BIRDS IN RELATION TO MAN 429 



455. Undesirable birds. It is impossible to class every spe- 

 cies of bird as altogether useful or altogether injurious. A bird 

 may be very useful in one region and injurious in another. 

 The red-tailed hawk feeds on field mice in one region and dis- 

 covers that chickens are good to eat in another. The bobolink 

 is a serious menace to the rice fields in the South, but is a 

 valuable insect destroyer in the North. The red-winged black- 

 bird ate so much grain in Nebraska a number of years ago that 

 the farmers just took up arms and killed the bird off. The 

 following year, however, the absence of the blackbirds enabled 

 the locusts to multiply so rapidly that many of the grain crops 

 were ruined. 



456. Direct economic value of birds. The poultry and eggs pro- 

 duced in this country and sold for food every year are valued at over 

 five hundred million dollars. To this must be added game birds used 

 as food, the value of which it is practically impossible to estimate, 

 and importations of bird products. Imported feathers and downs 

 come to about eight million dollars a year. 



The most valuable organic fertilizer consists of guano, which is 

 the refuse of millions of birds, accumulated through many years upon 

 various islands off the coast of South America (see p. 66). 



The satisfaction yielded to the observer by the song and chatter 

 and by the appearance of birds would seem to be enough to pay for 

 the maintenance of many of these interesting animals ; but we can 

 have these returns without paying for bird feed, and get in addition 

 the very considerable contribution that they make to the suppression 

 of undesirable insects, rodents, and weeds. 



