388 REPORT ON THE MIGRATION OF BIRDS. 



It is furtber pointed out by Prof. Cooke that the expression " bird 

 wave " may be taken in a double sense, and consequently answers to 

 two methods of investigation. First, a bird wave comprises a very 

 large number of individuals of one or of several species, which extend 

 at one time over a certain territory. In studying such a wave it is 

 necessary to determine the species of which the moving mass is com- 

 posed and the bounds of the territory over which the wave extends. 

 Second, certain species of birds which are proved to move in company 

 on the same day may also be regarded as a wave, whose progress from 

 day to day and from week to week must be accurately observed. 



By a critical study of these points of view and by a conscientious 

 use of the meteorological and ornithological observations which em- 

 brace a precise time and a precise region, the rapidity of the migra- 

 tion, on which so much has heretofore been written, can be calculated. 

 Only by attentive observation and multifariims labor can the migration 

 be folloAved until the moving flocks haAe reached their resting places. 



It is evident that Prof. Cooke's investigation of migration over a long 

 continuous route, apart from all unavoidable sliortcomings, must be 

 particularly adapted to elucidate migration with respect to its course 

 and its outward conditions; and that it is very desirable that similar 

 investigations may henceforth be undertaken in suitable regions. 



This course is opposed however by the difficulty of iintling a suffi- 

 cient numbei' of capable observers. Prof. Cooke has beeu able to rely 

 in essential degree upon one conscientious and expert observer, Mr. 

 O. Widmann, of St. Louis, whose methodically arranged notices he 

 submits in his work. In this connection the writer will only quote the 

 words of a comitetent Judge: 



''A dozen observers like Mr. Widmann, scattered at projjer intervals, 

 would give a fairer basis for generalizations than hundreds of observers 

 of the grade on wlioni Prof. Cooke was obliged to depend for many 

 of his data. This should stimulate the more experienced and well 

 qualified fiekl ornithologists to contribute to the fullest degree i)ossible 

 to the furtherance of this important investigation. — J, A. Allen, The 

 Aid; 1889, vi, p. (>1." 



The continiuHl meteorological phenomena were rendered in the usual 

 manner by synoptical ma])S, which alone made a view possible, and es- 

 sentially facilitated the study of the influence of weather on the migra- 

 tion of birds. It may not therefore be injudicious to here refer to an 

 attempt to lepresent graphically the migration of birds and the com- 

 jjosition of the avi-fauna, changing with the season, as Mr. AV. Stone 

 has proposed (Aiili, yi, p. 139). 



Besides this material of observations, made chietly with a view to 

 explaining the problem of bird migration, numerous faunal works 

 have appeared — minor local catalogues, and comprehensive works on 

 the birds of larger definite geographical areas, prepared with con- 

 scientiousness and intimate knowledge. ]^o one perhaps can value 

 these avifaunal works more highly than the writer, with regard to their 



