A small number of the species migrate by day; among these are the Hawks, Swallows, Ducks, and Geese. The last two groups also travel by night. The rate at which they proceed on their journey is not as great as was formerly supposed. From twenty to thirty miles an hour is the speed generally taken, and perhaps fifty miles an hour is the greatest rapidity attained. Flights are usually not long sustained, a hundred and fifty miles a day being above the {69} average. Individuals will at times pause and remain for a few days in a favourable locality before proceeding farther. When large bodies of water are encountered longer flights are of course necessary, for land birds cannot rest on the water as their feathers would soon become water-soaked and drowning would result. Multitudes of small birds, including even the little Ruby-throated Hummingbird, annually cross the Gulf of Mexico at a single flight. This necessitates a continuous journey of from five hundred to seven hundred miles. Some North American birds migrate southward only a few hundred miles to pass the winter, while many others go from Canada and the United States to Mexico, Central and South America. The ponds and sloughs of all that vast country lying between the Great Lakes and Hudson Bay on the east and the mountains of the Far West, constitute the principal nursery of North American waterfowl, whence, in autumn, come the flocks of Ducks and Geese that in winter darken the Southern {70} sounds and lakes. One stream moves down the Pacific Coast, another follows the Mississippi Valley to the marshes of Louisiana and Texas, while a third passes diagonally across the country in a southeasterly direction until it reaches the Maryland and Virginia coastline. Thence the birds disperse along the coastal country from Maine to Florida. [Illustration: Migration Routes of Some North American Birds]