UTILITY OF BIRDS IX NATURE. 21 



regarding the utility of birds in nature. It may be stated 

 confidently, as a general rule (not without exceptions, how- 

 ever), that, in the natural order of things, the species that 

 is kept within normal numbers without great fluctuations, 

 whether beast, bird, reptile, batrachian, or insect, will serve 

 a useful purpose ; while the species that increases unduly 

 will devour too nuicli animal or vegetable food, and, by dis- 

 turbing the balance of nature, become a pest. It is the 

 abnormal increase of the gipsy and brown-tail moths and 

 the " English " Sparrow in this Commonwealth that has 

 been responsible for the injury they have done. If birds 

 do well their part in holding in check native insects, small 

 mammals, reptiles, batrachians, and other forms of life on 

 Avhich they feed, they have fulfilled their mission, even if 

 in doing this they destroy some individuals of some species 

 that are classed as useful. 



This, then, is the chief mission of the birds in organic 

 nature : to fill their peculiar place in preserving the balance 

 of nature's forces, — a place that cannot be filled by any 

 other class of animals. 



In nmch of the foregoing it appears that the birds are 

 enofao:ed in checkino; the increase of insects and other ani- 

 mals, exerting that check constantly when and where it is 

 most needed. The vegetable food of birds is perhaps of 

 less importance, but here also they exercise a restraining 

 influence by destroying seed as well as in other ways. They 

 also exert a beneficial influence by planting seed. 



Birds also play a great part in the distribution of plants, 

 the upbuilding and fertilizing of barren islands, and a minor 

 part in the distribution of insects. Wild-fowl and Herons 

 may sometimes carry small seeds for many miles embedded 

 in particles of nuid which adhere to their feet. Where this 

 mud drops from their feet, the seeds may sprout and grow. 

 The fruit-eating birds are among the most valuable of tree 

 planters, distributing the seeds far and wide. Certain insects 

 which cling to the feet or feathers of birds are sometimes 

 distributed in this way. The part taken by birds in forest 

 planting and fertilizing barren lands will lie taken up far- 



