.54 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



What, under such cu-cumstances, becomes of the routes of birds b\' 

 river courses or mountains'? How many great rivers has Anilius ricli- 

 ardi to cross, ahnost all at right angles, during his autumnal flight from 

 Daouria to France and Spain "1 



I maintain that the migratorial movement, particularly the vernal one. 

 when in normal progress, is performed by the great majority of birds 

 far beyond the perception of man, and that what we see of the same 

 are but the irregularities and inferruptions thereof — brought about by 

 atmospheric agencies. 



Your oi>inion that i:he sirring line of flight is widely diflerent from 

 that of the fall, I most completely participate in. All the diftereuT 

 routes enumerated in the foregoing are dropped, and a luore or less 

 direct coirrse toward the polar regions adopted. The wide front of the 

 winter-quarters, extending from the west of Africa to the east of China, 

 the Philippines, Borneo, &c., concentrating during this northerly pass- 

 age to less than half its original stretch. 



A proof of this latter assertion is rendered by the fact that of all 

 the eastern birds which visit Heligoland during their autumnal migra- 

 tion, none appear during their return journey, the track to the south 

 which terminated their western flight having brought them to far lower 

 latitudes ; while in spring, as they pursue a direct course to their north- 

 ern breeding-grounds, they leave all these western countries to their 

 left. 



While the " rare birds" here during autumn are, without exception, 

 eastern species, those of the spring are as uniformly from the southeast — 

 Greece, Asia Minor, Turkestan, &c. Singular it is, that almost no ex 

 ceptional bird has come here from the south or west, i. e., so far as the 

 Old World is concerned. In what eminent manner the " tar west " is 

 represented, I have told you at an earlier period. 



And this leads me to the route which American birds follow to Eu- 

 rope. I do not much lean to the supposition that storms have in any 

 considerable degree to do with such extra tours, and why jSTewton and 

 others advance so strongly the Greenland, Iceland, &c., route, I cannot 

 comprehend. I fancy they never contemplated the x>ossibility of a bird 

 coming in a direct line from Newfoundland to Ireland ; in other Avords, 

 that a bird might be able to sustain an uninterrupted flight sufficient 

 to carry it across the Atlantic. My researches have led me to the be- 

 hef that such is not alone far from being imi^ossible, but that the proba- 

 bility of such a fact, wonderful as it may appear, is borne out by good 

 evidence. 



For instance, these old spring birds of these Sylvia sueciai which I 

 send you, have wintered in the middle or north of Africa. During their 

 vernal migration, the first point north thereof where they are regularly 

 found in considerable numbers is Heligoland, whilst during this time 

 they are of the utmost rarity in all countries intervening between the 



