LINES OF MIGRATORY FLIGHT 143 



ern end of Great Salt Lake as a regular stopping 

 station in the spring of the year. 



Some migrants through the Rocky Mountain 

 region continue south into Mexico, but few seem to 

 penetrate far beyond the Mexican tableland. Study 

 of migration in that part of the Rocky Mountain 

 region south of the area where severe winters come 

 to the valleys is complicated by many altitudinal 

 movements, in which birds merely move up and 

 down the mountain slopes as the seasons change. 

 The greater part of the species found are not exten- 

 sive travellers except for those finches, sparrows, 

 shrikes, thrushes, and water-birds that nest in the 

 far north and winter in this region. 



West of the Rocky Mountains there is a broad 

 line of flight down the Sacramento and San Joaquin 

 valleys in California, which is scarcely separated by 

 the coast ranges from a coastal line that passes 

 south to southern California and for some birds con- 

 tinues down the coast of Mexico. This coastal line is 

 marked strongly by species of migrant water-birds 

 which are restricted to the vicinity of salt water in 

 their search for food. Some of these are truly shore- 

 birds and follow the beaches. Others are maritime, 

 among which are included great numbers of shear- 

 waters and fulmars, and many auklets, that pass at 

 sea. 



Many peculiarities of distribution due to migra- 



