MIGRATION. 289 



decreased temperature of the earth and water, may all have 

 their influence." 



It will be observed that this theory, besides being intrin- 

 sically probable, derives a good deal of support from the 

 enquiries made by Mr. Darwin, which have shown that there 

 is a general relationship between oceanic islands which there 

 is independent reason to conclude have never been joined to 

 the mainland, and an absence of migratory birds.* 



It will also be observed this theory makes two important 

 assumptions — first, that the birds have a very accurate sense 

 of direction, and second, that a no less accurate knowledge of 

 the particular direction to be pursued is inherited ; for it is 

 certain that the young Cuckoo (which leaves England after 

 its parents) cannot be guided on its first journey by any other 

 means, and it is asserted that the same is true of theyoimg 

 of many other species.t Taking then these assumptions 

 separately, the first is no more than a statement of fact, un- 

 accountable though the fact may be. That is to say, a verv 

 accurate sense of direction migratory birds unquestionably 

 possess, and it is probably the same in kind as the so-called 

 " homing " faculty which is shown by many domesticated 

 animals, and also, as Mr. Darwin points out, by savage man. 

 I could fill pages with letters which I have received from 

 all parts of the world describing more or less remarkable 

 cases of the display of this faculty by dogs, cats, horses^J 



* To be quite fair, however. I must here allude to the only fact I have 

 met with which seems to me opposed to this theorr. Mr. Uurdis in his 

 work entitled The XaturaU-st in Bermuda, obserres that the miffratorv golden 

 plover (CA<7ra<f /-/«.? marmorafus) passes over the islands in countless multi- 

 tudes (but without ever alighting") on the journey south, while they are never 

 s?en passing over the islands on their return journey north. Now. if it is a 

 fact that the two journeys are taken by ditferent routes, a difficulty would be 

 encountered by the above theory ; but as MJr. Hurdis says that the birds fly 

 at an enormous height while passing over the islands on their southern 

 journey, it is not, I think, impossible that they may take the same route on 

 their northern journey, although at a still higher elevation, and thus escape 

 notice. 



+ See Temminck, If an. <fOrm., ed. 2, iii. Introd., p. xliii, and Seebohm, 

 Siberia in Europe. On the other hand Leroy says that in the case of swallows 

 • those who have had no instruction do not migrate, and the young birds 

 a "e seen to be led by those whose age and exj)erience give them knowledge 

 and authority ;"' and adds that if a brood are hatched out too late to accom- 

 pany the old birds in their migration, *' it is in vain that they reach maturity 

 . . . . they perish the victims of their ignorance, and of the tardy birth 

 which made them unable to follow their parents '' (ioc. cif.. pp. 1S3— 4>. 



J I have one instance of a cat returning in four days firom London to 



