“The day for starting on this momentous journey is decided upon in a great assembly, toward the end of August for the window-swallow, and considerably later, even as late as November, for the chimney-swallow. [[320]]When once the date has been fixed, the window-swallows gather together daily for several days on the roofs of tall buildings. Every few minutes small parties detach themselves from the general conclave and circle about in the air with anxious cries, taking a parting look at their native haunts, and paying them a last farewell. Then they return to their places among their companions and join in noisy chatter on the subject of their hopes and fears, all the while preparing themselves for the distant expedition by a careful inspection of their plumage and a final touch to one lustrous feather after another.
“After several repetitions of these farewells a plaintive twittering announces the fateful hour. The moment has come, it is time to start. The flock rises, the emigrants are off for the south. If one of them has been marked with a red string around the claw in order to be recognized, you may be sure you will see it come back the next spring and take possession of its nest again with little cries of joy at finding it intact and ready for occupancy after a few repairs.
“With their vigorous wings the duck and goose, in their wild state, are ardent travelers. On a gray day in November, when there are signs of snow, it is not unusual to see passing from north to south, at a great height, birds arranged in single file, or in a double file meeting in a point, like the two branches of the letter V. These birds are a flock of either ducks or geese in the act of migrating.
“If the flock is of no great size, the birds composing [[321]]it arrange themselves in one continuous file, the beak of each following bird touching the tail of the preceding, in order that the passage opened through the air may not have time to close again. But if the flock is a large one, two files of equal length are formed, which meet at an acute angle, the front of the moving mass.
“This angular arrangement, of which we find examples in the ship’s prow, the plowshare, the thin edge of a wedge, and a multitude of utensils designed for cleavage, is the most favorable for pushing through the mass of the air with the least fatigue. If in marshaling their flying battalions the goose and the duck had taken counsel of the engineer’s science, they could not have managed better. But they have no need of others’ advice: instructed by their own instinct, they utilized long before we did the principle of the wedge.
“Moreover, to divide among all the members of the flock the excess of fatigue incurred by the file-leader in opening a passage through the air by strength of wing, each in turn takes the post of honor, the forward end of the single file or the point of the angle formed by the double file. Its term of service ended, the bird at the head retires to the rear to recuperate, and another leader takes its place. By this equitable division of labor the fatigue does not prove excessive for any one bird, and the flock leaves no stragglers behind.” [[322]]
CHAPTER LVIII
CARRIER-PIGEONS
Resuming the subject of bird instinct as illustrated by the migratory flock’s unerring precision in finding its way over thousands of miles to a desired nesting-place, Uncle Paul continued as follows: