xlvi 
INTRODUCTION. 
is composed, is attached with great art and labor. The bird first spreads it 
close to the former depositions, and then intermingles it, by passing its bill 
down through it and the upper part of the lower layers, by a continual 
motion of its head; an act similar to the movement of the spill in drilling. 
By this operation a hole is made through the portion of clay added to 
the nest, and extended slightly through the layer beneath it. The next 
addition fills up this orifice, and overspreads it at the top, so as to connect 
it with the contiguous parts. A similar method is again employed ; and the 
whole of the external shell, or incrustation, is raised on the principle of tubes 
fixed one in another, each at the top, as it is inserted, lapping over the one 
beneath. These overlappings are united, in a similar manner, across the 
intermediate space. A small orifice remains open for the ingress and egress of 
the owners ; and when the exterior is completed, they line the interior with 
straw and feathers. The male and female sometimes work together, at 
other times in suecession, each waiting till the other has finished its labor ; 
the erection and the lining of the structure commonly employ them a month. 
The nest of the long-tailed Titmouse, though different in form and materials 
from that of the Martin, is equally as curious ; and it is not a little surprising 
to mark this active, but diminutive bird, inserting in the bark of the tree, or 
twining round some small limb, the mossy materials of its foundation. 
Few birds use the same nests again ; but the Eagle, the Martin, and the 
Swallow, resort to their former habitations for many years successively; 
and the Hedge Sparrow, the Robin, the Titmice, the Nuthatch, the Shag, and 
numerous species of the Gull kind, return to the neighbourhood in which 
they had before reared their young. When the nests of birds are finished, 
the important business of depositing their eggs commences; the greatest 
numbers of which are produced by the Duck, and gallinaceous tribes, the 
Titmice, and the Wrens. The smallest, and weakest kinds, or those that 
are most exposed to various enemies, without weapons to repel their 
assailants, which trust to their minuteness, their color, or their art, to escape, 
are commonly most prolific. To repair the devastations committed on their 
numbers, nature, careful to continue the species in the preservation of the 
