1S04 J Loomis 0)1 Birds of Chester County, South Carolina. IOO 



plain remotely anticipate the failure of food of the winter season, 

 for the birds must go sooner or later on account of winter. In 

 order that the depopulation of the continent may not be a disas- 

 trous retreat, it must be gradual, must be an orderly evacuation. 

 The later movements can be delayed, and winter birds can fluc- 

 tuate with the advance and retreat of the ice and snow, for popu- 

 lation has been so reduced through migration that means of 

 subsistence are still to be found. Such would evidently not be 

 the case if movement was deferred until famine was imminent. 

 The vast population of the continent would be so crowded in the 

 advance that food would fail. There could be no relief through 

 scattering of forces, as in the Passenger Pigeon in the daily 

 excursions after food in the region contiguous to a 'nesting.' In 

 short, it is maintained that the only way that the depopulation 

 could take place in an orderly manner is by gradual migration, 

 beginning early in the season. 



The question why some birds protract their migration south- 

 ward and others do not should here be considered. Apparently 

 other than climatic reasons must be sought. The American 

 Golden Plover, Snowfiake, Orange-crowned Warbler, Black- 

 poll Warbler, GrinnelPs Water-Thrush breed in Arctic regions. 

 The Snowfiake hardly reaches beyond the northern parts of 

 the United States, but the American Golden Plover penetrates 

 to Patagonia. The Orange-crowned Warbler winters as far 

 north as the South Atlantic and Gulf States and Grinnell's 

 Water-Thrush as the southern border of the United States, 

 while the Black-poll Warbler is said to pass the winter entirely 

 south of our limits. Difference in constitution 1 might explain 

 why Snowy Owls remain within the Arctic Circle through 

 winter and why the Yellow Warblers that breed there seek 

 milder climes, but it does not explain why the Bobolink ci-osses 

 the equator while the Phoebe endures the ice and snow in 

 Upper South Carolina, nor why the Hermit Thrush winters 



1 The relative hardiness of different species is not easy of determination. If prone- 

 ness to migration be taken as a criterion, the Robin, as a summer migrant from 

 Chester County, would rank as a feebler bird than the Blue Grosbeak, and, in the 

 vernal movements, the Black-poll Warbler, among the latest of transients in this 

 region, than the Black-and-White Warbler, Blue-gray Gnatcatcher, and Yellow- 

 throated Warbler, which are the first migrants to arrive in this locality that do not 

 belong to winter species. 



