Fall flights not far south of breeding ranges
Some other species that have extensive summer ranges, for instance the pine warbler, rock wren, field sparrow, loggerhead shrike, and black-headed grosbeak, are found to concentrate during the winter season in the southern part of the breeding range, or to occupy additional territory that is only a short distance farther south. The entire species may thus be confined within a restricted area for the period of winter, and then, with the return of warmer weather, spreads out to reoccupy the full range.
There are many species, including the tree sparrow, slate-colored junco, and Lapland longspur, that nest in Canada and winter in the United States; while others, including the vesper sparrow, chipping sparrow, grackles, red-winged blackbirds, bluebirds, the woodcock, and several species of ducks, nest in the northern United States and move south for the winter to areas along the Gulf of Mexico. This list includes the more hardy species, some individuals of which may linger in protected places well within the reach of severe cold, as, for example, Wilson's snipe or jacksnipe, which frequently is found during subzero weather in parts of the Rocky Mountain region where warm springs assure a food supply. More than 100 of our summer birds leave the United States entirely and spend the winter in the West Indies, or in Central America or South America. For example, the Cape May warbler, which breeds from northern New England, northern Michigan, and northern Minnesota, north to New Brunswick, Nova Scotia, and nearly to Great Slave Lake, is concentrated in winter chiefly in the West Indies, its metropolis at this season being the island of Hispaniola.