Song Birds and Water Fowl 
of their peculiar structures, and their lack of 
timidity gave good opportunity to watch the 
process. ‘This nest differs from that of all our 
other birds in having its walls composed en- 
tirely of mud, which the bird moulds into little 
pellets, fastening them together with its own 
saliva; and thus the entire nest, which is very 
thick and heavy, is supported only by adhesion 
to the wall against which it is built. The 
architectural taste of these swallows involves a 
peculiar difficulty and danger, for the nest must 
always be placed where it will be protected 
from the rain by an overarching projection ; 
otherwise, from the added weight of moisture, 
and its disintegrating effect, it would suddenly 
collapse in a storm. ‘The rounded form of the 
pellets gives the exterior of the nest a peculiar 
corrugated appearance, but the inner surface is 
perfectly smooth. From its situation it results 
that the cavity is like a pocket, bending out 
horizontally at the top to afford egress. After 
the birds had worked diligently several days, I 
found, one morning, that some of the nests had 
fallen to the ground. But, without wasting 
precious time in vain regrets, they began at 
once to repair the loss. Everything went 
smoothly until the nests were almost completed, 
212 
