iq8 Stone t7« ///c Graphic Refresentatiou of Bifd Waves. [April 



Jan. 12. — Firht wave 3 



Jan. 13-Feb. II 4 



Feb. 12-14. — Second wave 4 



Feb. 15-25 6 



Feb. 26-27. — Tliird wave 5 



Feb 28-March II o 



March 12-13 — Fourth wave 6 



March 14-April 11 i^ 



April 12-14.— Fifth wave 20 



April 15-25 •- 



April 26-27. — Sixth wave i(j 



April 28-29 • 4 



April 30-May I . — Seventh wave 48 



May 2-3 8 



May 4-5. — Eighth wave 28 



May 6-9 ^^ 



May lo-ii. — Ninth wave 26 



May 12 3 



156 69 



Summing up the result we find that on 19 days during which 

 bird waves were in progress there were 156 first arrivals, or an 

 avera<J-e of 8.21 per day; while on I03 days when no waves were 

 in progress there were but 69 arrivals, or an average of only .68. 



It may be imagined that inore careful observations were taken 

 on the days upon which the waves appear to have occurred, l)ut 

 such was not the case, as the observers were aware of this possi- 

 bility and guarded against it, endeavoring to spend a portion of 

 every day in the field and to cover nearly the same ground daily.* 



The increase in the numbers of individuals of each species seen 

 daily, and the dates w^hen the species became common, show a 

 still greater coincidence with the dates which 1 have just men- 

 tioned as those of bird waves, than do the records of first arrivals 

 just o-iven. This is quite natural, so many of the latter are mere 

 stragglers, and it is really sin-prising that so large a proportion of 

 them as is shown by the summary do coincide with the waves. 



In conclusion, I may say that this paper does not pretend to set 

 forth any new theories in regard to bird migration, but simply to 

 otfer a few facts in corroboi'ation of the already well-accepted 

 wave theory ; and to suggest a method for the graphic represen- 

 tation of the waves of migration and their coincidence with vari- 

 ations of temperature. 



* See beyond, 'Work of the Delaware Valley Ornithological Club during 1890, 

 under 'Correspondence,' in this number of "The Auk.' 



