THE DIPPER 311 



glued to the face of the rock, as one discovers when tearing it away. 

 The cohesiveness is probably obtained by the application of the 

 material in a wet state with admixture of mud, and it is not always 

 strong enough to ensure the safety of the home, which after a time 

 often falls away from the rock into the stream. In one case this 

 occurred before the young were fledged. 1 



There are normally two distinct parts in a dipper's nest, the 

 outside oval case, chiefly of felted moss, and, inside it, a round open 

 nest, built of various materials. The need for the outside case 

 becomes clear when one sees some of the sites in which the nest may 

 be placed. It has very frequently been found under a continuous 

 drip of water, and many a time behind a waterfall, through which the 

 birds have been seen to dash each time they went to feed their 

 young. Possibly the thick mossy case is a comparatively late develop- 

 ment that began when the species became definitely aquatic in its 

 habits. 



When the bird places its nest in a hole, it will dispense with the 

 dome, and is probably, in most such cases, compelled to do so by lack 

 of space. Such was the case with one that built in a sandmartin's 

 hole two feet long. 2 In this the nest resembled a blackbird's. 



The dipper does not always trouble to build a new nest each year. 

 It may repair the old one and use it year after year, and often rears 

 two broods from it each year. One has been known to be used for 

 at least eleven years in succession. 3 And one site has been known to 

 be occupied by the nests of a pair and their heirs for 128 years (1785- 

 1908). 4 



The dipper shares with the sandmartin and housemartin the 

 distinction of being one of the three British breeding Passerine 

 species that lay white eggs. This has been explained by the fact 

 that the eggs of these species, like those of owls, woodpeckers, and 

 others, are deposited in holes or domed nests, where the white 



1 P. C. R. Jourdain (in litt.). 2 Nelson, Birds of Yorkshire, pp. 101-3. 



3 J. Patterson, Yorks (in litt.). H. Gladstone, Birda of Dumfries. 



