92 THE MIGRATION OF BIRDS. 



visit these islands on passage are Ducks and other 

 aquatic species ; and it seems more than probable 

 that all the land birds which do so are individuals 

 blown out of their normal course along the eastern 

 coasts of North America by violent storms. The 

 passage south (the period when the occurrences are 

 most numerous) is made at a season when storms 

 are remarkably prevalent. Violent gales are almost 

 of weekly occurrence in this region, and seldom 

 fail to bring numbers of migratory birds to the 

 islands. It is suggested that many of these 

 wind-driven migrants may have been carried up 

 by local whirlwinds, and borne out to sea by 

 westerly or north-westerly gales prevailing in the 

 upper atmosphere. The greater number of these 

 birds most probably perish, but a few manage to 

 reach these islands more or less regularly every 

 year, the regular arrivals (such as Cerijle alcyon^ 

 Sciurus novce boracensis, and Dolichonijx oryzivora) 

 being those whose migrations, either from their 

 altitude or date of progress, are probably most 

 exposed to sudden atmospheric disturbance. 

 Migration, as we have seen, does not generally go 

 on during gales, so that the visits of these birds 

 to the Bermudas seem compulsory rather than 

 voluntary, abnormal rather than regular, and we are 

 perfectly justified in concluding that these islands 

 as well as the Azores are far removed from all 

 ordinary Routes of Migration. 



Wherever islands dot the narrow seas between, 

 or fringe the coast-line of continents, migration 



