SHELTER AND HOUSING MATERIAL COACTIONS 



113 



maintain themselves against protozoan predators when cover was 

 provided. The importance of eelgrass in connection with young fishes 

 in the sea is discussed in Chapter 10 (page 336). 



Home building, with a few exceptions among burrowers, involves 

 the selection of materials which are nearly always parts or products 

 of plants or animals. Burrowers and ground-nesting species com- 

 monly line their nests or breeding chambers with grass or grasslike 

 fibers, sometimes supplemented with hair or feathers from the builder's 



Fig. 27. — Banner-tailed kangaroo rat (Dipodomys spectabilis Mer.) burrows under 

 mesquite {Prosopis juliflora). (Photo by Edith Clements.) 



own body. Ground birds commonly choose sites arched over by 

 grasses or forbs. Animals that build nests in trees and shrubs employ 

 a great variety of materials, and the use of the tree or shrub is in itself 

 a coaction. Usually fiber from bark or the stems of forbs, grasses, or 

 sedges, often mixed with leaves from the trees concerned, are employed 

 by the smaller species. The gray and fox squiiTels make summer 

 nests or platforms of green twigs with leaves, and certain apes and 

 lemurs have similar habits. Many of the larger birds use sticks to 

 make a nest platform on the limbs of trees or other high points (Figs. 

 22 and 25) . A number of insects fasten leaves together to make tem- 



