UTILITY OF BIRDS IN NATURE. 17 



do not neglect any one element of their ordinary food in 

 such cases. They neglect them all, both animal and vegetal, 

 for the time being, and turn to the now abundant insect food 

 that is more readily accessible. This I have observed in 

 studying outbreaks of canker worms, and Professor Forbes 

 records a similar experience with birds feeding on canker- 

 worms. 1 



This apparently agrees with the experience of the forest 

 authorities in Bavaria during the great and destructive out- 

 break of the nun moth (Liparis monacha) which occurred 

 there from 1889 to 1891. The flight of Starlings collected 

 in one locality alone was credibly estimated at ten thousand, 

 all busily feeding on the caterpillars, pupa?, and moths. 

 Enormous flights of Titmice and Finches were similarly 

 engaged. The attraction of Starlings to such centers be- 

 came so great that market gardeners at a distance felt their 

 absence seriously. 2 



Evidently in such cases the birds, changing their usual 

 fare entirely for the time being, remove their restraining 

 influence from both useful and injurious insects, leaving one 

 to exert its full force as a check on the other, until the urgent 

 business of the serious outbreak of grasshoppers, caterpillars, 

 or some other pest has been attended to ; then the birds 

 return to their usual haunts and food, and exert the same 

 repressive influence as before. 



Although the insects which are potentially injurious are 

 greatly in the majority, there are many species which per- 

 form a very apparent useful function in nature. Such are 

 the bees and some of their allies of the order Hymenop- 

 tera, insects which travel from flower to flower in search 

 of sweets, and, becoming loaded with pollen, fertilize the 

 blossoms, rendering the trees fruitful. Other insects seem 

 especially adapted to hold the potentially injurious species 

 in check. Some which are called predaceous insects attack 

 other insects and devour them, as do the ground beetles 



1 The Regulative Action of Birds upon Insect Oscillations, by S. A. Forbes. 

 Bulletin No. 6, Illinois State Laboratory of Natural History, 1883, p. 21. 



2 Protection of Woodlands, by Herman Fiirst. English edition, translated by 

 John Nisbet, 1893, p. 126. 



