. Birds of America;. Birds -- North America. xviii BIRDS OF AMERICA uneconomical way of applying power, since all the force required to bring the wing forward for the beginning of the stroke is not only wasted, but more than wasted, as it largely increases the air friction and retards the speed. On the other hand, the screw propeller of the aero- plane has no lost motion. Yet less than 2 ounces of fuel in the shape of body fat suffice to force the bird at a high rate of speed over that 2,400-mile course. A thousand-pound aeroplane, if as economical of fuel, would consume in a 20-mile flight no
. Birds of America;. Birds -- North America. xviii BIRDS OF AMERICA uneconomical way of applying power, since all the force required to bring the wing forward for the beginning of the stroke is not only wasted, but more than wasted, as it largely increases the air friction and retards the speed. On the other hand, the screw propeller of the aero- plane has no lost motion. Yet less than 2 ounces of fuel in the shape of body fat suffice to force the bird at a high rate of speed over that 2,400-mile course. A thousand-pound aeroplane, if as economical of fuel, would consume in a 20-mile flight not the gallon of gasoline required by the best machines but only a single pint. The Canada Goose is typical of what may be called regular migration. This bird fulfills the popular notion of bird migration, /. c, it moves northward in spring as soon as. ISOTHERM or 35° F ISOCHRONAL MIGRATION LINES Tnurtesy of U. S. Dept. of Agriculture MIGRATION OF THE CANADA GOOSE An example of migration keeping pace with the advance of spring the loosening of winter's fetters offers open water and a possibility of food. It continues its progress at the same rate as spring, appearing at its most northern breeding grounds at the earliest possible moment. The isotherm of 35° F. seems to be the governing factor in the rate of spring migration of the Canada Goose and the isotherm and the vanguard of the Geese are close traveling companions throughout the entire route. Moreover, the isochronal lines representing the position of the van at various times are approximately east-and-west lines during the whole migration period. But this so-called regular migration is performed by a very small percentage of species, the great majority choosing exactly the opposite course — to remain in their winter homes until spring is far advanced and then reach their breeding grounds by a migration much more rapid than the northward advance of the season. Much has been learned about bird migration in these latter d
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