^'°'"i9lO^'"J Henshaw, Migration of the Pacific Plover. 255 



when the hind connections were very different, and when, by means 

 of continental extensions and ishmds 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, succeeding generations of migrants are suj)posed to 

 have scarcely noticed the difference, and, even after the old land 

 marks had disappeared, 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 

 isolation 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 continent, it finds little support from biologic, botanic, 

 or hydrographic investigations. Moreover, such a continent 

 extending southward towards Australia would have been of no 

 assistance to birds migrating from America, though its former 

 existence, could it be proven, would render easy the explanation of 

 the derivation of the Australian 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, 

 especially the steady trades, offer a reasonable explanation of the 

 way certain birds are, or may be, guided in migrating. Such an 

 explanation seems to apply peculiarly to the case of the American 

 Golden Plover which, as is well known, abandons the North 

 American continent at Labrador and Nova Scotia, and, under 

 ordinary circumstances, makes no landfall till it strikes the Guiana 

 coast, a distance of about 2000 miles. It is perhaps more remark- 

 able that, instead of returning in spring to its breeding grounds 

 by the same route it takes in fall to its winter quarters, it follows 

 an all land route, and traverses the length of two continents, thus 

 furnishing the most extraordinary migration route of any existing 

 bird, as pointed out by Professor Cooke. 



