THE NIGHTJAR AND THE SWALLOW. 55 
times, when the wall against which it is fixed is 
comparatively smooth, and affords no firm hold for 
the clay, the nest is supported on a kind of pedestal 
formed of the same material, and often of some little 
size. Although similar in many respects, there is 
one very striking difference by which a martin’s nest 
may be distinguished from that of a swallow ; for, 
The Martin. 
while the abode of the latter bird is invariably open 
above, the martin always contrives that an overhang- 
ing roof or beam may form a ceiling to its dom1- 
cile ; and this 1s a rule which seems never to be 
broken. 
