82 THE POPULAR SCIENCE MONTHLY 
INSTINCT AND INTELLIGENCE IN BIRDS—II 
By Proressor FRANCIS H. HERRICK 
ADELBERT COLLEGE 
HE cyclical instincts of birds, present, as we have seen, a well- 
ordered series, rising and waning in due course, until the re- 
productive cycle is complete. Nevertheless, the order and harmony 
which commonly prevail are subject to many disturbances of a tran- 
sient, or of a more lasting character. When variations in the cycle, 
whatever their nature, become regular and permanent, any consequent 
loss or injuiry to the species seems to be counterbalanced by the rise 
of new instincts in both young and adult, which may involve marked 
structural changes, as shown in the parasitic cuckoos of the old world 
and their non-parasitic relatives of the new. If transient merely, 
there is more or less individual loss, according to the nature and ex- 
tent of the disturbance. | 
We shall now consider some of these variations in the cyclical series, 
and we may assume, though with little exact knowledge, that when 
any character of the sort to be described has become general or perma- 
nent this has been effected through a gradual process of selection, with 
or without environmental influence and other unknown agencies. We 
may further assume that all modern birds originally built proper nests, 
and there can be little doubt that many either falter or fail in this 
work at present through the loss of an instinct which they once pos- 
sessed; but this question aside, we can be reasonably assured that all 
originally concealed or guarded their eggs. 
The nest, in the first instance, tends to secure a more equable dis-. 
tribution of warmth and moisture for eggs or young; incidentally it 
may conceal and therefore protect both young and adult, and add to 
the comfort of the whole family. There would seem to be a vast dif- 
ference between digging a hole in the warm, moist sand, as we see the 
turtle, or the moleo, one of the brush turkeys, doing, and weaving 
through the unremitted efforts of many days, a beautiful pouch like the 
oriole’s, so admirably adapted for protection, both by its form and by its 
position. Yet it is by no means certain that the fundamental nest- 
building instinct is entirely wanting in the moleo, the peculiar habits 
of which will be later considered. 
Nest-building of one kind or another is found in all classes of 
vertebrates, and the guarding and fighting instincts at nesting-time 
are as strong in some of the fishes as in birds, but while the practise is 
