BIRDS 463 



The majority of birds do not associate for nesting purposes, 

 though a very large number are social in this respect, and several 

 examples have already been described. Among British species 

 Rooks, Herons, and Fieldfares may be added to the list. The 

 most extraordinary instance of this kind is afforded by the Sociable 

 Grosbeak (Philket&rus socius, fig. 985) of South Africa. By the 

 combined efforts of a large number of these birds a huge struc- 

 ture resembling the top of a mushroom is built round a tree, 



Fig. 985. Nest of Sociable Grosbeak (Philhetcerus sod**} 



grass being the material employed. It consists of from 100 to 

 over 300 associated nests. 



Related species not infrequently differ greatly as regards their 

 nesting-habits, the most remarkable case being that of the South 

 American Tree- Creepers or Picucules (Dendroeolaptida), which 

 include the Oven- Birds already noticed. These Tree-Creepers 

 differ remarkably among themselves in appearance and struc- 

 ture, as the result of adaptation to various modes of life. And 

 that they provide for the welfare of their eggs in widely different 

 ways will be obvious from the following account given by Hudson 

 (in The Naturalist in La Plata]: "In the nesting habits the 

 diversity is greatest. Some ground species excavate in the 

 earth like kingfishers, only with greater skill, making cylindrical 



