v "i' XI l Loomis on Birds of Chester County, South Carolina. 107 



north, it is not disproved that there may exist urgent necessity 

 for migration in the bulk of the species in a region further south. 

 If the Snowy Owl does not visit the United States regularly in 

 great numbers, neither does the Prairie Horned Lark visit South 

 Carolina every winter in numbers equal to those of the season 

 of 1S76-77. As abridgment of feeding grounds is promptly met 

 in the Prairie Horned Lark by protraction of migration, it would 

 not be remarkable if there should be protraction of migration 

 in the Snowy Owl, owing to temporary failure of food, though 

 the cause of the failure be different. It is well authenticated 

 that its presence in spring and summer in portions of Aixtic 

 regions is dependent upon the lemming (Murdoch, 1. c, p. 107 ; 

 Nelson, 1. c, p. 153). Mr. Nash, as quoted by Mr. Thompson 

 in 'The Birds of Manitoba' (Proc. U. S. Nat. Mus., XIII, p. 

 545), says, "During the winter of 18S2-S3 they were very 

 common. ... In the winter of 1883-84 they were less numer- 

 ous ; in the winter 1884-85 very few were seen; the same in 

 iS85-'S6 as in the last three [two] mentioned years; hares were 

 extremely abundant in the north ; they probably found sufficient 

 food to maintain them there." Insufficiency in food is ascribed 

 as the cause of the exceptional extensions of this Owl into the 

 United States, not unusual failure on the breeding grounds, but 

 shortness in the region generally the limit of southward migra- 

 tion of the numbers. The vanguard appears to penetrate so far 

 into the land of plenty, as to open the way for an early return, 

 the beginning of the northward migration at the southern ter- 

 minus not being long deferred in the majority. A counterpart 

 is found in the brief sojourn of the Prairie Horned Larks in this 

 vicinitv (Auk, VIII, p. 57). The term of residence in all birds 

 at the southern points of winter distribution is doubtless deter- 

 mined by the extent of the food area available to the northward. 



In fine, exceptional movement in the Snowy Owl is interpreted 

 as liberal adjustment of population to food-supply — adjustment 

 in which emigration is not put off until actual starvation is immi- 

 nent (because of unusual insufficiency in food in the ordinary 

 winter range), but emigration which takes place in advance of 

 such impending calamity and which extends far into the region 

 of bountiful store. 



The rarity of the Snowy Owl in the United States west of the 

 Rocky Mountains is attributed to southeasterly migration, — the 



