THE MIGRATORY MOVEMENTS OF BIRDS IN RELATION 

 TO THE WEATHER. 



By WELLS \V. COOKE, 

 Assistant, Biological Survey. 



INTRODUCTION. 



Accurate knowledge of the periodic movement of birds is essential 

 as a basis for intelligent study of their economic relations, and is 

 equally necessary for intelligent effort for the protection of migra- 

 tory species two subjects which form important parts of the work 

 of the Biological Survey. Ever since its organization the Survey 

 has devoted much attention to collecting data on food habits and 

 migration, and interest in these investigations is widespread. Thus 

 more than 2,000 observers in the United States and Canada have 

 Contributed notes on bird migration. Some of these notes cover only 

 the dates of arrival of a few birds for a single season, others form 

 an elaborate resume of both spring and fall migration at a given 

 locality far 25 years or more. The whole, aggregating more than 

 400,000 records, forms the largest mass of migration data ever 

 resembled in this country. 



To ascertain the relation of bird migration to the weather, two 

 things are essential: (1) Records for many years of the times of 

 arrival of birds, made by a thoroughly reliable and competent ob- 

 server constantly in the field; (2) observations taken in a district 

 without mountains or valleys, which might interfere with the course 

 of migration. 1 



MIGRATION WAVES AND TEMPERATURE WAVES. 



In the middle of May, 1882, the whole city of Washington swarmed 

 with large flocks of brilliantly colored birds. Scarlet tanagers, 

 orchard orioles, and rose-breasted grosbeaks by the score flitted 

 through the Mall and flashed among the trees of parks where ordi- 

 narily a half dozen would be a full season's quota. Rare species 

 were common, and among them were warblers never before seen in 

 Washington in spring. Even the Cape May, the mourning, and the 



tf In the first part of this article use has been made of the notes of Dr. I. r. Tlvoslef. 

 ot Lanesboro, Minn., who contributed excellent memoranda for 10 consecutive years. 

 IT is work \\;is supplemented by that of several other observers immediately south of 

 Lanesboro. The latter part of the article is based on the combined records of all our 

 migration observers. 



379 



