1891.] The Origin of the Avifauna- of the Bahamas. 537° 
also refers to those species which, being non-migratory, are at 
the same time species of retiring habits,—that is, are terrestrial or 
thicket-loving, and do not, as a rule, make extended flights. It is 
obvious that birds of this character would not be exposed to the 
action of storms and gales, and we rarely find them inhabiting 
islands. Wrens are excellent examples, and with the exception 
of a small group found on the southern Windward Islands, are 
unknown from the West Indies, although they are abundant on 
all the surrounding mainlands. The Carolina wren, one of the 
most common birds of Florida, has never been found in the 
Bahamas, nor indeed in Cuba. On examining the Bahama fauna, 
therefore, we find that the birds, although resident now, are 
descendants of, or are co-specific with, either migratory species 
or species whose non-sedentary habits have rendered them sus- 
ceptible to the influences of that island populator, the wind, to 
which many Bahaman birds doubtless owe their original appear- 
ance on the islands. But we have also found that the descen- 
dants of the migratory species which have become endemic are 
residents in the same latitude on the mainlands. Birds of strictly 
migratory habits, therefore, are not apt to form a part of island 
life, unless the islands occur near the limits of their breeding 
habitats. The Bermudas are annually visited by large numbers 
of South American migrants, but the “number of resident land 
birds is restricted to six. 
Thus the Bahamas do not owe their avifauna to purely migra- 
_tory species, but to the occurrence there of resident species from, 
generally contiguous areas ; and their original appearance may 
š havė been due to a gradual extension of range, Or, as we have 
' said, to their accidental occurrence through the influence of violent 
winds. With the exception of two bi-continental species, which 
throughout their ranges are subject to local specialization under 
favorable conditions, the endemic Bahaman birds are derived from 
species which in their generally limited ranges and close relation- 
ships with other species prove their susceptibility to the influences 
(Of their surroundings. 
As to the causes which have produced differentiation in the 
forms we have just discussed, we can say very little. We may 
