Some other species that have extensive summer ranges, for instance,
the pine warbler (_Dendroica pinus_), rock wren (_Salpinctes
obsoletus_), field sparrow (Spizella pusilla), loggerhead shrike
(_Lanius ludovicianus_), and black-headed grosbeak (Hedymeles
melanocephalus), 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 (_Calcarius lapponicus_), that nest in
Canada and winter in the United States; while others, including the
vesper sparrow (_Pooecetes gramineus_), chipping sparrow (_Spizella
passerina_), grackles, red-winged blackbird, bluebird, the woodcock
(_Philohela minor_), 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
(_Capella delicata_), 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 id the West Indies or in
Central America or South America. For example, the Cape May warbler
(_Dendroica tigrina_), 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.
[Illustration: B3763M
Figure 13.--Barn Swallow, a bird that has so long a migration route
that some individuals breed north to Yukon and Alaska, while the
winter range extends south to Argentina, 7,000 miles away.]