258 



Bird Migration in the Mississippi Valley. 



servers admitted of. Some of these ob- 

 servers had but an indifferent knowledge 

 of ornithology, and as their records dealt 

 wholly with questions of fact their returns 

 were criticised closely before being accepted 

 as facts. On this subject the editor, Dr. C. 

 Hart Merriam, in his prefatory report says, 

 "Here the editor has deemed it his duty to 

 make the subject matter conform to the 

 present state of knowledge on the subject. 

 With this end in view changes have been 

 made freely, and the portion relating to 

 the geographical distribution of the various 

 species and subspecies have been largely re- 

 written." This revision he tells us in a foot 

 note "consisted in rewriting the habitats of 

 most of the species and subspecies; in cast- 

 ing out some forms which had been in- 

 cluded upon erroneous identification or in- 

 sufficient evidence, in correcting statements 

 of fact, in transferring (in a few cases) the 

 notes sent under a stated species or sub- 

 species to a nearly related species or sub- 

 species," and a variety of other matter in- 

 volving a vast amount of labor in which he 

 acknowledges having received valuable as- 

 sistance from Mr. Robert Ridgway, Curator 

 of Birds in the U. S. National Museum. 

 Indeed, as Dr. Merriam observes in his 

 prefatory letter, there need be no hesitancy 

 in expressing the belief that the present 

 report is the most valuable contribution 

 ever made to the subject of bird migration. 

 It is only natural that a man of Professor 

 Cooke's attainments while engaged in re- 

 cording the facts of bird migration, should 

 be tempted to speculate upon the causes of 

 this remarkable phenomenon, and give the 

 world the benefit of his conclusions. On 

 this subject he says: "Without entering 

 into a discussion of the causes which long 

 ago started birds on their periodical change 

 of habitation, we shall not be far out of the 

 way in considering their present migrations 

 the result of inherited experience. To be 

 more explicit, the first migrations were 

 doubtless very limited in extent, and prob- 



ably were intelligent movements which, 

 through repetition, became habitual, and 

 the habit was transmitted from parent to 

 offspring until it has become as we see it 

 now, the governing impulse of the bird's 

 life. It is undoubtedly true that love of 

 the nesting ground, which is to them their 

 home, is the foundation of the desire for 

 migration; and year after year they find 

 their way thousands of miles back to the 

 same box or tree by the exercise of memory. 

 Not always the memory of the individual, 

 but the memory inherited from numberless 

 preceding generations which have passed 

 and repassed over the same route. * * * 

 The return movement is obviously the re- 

 sult of two causes — the approach of winter 

 and the failure of the food supply. * * * 

 Nevertheless it is as yet unexplained why 

 some birds, notably many of the warblers, 

 retire in winter to such a great distance 

 south, some even crossing the equator and 

 passing several hundred miles beyond. 

 Certainly neither cold nor hunger can be 

 be the cause of such wanderings." 



Dr. Merriam in his prefatory letter ex- 

 presses himself as dissenting generally 

 from Professor Cooke's theories, and one 

 point in the theories above enunciated is 

 so opposed to his views, that he has no 

 hesitation is criticising it sharply in a foot 

 note. 



"I cannot concur," he writes "with Pro- 

 fessor Cooke in the belief that love of the 

 nesting ground * * * jg |-]^g foundation 

 of the desire for migration. In a lecture 

 on Bird Migration which it was my privilege 

 to deliver in the U. S. National Museum, 

 April 3, 1886, I said "Some ornithologists 

 of note have laid special stress upon the 

 strong home affection which prompts birds 

 to leave the south and return to their 

 breeding grounds. To me this explanation 

 is forced and unnecessary. Birds desert 

 their winter homes because their food 

 supply fails; because the climatic conditions 

 become unsuited to their need, because 



