HISTORICAL AND EXPERIMENTAL STUDY OF HOMING. 13 



HABIT THEORIES. 



THEORIES AND EXPERIMENTS ON THE FUNCTION OF VISION IN HOMING. 



Hachet-Souplet* advances some positive proof that vision furnishes the 

 data for distant orientation. He has made a number of experiments with 

 travehng cotes. These travehng cotes are used quite commonly in France and 

 in Belgium. We give here his account of some recent experiments: 



After having put in a basket and left at a point (A) a part of the inhabitants of the 

 traveling cote, the exterior aspect of which was known to the birds, we sent the carriage 

 forward to a distance of about 5 km. from the point A. The pigeons, released as soon as 

 the carriage arrived at B, found it very rapidly. We have repeatedly tested this, increasing 

 the distance from A to B up to 10 km. We have found it necessary to place the carriage, 

 which i.s supplied with a large drapery, in an open territory. The birds have always found 

 it. If this distance of 10 km. is passed we begin to undergo losses of the birds, and we have 

 never obtained returns beyond the distance of 12 km. It is necessary to consider here that 

 the birds know nothing of the entourage of their cote. If, proceeding otherwise, we make 

 the carriage stationary on its arrival at the new place and allow the birds to reconnoiter 

 the immediate environs before placing them in the basket (in accomplishing this we attach 

 the birds to the carriage by cords which allow them to fly up to a height of 35 m.; in 

 order to avoid accidents one attaches only two birds at a time) we have been able to obtain 

 on the first attempt, without preliminary training, a return of 100 km. This was accom- 

 plished by 8 pigeons. At the time this test was made we had sent to the same point of 

 release (100 km.) 10 pigeons which had been brought in the caravan without being allowed 

 to leave it (that is, they were not allowed preliminary observation). All 10 of the birds were 

 lost. This experiment was repeated with the same result several times. 



Hachet-Souplet supposes that the view from the carriage supplied the birds 

 with a set of "visual memories" which they could utilize — i. e., that orienta- 

 tion is effected through sight. With regard to the limits within which a bird 

 can return through direct sight he states that the limit is much further than 

 it is at present believed to be. He considers what he calls the "law of the 

 diminution of the necessary intensity of the excitant which determines the 

 reaction." (He has in mind here, of course, decrease in the intensity, etc., of 

 the visual stimulus through distance.) Naturally one would expect that a 

 visual excitation {i. e., one accurate enough to assist in orientation) would 

 cease at the point where a clear image ceased to be formed on the retina. But 

 the disappearance of a clear image on the retina does not mean a lack of visual 

 excitation, according to Hachet-Souplet; for, as the bird gets further and 

 further away, the clear image gives place to an "imprecise" visual impression, 

 corresponding less to the perception of form and determined colors than to a 

 sense of "dejd vu familier." The impression becomes "mixed" in the sense 

 that it bears elements of many different objects. He likens the view that the 

 bird gets of a distant goal to our view of a distant forest. When one looks at 

 a distant forest one does not see the leaves, and not even the trees separately. 

 This author thinks that the " mixed impression" is serviceable at a much greater 

 distance than is ordinarily supposed, and he states that refraction adds greatly 

 to the distance at which it may function. He maintains that all of the 

 calculations showing the heights to which birds must fiy to see the cote have 

 been exaggerated because they have not been properly corrected for refraction. 

 Given the curve for refraction, it will be possible for the birds to obtain these 



♦Hachet-Souplet: VI. Cong. Int. de Psy., 1909, p. 063. 



