INTRODUCTION. xxi 



widely spread, in localities where they are subjected to various conditions. 

 If this was strictly true, I think it would go far to prove the existence of 

 instinct ; but it is not ; for birds, even within the memory of living men, 

 have been known to change and improve their nests under the influence of 

 altered conditions. If a bird built by instinct, it is fair to assume that that 

 instinct is unchangeable, and only allows the bird to build on a certain 

 plan. Instinct practically remains stationary ; reason, however, advances. 

 What proof have we of this ? Swallows are a most interesting instance, 

 they having partially ceased to build on rocks or in caves, choosing houses 

 and sheds instead. Starlings and many other birds will readily take 

 advantage of a box placed on the house-side for them, and abandon their 

 hole in the trees for the new quarters. The House-Sparrow is another 

 instance of a recently changed mode of nest-building ; so is the Waterheu, 

 which often builds in trees in districts liable to sudden floods. Another 

 instance : the Penguins on the Tristan d'Acunha group of islands have 

 changed their mode of nesting from an open to a covered site, in conse- 

 quence of the incessant persecution of the recently introduced wild pigs 

 with which these islands now abound *. Many other instances might be 

 cited all tending to prove that birds take advantage of any favourable 

 circumstances to alter and improve their nests a fact which can only be 

 accounted for by the direct influence of their reasoning faculties. What 

 may be regarded as direct evidence of a reasoning power employed by 

 birds in making their nests may be seen in the wonderful way that many 

 species assimilate their nests so closely to surrounding objects as to render 

 their discovery very difficult, and the admirable plan on which some nests, 

 especially of tropical species, are constructed. A good example is to be 

 seen in the nest of the Common Tailor-bird of India (Orthotomus longi- 

 cauda) . This bird selects a broad leaf and draws the edges together with 

 fibres, lining the cone, thus formed, with fine grass and vegetable down, and 

 the ends of the fibres with which it is sewn are knotted as a tailor knots 

 his thread ! 



I do not think, however, that Mr. Wallace is correct in all his details 

 respecting the manner in which nests are built. I think we should be 

 very careful in imputing the various apparent imperfections (and the per- 

 fection, too) in the architectural qualities of birds' nests to the appliances 

 or tools with which they are constructed. To far more important causes 

 I believe the many differences in these structures may be safely attributed ; 

 and instead, therefore, of viewing the Swift's rude nest, or the Ring-Dove's 

 wicker cradle as the inevitable results of imperfect natural appliances, they 

 should be viewed as structures made perfect for the purpose they serve, and 

 completely in harmony with the requirements of their builders. Instead 

 of viewing the nests of the Chaffinch and the Wren as mere structures the 



* Notes by a Naturalist on the ' Challenger,' p. liio. 



