Page:The Migration of Birds - Thomas A Coward - 1912.pdf/40

24 southward is surely due to the fact that the temperature is falling in the north more rapidly than in the south. That they are not always clue south is certain. The American golden plover, as Mr Wells W. Cooke so lucidly demonstrates, at first travels eastwards from its home in western Arctic America to the fruit-laden lands of Labrador and Nova Scotia, where it feeds for some time, staking up for its long over-sea journey due south. Mr Cooke says, "It can also be said that food supplies en route have been the determining factor in the choice of one course in preference to another, and not the distance from one food base to the next. The location of plenty of suitable provender having been ascertained, the birds pay no attention to the length of the single flight required to reach it" (21). During the evolution of the route many bases would be found which were superior to others, and skipping and the gradual shortening of the journey from one to another would result, The final goal, the food base which in any weather or season provide the safe sufficiency of food, having been reached by the birds, this becomes the Winter quarters. The return to this secure retreat each winter, instead of aimlessly wandering in search of a better, and thus the long-distance migratory habit is formed. Heredity tends to confirm this and it becomes an instinct.