20 NATURAL HISTORY OF BIRDS. 



indicate the ancient coast-lines along which the birds originally migrated, and further- 

 more, that they show the ways by which the species immigrated into the countries 

 where they now pass the summer. 



This conclusion, however, is also applicable to the land routes C and I). The 

 o-eological history of that part of the earth shows most conclusively that the great 

 Russian and the central European low-lands, during a not very distant period, geolo- 

 o-ically speaking, were submerged, forming the bottom of a rather shallow sea, the 

 shores of which, at different times, are well indicated by the lines alluded to. Even 

 when crossing the continents, the migrating routes of marine birds indicate ancient 

 coast-lines, and the immigration-road of the species inhabiting the north. We note 

 how closely these results agree with those arrived at above, where theorizing about 

 the origin of the migrating habit. 



Having thus accounted for the theory as first proposed by Palmen, and nearly 

 simultaneously by Wallace, it remains to be shown how the birds are enabled to find 

 their way, often thousands of miles. We need not assume a miraculous or imperative 

 instinct, nor a sixth sense, nor the influence of terrestrial magnetism, in order to explain 

 the remarkable fact that small birds travel over large continents and vast seas twice a 

 year to and from the very spot where they were born. Practice is the mysterious 

 agent, though not only the practice of the individual, but the practice of the' species, 

 the accumulated practice of thousands of generations, originating and strengthening 

 the faculty of orientation. "It is an ascertained fact" says Wallace, "that many 

 individual birds return year after year to build their nests in the same spot. This 

 shows a strong local attachment, and is, in fact, the faculty of feeling, on which then- 

 very existence probably depends. For were they to wander at random each year, 

 they would, almost certainly, not meet with places so well suited to them, and might 

 even get into districts where they or their young would inevitably perish. It is also 

 a curious fact that in so many cases the old birds migrate first, leaving the young 

 ones behind, who follow some short time later, but do not go so far as their parents. 

 This is very strongly opposed to the notion of an imperative instinct. The old birds 

 have been before, the young have not, and it is only when the old ones have all or 

 nearly all gone, that the young go too, probably following some of the latest stragglers. 

 They wander, however, almost at random, and the majority are destroyed before the 

 next spring. This is proved by the fact that the birds which return in spring are as 

 a rule not more numerous than those which came the preceding spring, whereas 

 those which went away in autumn were two or three times as numerous. Those 

 young birds that do get back, however, have learnt by experience, and the next year 

 they take care to go with the old ones." 



Taking into account the " inherited talent for geography," as Weissmann happily 

 styles it, with which every migratory bird is born, and remembering that the birds, 

 when traveling, fly very high, and consequently overlook a great distance of their 

 route, taking a 'bird's-eye view' of the country spread out beneath them, their 

 performance is scarcely more wonderful than is that of the pilot who safely guides tin- 

 vessel for hundreds and hundreds of miles along rocky shores and islands, all of which 

 seem identical and indistinguishable to the inexperienced passer-by; or more admir- 

 able than the infallibility with which the Indian finds his way back, even if he has 

 passed that way but once, through an endless forest of trees, which to any of us 



seem to be absolutely alike. 



LEOXHARD STE.TNEGEK. 



