5°6 



BIRD BEHAVIOUR 



XVII. 10- 



nest-building materials for some generations then build clumsily at 

 first, though they quickly improve. 



The methods used, of course, vary with the materials. Many of them 

 involve most elaborate tying of grasses to the branches, which is done 

 with the beak or the feet or both (Fig. 306). The shape and construc- 

 tion of the nest varies with the habits of the bird. Many sea-birds, 

 nesting safely on the cliffs, make only very simple nests or none at all. 



Fig. 306. Process of nest-building by a weaver bird (Quelea). The arrows show 



directions in which the piece is pulled. A, the points of holding by the beak; 



4, 5, and 6 show successive stages of co-operative weaving by the foot and beak. 



(From Stresemann, after Friedmann.) 



In such birds as the plovers or larks the nest is a cup in the earth, the 

 eggs being procryptically coloured with a blotched green and brown 

 pattern, so that it is very difficult to see them on the spring ploughland 

 or partly green earth. Nests constructed in trees vary from the simple 

 sticks of rooks or pigeons to the elaborate domed and lined nests of 

 many passerines. The nest is woven from materials brought in with 

 the beak and often lined with moss or in ducks with feathers from the 

 breast of the bird. The thrush lines its nest with mud moistened with 

 saliva and the swift makes nearly the whole nest of saliva. Many birds 

 build roughly and often use the old nests of others, for instance, kes- 

 trels are often found using the nests of crows. Others build in burrows, 



