GUANO 211 



marauding creatures, such as condors, eagles, 

 skuas, and gulls, which extract a considerable toll 

 from the young birds and eggs. The psychology 

 of the sea-birds was studied and steps were 

 taken to avoid disturbing them as much as possible 

 during the gathering of their excreta. This was 

 removed with all speed once every thirty months 

 and the island vacated immediately afterward. 

 In short, every manner of means was attempted to 

 cause the birds to multiply. 



The result of this careful treatment, after thir- 

 teen years, is entirely satisfactory. The number 

 of birds using the guano islands has visibly in- 

 creased. They are tame, contented, and prolific. 

 In a single decade, from 1909 to 1919, their annual 

 deposits rose from 25,350 tons to 80,517. Peru- 

 vian agriculture called for 50,000 tons in 1907 and 

 received only 26,000; in 1920 it demanded 70,000 

 and got them. What is more, the nitrogen con- 

 tent of the guano, which in 1913-14 averaged about 

 8.65 per cent., had through some unknown cause 

 reached 12.52 per cent, in 1920. 



The extraction of guano is not permitted during 

 the main breeding season of the birds, from 

 November to March. As each bird is valued at 

 fifteen dollars by the Peruvian Government, it 

 has been made a penal offense to destroy either 

 the birds or their eggs. Thus the feathered popu- 

 lation of certain islands, which ten years ago had 

 fallen to a few score thousand, now totals a million 



