QA Loomis on Birds of Chester County, South Carolina. Ta "ri 



A FURTHER REVIEW OF THE AVIAN FAUNA OF 

 CHESTER COUNTY, SOUTH CAROLINA. 



by leverett m. loomis. 



Concluding Observations on Migrations. 1 



III. Migratio7i Considered with Reference to Cause. 



In the study of bird migration we find two sources of causa- 

 tion — physical and psychological ; the former embracing the 

 conditions entailed by winter, cold and failure of food, necessi- 

 tating southward migration and restraining northward ; the 

 latter, the adaptation to these conditions, implying education and 

 probable heredity. The physical, as the primary or fundamental 

 cause, will be considered first. 



Physical Cause. — As a statement of the phenomena of migra- 

 tion is largely a statement of its physical cause, it may be well to 

 pass in review the cycle of a year's migration. 



June 20 may safely be said to mark the opening of the south- 

 ward migration in this region, the scarcity of adult birds in a few 

 species, whose breeding season is over, then becoming apparent. 

 Mr. Brewster assures me that the date of inception of this early 

 movement of adult birds in Eastern Massachusetts is about July 

 20 — a month later than in the Piedmont and Alpine Regions of 

 South Carolina. In July, particularly toward the end, arrive 

 the first Warblers that do not breed, so far as known, in Chester 

 County. As the Southern Alleghanies are a part of their breed- 

 ing habitat, the movement is presumably from these highlands. 

 Breeding birds continue to depart during this month, and toward 

 the close a few species have nearly or entirely disappeared, both 

 the old and the young. In July, too, representatives of some 

 of the species breeding here make their appearance from other 

 localities, inaugurating the fluctuations noticeable in all the 

 movements that follow, whether of breeding or of strictly 

 transient species. The waves of migration become pronounced 



1 Concluded from p. 39. 



