140 REV. W. SERLE ON 
cal food, are in no way disposed to migrate. They are what are 
called residents: so indisposed are they to take flights, that 
but a narrow strait of sea will mark very striking differences. 
in the species of birds. I suppose there is hardly an island, 
or group of islands, of any dimensions but has its list of 
peculiar birds—a feature so very different from what holds 
in temperate and Arctic regions. Besides these residents there 
is a class of birds, extending into temperate parts, that are 
known as local migrants. It may be that they only follow 
summer on to the higher grounds and retire to the adjoining 
valleys during winter, like many of the smaller birds of India, 
or like our familiar songthrush that retires regularly in Sep- 
tember from the moors of Peeblesshire into the wooded 
valley of the Tweed, whilst the marsh birds of the mountain 
and the interior draw during winter to suitable feeding 
grounds at the seaside, and in open weather make short 
visits to these summer haunts to see that all goes well there. 
There is also the brave class of birds—sometimes called 
gipsies—chiefly of the hard-billed order, aud more or less 
fond of seeds, that in winter wage continual battle with 
the elements. The rigours of winter force them southwards, 
but they yield no more than they can help, and fight con- 
tinually, and, I must say, fairly successfully, for an existence 
on the border of the debatable land. Every now and again 
a wild winter rises into white fury, and it is on such 
occasions we hear of the Little Auk being washed in along 
our shores, or of Mountain finches of North Europe seeking 
shelter around our homesteads. 
These facts warrant us in asserting that migration is in all 
stages. Some birds do not migrate, some only from the 
hillside to the valley, and some, thousands of miles, like 
the Knot of the Arctic Circle that passes twice a year from 
one pole to the other. Such variation, moreover, may be a 
clue to the cause of migration. May it not be that there 
was a time when species of birds had a contracted area in 
which to live and multiply; the home became too small for 
all members of the family, and the struggle for existence 
compelled emigration to a short distance, or let us call it 
expansion? Thus new favourable environments were 
discovered, or if not, the less favouring circumstance of 
