272 
ISLAND LIFE. 
[part it. 
distant Bermudas almost every year, and extending its range as 
far as Paraguay, is the only species of land-bird which remains 
completely unchanged in the Galapagos ; and we may therefore 
conclude that some stragglers of the migrating host reach the 
islands sufficiently often to keep up the purity of the breed. 
Next, we have the almost cosmopolite short-eared owl (Asio 
brachyotus), which ranges from China to Ireland, and from Green- 
land to the Straits of Magellan, and of this the Galapagos bird 
is probably only one of the numerous varieties. The little 
wood warbler ( Dendrceca aureola) is closely allied to a species 
which ranges over the whole of North America and as far south 
as New Grenada. It has also been occasionally met with in 
Bermuda, an indication that it has considerable powers of flight 
and endurance. The more distinct species — as the mocking- 
thrushes (Mimus), the tyrant fly-catchers (Pyrocephalus and 
Myiarchus), and the ground dove (Zenaida), are all allied to noil- 
migratory species peculiar to tropical America, and of a more 
restricted range ; while the distinct genera are allied to South 
American groups of finches and sugar-birds which have usually 
restricted ranges, and whose habits are such as not to render 
them likely to be carried out to sea. The remote ancestral 
forms of these birds which, owing to some exceptional causes, 
reached the Galapagos, have thus remained uninfluenced by 
later migrations, and have, in consequence, been developed into 
a variety of distinct types adapted to the peculiar conditions of 
existence under which they have been placed. Sometimes the 
different species thus formed are confined to one or two of the 
islands only, as the two species of Certhidea, which are divided 
between the islands but do not appear ever to occur together 
Mimus parvulus is confined to Albemarle Island, and M. trifascia- 
tus to Charles Island ; Cactornis pallida to Indefatigable Island, 
and C. abingdoni to Abingdon Island. 
Now all these phenomena are strictly consistent with the 
theory of the peopling of the islands by accidental migrations, 
if we only allow them to have existed for a sufficiently long 
period ; and the fact that volcanic action has ceased on many of 
the islands, as well as their great extent, would certainly 
indicate a considerable antiquity. 
