. Bird migration . pre-senting distinctly segregated pathways with clearly defined the contrary, they are merely convenient subdivisions of the onegreat flightway which extends from JTorth to South America. Thereis probably no single mile in the whole east and west line from north-ern Mexico to the Lesser Antilles which is not crossed each fall bymigrating birds. What is meant is that the great bulk of bothspecies and individuals cross the GuK to eastern Mexico, while to theeastward their numbers steadily diminish. The map of the migration routes (fig. 2) shows route No. 1 that hasn
. Bird migration . pre-senting distinctly segregated pathways with clearly defined the contrary, they are merely convenient subdivisions of the onegreat flightway which extends from JTorth to South America. Thereis probably no single mile in the whole east and west line from north-ern Mexico to the Lesser Antilles which is not crossed each fall bymigrating birds. What is meant is that the great bulk of bothspecies and individuals cross the GuK to eastern Mexico, while to theeastward their numbers steadily diminish. The map of the migration routes (fig. 2) shows route No. 1 that hasnot yet been described. It extends in an approximately north andsouth fine from Nova Scotia to the Lesser Antilles and the northerncoast of South America. Though more than a thousand milesshorter than the main migration route, it is not employed by any 16 BULLETIN 185, XT. S. DEPARTMENT OP AGRICtTLTUEE. land bird. But it is a favorite faU route for thousands of waterbirds, notable among which is the golden Fig. 6.—Migration of the cliff swallow (Petrochelidon lunifrons). This is a day migrant, feeding on thewing; hence it keeps near land and journeys around the Gulf of Mexico, instead of flying across it as isdone by the black-poll warbler (fig. 5) which migrates at night. (See pp. 19 and 26.) The journey of this plover is wonderful enough to be given indetail. Its most striking characteristics are a single flight of 2,400miles—the longest known flight of any bird—and an elliptical migra-tion route following different paths for the spring and the fall BIED MIGRATION. 17 migration (see fig. 4). In the first week of June the golden ])l()vcrarrive at their breeding grounds on the barren grounds above theArctic Circle far beyond the tree line. While the lakes are still ice-bound they build their shallow nests in the moss only a few inchesabove the frozen ground. As soon as the young are old enough tocare for themselves fall migration is begun by a trip to the Labrador
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