 



(2) The present paper seems to call for a separation between proximate 

 orientation and distant orientation. We have never in the work on the hom- 

 ing pigeon been able to obtain sufficient evidence to reach such a conclusion. 

 This arises from the fact that the pigeon has always been trained over a large 

 part of its route. Such training allows the formation of numerous visual 

 habits; hence all orientation maj' be looked upon as being of the proximate 

 kind (we do not affirm such to be the case, however). The work at Tortugas, 

 on the other hand, has placed us squarely before the problem (to take the 

 limiting case) of accounting for the return of an untrained bird from a distance 

 of 800 to 1,000 miles over a body of water which apparently can not offer any 

 basis for controlling flight direction. 



Note. — Two suggestions looking toward a simple ex])Ianation of the homeward flight of 

 the terns have been made: (1) that the Hatteras birds simply followed the coast-line back 

 to Key West, from which point they could sec (?) Tortugas, and further, that they followed 

 the coast-hne south rather than north by reason of the fact that the former direction led 

 them into warmer regions, which they instinctively seek; (2) that the Galveston birds and 

 those released en route were aided by a well-marked water-current which sweeps around the 

 coast of Texas, Louisiana, Alabama, Florida, and out past Tortugas through the Straits of 

 Florida. This main current differs in color both from the surrounding and more stationary 

 water, and from the return current, which runs nearer the coast hne. We are indebted to 

 Dr. W. J. Humphreys for the latter suggestion. Interesting as these suggestions are, it re- 

 mains to be said that the explanation offered by (1) does not bear at all upon the more diffi- 

 cult Galveston flight. Dr. Humphreys' suggestion (2) meets with difficulty when we remem- 

 ber that some of the (successful) birds were released at night and that all of the birds were 

 out from 4 to 20 nights. Furthermore, they had to win their way through rain, haze, and 

 cloudy weather. Nor were aU the birds which returned released at Galveston. They home 

 equally well, no matter at what point between Galveston and Tortugas they are put down. 

 Then, too, the difference in brightness or color between the current in question and the 

 surrounding water depends largely upon the position of the sun with respect to the observer. 

 Apparently the birds flew steadily (zigzagging, of course, for food) from morning to night 

 (if not through the night), and during only a part of this time would the sun have a position 

 such that the current could offer a difference in color or in white value. Even granting the 

 existence of such data, the question as to why the bird follows the current towards the Straits 

 of Florida rather than in the opposite direction is pertinent. There can be no question of 

 any permanent temperature differences among these regions during May and .June, nor 

 can theae be any question of chance, when the whole group of birds is considered. 



(3) Mathematical considerations show that at such distances the goal 

 can not possibly (directly) visually stimulate the bird, even granting absolute 

 visual acuity and complete absence of haze, etc. The vertical height to which 

 the bird would have to fly in order to overcome the sphericity of the earth is 



