INTRODUCTION. a 
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 Waterhen, 
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. 125, 
