294 SWALLOWS AND MARTINS 



thereby saved. A bit of mud here, a bit there, a new lining, and the 

 nest is ready for the eggs. Those birds which have, or prefer, to build 

 new nests are much later in hatching their broods. 



In their method of building the two species are much alike. 

 They begin by collecting wet mud either at the edge of a puddle, 

 pond, or elsewhere convenient. They are easily watched when thus 

 employed, and what chiefly strikes one is the contrast between the 

 neat, clean, bright-feathered little birds, especially the martin with 

 his spotless white gaiters, and, on the other hand, the dirt through 

 which they walk as if not liking it, but which they nevertheless cheer- 

 fully pile upon their bills and also scoop into their mouths. Thus 

 loaded, they depart to the chosen site. As the swallow usually builds 

 upon a ledge, his task is comparatively easy. It is not so with the 

 martins. He builds under a ledge, attaching the top of his nest to its 

 undersurface and the back to the flat wall or rock below, often with- 

 out any kind of supporting projection. There is usually nothing to 

 prevent his home from falling to the ground except the strength of 

 its adhesiveness. Now wet mud, especially if clay, adheres firmly 

 enough, as our boots show us after a tramp through heavy soil. And 

 the maid who cleans those boots next morning can tell us that dry 

 mud is quite adhesive enough to be a nuisance. The chief difficulty 

 that the martins have to encounter is to ensure that the weight of the 

 mud, when wet, will not more than counteract its adhesiveness. The 

 difficulty is usually met by the habit the birds have of building up the 

 walls a little at a time, and by waiting till each successive layer is dry 

 before applying the next. As dry mud is about a third less heavy 

 than wet a statement which any one can test, by weighing a given 

 piece of mud in the wet and the dry state it will be evident that the 

 precaution is a wise one. Wet mud, again, being soft, might yield 

 under weight, and lose shape or give way. The birds, therefore, gain 

 by putting the new wet layer on a basis that has become firm and 

 hard. But to what extent the precaution is essential to the safety of 

 the nest has never been tested. Normally it takes about ten days to 



