358 
DARWINISM 
CHAP. 
ing nightjars, huntings, white-throats, willow-wrens, cuckoos, 
house-sparrows, robins, wheatears, and blackbirds. These 
had probably crossed from Somersetshire, and had they been 
caught by a storm the larger portion of them must have been 
blown out to sea. 1 
These facts enable us to account sufficiently well for the 
birds of oceanic islands, the number and variety of which are 
seen to be proportionate to their facilities for reaching the 
island and maintaining themselves in it. Thus, though more 
birds yearly reach Bermuda than the Azores, the number of 
residents in the latter islands is much larger, due to the 
greater extent of the islands, their number, and their more 
varied surface. In the Galapagos the land-birds are still more 
numerous, due in part to their larger area and greater proxi¬ 
mity to the continent, but chiefly to the absence of storms, 
so that the birds which originally reached the islands have 
remained long isolated and have developed into many closely 
allied species adapted to the special conditions. All the 
species of the Galapagos but one are peculiar to the islands, 
while the Azores possess only one peculiar species, and 
Bermuda none — a fact which is clearly due to the continual 
immigration of fresh individuals keeping up the purity of 
the breed by intercrossing. In the Sandwich Islands, which 
are extremely isolated, being more than 2000 miles from 
any continent or large island, we have a condition of things 
similar to what prevails in the Galapagos, the land-birds, 
eighteen in number, being all peculiar, and belonging, except 
one, to peculiar genera. These birds have probably all 
descended from three or four original types which reached 
the islands at some remote period, probably by means of 
intervening islets that have since disappeared. In St. Helena 
we have a degree of permanent isolation which has pre¬ 
vented any land-birds from reaching the island ; for although 
its distance from the continent, 1100 miles, is not so great 
as in the case-of the Sandwich Islands, it is situated in an 
ocean almost entirely destitute of small islands, while its 
position within the tropics renders it free from violent storms. 
Neither is there, on the nearest part of the coast of Africa, 
a perpetual stream of migrating birds like that which 
1 Report of the Brit. Assoc. Committee on Migration of Birds during 1886. 
