ngs, while all the nests I have ever found of this sparrow were in
open grassy fields upon the ground. The chipping or social sparrow is
usually very constant in its song and its nesting-habits, and yet one
season a chippy built her nest in an old robin's nest in the vines on
my porch. It was a very pretty instance of adaptation on the part of
the little bird. Another chippy that I knew had an original song, one
that resembled the sound of a small tin whistle. The bush sparrow,
too, is pretty constant in choosing a bush in which to place its nest,
yet I once found the nest of this sparrow upon the ground in an open
field with suitable bushes within a few yards of it. The woodpeckers,
the jays, the cuckoos, the pewees, the warblers, and other wood birds
show only a low degree of variability in song, feeding, and nesting
habits. The Baltimore oriole makes free use of strings in its
nest-building, and the songs of different birds of this species vary
greatly, while the orchard oriole makes no use of strings, so far as I
have observed, and its song is always and everywhere the same. Hence
we may say that the lives of some birds run much more in ruts than do
those of others; they show less plasticity of instinct, and are
perhaps for that reason less near the state of free intelligence.

Organic life in all its forms is flexible; instinct is flexible; the
habits of all the animals change more or less with changed conditions,
but the range of the fluctuations in the lives of the wild creatures
is very limited, and is always determined by surrounding
circumstances, and not by individual volition, as it so often is in
the case of man. In a treeless country birds that sing on the perch
elsewhere will sing on the wing. The black bear in the Southern States
"holes up" for a much shorter period than in Canada or the Rockies.
Why is the spruce grouse so stupid compared with most other species?
Why is the Canada jay so tame and familiar about your camp in the
northern woods or in the Rockies, and the other jays so wary? Such
variations, of course, have their natural explanation, whatever it may
be. In New Zealand there is a parrot, the kea, that once lived upon
honey and fruit, but that now lives upon the sheep, tearing its way
down to the kidney fat.

This is a wide departure in instinct, but it is not to be read as a
development of reason in its place. It is a modified instinct,--the
instinct for food seeking new sources of supply.