migration retreats to follow him to the southern hemisphere* 

 Migratory birds come north to breed, and rear their young in a, 

 climate where the temperature is best suited to their several 

 requirements. The adult birds are the first in the spring. The 

 young of the previous year often do not quite reach the usual 

 breeding grounds of their species, and sometimes stay near their 

 winter homes all through the summer. The spring migration is 

 made with greater rapidity than that in the autumn. The birds 

 that go farthest north, leave their southern homes last. The 

 swallows that breed in South Europe begin to leave South Africa, 

 about the middle of J'ebruary, but those that breed in North 

 Eussia delay their departm-e until the middle of April, as though 

 aware that their summer quarters were not yet ready for them. 

 This spring migration lasts till about the middle of June, say 

 four months. Some birds take different routes in spring an^ 

 autumn. The nightingale (Erithacus lusciniaj, passes over Heligo- 

 land in April and May, but has never been caught there in 

 autumn; the turtle dove (Turtur auriUis), passes Heligoland com- 

 monly in May and June, but it is much less abundant in autumn. 

 The dotterel (Eudromias morinelhis), is rarely or never seen in Malta 

 in spring, but passes that island regularly in autumn. The quail 

 travels by day in autumn, and by night in spring ; the common 

 .bee-eater does exactly the reverse. 



In the autumn the birds that have the longest journeys before 

 them, start first. Young knots (Tringa canutus), and young gray 

 plovers (Charadrius helveticus), begin to pass Hehgoland and the 

 British Islands early in August, some even with bits of down 

 sticking to their plumage. Both these birds winter far in the 

 isouthern hemisphere, reaching Australia, South Africa, and South 

 America, with fly-lines more than 10,000 miles in length. Young 

 sanderlings {Calidris arenaria), sometimes arrive on the British 

 coasts at the end of July ; their fly line is equally lengthy, extend- 

 ing to South Africa, South America, and the Malay Archipelago. 

 The cuckoo {Cuculus canorus), with a fly-line reaching from the 

 North Cape to South Africa, migrates early, passing Heligoland ia 

 July. In this species, the old birds begin their autumn migration 

 before the young, an anomaly due to its declining any pareutal 

 ^duties, and being therefore free to set off early. Species of cuckoo 

 that nest like otlier birds migrate in the usual order. Autumn 

 migration lasts also about four mouths, from mid July to mid 

 llTovember, being at its height in September and October. The 

 great intensity of migration is much more sudden in autumn than 

 .in spring, and many more birds are observed on passage. The 

 •birds that have appeared earliest in the spring are usually the last 

 to leave ; thus the wbeatear and chiff-chaff arrive amongst the 



