GLACIAL EPOCHS AND POLAR CLIMATES. 55 



the beginning of the Glacial Epoch ; and yet again 

 whilst that epoch was slowly pursuing its terribly 

 majestic course along 200,000 years of time, with 

 alternating mild periods at its inception and its 

 close. We may instance among many others the 

 Gray Phalaroi)e {Plialaropus J'niicariiu), Ross's 

 Gull {R/wdostetJiia rossi), the Glaucous Gull 

 [Giaucus giaucus), the Iceland Gull {Glaucus leu- 

 copteriis), the Little Auk {Merguhis alle), the 

 Harlequin Duck {Clangula histrioiiica), Steller's 

 Eider [Somaleria ste/Ieri), and the King Eider 

 {Somateria spectabilis). Now all these species are 

 either Polar or Arctic in their distribution, more or 

 less stationary (in the sense of having but a slightly 

 marked southern flight in winter), and only appear 

 very irregularly in localities far south of their usual 

 habitat, and then only when exceptionally severe 

 winters in the north compel a southern movement. 

 None of these birds remain long in the south ; they 

 retire as soon as milder conditions prevail, and their 

 movements although migratory are irregular and un- 

 certain. They are examples of what may be termed 

 Incipient Migration. Whenever climatal conditions 

 become more severe, entailing absence of food, regu- 

 lar and more extended flights may become the rule 

 among at least some of these species. We shall refer 

 more particularly to this matter in a future chapter. 

 From species whose migratory movements are 

 at the present time incipient, we will now pass to 

 others in which they are decidedly regular, though 

 small. Excellent examples of short migration flight 



