BEGINNING OF TIIE SEASONAL :MOVEMENT. As the close of the rainy season approaches in the tropics migratory strangers gradually separate themselves from the resident birds, now beginning domestic cares. and disappear. \\Int starts them off, just as the rains are bringing an increase of both plant. and insect food, we do not know. Their ovaries show little preparatory enlarge ment, and few or none are Mated. AFI they slowly proceed, keeping pace with the lifting sun and the opening spring, they will gradually concen trate upon certain highways, or migration routes.' The old males take the lead, probably merely through superior strength of wing: and it is not until the bulk of these have passed by that the females appear, followed. after an interval, by yearling birds, The weather eneountered, always uncertain, influences this progress decidedly. warm souther ly winds eneottraging the hirds to go forward, while cold spells or northerly storms check them, sometimes for a fortnight or more, and occasion ally destroy large numbers. When sunshine and southerly breezes again prevail the aceumulated host goes forward in what observers call a VI.' of migration. Such cheeks are local: and larger influences have all effect, so that the movement is uniformly earlier in sonic parts of the eon tincnt than in others.
Modtmriox llot-rEs. it is also true that the IDOVCDIPIlt is not uniformly distributed. On the contrary, there are certain definite routes or paths which birds follow in especially great numbers. The greater of these routes or 'fly lines' are generally recognized end seem to be determined partly by topography, but to a greater degree by considerations of seenrity and sub sistence. The most thickly frequented routes are
along ocean coasts, river-valleys, or mountain ranges. European specialists, like Palmeri and Middendorf, have outlined several such lines' with great particularity, and when sketched upon a map they are seen to coincide in a general way with the valley system of that continent. Simi lar highways are traceable in North America. One runs along the Pacific coast, and another up the valley of the Rio Grande and along the connected valleys and parks between the parallel ranges of the Rocky Mountains. East of the plains a horde of spring birds enters the United States along the eastern lowlands of Mexico, and by way of the West Indies, and soon divides into definite streams of travel. Parted first by the southern extremity of the Alleghenies into two main currents. one goes to the right tip the Atlantic- coast and through the Hudson Valley and New England, while a second, to the left, ascends the :Mississippi. Missouri, and Ohio, di verging more and more up tributary valleys, until all the central and northern parts of the continent are supplied. A little reflection will show how likely, from the nature of the case, arc these routes. They are natural bird-roads, without obstacles, and they afford easy guidance, plentiful vegetation, and eonsequent protection against enemies and storms, and the abundance of insect food belonging to watercourses.