UTILITY OF BIRDS IN 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 much 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 
which 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 wuch of the foregoing it appears that the birds are 
engaged in checking 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 wellas 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 mud 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 be taken up far- 
