306 BIOLOGY FOR BEGINNERS 



vast deposits of manure, called guano, have accumulated, which 

 are very valuable for fertilizer. 



A curious and rather pitiful use for birds is to detect poisonous 

 gases in mines and in warfare. Their rapid respiration and delicate 

 nervous system make them more sensitive than man to the presence 

 of dangerous gases. They are taken in cages into the mines or 

 trenches where their symptoms of suffocation give warning in 

 tune for the men to take precautions. 



Another very specialized use for birds, which the war has greatly 

 developed, is the carrying of messages by pigeons, carefully trained 

 to return to their homes, when carried to the front and liberated. 

 Often they have been able to bring back messages through shell 

 fire where no man could live. 



Last, but by no means least, is the value of birds to man as 

 companions and pets. If the world were deprived of all bird song 

 and color, it would be a dreary place, and even those who now 

 overlook them, would miss their accustomed presence. 



There is no large group of animals with so few harmful members. 

 The food table indicates a few which destroy fowls or useful birds 

 and a few others that eat grains and useful fruits. Another class 

 of damage is in cases like that of the English sparrow and starling 

 where a foreign bird is interfering with our native species. The 

 accompanying " Black List " includes all having even a suspicion 

 against them, and shows how few there are, which do any harm 

 at all. 



Positively harmful Possibly harmful 



Cooper's Hawk Blue Heron 



Sharp Shinned Hawk King Fisher 



Pigeon Hawk Crow 



Great Horned Owl Blue Jay 



Snowy Owl Grackle 



English Sparrow Cow Bird 



COLLATERAL READING 



Migration: Birds of North America, Chapman, pp. 5-6, 13-20; Bird 

 Life, Chapman, pp. 48-61; Travels of Birds, Chapman, entire; Citizen Bird, 



