CHAPTEE V. 



MIGRATION. 



It is a very remarkable fact that the evidence of the most trustworthy witnesses cannot Hibernation 



always be relied upon. The old superstitions that Bernicle Geese were hatched from the 



mollusk whose name they bear, that Cuckoos turned into Sparrow-Hawks in autumn, and 



that Swallows spent the winter biu-ied in the mud at the bottom of rivers, are too absurd 



to be worthy of refutation ; but there are still a few credulous ornithologists who are not 



yet convinced that birds have not occasionally been found in a state of Hibernation. There 



cannot, however, be the shadow of a doubt that the well-authenticated stories of Swallows 



having been found in a torpid state in hollow trees, or in holes of walls or rocks, are pure 



myths. There is not a shred of truth in these narratives, any more than there is in the 



equally impossible stories of live toads being found in solid rocks ; and it is most curious 



that, now science has proved these alleged facts to be impossible, no further evidence of 



their truth is forthcoming. It only shows how cautiously evidence apparently the most 



trustworthy should be received. 



The Hibernation of birds is a theory, the evidence in support of which has completely 

 broken down. The Migration of birds is a/ac/, as completely authenticated as the fact of 

 their existence. Not only is the disappearance of a species from its breeding-grounds the 

 signal for its appearance at its winter-quarters, but there are numerous halfway houses, so 

 to speak, where any observer may, at the proper season of the year, see birds by the 

 thousand in the act of migration. 



All birds do not migrate, neither is migration confined to any family or genus of Migration 

 birds ; nor does it invariably extend to aU the individuals which collectively represent a ^f^^^ 

 species. The habit of migration is to a large extent climatic. The Robin is a resident in 

 England, where the winters are comparatively mild ; it is a migrant in Germany, where 

 frost is much more frequent and severe. Birds breeding in the tropics are always resident, 

 except when they breed on mountains, where a subtropical, or even an arctic chmate, 

 causes them to descend into the valleys for the winter. 



To old-fashioned ornithologists who still believe that each species of bird was separately 

 created in the locality where it now breeds, migration appears to be an exceptional factor 

 in the life of birds, whilst they regard any theory of the emigration of birds as a myth. 



