194 BIRD STUDIES WITH A CAMERA 
questions of food and climate must be considered, 
we have here the problem reduced to its simplest 
terms; and in the desire for seclusion during the 
breeding season which induces birds to conceal their 
nests, if possible perhaps near by, but if necessary 
after a journey of varying length undertaken espe- 
cially for the purpose, we have a good and sufficient 
cause for the origin of bird migration. 
An attempt to explain the present manifestation 
of the migratory movement involves a study of the 
climatic changes to which our globe has been sub- 
jected. No doubt many birds controlled by “he- 
redity of habit” make semiannual journeys which 
at one time were necessary, but under existing cir- 
cumstances are no longer required. Why, for ex- 
ample, should the Bobolink winter south of the 
Amazon, while its ally, the Red-winged Blackbird 
(Agelaius phoeniceus), does not leave the eastern 
United States? I have, however, no intention of 
writing an essay on bird migration, and these 
thoughts are presented merely as preliminary to a 
study of the life of Pelican Island, of a visit to 
which they are in part the outcome. 
Pelican Island is situated midway between the 
northern and southern extremities of Indian River, 
near the eastern shore of a key which here makes 
the river about three miles wide. It is triangular 
in shape and contains about three acres of ground, 
on which grow a few black mangroves, a cabbage 
palm or two, and great patches of grass; but at 
least one fourth of its surface is bare ground. 
On one of the islands of the near-by Narrows a 
few pairs of Brown Pelicans are said to have nested, 
