200 THE IMPORTANCE OF BIRD LIFE 



cliffs which are their home. The performance is 

 repeated daily throughout the year, and daily tons 

 of fish are consumed ; but there seems to be no end 

 to the anchovies. Despite the steady inroads 

 upon their hosts they are as plentiful now as they 

 were a thousand years ago. 



Only four species of birds are responsible for 

 the main deposition of guano. Of these the cor- 

 morants, or, as they are locally named, guanayes, 

 are by far the most numerous. Their rookeries 

 lie like great dark shadows of immovable clouds 

 on the sloping expanses of rock whitened with 

 chalky guano. The nests occur in the ratio of 

 about three to the square meter, a single rookery 

 often covering as much as a hundred acres. 



The nests are merely slight depressions in the 

 guano layer which overlies the rocks, and each 

 contains a pair of young who have to be fed. 

 This necessitates a continual flight of parent birds 

 to and from the ocean, a never-ending stream of 

 hurriedly moving bodies. The young gobble what 

 fish are brought, leaving the residue which they 

 cannot swallow to rot on the ever-growing walls of 

 refuse that surround the nest cavity. Daily these 

 ramparts mount higher. Each bird of the family 

 contributes its share, mother, father, and off- 

 spring. Excrement is also plentifully distributed 

 on the floor of the home; it is trampled down, 

 and the level of the nest rises higher. Gradually 

 a fresh layer of guano forms over the rookery 



