SWALLOWS AND SWIFTS 149 



terrified at the human figures haunting the new artificial caves. 

 At any rate, they took very readily to the new nesting-sites, 

 and in most civilised and well- populated countries have 

 almost abandoned the old ones, though they still faithfully 

 preserve traces of their old distinctive preferences. Swifts 

 harbour in dark holes under the eaves and narrow crevices, 

 which give them the same kind of shelter as their clefts 

 and crannies in the cliffs, where they still occasionally breed. 

 The house-martins' characteristic nesting-place is more 

 open; they cling beneath the eaves and window-frames on 

 the outer walls, just as the most conservative remnant of their 

 kind still build under jutting cornices near the top of the 

 Cornish cliffs. Swallows are intermediate between the two ; 

 they avoid wind and weather more than swifts, but less than 

 martins, and habitually nest inside out-buildings and cow- 

 sheds, which provide the closest imitation of a cave. The 

 nests of swallows and martins correspond to their site. 

 Martins' nests, built to keep out wind and weather, have only 

 a small hole ; in swallows' nests, the mud wall is not carried 

 up so high, and there is a considerable space all round. 

 Sometimes, indeed, a swallow's nest built in a well-sheltered 

 place is no more than a segment of a mud saucer, clinging to 

 a beam or joist ; but when it is in an unusually exposed posi- 

 tion, the walls may be built up till they are nearly as complete 

 as those of the martin's nest. And when a martin builds in 

 some swallow-like place, as under the glass roof of a station 

 platform, the nest may be so flat and widely open at the 

 top that it might almost be taken for a swallow's. Though 

 colonies of house-martins' nests are not very uncommon on 

 tall cliffs, both inland and by the sea, swallows' nests are very 

 rarely indeed found in caves, though the habit in England is not 

 yet quite extinct. Swallows are less gregarious than martins 

 in the wild state ; and this characteristic is preserved in their 



