120 RAMBLES ABOUT HOME. 



starting-point in time of birds' migratory movements. The 

 progenitor of our score of warblers, the one tyrant fly- 

 catcher, from which all our species have sprung, the 

 vireos, the goatsuckers, and cuckoos, then very few in 

 species, if indeed there were more than one of each, must 

 have been influenced by the presence of the icy barriers 

 that shut them off for the time being from a vast portion 

 of the northern world, and at the close or closing of that 

 wonderful period it may be that migration commenced, 

 yet why and how it is hard even to conjecture. Knowing 

 that it commenced then or recommenced, if previously 

 a feature of bird life, we have now to inquire what are 

 its apparent causes at present ; but, before inquiring into 

 these, may we not, after all, ask if migration be not an 

 inherited habit, the originating causes of which are not 

 now in operation? The conditions not obtaining that 

 necessitate migration, does it not become a case of sur- 

 vival of habit, just as in man many customs now exist, 

 the origin and proper meaning of which are wholly lost ? 

 That this is true of the migration of all birds I do not 

 believe, but that it partially holds good with some species 

 I am fully convinced. As an inherited habit, but one 

 now not absolutely necessary to the birds' welfare, I can 

 see why it should be, as it frequently is, so greatly influ- 

 enced by surrounding circumstances and conditions. 



Taking the movement from its proper starting-point, 

 which I assume to be the movement from south to north 

 in the three spring months, we must now look for suf- 

 ficient causes to induce the undertaking of such long jour- 

 neys. These causes are suggested by the two principal 

 objects effected on their arrival at their northern destina- 

 tion the rearing of their young, and procuring suitable 

 and sufficient food for both themselves and offspring. 

 If migration is for these two purposes only, then it should 



