^°''l910^"] Henshaw, Migration of the Pacific Plover. 261 



are not stirred by the impulse to nest, either because too immature 

 or too old, do not migrate; and the intimate connection between 

 migration and reproduction appears further from the fact that all 

 the individuals that migrate don the nuptial dress before they 

 start, a sufficient declaration of their purpose in undertaking the 

 trip; while those that remain retain the dull winter plumage. 



It appears to be true of all birds that having once reached their 

 winter quarters, be they near or far from the summer home, no 

 migrating species attempts to return to its summer haunts till 

 stimulated thereto by the profound physiological change conse- 

 quent upon reproductive activity. This impulse is not primarily 

 due to change of season or to change of temperature, but is periodic 

 and physiological. When once felt, every instinct seems to impel 

 birds to take the shortest route to the spot where they first saw .the 

 light, or where they have reared young. This has often been called 

 the home instinct. In the case of many species the phrase is not 

 very happily chosen, though I myself have used it, since that 

 locality is more properly to be called a bird's home where it spends 

 the greater part of its life, rather than where it spends a few brief 

 weeks annually. Nevertheless the power of habit transmitted 

 through thousands of years is very great, and it is probably this 

 influence associated with the reproductive instinct which so far has 

 prevailed over other considerations and caused the plover to migrate 

 from Hawaii in spring. 



If the Charadriidine birds, the plovers, sandpipers, and curlews, 

 originated in the Arctic, as Seebohm and others believe, and were 

 forced by the exigencies of the ice age to become wanderers over 

 the face of the earth, then indeed the spring migration of the 

 waders from their distant winter resorts is more fitly termed a return 

 home, and the instinct prompting the flight the homing instinct. 

 Originally forced by the ice invasion to abandon their then Arctic 

 Paradise and seek shelter and food in distant parts, as the ice 

 receded they gradually formed fly lines to and from their summer 

 and winter homes till the habit formed during thousands of years 

 became so fixed as to absolutely dominate many species. That it 

 did not dominate all of the original migrants, however, appears 

 from the fact that permanent colonies settled here and there even 

 in tropical regions, showing that under certain circumstances the 



