LINES OF MIGRATORY FLIGHT 153 



from the hills, which migrate temporarily to the 

 warmer lowlands and then return to higher regions 

 after the stress of weather has passed. 



In considering migration among birds of this por- 

 tion of the southern hemisphere we must not neglect 

 to examine the remarkable habits of some of the 

 shearwaters and petrels. The sooty shearwater, for 

 example, nests on islands in New Zealand seas and in 

 the vicinity of Cape Horn, and in May, after the 

 breeding season, migrates northward, to cross the 

 Equator through both great oceans, and reach the 

 latitude of southern Greenland and the Kuril and 

 Aleutian islands. In September, it returns south- 

 ward. The slender-billed shearwater, at the same 

 season, from breeding grounds in southern Austra- 

 lian and New Zealand waters, comes north along the 

 western side of the Pacific, and in May passes south 

 along the eastern shores of that ocean. One or the 

 other of these two species in Alaskan waters, ranges 

 in flocks numbering tens of thousands. Wilson's 

 petrel, the little Mother Carey's chicken of the 

 sailor, also nests in extreme southern latitudes and 

 passes north in March, April, and May, on erratic 

 flights that carry it through the oceans of the entire 

 world with the exception of the North Pacific. These 

 species and some others penetrate as far north of the 

 Equator, as some terns, jaegers, and shore-birds 

 which breed in the Arctic travel south of it. 



