208 



FIRST LESSONS IN ZOOLOGY. 



the visible signs of emotions 



can be set to music. Mr. X. Clark has published* the 

 songs of a number of our birds. The singular antics, 

 dances, mid-air evolutions, struts, and posturings of differ- 

 ent birds are without doubt 

 which in other birds find vent in vocal music. 



The nesting habits of birds are varied. Many birds, as 

 the gulls, auks, etc., drop their eggs on bare ground or 



rocks ; as extremes in the series are 

 the elaborate nests of the tailor-bird, 

 and the hanging nests of the Balti- 

 more oriole, while the woodpecker 

 excavates holes in dead trees. As 

 a rule, birds build their nests con- 

 cealed from sight; in tropical forests 

 they hang them, in some cases, out 

 of reach of predatory monkeys and 

 reptiles. Birds may change their 

 nesting habits sufficiently to prove 

 that they have enough reasoning 

 powers to meet the exigencies of 

 their life. Parasitic birds, like the 

 cow-bird, lay their eggs by stealth 

 in the nests of other birds. " Some 

 of the swifts secrete from their sali- 

 vary glands a fluid which rapidly 

 hardens, as it dries, on exposure to 

 the air, into a substance resembling 

 isinglass, and thus furnish the ' edi- 

 ble bird's-nests ' that are the delight 

 of Chinese epicures. In the architec- 

 ture of nearly all the Passerine birds, too, some salivary 

 secretion seems to play an important part. By its aid they 

 are enabled to moisten and bend the otherwise refractory 

 twigs and straws and glue them to their places. Spider's 

 webs also are employed with great advantage for the purpose 



FIG. 2Vt. Nest of the Tailor- 

 bird. 



* American Naturalist, vol. xiii. p. 21. 



