iSod 1 Loomis on Birds of Chester County, South Carolina. "? I 



Variability imputed to variableness in the location of isolated 

 communities, entailing variation in paths of movement, is yet to 

 be spoken of. Upon such ground appears to be explained the 

 lateness of arrival from the south of the Yellow-throated Warbler 

 in years when other early migrants were not belated — a varia- 

 tion within narrow limits in the route pursued by the vanguard 

 being the probable cause of tardiness. In the years of early 

 occurrence there was no indication that the migration of this 

 species was obstructed, either by influences in this locality or 

 above it. The conditions seemed especially favorable, rather 

 than adverse. 



The reported wandering northward of hornotines in certain 

 species (as the American Egret and Little Blue Heron — Rep. 

 Bird Migr. Miss. Vail., pp. 82, S3) presents a curious phase of 

 erratic movement. A sort of irregular migration is manifested 

 in the occurrence of 'accidental visitants.' It is surprising, rather 

 than otherwise, that birds do not stray more frequently from their 

 normal range, considering the possibilities of their being storm- 

 driven or of becoming bewildered and losing their course. As 

 movements pass over and around localities it follows that a station 

 in advance may sometimes be occupied earlier than an inter- 

 vening one. 



To recapitulate: Periodic variability — habitual absence or 

 habitual comparative scarcity in one movement and customary 

 presence or customary greater abundance in the opposite — in 

 this locality is ascribed, aside from the influences of environment, 

 to semi-annual change in line of migration, a different route being 

 followed in the northward movement than in the southward. 

 Erratic variability — irregular and uncertain occurrence, in 

 transient migrants — is attributed to variation of route through 

 variation, eastward or westward, in the location of isolated com- 

 munities, and to diverting meteorological agencies, causing 

 deflection and interruption of movement, the former manifested 

 particularly through the presence or increased abundance of 

 species whose ordinary highway of migration lies further to the 

 east or west, the latter by the stoppage of progress in the locality, 

 above, or below it, resulting sometimes in ingurgitated and 

 involuntaiy migration. 



Local Causes, affecti?ig Distribution, producing the Appear- 

 ance of Irregtdarity of Migration. — Causes underlying local 



