INTRODUCTION. xxiii 



Jackdaw, well provided with the requisite appliances for building an elabo- 

 rate nest, rear their young in structures poorly fabricated in the holes of 

 trees, rocks, banks, or buildings, or do not make a nest at all. From the 

 above-mentioned facts I think that we are perfectly justified in drawing 

 the inference that birds are in no way influenced by the appliances they 

 possess in building their nests. We have seen that birds are capable, quite 

 irrespective of the form of their biUs and feet, of making elaborate nests of 

 matchless beauty, or poorly fabricated and very plain in appearance, 

 respectively, and according to circumstances ; and we may therefore 

 rest assured that the nest-building capabilities of birds are not in any 

 way subordinate to their natural appliances or tools for making their 

 nests, but are regulated by, and subordinate to, the various conditions 

 under which their young are produced, and especially by the colour of the 

 eggs. Why does each species build a different kind of nest ? I am at 

 present quite unable to say what influences birds in the choice of their 

 materials. Mr. Wallace says that birds select those materials which are 

 nearest to hand and easiest to obtain. He may be right ; but when we find 

 very differently constructed nests in the same localities, almost side by side, 

 this explanation does not seem reasonable or sufficient. The above re- 

 marks on the nests of birds naturally draw our attention to 



Birds' eggs studied in relation to their colour. — In these objects 

 the chief peculiarity which claims our notice is their beautiful ground- 

 colours and varied markings. Why, we naturally ask, do these eggs exhibit 

 such diversity of colour ? Why are some eggs white, whilst others are 

 painted in tints rich and beautiful ? or why are some spotless and others 

 thickly marked ? Some persons, may urge that these colours are deve- 

 loped for no object beyond that of adding to the beauty and harmony of 

 Nature^s works, as they similarly urge the colours of the plumage of the 

 birds themselves ; but let us see what an important part the colouring- 

 matter of birds' eggs plays in the economy of the birds — let us see how 

 their complex and ever varying colours conform to the subtle influence of 

 Law. The colouring-matter of birds' eggs is influenced by the bird's 

 mode of nidification, and is partly subordinated to the colours of the parents' 

 plumage. For convenience of treatment it is advisable to divide birds' 

 eggs into two great classes, quite irrespective of the affinities of the birds 

 themselves, but solely in accordance with the fact of their being coloured 

 or uncoloured, spotted or unspotted. Each of these great groups may be 

 further subdivided into two subgroups which will include the exceptional 

 cases to each. As regards white eggs, our first division will be 



White eggs laid in covered nests. — I think we must start with the 

 very probable supposition that the eggs of the earliest forms of bird-life 

 were white. Colour is a development for protective purposes, and to that 

 cause alone must be ascribed all the wonderful and beautiful diversity of 



