262 
As a proof that “ non-intelligent habits of a non-adaptive 
character occur in individuals,” Mr. Romanes says :— 
“ Almost innumerable instances might be given of indi 
vidual variations in the instincts of nest-building.” But if 
this be admitted, it would only show that the instinct of 
nest-building is far from being perfect, and that it requires 
to be supplemented as so many imperfect instincts do. 
We can scarcely doubt that this is so, when we are assured 
that young birds brought up alone in cages either build 
very bad nests or none at all ; that old birds build better 
nests than young ones, and that birds—like the rooks, 
for example—have their work inspected and are not 
allowed to go on with a nest which is badly begun. 
Sometimes, no doubt what seems like want of skill and 
a palpable decline from parental excellence, may be due 
to want of material or to a perception that a much simpler 
nest will suffice under new conditions. 
It only remains to say that some modifications of nest 
building are obviously acts of a high intelligence, of which 
the following may be taken as an illustration :— 
“A pair of jackdaws endeavoured to construct their nest in one of 
the small windows that lighted the spiral staircase of an old church 
tower. As is usual, however, in such windows, the sill sloped inwards 
with a considerable inclination, and consequently, there being no 
level base for the nest as soon as a few sticks had been laid and 
it was beginning to acquire weight, it slid down. This seems to have 
happened two or three times. Nevertheless the birds clung with 
great pertinacity to the site they had selected, and at last devised 
a most ingenious method of overcoming the difficulty. Collecting 
a great number of sticks, they built up a sort of cone upon the 
staircase, the summit of which rose to the level of the window-sill 
and afforded the requisite support to the nest. This cone was not 
less than six feet high, and so large at its base as quite to obstruct 
the passage up the staircase. Yet, notwithstanding the large amount 
of material which it contained, it was known to have been constructed 
within four or five days.”—(Jesse. Apud Carpenter. Menial Physi 
ology. p. 86.)