182 NATURAL HISTORY 



vident architect has prudence and forbearance enough not 

 to advance her work too fast; but by building only in the 

 morning, and by dedicating the rest of the day to food and 

 amusement, gives it sufficient time to dry and harden. 

 About half an inch seems to be a sufficient layer for a day. 

 Thus careful workmen when they build mud walls (informed 

 at first perhaps by this little bird) raise but a moderate 

 layer at a time, and then desist ; lest the work should be- 

 come top-heavy, and so be ruined by its own weight. By 

 this method in about ten or twelve days is formed an hemi- 

 spheric nest with a small aperture towards the top, strong, 

 compact, and warm ; and perfectly fitted for all the purposes 

 for which it was intended. But then nothing is more 

 common than for the house sparrow, as soon as the shell is 

 finished, to seize on it as its own, to eject the owner, and to 

 line it after its own manner. 



After so much labour is bestowed in erecting a mansion, 

 as Nature seldom works in vain, martins will breed on for 

 several years together in the same nest, where it happens to 

 be well sheltered and secure from the injuries of weather. 

 The shell or crust of the nest is a sort of rustic-work full of 

 knobs and protuberances on the outside : nor is the inside 

 of those that I have examined smoothed with any exactness 

 at all ; but is rendered soft and warm, and fit for incubation, 

 by a lining of small straws, grasses, and feathers ; and some- 

 times by a bed of moss interwoven with wool. In this nest 

 they tread, or engender, frequently during the time of 

 building ; and the hen lays from three to five white eggs. 



At first when the young are hatched, and are in a naked 

 and helpless condition, the parent birds, with tender assi- 

 duity, carry out what comes away from their young. Was 

 it not for this affectionate cleanliness the nestlings would 

 soon be burnt up, and destroyed in so deep and hollow a 

 nest, by their own caustic excrement. In the quadruped 

 creation, the same neat precaution is made use of; particu- 

 larly among dogs and cats, where the dams lick away what 

 proceeds from their young. But in birds there seems to be 

 a particular provision, that the dung of nestlings is en- 

 veloped in a tough kind of jelly, and therefore is the easier 



