1908.] NATURAL SCIENCES OF PHILADELPHIA. 129 



first called attention to the possibilities of combining a number of 

 individual records, and later Prof. W. W. Cooke of the U. S. Department 

 of Agriculture discussed the same question in a short paper in The 

 Auk for July, 1907, p. 346. These are, I believe, the only papers dealing 

 with this phase of the question. The well-known work of Mr. Otto 

 Herman in Hungary, while probably based upon the most extensive 

 series of data ever collected, does not, so far as I am aware, touch 

 upon the comparison of individual records, at a single locality. 



Individual and Bulk Arrivals. 



One of the most important points for consideration in a bird-migra- 

 tion record is an understanding of just what our date of arrival indicates, 

 A migrating species is not a definite mass, like a railroad train, but a 

 scattered host of individuals requiring weeks or even months to pass a 

 given point and moving intermittently; consequently there may be a 

 great many dates of arrival at that point, according to what part of 

 the moving procession we are considering. 



In the schedules furnished by the U. S. Department of Agriculture 

 the date of "first arrival" is called for, and in addition the date when 

 the species was next seen and when it became common. The object 

 being to differentiate between the arrival of the main flight or "bulk" 

 ■of the species and that of individual early stragglers. 



With the exception of these schedules, nearly all the American 

 migration records with which I am familiar deal only with the date of 

 ■"first arrival," and in the publications that have been based upon the 

 records of the U. S. Department of Agriculture, only one date is usually 

 ^iven, presumably the date of first arrival. 



This would seem to indicate the unsatisfactory nature of the records 

 of bulk arrival, as estimated by an individual observer, a fact which 

 has impressed itself upon me after twenty-five years' experience in 

 recording and tabulating bird migration data. It seems altogether too 

 variable a quantity to be of practical value in making any sort of com- 

 parisons except in special instances. 



Different species of birds vary in the way in which they become 

 abundant at any point; some may come in considerable numbers on 

 the very first day upon which they are seen or a day or so after the 

 ■"first arrival," while others gradually drift in, a few each day, until all 

 the usual haunts are populated, though it is impossible to say upon just 

 which day they became common. In other cases large flocks may 

 "be seen passing overhead some time before an}^ individuals establish 

 themselves in their local summer haunts. It seems, too, that certain 



