38 BIRDS OF SOUTH DAKOTA 



winter in the State were very likely raised some distance farther 

 north; and yet such questions are very difficult to settle. We 

 have Crows, Hawks, Owls, Downy and Hairy Woodpeckers, 

 and sometimes Flickers, summer and winter. Are they the 

 same ones? Some think that the greater portion of the bird pro- 

 cession simply "moves up"; that is, with many species those 

 that winter farther north go farther north to nest, while others 

 come from farther south to nest where the first wintered, and 

 so on. However this may be with numerous species, the ex- 

 ceptions are many and marked. For example, the Arctic Tern 

 summers in the North Polar regions and winters in the South 

 Polar regions, seeing practically no darkness the year round. 

 The Golden Plover nests in northern North America and winters 

 in southern South America. 



One seeing birds in flight would think that they migrate 

 at tremendous speed, but the average for all species is not over 

 twenty-five miles a day. Land birds that migrate by day do 

 not average so much, some of them not over half of it. Mr. 

 Wells W. Cooke shows that the van of the migrating procession, 

 though constantly changing in bird personnel on account of 

 birds dropping out when they have reached their nesting places, 

 moves with increasing rapidity as it comes north. He says: 

 "The average speed of migration from New Orleans to southern 

 Minnesota for all species is close to twenty-three miles a day. 

 Sixteen species maintain a daily average of forty miles from 

 southern Minnesota to southern Manitoba; and from this point 

 twelve species travel to Lake Athabasca at an average speed of 

 seventy-two miles a day, five others to Great Slave Lake at 116 

 miles a day, and five more to Alaska at 150 miles a day." 



Both the time of arrival and speed would seem to be gov- 

 erned largely by temperature. The Canada Goose and the Robin 

 move at the same speed as spring temperature, which is 35* F. 

 The hosts of Warblers come with the blossoms, which usually 

 appear at a certain general temperature ; and temperature moves 

 north with increasing rapidity as the season progresses. This 

 is especially true in the Northwest, where it is affected by the 

 Chinook winds. 



In addition to the regular migration of birds there are also 



