I Q J. Stone £>w ///t' Graf hie Repres.eiitation of Bird Wax^es. [April 



BIRD WAVES AND THEIR GRAPHIC REPRESEN- 

 TATION. 



BY WITHER STONE. 



In studying the migration of birds I have always recognized 

 the need of some method of representing graphically the great 

 conil)ined movements or waves of the spring and fall and their 

 ccjincidence with changes in temperature. It is hard to get any 

 idea of this coincidence from consulting a mass of data unless 

 one spends a consitlcrable amount of time in studying it over, but 

 in a graphic representation the whole matter can be seen at a 

 glance. 



The lack of exact data is a considerable hindrance to a satis- 

 factory graphic representation, as the majority of the observers of 

 migration have been content with noting the first and secontl 

 arrivals and the so-called 'arrival of the bulk,' while the subse- 

 quent fluctuations in the number of individuals of the species 

 have gone unrecorded. This year I have l)een fortunate enough 

 to have at my disposal the observations recorded by the members 

 of the Delaware Valley Ornithological Club on the spring migra- 

 tion of 1890 in the vicinity of Philadelphia. These records con- 

 sisted mainly of the exact numbers of the various species seen 

 tVom day to day at the several stations of the members of the 

 Clul). In some cases, however, after the early anivals were 

 recorded, sucli terms as 'common,' 'several,' etc., have been 

 used to show the comparative numbers of the species present. 

 This method is much less satisfactory, and but little easier to tlie 

 observer, than noting the exact lumibers seen or as close an esti- 

 mate of them as possible. With this material I have been able 

 to construct several charts which show quite satisfactorily the 

 successive waves of the spring migration. 



The method can best be understood by reference to the accom- 

 panying cuts. Across the top of the chart is a temperature cur\e 

 showing the variation in the maximum daily temperature at Phil- 

 adelphia. Beneath are recorded the daily observations on a few 

 species of birds at five stations, — Haddontield, N. J. (Saml. N. 

 Rhoades) ; Wymiewood, Pa. (Wm. L. Daily) ; Tinicum, Pa. 

 (J. Harris Reed) ; Olney, Pa. (Geo. S. Morris) ; and German- 



