THEIR RELATION TO ANIMALS 



^35 



sway is just as likely to be defoliated by the elm-leaf 

 beetle as its fellow in the city streets where the English 

 sparrow holds the fort. It is correct to say that as 

 against the common pests of the farm, the field, the or- 

 chard and the garden, neither birds nor other vertebrate 

 animals are of the least practical benefit and that the 

 farmer and fruit-grower would as to them be no worse off 

 if every insectivorous bird and other animal were killed. 



And yet withal it is not a fair conclusion, to con- 

 tend that insectivorous birds and animals do no good. 

 They do, no doubt, constitute a very useful and im- 

 portant check to many species that would otherwise 

 be much more abundant than they are, and a careful 

 preservation of every insectivorous bird and animal is 

 good policy — even such forms as quail, partridges and 

 their allies, which are now guarded at one season simply 

 that they may be shot at another. 



It must again be emphasized that birds and other 

 animals constitute only one of the checks to insect in- 

 crease and, as against climate, disease, parasitic and 

 predatory insects, a very minor and insignificant one. 

 We must also remember again that for a naturally 

 abundant species the abundance was fixed in spite 

 of all the natural checks, including birds and animals. 

 Now when such an abundant insect becomes destruc- 

 tive by reason of undue increase from any cause, the 

 very last factor to become important in bringing it 

 back to normal conditions is the vertebrate enemy 

 list, including birds, because their number and ability 

 to consume remains practically a fixed quantity due 

 to their slow rate of multiplication. It sounds large 

 when we find loo larvae of an elm-leaf beetle in a bird 

 stomach and find loo birds to an acre; but when we 

 find loo larvae on a dozen leaves and many thousands 

 of leaves on a tree, the figures lose in impressiveness. 



