INTRODUCTORY 13 



where species have completely changed their method 

 of nesting when threatened by some new danger. 

 The Penguins of Tristan d'Acunha have since the 

 introduction of pigs into the islands sought safety for 

 their eggs and young by changing the site of the nest 

 from an open to a covered one. Other instances of 

 avine intelligence as opposed to fixed inherited habit 

 are the departures from the general rule in the 

 method of reproduction, so remarkable in not a few 

 species. Herons will nest indiscriminately upon cliffs 

 or trees or upon the ground in fens and marshes. 

 Eagles in some countries nest upon trees and cliffs ; 

 elsewhere on the ground. The Cormorant is as much 

 at home when nesting in a tree as upon a maritime 

 cliff or a low rocky reef; w^hilst the Moorhen and 

 some other ground-breeding birds have been known 

 to make their nests in trees, in districts subject to 

 sudden floods — another interesting proof of avine 

 intelligence and reasoning power. 



Lastly, we have the most important evidence of all 

 against the theory of blind instinct or inherited habit 

 in the now absolutely proved fact that birds are 

 incapable of building a nest typical of their species 

 without the aid of imitation or experience. Although 

 we have recorded the facts in NaHire and elsewhere, 

 they are sufficiently important and interesting to 

 be fully repeated in a work dealing exclusively with 

 nests. The striking illustration here given is from 

 an actual photograph of a nest made by a pair of 



