INTRODUCTION. 21 



convenient hole in a building or among thatch, or in any 

 well- sheltered place, he takes much less trouble, and forms 

 a very loosely built nest." Our little golden- crested wren also 

 changes his nest to suit circumstances : he builds a simple 

 cup-shaped nest, where a natural canopy of sheltering 

 leaves is to be had, and in more exposed situations he 

 builds a spherical nest, with an opening at the side. 



The little bittern, Ardetla minuta, according to Brehm, 

 ("Pictures from the "Animal World," p. 158) is wont to 

 build his nest on old reed straw, or on reeds standing over the 

 water, or on an over-hanging willow. If it floats, as at 

 other times, on the water itself, it is then only loosely 

 attached to the reed, so that it may rise and fall with the 

 water. 



A remarkable instance of a change of instinct is recorded 

 by Wallace as lately happening in Jamaica. " Previoiis to 

 1854 the palm -swift, Tachornis phcenicobea, inhabited ex- 

 clusively the palm trees in a few districts in the island. A 

 colony then established themselves in two cocoa nut palms 

 in Spanish Town, and remained there till 1857, when one 

 tree was blown down, and the other stripped of its foliage. 

 Instead of now seeking out other palm trees, the swifts drove 

 out the swallows which built in the Piazza of the House of 

 Assembly, and took possession of it, building their nests on 

 the tops of the end walls, and at the angles formed by the 

 beams and joists, a place which they continue to occupy in 

 considerable numbers. It is remarked that here they form 

 their nests with much less elaboration than when built in 

 the palms, probably from being less exposed." 



Birds especially, which build their nests on or in human 

 dwellings, buildings, etc., have largely changed their method 

 of building to suit the changed circumstances, and have so 

 changed it as to save their work and pains. In the same 

 way the lake dwellers, who formerly lived 'over the water, 

 carried on to dry ground their fashion of building on 

 piles, although the fashion had no longer any reason ; while, 

 on the contrary, over the whole American continent the 

 houses of the natives are built in a way which was suit- 

 able to the cold climate whence the Indians originally came. 

 Wallace finds himself led by his investigations to say : "I 

 believe, in short, that birds do not build their nests 

 by instinct ; that man does not construct his dwelling by 



c 



