“Yes, it closes as tightly as it can the draft in the vital stove—that natural stove, you know, that gives us heat, movement, and animation by burning up our blood with the help of air. The bat almost stops its breath in order to economize the fuel stored up in its little veins and make it last until the reappearance of insects at the approach of summer. In a word, it goes to sleep in the depths of some grotto, falling into an unconsciousness resembling death. Birds, however, cannot thus save their fuel. Their little stoves are always burning away under forced draft, because of the violent exercise of flying. Their temperature, summer and winter, is forty-two degrees, centigrade, whereas man’s is only thirty-eight. When such a fire has to be kept going, imagine if you can take a six months’ nap because there was nothing to eat in the larder. It is quite out of the question. What, then, do birds do? “Unable to do as the bat does, they form a bold resolve: they leave their native land, which is about to be stripped of flying insects by the cold, and go far away, sad to leave but not without the hope of returning some day. They migrate, the strong helping the weak, the old and much-traveled ones guiding the young and inexperienced. They form in flocks and fly southward to Africa, where abundant food and a warmer sun await them. With no compass but instinct to direct their course, they cross the sea, the vast expanse of water in which only an occasional islet offers them a halting-place. Many perish in the crossing, and many arrive faint with hunger and spent with fatigue, but they do arrive at last.” “It must be a trying time for the swallows when the day for starting comes,” Jules observed. “A very trying time indeed, for the bird has to tear itself away from its beloved haunts, the place where it was born, to face the fatigues and dangers of a tremendous journey, a journey never before taken by the greater number of the emigrants. In a general assembly the date of departure is fixed for about the end of August in the case of martins and sand-martins, and later, even as late as October, for house-swallows. This being arranged, the martins gather for several successive days on the roofs of high buildings. Every now and then small groups detach themselves from the rest and circle about in the air with anxious cries, taking a last look at their birthplace and bidding it farewell; then they return to their companions and, we may imagine, fall to chattering about their hopes and fears as they prepare for the journey by a careful examination of their plumage, which they oil a feather at a time. After several repetitions of these touching farewells a plaintive twittering announces the fateful hour: they must start. Launching themselves on their desperate adventure, they take flight in a body toward the south.