The geographical distribution of animals, with a study of the relations ...

20 DISPERSAL AND MIGRATION. [part i.of April, however cold it may be, while its departure may takeplace from the end of September to late in October, and is said byForster to occur on the first N. or KE. wind after the 20th ofSeptember.Almost all the migratory birds of Europe go southward tothe Mediterranean, move alongover in three places only ;its coasts east or west, and crosseither from the south of Spain, in theneighbourhood of Gibraltar, from Sicily over Malta, or to theeast by Greece and Cyprus. They are thus always in sight ofland.The passage of most small birds (and many of the largerones too) takes place at night ;and they only cross the Mediterraneanwhen the wind is steady from near the east or west,and when there is moonlight.It is a curious fact, but one that seems to be well authenticated,that the males often leave before the females, and bothbefore the young birds,later and alone.old ones ;which in considerable numbers migrateThese latter, however, seldom go so far as theand numbers of young birds do not cross the Mediterranean,but stay in the south of Europe.The same rule appliesto the northward migration; the young birds stopping shortof the extreme arctic regions, to which the old birds migrate. 1When old and young go together, however, the old birds takethe lead. In the south of Europe few of the migratory birdsstay to breed, but pass on to more temperate zones ;thus, in thesouth of France, out of 350 species only 60 breed there. Thesame species isoften sedentary in one part of Europe and migratoryin another ; thus, the chaffinch is a constant resident inEngland, Germany, and the middle of France ;the south of France and in Holland :thebut a migrant inrook visits the southof France in winter only : the Falco tinnunculus is both aresident and a migrant in the south ot France, according toM. Marcel de Serres, there being two regular passages everyyear, while a certain number always remain.1Marcel de Serres states this as a general fact for wading and swimmingbirds. He says that the old birds arrive in the extreme north almost alone,the young remaining on the shores of the Baltic, or on the lakes of Austria,Hungary, and Russia. See his prize 'essay, Des Causes des Migrations, &c.2nd ed., Paris, 1845, p. 121.