CHECKS UPON INCEEA8E OF USEFUL BIRDS. 361 



sprayed. Mr. Rol)ert Ridgway noticed that birds decreased 

 verj^ much in nunil)ers in a .section of Illinois whc^re ])racti- 

 cally all the farmers Ix'gan sin-aying their orchai'ds ; but in a 

 recent letter he expresses sonu! doubt as to whether spraying, 

 or a bounty crusade against the Sparrows, caused the dimi- 

 nution of birds. The reduction of l)irds in such cases may 

 perhaps be explained ))y the fact that tlu; insects had been 

 destroyed by spraying, leaving the birds without food. Mr. 

 William Brewster has o])served two instances where the 

 spraying of shade trees caused a sudden decrease in the 

 numl)ers of birds, and in both cases several dead l)irds were 

 found. The stomachs of some of these })irds are to be; ex- 

 amined for traces of arsenic, and this ought to determine 

 whether they have been poisoned. Birds usually reject 

 sickly insects, and would not be likely to eat those which 

 showed the effects of poison ; l)ut gipsy caterpillars will 

 carry more poison in proportion to their size than would 

 kill a man, and they will still apjjcar healthy. It has been 

 noticed in some cases that birds have avoided tn^es that 

 have been sprayed with arsenate of lead, but in other cases 

 thev have not. This subject should be further investigated. 



THE NATURAL ENEMIES OF BIRDS. 



Under nature, the indigenous natural enemies of birds 

 cannot be regarded as the cause of any material reduction in 

 the numbers of the smaller species. Under man's rule, how- 

 ever, the conditions may be so changed that certain natural 

 enemies of birds may become i)ositively harmful. For this 

 reason, if for no other, the bird ])rotectionist should care- 

 fully study the effect produced upon birds by their enemies. 

 Any natural enemy of birds which becomes unduly numer- 

 ous may prove seriously restrictive to their increase, and 

 may require severe checking. 



Foreign species introduced and liberated in a new country 

 may constitute a serious danger to bird life. Still, many 

 people have deliberately introduced mammals and birds from 

 other countries and liberated them here. Fortunately, per- 

 haps, few of these attempts to saddle foreign species up(^n 

 us have proved successful. There can be but little objection 



