MIGRATION OF PACIFIC PLOVER HENSHAW. 553 



or more, quite long enough to permit the pairs to attend to their 

 parental duties, to get into condition for the return journey, and to 

 make the trip. So far as my observations extend, all the first arri- 

 vals in Hawaii in fall, both plover and turnstone, are adults in breed- 

 ing plumage. I may add that they are invariably in good flesh and 

 that some are very fat. Later arrivals, however, no doubt young of 

 the year, are comparatively poor in flesh and require considerable 

 time to fatten. 



How migrants find their way across the ocean. — It thus appears 

 that thousands of birds, large and small, make a 2,000-mile flight 

 from Alaska to Hawaii in fall and return in spring. To answer the 

 question how they find their way across the trackless waste we must 

 leave the realm of fact and enter that of speculation. Ocean migra- 

 tion routes have generally been plausibly accounted for on the theory 

 that the present fly lines were established ages ago when the land 

 connections were very different, and when, by means of continental 

 extensions and islands now sunken, part land, part water routes were 

 easily followed. As such changes as the raising or depressing of 

 continents are very gradual and extend through long periods, suc- 

 ceeding generations of migrants are supposed to have scarcely no- 

 ticed the difference, and, even after the old landmarks had disap- 

 peared, to have been able to follow the ancient routes through the 

 power of transmitted habit. 



This explanation, however, does not apply to the case of the 

 Hawaiian migrants, since there is no reason to suppose that the isola- 

 tion of the Hawaiian Islands in relation to continental areas was ever 

 less complete than now; and, although a theory has been advanced 

 that the archipelago is the northern apex of a former southern con- 

 tinent, it finds little support from biologic, botanic, or hydrographic 

 investigations. Moreover, such a continent extending southward 

 toward Australia would have been of no assistance- to birds migrat- 

 ing from America, though its former existence, could it be proven, 

 would render easy the explanation of the derivation of the Austra- 

 lian elements of the Hawaiian fauna and flora. The presence of two 

 shoals, situated, roughly speaking, midway between San Francisco 

 and Hawaii, has suggested the former existence here of large islands, 

 now sunken. If such islands really existed, which is doubtful, they 

 unquestionably would have aided the passage of American birds and 

 plants to the Hawaiian Islands. 



In his interesting article on "The migration of certain shore 

 birds," quoted above, Mr. Clark argues that prevailing winds, espe- 

 cially the steady trades, offer a reasonable explanation of the way 

 certain birds are or may be guided in migrating. Such an explana- 

 tion seems to apply peculiarly to the case of the American golden 

 plover, which, as is well known, abandons the North American Con- 



