26 LoOMlS on Birds of Chester County, South Carolina. ,. ln 



Robin locally far north where the snow covers the ground for 

 months dispels, too, all idea that its absence is due to removal 

 wholly to the southward. 



Cold and warmth apparently affect only the winter migratory 

 movements of isolated communities, not otherwise controlling 

 location in any particular locality in the normal winter range. 

 For example, Bewick's Wren may be rare here during December 

 and January in a mild winter and quite common during a 

 severe one, or the opposite may be true, in either case the 

 species being fairly numerous during the height of migration. 

 In the phenomenally mild winter of 18S9-90 they wex - e absent 

 until the close of December when a slight movement occurred, 

 apparently the advance of an isolated community from below, for 

 there was unmistakable northward movement in other species. 

 The height of its migration was reached in March as in ordinary 

 years. The sudden influx of Robins in the early part of January, 

 1SS7 (Auk, IX, p. 29) with the coming of snow, and their dis- 

 appearance on the return of milder weather seems to have been 

 an instance of migratory movement of a large community from 

 above, for the regular northward migration took place at the usual 

 time. Severer December and January snows, too, have failed, 

 before and since, to occasion such intrusions. It is a curious fact 

 that migration should take place in the Robin with the advent 

 of snow at the South while flocks remain during the entire winter 

 "in the valleys among the White Mountains, where snow covers 

 the ground from October to June, and where the cold reaches the 

 freezing-point of mercury" (Brewer, Hist. N. A. Birds, Land 

 Birds, I, p. 26). x The explanation I would offer is, that the birds 

 which visited us had been residing below the snow-line and were 

 dependent on account of their great numbers chiefly upon the 

 ground for food, and when the ground was covered by snow, they 

 had no alternative but to remove southward and await its dis- 

 appearance. The closing words, which I have omitted, in the 

 quotation just cited, "attracted by the abundance of berries,'' 

 explain their presence in New Hampshire. 



Food as bearing upon the location of isolated communities re- 

 mains to be considered. In 'off years' of species whose absence is 

 attributed to variability in location of such communities there has 



1 See Auk, VIII, p. 317, for instance of Robins wintering in numbers in Quebec. 



