OCTOBER, 1902. 
THE MIGRATION OF BIRDS. 
193 
diate vicinity of their old homes. There can be no doubt that 
birds are endowed with weH-developed mental capacities, and 
that it is by virtue of these that they return to the same tree or 
the same box. But even here we must consider the fact that if 
any individual, or species, develops certain characteristic habits 
in feeding, breeding, or whatever they be, so long as they are ad- 
vantageous it will endeavor to find conditions where these habits 
may be practiced. While we may thus find birds returning to, 
their old homes year after year, and while memory, home affec- 
tion and habit all contribute as explanations for this periodical 
return to the same place, we must not forget that these influences 
may be merely local. The facts pointed out above show that 
they are local, but there are no facts from which we can infer 
that they are more than local. 
We know that migration takes place in a general north and 
south direction, that definite physiographic courses are used as 
guide-lines in migration, and that some birds return year after 
year to the same home. It has been shown that there are rea- 
sons why birds should leave the south in spring, and it will be 
shown that even in the absence of home affection migratory 
routes will lead them back to the locality from which they came. 
Another favorite argument for the love of home and 
nesting ground is to be found in the fact that our early spring 
arrivals are often met with conditions that are most unfavorable; 
It is argued that birds show a desire to return to the familiar 
scenes of the previous summer because they push northward in 
the spring in spite of cold, sleet and snow. This argument, even 
more than the preceding, is extremely conjectural. It is only in 
a comparatively small number of species, and of many of those 
only in a certain number, that we have anything we might call 
a rapid pushing northward in spite of cold, sleet and snow. Fur- 
thermore, we must consider that the birth rate in birds is very 
limited. The majority of them lay less than twelve eggs to the 
set. This rate is very limited, especially when we consider that 
the destructive agencies in bird life are numerous. Beside the 
number of birds that are killed each season in migration, various 
animals depend largely upon birds for their existence. The 
young, too, require a definite period of time before^ they become 
sufiiciently matured to perform a migration. Without here going 
into the principles of perpetuation, it is obvious that it is of im.- 
portance to birds to return to their parental duties in spring as 
soon as possible. We do find it a quite general rule that several 
sets of eggs are hatched by one pair of birds each season, which 
