ZooL.— Vol. II.] LOOMIS— CALIFORNIA WATER BIRDS. 313 



Winter with Its Failure of Food. — Because of winter 

 with its failure of food all birds can not remain through the 

 whole year at the place of their birth. The only escape 

 from extensive extermination lies in depopulation, which 

 is successfully accomplished by migration. This periodic 

 movement, however, is not effected simply by the inhabi- 

 tants of colder regions temporarily retreating to a warmer 

 climate when they feel the pressure of winter, for there is 

 migration in all latitudes where birds find a home, in all cli- 

 mates, and at all seasons of the year. Some birds breeding 

 in the Arctic migrate to the North Temperate Zone, some 

 to the tropics, or even to the South Temperate Zone. Sim- 

 ilar diversity in migration exists in birds nesting in more 

 temperate regions; for example, the Bobolink penetrates far 

 into South America while the Ipswich Sparrow does not 

 pass beyond the United States. In the opposite hemisphere, 

 the Dark-bodied Shearwater and some other Petrels breed 

 on the oceanic islands during our winter and afterward 

 apparently change their abode to northern seas in the time 

 of our summer. Other birds still of the Southern Hemi- 

 sphere do not journey beyond the equator.^ There is migra- 

 tory movement confined to the tropics, contemporaneous 

 with the wet and dry seasons,^ and there appears to be 

 migration northward from the subtropics and tropics after 

 the breeding period to an area of greater food-supply, as in 

 the Black-vented Shearwater and Black-footed Albatross. 

 There is also much minor movement, like the migration of 

 the Brown-headed Nuthatch on the approach of winter 

 from the upper to the lower country in the Carolinas, and 

 of the Mountain Partridge from the eastern slope of the 

 Sierra Nevada across the summit to the warmer western 

 slope. There is migration that is delayed until the ground 

 is covered with snow, and migration that takes place before 

 midsummer, for birds begin to migrate, after breeding, as 

 soon in temperate as frigid climes, the Murres of the 



1 As to migration in the Southern Hemisphere, consult Hudson, 'Argentine Orni- 

 thology;' Durnford, 'Ibis,' 4th Ser., Vol. I, p. 166; Aplin, ibid., 6th Ser., Vol. VI, p. 149; 

 Seebohm, Geogr. Distr. Charadr., p. 37; Buller, Hist. Birds N. Z., 2nd Ed., Vol. I, p. xli. 



2 Gaumer, P. Z. S., 1883, p. 436. 



