n6 SPRING 



the mud a little later ; and the unsuccessful blackbirds' nests 

 collapse before the stage of adding mud is reached. 



Houses built against cliffs so that they are really only 

 the halves of houses are curiosities sometimes seen in 



mountainous countries and 

 by the sea. Birds often 

 accommodate their building 

 in this manner ; it is one 

 of the ways in which they 

 display an adaptable intel- 

 ligence. Robins habitually 

 leave out the back wall of 

 their nests, fitting them into 

 holes, where the outer layers 

 are not required on the 

 sheltered side. The inner 

 cup is shaped perfectly, 

 though the lining is often 

 very thin at the back. 

 Blackbirds adopt the same 

 design when they build, as 

 they often do, against a 

 bank or tree-trunk or wall. 

 The mud nests of swallows 

 and house - martins show 

 another application of the same plan. The little felted 

 cradle of the spotted flycatcher is often hardly more than 

 a crescent of cobweb and moss, when it is lifted out of the 

 garden trellis or off the ivy bough after the birds are gone. 

 But the irreducible minimum is perhaps reached by the 

 tree-creeper, when it nests, as it occasionally does for 

 some years in succession, under the tiles or slates of an 

 old roof. The nest which it builds in such a situation is 



NEST OF SPOTTED FLYCATCHER 



