THE NATURAL HISTORY OF NESTS 165 



is that the character of the nest is distinctive of the species. 

 Each kind of bird keeps to its own kind of nest with 

 relative constancy. In short, the nature of the nest is 

 specific, with a measure of variability such as we find in 

 structural specific characters. The blackbird is first 

 cousin of the thrush, but every country schoolboy knows 

 that the nests are very different, and so it is all round. 

 When birds build on an unusual site, or when they nest in 

 a locality where their favourite materials are scarce, the 

 nest may vary considerably from type, and we read every 

 year in the newspapers of extraordinary vagaries (doubtless 

 more extraordinary to us than to the bird !) as to site and 

 materials. Apart from cases of nests inside station-lamps 

 or letter-boxes, there is considerable variability in the open 

 country. The Golden Eagle may use a ledge of rock, a 

 forest tree, or even the thick herbage ; the heron may rest 

 on a lofty tree, in a sea-bank, or in the open fen. It is 

 well known that a bird may lazily use another bird's nest, 

 and the habit has become normal in the European cuckoo. 

 The familiar sight of sparrows evicting swallows is sugges- 

 tive of the possible origin of a regularly parasitic habit if 

 it could be regularised so as not to kill off the swallows ! 



THE FASHIONING OF THE NEST 



It is possible nowadays to see in a cinematograph series 

 the whole business of nest-building in a few cases of more or 

 less exposed nests. In regard to many more difficult cases, 

 persistent and patient observation with the help of a 

 good field-glass has enriched science with detailed descrip- 

 tions of one of the most interesting of animal activities. 

 It is difficult, however, to venture on any general 

 statements. The hens do most of the work of building the 

 cradle, but the cocks often help. As birds are practically 



