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1878.] Variations in the Nests of the same Species of Birds. 39 
I might go on and prolong this article by other accounts of con- 
spicuous variations made by the same species in its nest-building, 
citing the lammergeyer that builds indifferently a huge nest on a 
tall tree, or lays its eggs on the bare ground or some tall cliff, 
without any nest at all, but I have given enough to show how 
marked these variations often are. To speculate on the whys and 
the wherefores would be a very tempting theme were it not that 
we are so often at fault in attempting.to explain them. But I do 
not believe it is logical to call the intellectual promptings that 
inspire these variations mere instinct, though we may not be able 
„tò read clearly the hidden motives. If experience taught the 
European martin that its old-fashioned nest, which perchance it 
had built since the flood, was inconvenient, ill-ventilated and 
unsafe, and they were prompted by the example of some wiser 
intellect among themselves to improve upon the hovels of their 
fathers, so that all at once the whole race made a long stride in 
improvement, can we call this instinct ? Grant that the changes have 
been slow—extending over fifty years—so gradual that no one 
has noticed the change while it was going on, we cannot deny 
the advance, and advance is inconsistent with our ideas of instinct 
which is unchangeable and incapable of education. It is a clear 
case of reason and instruction, yielding marked fruits, and is ona 
higher plane. That birds like the Dendræca dominica and the 
Icterus cucullatus build a typical nest, like their congeners, where 
nothing tempts them to do differently, but where the long branches 
of Tillandsia offer a safe shelter and the absence of labor, shows 
something higher than instinct, there must be a rational intellect 
that prompts them to avail themselves of the opportunity. 
If we cannot understand what it can be that stimulates an 
Empidonax in Staten Island to build a pensile nest, while its fel- 
low in Indiana builds one like a deep cup and surrounded with 
thorns, and another group in Pennsylvania put theirs on an 
_ exposed tree-top, and so flat that the eggs seem liable tọ roll out, 
we must see that some cause, hidden to us, is gradually effectin 
_ changes that sooner or later may become universal in the species, 
_ though which it is to be we may not be able to imagine. 
Our eastern song-sparrow’s natural instinct prompts it to build 
on the ground. A series of disasters to its eggs or brood impress 
it with the need of a safer place. It draws nearer the: friendly | 
= shelter of a dwelling, and there, no longer on the ground, but up 
_ in some thick bush or vine, it makes its nest. For want of the 
