46 GEOGRAPHICAL DISTEIBUTION. 



tend over one or more thousands of miles. The flights of the 

 wild-goose and the swallow have been estimated to be performed 

 at the almost incredible velocity of from sixty to ninety miles per 

 hour, and the flights of many of the smaller birds at not very 

 much less. A sustained flight of ten or more hours in duration, 

 especially when assisted by a favourable wind, involving an amount 

 of muscular exertion probably within easy command of many birds, 

 would carry them over an enormous stretch of territory, during a 

 period of time which, by its brevity, would render the question of 

 food-supply comparatively unimportant. Land-birds have been en- 

 countered in the North Atlantic at almost all points of the oceanic 

 expanse ; but to what extent these stragglers have received assist- 

 ance in their flight, by taking temporary shelter on board the nu- 

 merous vessels plying between. Europe and America, can hardly be 

 determined. There is no question as to such assistance in numerous 

 instances, but whether it is afiEorded in all or most cases is a matter 

 of pure conjecture. By whatever means or methods the oceanic 

 travel of birds may be eSected, it is a matter placed beyond all ques- 

 tion that numerous American birds make their appearance at inter- 

 vals along the European coast. Upwards of sixty species of such 

 foreigners, embracing examples from nearly all the orders of birds, 

 have at different times been noted on the eastern coast of the At- 

 lantic, principally in the British Isles and the Island of Heligoland." 

 Singularly enough, no distinctively European birds make their ap- 

 pearance on the American coast, except a few whose journey over 

 is made by way of Greenland and Iceland.* Despite the long- 

 sustained flight of which birds are capable, it may be considered 

 exceedingly doubtful whether many or any of them undertake 

 these protracted journeys as a matter of their own pure choice or 

 volition. It seems hardly possible that an animal would subject 

 itself to such an amount of exertion and privation as would appear 

 to be involved in journeys of this length, when no material ad- 

 vantage could in the end be derived therefrom. It therefore ap- 

 pears more than probable, as has been urged by Baird, Wallace, 



* No account is hero taken of the purely pelajiio forms, which are found 

 on the opposite border.-* of the oceanic e.xpanse, and which find suitable rest- 

 ing-places on the surface of the waters. The greenshanks (Tetanus glottis) 

 has been obtained once m Florida, and appai-ently nowhere else in the United 

 States. 



