of Selbonie 137 



be formed of such dirt or loam as comes most readily to 

 hand, and is tempered and wrought together with Httle 

 bits of broken straws to render it tough and tenacious. 

 As this bird often builds against a perpendicular wall 

 without any projecting ledge under, it requires its utmost 

 efforts to get the first foundation firmly fixed, so that it 

 may safely carry the superstructure. On this occasion 

 the bird not only clings with its claws, but partly supports 

 itself by strongly inclining its tail against the wall, 

 making that a fulcrum ; and thus steadied it works and 

 plasters the materials into the face of the brick or stone. 

 But then, that this work may not, while it is soft and 

 green, pull itself down by its own weight, the provident 

 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 become top-heavy, and so be ruined 

 by its own weight. By this method in about ten or 

 twelve days is formed an hemispheric nest with a small 

 aperture towards the top, strong, compact, and warm ; 

 and perfectly fitted for all the purposes for which it wa> 

 intended. IBut 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 sometimes by a bed of moss interwoven 



