tHE NATURAL HISTORY OF NESTS 161 



incubation, they seem to trust partly to the heat of decom- 

 position. Here we have another illustration of the subtle 

 ways in which Bacteria are wrapped up in the bundle of 

 life. They bring about the decomposition which produces 

 heat, and this fosters the development of the unhatched 

 birds. The minions of decay and death are here utilised 

 in the production of life. There are many similar illustra- 

 tions of a sort of " inter-regnal co-operation," the best, 

 perhaps, being the internal partnership or symbiosis of 

 unicellular Algae with Radiolarians, with Sea-Anemones 

 and Corals, with simple " worms," and so on. Analogous, 

 though not " inter-regnal," is the intimate and most 

 profitable partnership between Bacteria-like microbes and 

 Leguminous plants, like Clover. This has led us far from 

 the grebe's nest, but the digression may be pardoned, since 

 there is no more fundamental conception in Natural History 

 than that of the Web of Life or the interlinkage of interests 

 in the economy of Nature. 



We gradually work up from ground-nests to the earth- 

 mounds on which the flamingos sit, and on to rough 

 platforms like that of the wood-pigeon, through the floor 

 of which the eggs may be seen from below. Making a 

 fresh start, we reach the more elaborate stick nests of the 

 rooks and crows ; from these we pass to the heron's, where 

 a little bedding is added ; or to the magpie's, where the 

 erection is fenced round with thorns. 



An offshoot in a different direction is represented by 

 birds that make burrows or tunnels or excavations of some 

 sort, getting as far as possible into private life. In its safe 

 retreat the sand-martin makes a scant bed of roots and 

 feathers collected from far and near. The kingfisher makes 

 a stranger one of undigested fish-bones. Sheldrakes and 

 puffins often utilise rabbit-holes. The woodpeckers carve 

 out holes in decaying trees ; the nuthatch plasters up part 

 ii 



