204 BIRDS' NESTS 



under which the reproduction of the affected species 

 is conducted, the most important of which is most 

 probably the concealment of showy or conspicuous 

 plumage, the elusion of certain enemies, and adapta- 

 tion to certain climates. Unfortunately in a vast 

 number of instances, especially amongst the tropical 

 species (notably those in South America), the habits 

 of these open nest-building species are nearly if not 

 quite unknown, as are likewise the nests themselves 

 of not a few, so that we are as yet quite unable to 

 comprehend the philosophy of their nidification — the 

 relation between the open nest and the conditions of 

 existence of its feathered architect. In a great many 

 cases (in fact we may safely say in the majority) these 

 open nests belong to the largest and most powerful 

 of avine forms — to species that require no special 

 protection, well able to defend their nests from 

 ordinary enemies, or that derive their safety by build- 

 ing in societies, or in "Very inaccessible situations, such 

 as in marshes or deep trackless forests ; or yet again 

 (more especially in tropical countries) by placing their 

 homes in isolated trees or groves, which predatory 

 creatures are not likely to visit under ordinary cir- 

 cumstances. Then, on the other hand, many of these 

 open nest-builders, especially the weaker, smaller, and 

 least aggressive species, take great pains to conceal 

 them in a variety of ways, one of the most remark- 

 able being that of mimicry, or assimilating the outer 

 materials with surrounding objects. I have pointed 



