191-] Bryant: Eclafioii of Birds to a Grasshopper Outbreak 13 



daily destroyed by this tlock of ducks. The owner of the ducks 

 claimed that from 300 to iOO of the pests wei-e consumed daily 

 by each duck. From 200 to 250 were actually counted in the 

 crops of some of the ducks examined. 



Since the time of the Mission Fathers, when grasshoppers 

 were first recorded as giving trouble, these insects have continued 

 their ravages. The bird population during that time has under- 

 gone a considerable change. Certain water- and shore-birds, 

 many of them known to be efficient grasshopper destroyers, and 

 especially important because of their migratory habits, have been 

 greatly reduced in numbers. On the other hand certain land 

 birds, owing to a better food supply and cover, have increased 

 in number. Perhaps the most notable example of this increase 

 is to be found in the meadowlark, a bird which feeds almost en- 

 tirely on grasshoppers when they are abundant. It seems reason- 

 able to believe that the increase of birds has in part, at least, 

 paralleled whatever increase of grasshoppers may have been due 

 to the increased food supply furnished by man. But in spite 

 of what the birds have accomplished in the destruction of these 

 insects, they continue to give trouble. Consequently we should 

 not be justified in saying that birds are capable of controlling 

 all grasshopper plagues so as to prevent damage. 



There is danger of overestimating the real economic value 

 of birds at the time of an insect outbreak. On the other hand, 

 however, there is little danger of overestimating the economic 

 value of birds when insects are in normal numbers. 



Evidence of the danger in the first instance is afforded in a 

 type of presentation sometimes used in the endeavor to show 

 the economic value of a bird. This type of presentation if ap- 

 plied to the subject in hand would read something like this: 

 The number of grasshoppers destroyed by a flock of 200 red- 

 winged blackbirds working in the infested areas was great. Com- 

 putation shows that such a flock must have destroyed about 500 

 grasshoppers an hour, and at least 5,000 in a day. This means 

 that such a flock could theoretically clear up an equivalent of 200 

 square yards of the worst infested area a day, and almost arr 

 acre and a half in a month. The loss of two crops of alfalfa 

 on the same acre means a loss to the rancher of at least $20. 



