14 CIRCULAR 363, U. S. DEPARTMENT OF AGRICULTURE 
everyday purposes and also for migration, and an accelerated speed 
for escape or pursuit; this in some cases may be nearly double the 
normal rate of movement. Nevertheless, the effort required for the 
B4749M 
FIGURE 5.—Migration of the cliff swallow; a day migrant that, instead of flying across the Caribbean Sea 
as does the blackpoll warbler (fig. 11), follows around the coast of Central America, where food is readily 
obtained. 
high speeds could not be long sustained, certainly not for the long- 
distance migratory journeys that are regularly made by most birds. 
The theory that migrating birds attain high speeds received en- 
couragement from the German ornithologist Gatke, who _ for 
many years, made observations on birds at the island of Heligoland - 
