488 Recent Literature. Fo^t' 



RECENT LITERATURE. 



Stone on 'Methods of Recording and Utilizing Bird-Migration Data.' — 



In a paper of thirty pages ' Mr. Witmer Stone discusses present methods 

 of recording and utilizing bird-migration data. As is well known, Mr. 

 Stone has long been active in this line of research and has given the subject 

 of migration data thorough consideration, so that his conclusions on the 

 subject are of special interest. 



The data mainly utilized in the present paper are those collected 

 during the last seven years by the Delaware Valley Ornithological Club, 

 by thirty-five observers, within a ten-mile radius of the center of Phila- 

 delphia. These observations are carefully analyzed from various points 

 of view and the results graphically shown by means of maps and diagrams, 

 the latter, by means of curves, showing the relation of migration movements 

 to meteorological conditions for the years 1902-1906. 



In general, migration records are, for the most part, the work of single 

 observers at isolated stations, and until very recently no attempt has been 

 made to compare the records of several observers at practically the same 

 locality. This was first done by Mr. Stone for Philadelphia in 1905 

 (Condor, 1906, pp. 88-90), and later by Prof. W. W. Cooke for Washington 

 (Auk, 1907, pp. 346-348). In general our records give only the date of 

 'first arrival'; the U. S. Department of Agriculture (Biological Survey) 

 schedules also call for arrival of the main flight or 'bulk.' Reasons are 

 given for considering both these methods unsatisfactorj'-, from the very 

 natm-e of the case, since the first arrival may be merely a straggler, and 

 the 'bulk arrival' a matter of estimate, subject to the element of personal 

 equation. In commenting on these points Mr. Stone calls attention to the 

 fact "that while a date of 'first arrival' may be perfectly accurate for the 

 limited area covered by an observer, it would differ very materially from 

 the earliest date of arrival for the species in a circle of five or ten miles 

 around that observer's station," as demonstrated by the records for the 

 vicinity of Philadelphia. Thus "the average date of arrival for a number 

 of years, based upon the observations of a single individual, varies materi- 

 ally from the average date obtained by another equally accurate observer 

 stationed a few miles distant." He concludes "that results based upon 

 such individual records are really of but little value for comparative work, 

 so great is the possibility of error." This is rather disheartening, not to 

 say startling. Mr. Stone, however, suggests an obviously better method, 

 which it is to be hoped will be systematically adopted by local bird clubs 

 and societies, He says: 



"After discrediting the value of individual records, one must naturally 

 suggest some method of recording migration by which results sufficiently 



1 Methods of Recording and Utilizing Bird-Migration Data. By Witmer Stone. 

 Proc. Acad. Nat. Sci. Pliiladelphia, 1898, pp. 128-156, July 22, 1908. 



