BIRDS. 235 
tracted winter with great paucity of food. Food 
however is not without its power also, though cer- 
tainly of a secondary order. Plenty of provision 
conjoined with mildness and serenity of climate 
will induce a summer visitant to stay with us be- 
yondits usual period, and again, scarcity of provender 
with mildness of season will cause a winter visitor 
to hasten its northward flight. ‘These remarks on 
migration are supported by those of Mr. White, who 
apparently however had not adopted this very theory 
except in part. In Letter vii. Part 2nd, he says, 
“ Swallowsand House-martins abound yet,(Oct. 8th) 
“induced to prolong their stay by this soft, still, dry 
“ season ;” and again in Letter viii. he says, “ From 
“hence it appears, that it is not food alone which 
“‘ determines some species of birds with regard to 
“ their stay or departure. Fieldfares and Redwings 
“ disappear sooner or later according as the warm 
““ weather comes on earlier or later, for I well re- 
““ member after that dreadful winter 1739—40, that 
“ coldnorth-east winds continued to blow on through 
“¢ April and May, and that these kinds of birds (what 
“few remained of them) did not depart as usual, 
“put were seen lingering about till the beginning 
“of June.” —See also Journal of a Naturalist, 
p. 395, 396. 
E 5 2 
