518 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



The role of insectivorous birds in pest control lias been threshed over 

 for decades, sometimes with extravagant claims and assumptions. In 

 my opinion, the desirability of having birds around can be well advo- 

 cated on grounds other than the quantities of insects that they eat, 

 without straming to justify economically what is not economic. 

 Wlien it comes to appraisal of bird predation upon insects, worms, 

 slugs, and the small creatures that do what we do not want them to, 

 the questions continue to arise as to whether such predation does have 

 a controlling influence or genuinely contribute to control. 



The few case histories of control of insect populations through bird 

 predation that look convincing to me have one thing in common: 

 superlative intensity of predation. A small garden enclosed by lux- 

 urious shade trees and shrubbery may concentrate the feeding of a 

 large number of birds and thus have its insect populations reduced 

 by the sheer weight of the predatory effort exerted. A homely anal- 

 ogy may be seen in neighborhood robin depredations on the cherry 

 crop ripening on someone's lone backyard tree. But, in considering 

 predation by birds upon invertebrates on a more spacious scale, it 

 becomes more difficult to argue from sober facts. The property on 

 which I live never seems to have any dearth of earthworms, however 

 much the local robins may be observed pulling them out of the ground 

 or collecting them in their bills after rains. (Neither do the ground- 

 plowing moles seem to affect earthworm numbers appreciably, as a 

 spadeful of soil turned in any place suitable for earthworms will 

 reveal at almost any time.) We see the chickadees working the tree 

 branches, the flickers and meadowlarks out in the fields, the swallows 

 feeding in the air ; and we know that they are eating insects, perhaps 

 of known kinds and in quantities that might be calculated, but, aside 

 from that, what do we really know about it ? 



Considering predation by birds on a still more spacious scale, I am 

 willing to concede that the early Mormon settlers of Utah may have 

 had good cause to erect a monument to cricket-eating gulls. The 

 gulls, flocking to feed on the hordes of crickets that threatened the 

 Mormon crops, very possibly brought the crickets under sufficient 

 control to save the crops; but, from what I have been able to learn 

 about this event, it would seem to have been a matter of rather local 

 concentration of gulls in response to a concentrated food supply ; and 

 I would doubt that the gull predation resulted in any significant 

 population control of the crickets over truly immense areas. 



This naturally leads to philosophical questions as to how much some 

 degree of predation here and there and now and then by this predator 

 or that may contribute to the control of an invertebrate species when 

 added to its other mortality factors ; and I am reminded, too, about all 

 of the confusion between facts of predation and effects of predation 

 that exists in the literature on vertebrates and invertebrates, alike. 



