14 HOMING AND RELATED ACTIVITIES OF BIRDS. 



"mixed impressions" at all the ilistances from which they ordinarily home. 

 It is well to note (1) tliat it is not during the forward journey that these "mem- 

 ories" are graven in the memory of the !)ird (they come from previous flights), 

 and (2) that these memories which are able to be considered as effective are 

 not memories of precise form, but of .s]iecial impressions of dejd vu. 

 Hachet-Souplet gets around many of the facts by denying them. He says: 



One fact which appears out of harmony with the theory of orientation by view are the 

 returna from 800 to 1,000 km. which pigeons have effected without training in a direction 

 entii'oly unknown to them, but these facts are controverted for the most part and are 

 always exaggerated. 



Where the facts are incontestable he would explain them on the basis of 

 chance. Most of the flights which are considered in our own paper are far 

 beyond this limit set by Hachet-Souplet.* 



Schneider'sf conclusions are numerous, the one of chief interest being as 

 follows : 



The assumption that the carrier pigeons possess an inborn sense of direction is an error; 

 for if this assumption were true, then the young pigeons ought to find their way equally 

 well. The investigations have shown, especially those at Kbnitz, that young pigeons, even 

 at relatively small distances from their home, have the greatest difficulty in finding their 

 way back when the vicinity is at all strange to them, and their home can not be directly seen. 



He then concludes that the young birds utilize, in their early flights, the 

 familiar groups of houses, mountains, etc., and that the distances to which a 

 bird may be taken safely may be increased commensurately with the increase 

 in the development of his "topographical memory." This author believes 

 that the pigeon can develop not only " Errinerungsbilder" but even "Gedacht- 

 ni.s.se." Schneider had had wide practical experience before reaching these 

 conclusions. 



Like the previously considered observers, HodgeJ finils no necessity for 

 assuming a sense of direction in the homing pigeon. His experiments were 

 made largely upon young pigeons. When they were fii'st released at the cote 

 they circled about the cote, then flew from one distant point to another, and 

 thereby (according to this author) established a system of visual landmarks. 

 Young birds taken in an open cage half a mile away from the cote returned 

 with few circling flights ; but young birds removed in closed cages circle, make 

 errors, and even fly for long distances in a wholly wrong direction. Training 

 produces almost immediate results in good birds. Only after training do they 

 take a straight line and behave as though they had a sense of direction. 



When i)laccd in an unknown neighborhood the iiird begins upon a "line of 

 search." "The logical curve of search is a peculiar spiral, the involute of a 

 circle, the characteristic of which is that the convolutions are always the same 

 distance apart. These distances will be, of course, twice the distance at which 

 the object is visible." 



♦According to S^tjillot, quoted by Hachet-Soupli-t, when homing pigeons are released at the 

 sea the altitude at which they fly increases proportionately to their distance from the land. At 

 146 km. tlie pigeons scarcely pass over the normal altitude of 150 to 300 meters; at 200 km., they 

 had visibly mounted much higher; at 300 km., the altitude was found to be at least 600 meters. 

 In the final test we lose the birds from view in the heights and not at the horizon. 



fSchneider, G. H. Zeitsch. f. Psychol, u. Phy. d. Sinnues., 1905, xl, pp. 252-279. 



IPopular Science Monthly, 44, p. 758. 



