48 
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 
oung of the previons year often do not quite reach the usual 
eee ou: 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 February, but those that breed in North 
Russia delay their departure until the middle of April, as though 
ware 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 and 
autumn. The nightingale (Erithacus lusciniaj, passes over Heligo- 
Jand in April and May, but has never been caught there in 
autumn; the turtle dove /Turtur auritus), passes Heligoland com- 
monly in May and June, but it is much less abundant in autumn, 
The dotterel (Eudromias morinellus ), 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 Heligoland and the 
British Islands early in August, some even with bits of down 
sticking to their plumage. Both these birds winter far in the 
southern 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 in 
July. In this species, the old birds begin their autumn migration 
before the young, an anomaly due to its declining any parental 
duties. and being therefore free to set off early. Species of cuckoo 
that nest like other birds migrate in the usual order. Autumn 
migration lasts also about four months, from mid July to mid 
November, 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 wheatear and chiff-chaff arrive amongst the 
