FIRST WEEK] December 311 



string or cord, but fasten it to a crotch, put some marbles 

 in it and visit it after the first storm. After you have 

 picked up all the marbles from the ground you will appre- 

 ciate more highly the skill which a bird shows in the con- 

 struction of its home. Whether a bird excavates its nest 

 in earth or wood, or weaves or plasters it, the work is all 

 done by means of two straight pieces of horn the bill. 



There is, however, one useful substance which aids the 

 bird the saliva which is formed in the mucous glands of 

 the mouth. Of course the first and natural function of 

 this fluid is to soften the food before it passes into the 

 crop ; but in those birds which make their nests by weaving 

 together pieces of twig, it must be of great assistance in 

 softening the wood and thus enabling the bird readily to 

 bend the twigs into any required position. Thus the 

 catbird and rose-breasted grosbeak weave. 



Given a hundred or more pieces of twigs, each an inch 

 in length, even a bird would make but little progress in 

 forming a cup-shaped nest, were it not that the sticky 

 saliva provided cement strong and ready at hand. So the 

 chimney swift finds no difficulty in forming and attaching 

 her mosaic of twigs to a chimney, using only very short 

 twigs which she breaks off with her feet while she is on the 

 wing. 



How wonderfully varied are the ways which birds adopt 

 to conceal their nests. Some avoid suspicion by their 

 audacity, building near a frequented path, in a spot which 

 they would never be suspected of choosing. The hum- 

 mingbird studs the outside of its nest with lichens, and 

 the vireo drapes a cobweb curtain around her fairy cup. 



