248 CHELIDONES. 



species which form their habitations in the chimneys or the 

 windows. The places in which the nests are excavated, 

 generally secure them from inundation; and as all birds that 

 burrow in the ground work with a little slope upwards, the 

 rain does not reach the nests. 



A colony of sand-martins, especially when they are in con- 

 siderable numbers, and forming a new establishment, presents 

 a busy scene, for they dig away with much assiduity, relieving 

 each other by turns, the one working while the other feeds; 

 / ^"Vand as they are at work early and continue late, they are not 

 V long in having the burrow ready for the withered grass, 

 4 feathers, or other materials of which the nest is carelessly 

 made. The eggs, which are often as deep as three feet from 

 i!he face of the bank, are generally one more than those of 

 7 > the house-martin ; but there are seldom two broods in the 



^.+3* VTJT^ 



year. The young are fed for a considerable time by the 

 parents ; and after they have attained as much maturity as 

 to be able to catch insects for themselves, they can be readily 

 distinguished from the old ones, by the rusty colour of the 

 margins of their feathers, an appearance which partially cha- 

 racterizes the female. The deep burrow of the sand-martin 

 is no more adapted for a winter residence than the mud 

 structure of the other species; for by the time that the 

 insects become scarce in the air, partly by the diminution of 

 their numbers, and partly because they are less on the wing, 

 the sand-martin retires to southern countries. 



THE COMMON SWIFT (Ci/pselus vulgaris). 



The swift, of which a figure is given on the plate at page 

 246, one-third of the lineal dimensions, is perhaps the most 

 powerfully winged, in proportion to its weight, of all British 

 birds, not even excepting the white-bellied swift, or even the 

 storm petrel, which extends its excursions so far from the land 

 as to traverse the surface of the whole Atlantic. But the petrel 



