238 
NATURAL HISTORY OF SELBORNE. 
struction, would often vary and do that by many methods which 
instinct effects by one alone. Now this maxim must be taken in 
a qualified sense ; for there are instances in which instinct does 
vary and conform to the circumstances of place and convenience. 
It has been remarked that every species of bird has a mode of 
nidification peculiar to itself ; so that a school-boy would at once 
pronounce on the sort of nest before him. This is the case 
among fields and woods, and wilds ; but, in the villages round 
London, where mosses and gossamer, and cotton from vegetables, 
are hardly to be found, the nest of the chaffinch has not that 
elegant finished appearance, nor is it so beautifully studded with 
lichens, as in a more rural district : 
and the wren is obliged to construct 
its house with straws and dry grasses, 
which do not give it that rotundity 
and compactness so remarkable in 
the edifices of that little architect. 
Again, the regular nest of the house- 
martin is hemispheric ; but where a wren. 
rafter, or a joist, or a cornice, may happen to stand in the way, 
the nest is so contrived as to conform to the obstruction, and 
becomes flat or oval, or compressed. 
In the following instances instinct is perfectly uniform and 
consistent. There are three creatures, the squirrel, the field- 
mouse, and the bird called the nut-hatch (sitta Europoia), which 
live much on hazle-nuts ; and yet they open them each in a dif- 
ferent way. The first, after rasping off the small end, splits the 
shell in two with his long fore-teeth, as a man does with his 
knife ; the second nibbles a hole with his teeth, so regular as if 
drilled with a wimble, and yet so small that one would wonder 
how the kernel can be extracted through it ; while the last picks 
an irregular ragged hole with its bill : but as this artist has no 
paws to hold the nut firm while he pierces it, like an adroit 
workman, he fixes it, as it were in a vice, in some cleft of a tree, 
or in some crevice ; when, standing over it, he perforates the 
stubborn shell. We have often placed nuts in the chink of a 
gate-post where nut-hatches have been known to haunt, and have 
always found that those birds have readily penetrated them. 
While at work they make a rapping noise that may be heard at a 
considerable distance. 
You that understand both the theory and practical part of 
