CHAPTER III 

 Regularity of Migration 



THE regularity of travel when birds are on mi- 

 gration constitutes one of the most interesting 

 facts in connection with this phenomenon and is one 

 familiar to all ornithologists. Through years of ob- 

 servation average dates of spring arrival and autumn 

 departure have been estabHshed for many localities, 

 and birds come and go with surprising regularity on 

 their appointed dates. Arrival in spring is particu- 

 larly punctual with the majority, and unusual is the 

 season when the first of the travellers fail to put in 

 their appearance within a few days of the average 

 date. Observations on dates of migration over a 

 considerable period of years are now available for 

 the United States and Canada, and similar data 

 have been recorded abundantly for western Europe. 

 At Washington, D. C, the barn swallow, on the 

 average, arrives April 12, the least flycatcher May 2, 

 the chipping sparrow March 22, and the house wren 

 April 18. On or near these dates one is always sure 

 to find them. Individuals which breed about our 

 homes, which arrive often with the bulk of the flight 

 following a few days after the earliest arrivals, come 



