10 UNIVERSITY OF COLORADO. 



the orchard was, on- account of the abundance of canker worms and cut- 

 worms, very much greater than in those collected elsewhere (17). The re- 

 spective percentages of caterpillars are as follows : 



Specimens Specimens 



from from 



orchard. elsewhere. 



Robin 54% 23% 



Catbird 26% 12% 



Dickcissel 88% 47% 



Indigo Bunting 29 % 19 % 



Thirty-six species of birds are known to feed upon the larvae of the 

 codling moth, whose ravages are often so disastrous to orchard crops. Many 

 other species doubtless take this pest. It is estimated that the birds destroy 

 from 66.% to 85% of the larvae (IS) in some localities. 



On the other hand, certain species of birds may themselves, under some 

 circumstances, become harmful. The failure of a natural food supply may 

 drive birds to cultivated crops. This is believed to be the cause of the raid 

 upon olive groves by robins in California, in 1900-1901 (19). Blackbirds 

 sometimes accumulate in such numbers as to damage crops, though under 

 normal conditions they are much more beneficial than harmful. Bobolinks 

 inflict great damage upon the rice crops, when they accumulate in vast flocks 

 in the South. The species which are occasionally harmful locally, during 

 most of the time are useful, and, by their occurrence in large numbers when 

 insect pests are overabundant, often actually save crops from destruction. 



When an insect or rodent pest has gotten beyond control, the birds can- 

 not, of course, in many instances, immediately restore the balance, so that 

 usually artificial means must be adopted to save the crops. Although they 

 are often able, unaided, to reduce pests in small areas and thus save crops 

 from great uprisings of insect or rodent pests, and in many other cases to 

 greatly aid the agriculturist in combating such uprisings, yet their greatest 

 value is their continuous work in preventing such uprisings. 



According to Forbes (20) it is estimated that in Illinois the birds destroy 

 about 70% of the insects, which, though it would not exterminate the in- 

 sects, certainly must act as a very efficient check upon their undue increase 

 usually. 



The number of species and subspecies of birds in the various states of 

 the Union varies from about 325 to 530, the latter number being credited t> 

 California, where many local races are found. Colorado claims 403 (21). So 

 varied are their habits that scarcely a pest of any kind can escape their at- 

 tention. Swallows, martins and nighthawks may be seen wheeling and zig- 



(17) Forbes, S. A., Tho Regulative Action of Birds upon Insect Oscillations, 

 Illinois Stato Lab. Nat. Hist., Bull., Vol. I, No. 3, pp. 3-32. 



(18) McAtee, W. L., Bird Enemies of the Codling Moth, U. S. Dept. Agric., Year- 

 book for 1911, pp. 243-245, 1912. 



(19) Beal, F. E. L., The Relation of Birds to Fruit Growing in California, U. S. 

 Dept. Agric., Yearbook for 1904, pp. 242, 252-253, 1905; Birds of California in Rela- 

 tion to the Fruit Industry, U. S. Biol. Surv., Bull. No. 30, p. 9, 1907. 



(20) Forbes, S. A., The Food of Birds, Illinois State Lab. Nat. Hist, Bull., Vol. 

 I, No. 3, pp. 86-87. 



(21) Cooke, W. W., The Condor, Vol. XIV. pp. 151-152, 1912. 



