558 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



most of them less than 50. Prior to their discovery by Europeans 

 all the islands were heavily forested, nearly or quite to the shore. 

 Possibly then the plover and other migrants have been slower to 

 realize the situation than the other species, and do not even yet appre- 

 ciate the advantages offered by continuous island life. 



It may be said, too, that the spring migration of the plover and 

 turnstone is so intimately interwoven with the function of repro- 

 duction that we are quite safe in assuming that, were it not for the 

 desire to nest, the birds would never migrate. Those, in fact, which 

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

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

 tion 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 stimu- 

 lated thereto by the profound physiological change consequent upon 

 reproductive activity. This impulse is not primarily due to change 

 of season or to change of temperature, but is periodic and physiologi- 

 cal. 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. Neverthe- 

 less the power of habit transmitted through thousands of years is 

 very great, and it is probably this influence associated with the repro- 

 ductive 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 grad- 

 ually formed fly lines to and from their summer and winter homes 

 till the habit formed during thousands of years became so fixed as to 

 absolute^ 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 



