SOMETHING ABOUT BIRDS [17] 



ECONOMIC STATUS 



No COUNTRY in the world has a better understanding of the food habits 

 of birds and their interrelationships to agriculture than the United States. 

 This is due to the economic studies that have been carried on by the 

 Biological Survey for more than 50 years and to the subsequent publica- 

 tion of the information acquired. The major groups of birds have been 

 covered in these publications, and the bird-protection laws have been 

 largely based on the data obtained from this source. Most biologists 

 agree that in general birds have a tendency to be economically beneficial 

 rather than harmful. There are times and places, however, where some 

 species become destructive to special agricultural interests, and there are 

 a few birds, including crows and magpies, that often are considered 

 injurious over wide areas. 



There is a great deal of honest difference of opinion between groups as 

 to the exact value of birds as weed-seed and insect destroyers. The earlier 

 students of bird interrelationships considered birds valuable as weed-seed 

 destroyers, a view that has been largely abandoned in more recent years. 

 It is now recognized that birds feeding on weed seed do not usually 

 destroy enough of the total production on a given area to make any 

 appreciable difference in the next year's crop of weeds. It is also recog- 

 nized that birds act as spreaders of weeds of many kinds. Economic 

 entomologists generally feel that the value of birds as insect checks has 

 been greatly exaggerated, and there is little doubt that statements some- 

 times made by enthusiastic bird lovers to the effect that the country would 

 become a vegetationless desert were it not for the insect-eating birds are 

 far beyond the truth. Such birds destroy, of course, not only insects that 

 are pests, but also valuable predatory and parasitic species that do have 

 a recognizable repressive effect upon destructive insects. 



Our own opinion is that the great congregations of birds sometimes 

 appearing at scenes of insect outbreaks are not always of real use in con- 

 trolling insects. In such cases the birds and other predators feed upon 

 enormous insect surpluses built up by particularly favorable conditions, 

 and though such activity may tend to shorten the duration or restrict the 

 area of local outbreaks, it may have little or no measurable effect upon 

 the permanent insect population of the area. The greatest value of birds 

 as insect destroyers lies in the steady toll they exact when insects are 

 present in normal or less than normal numbers. Such repressive effects 

 may go far toward preventing the building up of great surpluses but are 

 exceedingly difficult to measure in mathematical terms. Ornithologists 

 generally are agreed, however, that there is a large, if uncertain, value 

 in such activities. 



A consideration of the activities of birds will reveal that every ecolog- 

 ical condition finds species that are especially adapted to feeding under 



