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 
