MIGRATION OF BIRDS. 281 
there, others proceed to Scandinavia. The inference is fairly 
obvious that our English Swallows come from the northern- 
most winter quarters, and that the South African birds breed 
in Scandinavia. In the far north nesting conditions are not 
favourable till June, so South African birds have no need to 
migrate as early as those which nest in Central Europe and 
England. 
I have just mentioned that the Swallow is a day migrant, 
but this is not the case with many birds. A vast amount of 
the migration which takes place is unseen by us, as it is 
performed at night, and at altitudes and speeds which are still 
to a certain extent open to conjecture. The reason why birds 
chose night time for a long flight, especially across the sea, 
admits of a very probable explanation. Most birds spend a 
great part of the day hunting for food, so that if a bird takes 
an all-day flight, it must start on an empty stomach, spend an 
exhausting day without food, and on arrival pass another 
night of fasting before it can satisfy its hunger. A night flight 
can be taken without interfering with the feeding hours. 
Various and often accidental observations by astronomers 
have given interesting data of the height and speed of some 
migrations. An observer was measuring the height and 
velocity of clouds when some ducks came under his notice. 
He calculated that they were 958 feet up, and flying at a rate 
of 48 miles an hour. Other records based on somewhat 
similar observations give heights varying from 1,400 to 5,400 
feet. Mr. Eagle Clarke observed during his stay at the Kentish 
Knock lightship that many birds performing this North Sea 
journey of about 120 miles by day flew close above the waves, 
whatever the weather, and at no extraordinary speed. He 
says: ‘‘ Speaking generally, the migrants pursued their way 
at the steady rate characteristic of their respective species. 
There was no hurry, but at the same time there was a business- 
like manner about them in keeping with the important work 
on hand. Certain species habitually fly faster than others. 
He roughly gauged the speed of the Larks at 25 miles per hour, 
and of the Starlings at 35 to 40. 
Lastly, there remains a problem as difficult to answer as any. 
By what faculty do migrants find their way from point to 
