--how much more like an act of rational intelligence. So far as I
know, no bird does eject this parasitical egg, and no other bird
besides the yellow warbler gets rid of it in the way I have described.
I have found a deserted phoebe's nest with one egg of the phoebe
and one of the cowbird in it.

Some of our wild birds have changed their habits of nesting, coming
from the woods and the rocks to the protection of our buildings. The
phoebe-bird and the cliff swallow are marked examples. We ascribe
the change to the birds' intelligence, but to my mind it shows only
their natural adaptiveness. Take the cliff swallow, for instance; it
has largely left the cliffs for the eaves of our buildings. How
naturally and instinctively this change has come about! In an open
farming country insect life is much more varied and abundant than in a
wild, unsettled country. This greater food supply naturally attracts
the swallows. Then the protecting eaves of the buildings would
stimulate their nesting-instincts. The abundance of mud along the
highways and about the farm would also no doubt have its effect, and
the birds would adopt the new sites as a matter of course. Or take
the phoebe, which originally built its nest under ledges, and does
so still to some extent. It, too, would find a more abundant food
supply in the vicinity of farm-buildings and bridges. The protected
nesting-sites afforded by sheds and porches would likewise stimulate
its nesting-instincts, and attract the bird as we see it attracted
each spring.

Nearly everything an animal does is the result of an inborn instinct
acted upon by an outward stimulus. The margin wherein intelligent
choice plays a part is very small. But it does at times play a
part--perceptive intelligence, but not rational intelligence. The
insects do many things that look like intelligence, yet how these
things differ from human intelligence may be seen in the case of one
of our solitary wasps,--the mud-dauber,--which sometimes builds its
cell with great labor, then seals it up without laying its egg and
storing it with the accustomed spiders. Intelligence never makes that
kind of a mistake, but instinct does. Instinct acts more in the
invariable way of a machine. Certain of the solitary wasps bring their
game--spider, or bug, or grasshopper--and place it just at the
entrance of their hole, and then go into their den apparently to see
that all is right before they carry it in.

Fabre, the French n