47 



insects fail to keep down the increase of insect pests, even man 

 himself becomes unable to protect birds. In recent years I 

 have seen this illustrated in the increase of the gypsy moth 

 and the brown-tail moth in eastern Massachusetts, — two first- 

 class pests introduced into this country in the same region with- 

 out their natural enemies and therefore increasing inordinately. 

 Native birds and other enemies of insects are not numerous 

 enough to check their increase. Although State governments, 

 the national government, towns, cities and individuals are ex- 

 pending probably a million dollars each year in the effort to 

 suppress them, although the United States Department of Agri- 

 culture has introduced and propagated parasites and predaceous 

 insects, although about fifty species of native birds eat the 

 moth pests, still their increase and spread go on. Last year I 

 went over a large tract many square miles in extent where the 

 leaves had been stripped from the trees. Everywhere the young 

 birds or eggs in the nests in those trees had been destroyed 

 by the heat of the sun or exposure to their enemies. In such a 

 case no young birds can be reared except those on the ground 

 or those in hollow trees or nesting boxes. Similar irruptions 

 of grass-eating insects expose the nests of ground birds in the 

 same way. Birds are among the chief enemies of ticks, but 

 wherever for any reason the numbers of birds are reduced, 

 ticks increase and still further deplete the numbers of birds 

 by destroying their young. This happened in Jamaica after 

 the introduction of the mongoose, which so lessened the num- 

 bers of birds that ticks, no longer controlled by birds, destroyed 

 most of the young birds that escaped the mongoose and ren- 

 dered it almost impossible to raise domestic fowls on the 

 island. 



Birds which nest in colonies often suffer severely from para- 

 sites, particularly mites, which attack them at night. 



MISTAKES MADE IN ATTEMPTING TO CONTROL THE NAT- 

 URAL ENEMIES OF BIRDS. 



In considering the methods of controlling the natural ene- 

 mies of birds we must divide these enemies into two classes: 

 (1) Those introduced from foreign countries and which there- 

 fore tend to disturb the balance of nature, and should be elim- 



