348 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
local breeding area, such as the passenger pigeon, Esquimaux curlew, 
and Labrador duck, or to species, which, having a large range, are 
unable to resist slaughter at all seasons. Systematic egg stealing 
under the cloak of science, but which in reality is the travesty of 
science, is also responsible for such contraction of range, as in the 
case of so many birds which have within the last century ceased to be 
included among British breeding species. 
Indirect human agency has increased the breeding range of certain 
species, though only in a minor degree. The reafforestation of land 
and artificial sheets of water have, no doubt, helped in this manner, 
though in most cases it has been a case of reestablishment. The car- 
rying of migratory birds on ships comes under this heading. 
In like manner has interference with terrain, such as the draining 
of the fens, contracted the breeding range of birds. The introduction 
of a destructive element has had similar effect, as in the case of the 
arrival of the pig in Mauritius, which completed the sad fate of the 
dodo, or the great mortality among sea birds from the torpedoing 
of a tank steamer and the resultant film of oil spread over vast areas 
of sea. 
CONCLUSION. 
From these examples it will readily be seen how closely related are 
migration, distribution, and differentiation among birds. Without 
the framework of distribution the study of migration can only lead 
to theory. Each separate species or subspecies must be studied, if 
possible, throughout its range, and then we shall arrive at facts 
from which the whole narrative of migration can be read. No two 
species which have a similar geographical distribution are known 
to have similar migratory habits. We even get, among birds of the 
same species, vast differences in migratory habit, hence the great 
importance of detailed study. 
The task is gigantic, and though no one human life can hope to 
complete the work, a combined effort by all field naturalists and col- 
lectors, with the very great assistance supplied by the various organ- 
izations in Britain, America, and on the Continent for the study of 
local movement, not to mention that most valuable of all schemes, 
the “ ringing ” of birds, will go far to building up an edifice grounded 
on solid facts, whose completion we must leave to future generations 
of enthusiasts. 
Finally, it must be clear to any reader of this rather fragmentary 
paper that no exhaustive or complete study of the subject has been 
attempted. Many points connected with the relation between dis- 
tribution and migration have been merely suggested, in the hope that 
such preliminary mention will stimulate ideas on this, the most 
attractive phase of an absorbing science. 
