34 Loomis on Birds of Chester County, South Carolina. [^" n k 



surrounding country is not inhabited, or at best but very sparsely 

 so. Thus in this vicinity the Robin has been found to be of rare 

 occurrence in the breeding season except in a single locality 

 where a colony has flourished for years. The Grasshopper 

 .Sparrow, though very common, is likewise local here as a 

 summer resident. At northern extremes of breeding range this 

 gathering into isolated communities appears to be illustrated in 

 the Blue Grosbeak, Mockingbird, and Carolina Wren. In winter 

 time it is conspicuously exemplified in the Robin. Here in 

 Chester County they may be wanting in December and January, 

 and yet be abundant in a locality far to the northward. This, 

 too, when the bulk of the species on the Atlantic Slope winters 

 to the southward of this region. Certain essentially trans - 

 Appalachian species are inclined to be very local on this side of 

 the mountains, as the Dickcissel in summer and Leconte's 

 Sparrow in winter. Henslow's Sparrow and Bewick's Wren 

 appear to afford examples of local distribution where a species, 

 in the aggregate of individuals, is not sufficiently abundant to 

 populate the region embraced within the central portions of its 

 range. As has been indicated, isolated communities vary in 

 character. A single company or a small colony may alone repre- 

 sent a species in a locality, or numerous flocks may occur, as 

 is sometimes the case in the Robin, or there may be general dis- 

 persion, as in Bewick's Wren. It may be queried whether an 

 incipient disposition to gregariousncss, perhaps limited chiefly to 

 contemporaneous migratory movement, may not be a factor in 

 the geographical distribution of many birds, in the more common 

 species it being manifested by dispersion over widespread areas, 

 and in the rarer, either by restriction within narrow boundaries, 

 or by segregation into isolated communities or local centres of 

 distribution. 



It remains to be said that local distribution dependent 

 strictly upon environment is not to be confounded with the 

 isolated communities spoken of. Uncongenial situations are not 

 inhabited. Land birds do not resort to water, nor do typical 

 woodland birds frequent the fields. 



Variability in the Location of fsolated Commttnities. — 

 While the Robin may breed locally year after year in the same 

 locality, other species also local here in distribution may occur 



