Vol. XXI 

 igo4 



1 Cooke, Effect of Altitude on Bird Migration. 339 



As would be expected, spring migration is, on the whole, later 

 at Asheville than at Raleigh, and the voluminous records of the 

 Biological Survey furnish data for a quite exact statement of the 

 amount of variation in the times of arrival at the two places. 

 The late J. S. Cairns sent migration notes for the years 1890 to 

 1894, inclusive, from the town of Weaverville, ten miles distant 

 from Asheville ; Minot Davis recorded the dates of arrival of the 

 birds at Asheville in 1899, and W. M. Rackett the same data for 

 1902 at Weaverville. These seven years of observation furnish a 

 satisfactory basis for estimating the average dates of arrival in 

 this district. From C. S. Brimley, at Raleigh, the Biological 

 Survey has received a very full report on migration for eighteen 

 years, from 1885, the whole forming, probably, the largest amount 

 of migration data ever recorded by one person at any one locality 

 in the United States. With this amount of material at command, 

 the movements of the birds at Raleigh can be ascertained with 

 great accuracy. 



Twenty-one species of common birds arrive in the spring at 

 Raleigh, on the average, 3.6 days earlier than at Asheville, or one 

 day earlier for each 1.4° F. that Raleigh is warmer than Aslieville. 

 Most of these birds were migrating during April, and for this 

 month the temperature of the two localities differs scarcely four 

 degrees. Therefore, it can be said that with reference to these 

 two localities spring migration is delayed one day for each degree 

 of cold. This relation, of course, would not hold good for other 

 localities, though the migration between Raleigh and Washington 

 is not much different. During April Raleigh averages six degrees 

 warmer than Washington, and the birds average eight days in 

 making the journey of the two hundred miles between the two 

 places, or one and a third days for each degree of temperature. 

 The trip from St. Louis to St. Paul is performed at a rate of about 

 a day and a half for each degree of difference in temperature. 



These statements are the averages of such widely differing 

 quantities that they cannot be used to ascertain even approxi- 

 mately the time that any particular species requires in its passage 

 from one locality to another. 



The following dates show how greatly the different species vary 

 in the time of their arrival at the two places, Raleigh and 

 Asheville. 



