Economic Reasons for Protection 87 



stomach of a single tern. Sea-gulls also act as 

 scavengers, cleansing the waters of our harbors 

 and river mouths of offal and other refuse which 

 threaten to pollute them. And they are not the 

 least of the many agencies which make fertile 

 and habitable what would otherwise be rocky or 

 sandy, barren, and uninhabitable islands. Their 

 rotting nests make soil; they fertilize it with 

 their guano, and plant in it seeds which they 

 have carried from afar and which have passed 

 unharmed through their digestive tracts. Doubt- 

 less many a shipwrecked sailor owes his life 

 to the unconscious work of sea-birds. And as 

 Forbush points out they often save the mariner 

 from shipwreck, especially in foggy summer 

 weather. At such times the presence or the 

 clamorous voices of sea-birds in great numbers 

 often give warning of the presence of the rocks 

 or islands where they make their homes, and off- 

 shore fishermen receive similar warning from the 

 unerring flight of homeward-bound gulls and 

 terns. Chapman goes so far as to say that 

 Columbus, facing a discouraged and mutinous 

 crew, might never have discovered America had 

 not the fall flight of land birds passing from the 

 Bermudas to the Bahamas and Antilles, been 

 observed by the mariners, who were given new 

 courage by the unwearied and joyous songsters 



