AVES 187 



dried excrement of numberless sea birds (usually), deposited, during 

 long ages in a practically rainless region. On the Chincha Islands the 

 deposits were as much as 100 feet thick, but they have now been depleted. 

 These large fish-eating sea birds congregate at certain places in in- 

 credible numbers and with no rain to wash it away the excremental 

 matter would collect indefinitely. The term guano is applied also to 



PIG. 116. American egret, Ardea egretta. Length, 41 inches. Photograph 

 from specimen with neck extended. (From Dougherty, Principles of Economic 

 Zoology.) 



the collected excrement of bats, sometimes found in caves, and to ferti- 

 lizers artificially made from certain fishes menhaden for example 

 after extracting the oil. 



A number of birds are of some importance as scavengers, though per- 

 haps their usefulness in this particular way has been exaggerated. The 



