BROOD-CARE IN BIRDS 151 



out of the holes they have made, bring the edges of the leaf together, 

 transforming it to a hanging purse, within which the nest is built. 

 The ingenuity and diversity of the various woven nests are endless, 

 and aUied species show all the stages between rude structures and 

 exquisitely finished houses. There are so many instances of different 

 formations of the nest according to the different environment in 

 which the birds live, and so many cases where it seems plain that 

 the instinct is partly degenerate, that it is impossible to arrange a 

 parallel series between the complexity of the nest and the position 

 of a particular species in its family. Types of construction run 

 through the nests of allied species, but appear in all stages of per- 

 fection and degeneration. 



Just as it is impossible to draw a sharp line between birds which 

 lay on the ground or in holes, using no soft nesting material, or 

 little or much of it, so there are many transitions between nests built 

 chiefly of fibrous materials, animal or vegetable, partly cemented, 

 or lined or mixed with mud and saHva, and nests which are formed 

 of mud or saliva almost wholly. As, however, many of the nests of 

 plastic material conform with shapes naturally suggested by fibrous 

 substances, it is more than probable that sticks, twigs and wool were 

 used and then discarded. So also in the pursuits of man, rude 

 basket-work preceded pottery. Early human workers found that 

 they could improve their baskets by daubing them with clay, and 

 then some made the great discovery that clay alone was necessary. 

 Early pottery, however, is often ornamented with patterns that 

 suggest its primitive origin from smeared fibres. Similarly there 

 are transitions between mud nests and nests in holes. The hombill 

 selects a hollow tree, but the male shuts in his mate with a wall of 

 mud. A North American cliff-swallow selects a hole, but builds a 

 rim of mud round the aperture. Swallows build their familiar 

 dwellings, in comers under the eaves of houses, of pellets of earth 

 which they collect and moisten, but mix with fragments of hay. 

 The Australian grey struthidea makes a circular nest with vertical 

 walls wholly of mud, supporting it on the branch of a tree. 

 Flamingoes build very large conical mounds of mud, in the swamps 

 by the sea, and hollow a space on the summit for the reception of 

 the eggs. Several individuals, probably a male with two or three 

 hens, of the South American oven-bird combine to build a very large 

 oven-shaped structure. They choose the branch of a tree or the top 

 of a post and carry to it innumerable little pellets which they make 

 by kneading horsehair or rootlets with mud in a pool. They first 



