56 



ducks which doubtless thus save many young trout. The 

 influence of fish-eating birds is exerted to keep the balance true 

 between the fish and their enemies, and to prevent any undue 

 increase of either. If an increase of minnows or mosquitoes 

 occurs then the ducks are likely to eat more and more mos- 

 quitoes or more minnows, or they may eat more trout if the 

 trout are unduly numerous. This explains why fish-eating birds 

 may be very destructive to artificially raised trout, which are 

 kept in small ponds in numbers far exceeding those normally 

 bred in equal space in the streams. 



We sometimes hear complaints from fishermen that scoters 

 (commonly called coots), or other diving ducks, are destroying 

 shellfish and thus injuring the shellfish industry. But these 

 ducks feed only on very small shellfish, never on marketable 

 ones. They cannot swallow the larger ones. Moreover, Dr. 

 G. W. Field, formerly chairman of the Massachusetts Commis- 

 sion on Fisheries and Game, and now (1921) in the fisheries 

 service of Brazil, informs me that the thinning out of young 

 clams which is accomplished by these birds tends to promote 

 the rapid growth of those that are left, so that they more 

 quickly reach marketable size. At first the clams are often so 

 numerous that they have neither sufficient room nor food to 

 develop. He also assures me that these ducks feed on destruc- 

 tive enemies of shellfish. Though possibly harmful at times, 

 probably these birds are indispensable to the prosperity of the 

 shellfish industry. 



If we consider the fact that mosquitoes and flies are among 

 the most dangerous enemies to the life and health of mankind 

 because they carry and spread the germs of weakening and even 

 fatal diseases, we shall more readily appreciate the services of 

 birds in destroying these insects. The common house fly^ dis- 

 seminates on human food the germs of typhoid fever, tubercu- 

 losis and other diseases. Many birds, particularly poultry and 

 game birds, feed on fly larvae. Mosquitoes infect people with 

 the germs of malaria and yellow fever. Because of this distri- 

 bution of such diseases by insects, great tracts of fertile land 

 are rendered uninhabitable to white men, many deaths occur 

 annually, and there is an enormous yearly economic loss through 

 illness and death. Many birds destroy mosquitoes or their 

 larvae; among these the shore birds and wild-fowl stand pre- 



