their feeding habits, render incalculable aid to agriculture, horticulture, 

 and forestry. 



The greatest value of "birds in the role of insect destroyers lies in 

 the coordination of their feeding activities with all other natural factors 

 of the environment in preventing the development to plague proportions of 

 destructive insect eruptions. Birds aid in maintaining an equilibrium in 

 the biotic complex. Their repressive influence is constantly exerted, and 

 their great mobility and propensity to wander causes them to concentrate 

 at the scene of any local outbreak. Frequently, they not only control a 

 pest, but almost effect its local extirpation. Thus they level off the 

 waves of insect abundance and tend to maintain uniformity in numbers. W. L. 

 McAtee £/ has given many examples of the effectiveness of birds in the con- 

 trol or suppression of insect outbreaks and has pointed out that, realizing 

 this, entomologists had much to do with the establishment of economic 

 ornithology in this country and have constantly maintained their interest in it. 



Although birds often exert an important degree of control on insects, 

 over an extensive area, it is usually only in very limited sections that 

 they actually suppress them. In widespread, invasions, for example, the 

 grasshopper plagues of recent years in the Central and Western States, birds 

 and other predatory agents are not sufficiently numerous to exert any 

 noticeable control. Under these conditions other factors, as unfavorable 

 climate, fungus and other diseases, or artificial control (poisons), must 

 be relied upon. 



As a control agency, birds, of course, are not wholly effective, as 

 they do not kill all the posts, but the same is true of every other con- 

 trol measure, biological or artificial. It has been stated that because 

 of the great fecundity of insects in comparison with that of birds, the 

 work of the latter cannot be very effective. Excursions into the realm of 

 mathematics to demonstrate the inestimable number cf progeny that may be 

 produced from a single pair of insects profit little, as a continued un- 

 checked increase never occurs. Those resorting to mathematical arguments 

 fail to recognize the importance of the various insect predators, including 

 birds, working in conjunction with all other natural and environmental fac- 

 tors when insects arc present in normal numbers. Birds have a high rate of 

 metabolism, which gives them a most impressive consuming capacity. A bird 

 may destroy more insects at a single feeding than individual parasites 

 destroy in a lifetime. Furthermore, birds continue to feed during seasons 

 when unfavorable temperatures render insect parasites of little or no value 

 as control agents. 



The sea gull-cricket episode in Salt Lake Valley in 1848, which saved 

 the lives of the early Mormon pioneers, is perhaps one of the best-known 

 instances of effective control by birds of a serious insect pest. In 1855 

 a similar but less serious and less conspicuous incident occurred in the 

 same valley when another cricket plague developed, xvhich was again sup- 

 pressed by the California gull early enough in the summer to permit a second 



2/ McAtee, ¥. L. Local suppression of agricultural pests by birds. 

 Smithsn. Inst. Ann. Hpt . 1920: 411-438, 1922. The role of vertebrates 

 in the control of insect pests. Smithsn. Inst. Ann. Rpt . 1925: 415-437, 

 1926. 



