EAST COAST OF ENGLAND. 53 



Gradually the land now occupied by the North Sea has been 

 withdrawn from beneath the migrating flocks ; year after year 

 the middle passage became wider and more difficult ; yet the 

 habit once formed would be continued, and hereditary instinct, 

 or whatever other name we choose to give it, supply the 

 rest. 



Mr. Wallace has told us how, in the Eastern Archipelago, 

 comparatively narrow, and probably very ancient, straits of 

 water divide and wholly separate distinct races of birds ; and we 

 have instances of this in Europe, where species, common on the 

 opposite coast of the Continent, rarely or never occur in the 

 British Islands. 



Small birds, like the Goldcrest, do not cross great breadths 

 of water from choice ; they doubtless would prefer a migration 

 over land, from field to field, or hedge to hedge ; or at the most 

 closely following some old established coast-line. Why, except 

 on some such hypothesis as stated, should they attempt the 

 North Sea, not alone at the narrowest part, the straits of Dover, 

 or from Ostend to the coast of Kent, but in the very widest 

 parts also, from the Elbe to the Humber, or Danish coast to the 

 Pentland Firth and Scotch islands ? What impels our autumn 

 visitants, the young weeks in advance of their parents, to launch 

 westward across what, for anything they can possibly know to 

 the contrary, may prove an Atlantic, an ocean without a further 

 shore ? 



There are doubtless several causes, working separately or 

 together, which influence migration, and we must not look for 

 an explanation of the phenomena attending these great periodical 

 movements to one cause only, for by doing this we lose sight 

 perhaps of other equally powerful incentives. I have spoken in 

 previous reports of the probability of birds following ancient 

 coast-lines once linking now distant lands, impelled by what we 

 call, for want of a better term, hereditary instinct, that is, an 

 instinct derived through ancestors. It is, perhaps, an open 

 question whether the young, which undoubtedly arrive in the 

 autumn weeks in advance of the great mass of old birds, depend 

 entirely on this, or whether they are in any way dependent on 

 guidance and direction. It is a curious fact, which we have 

 frequently remarked, that the very earliest of their kind are 

 frequently a few old birds, — flocks of young, too, often contain a 



