PROTECTION OF BIRDS 465 



the fact that after the tree is cut down and sawed up into 

 lumber, the little holes formed in drilling lower the value of 

 the lumber. Some birds, such as the flycatchers and swal- 

 lows, eat beneficial insects. And finally some birds destroy 

 other valuable birds. More than half of the food of the 

 sharp-shinned hawk consists of small valuable birds. 



Summary. We may summarize briefly by saying that 

 birds may be divided into three groups : injurious, neutral, 

 and beneficial. To the injurious group belong four common 

 birds : the English sparrow, the sapsucker, Cooper's hawk, 

 and the sharp-shinned hawk. To the neutral group, in 

 which the harm and good about balance, belong -five com- 

 mon birds : the catbird, the cedar bird, the crow, the crow 

 blackbird, and the bluejay. The remaining common birds 

 are beneficial. If we take one hundred as the number of 

 species of common birds that might be found in a locality, 

 they would be divided as follows : injurious, four per cent ; 

 neutral, five per cent ; beneficial, ninety-one per cent. To 

 state the matter more briefly, four per cent do more harm 

 than good, and ninety-one per cent do more good than 

 harm ; that is, for every species of harmful bird, there are 

 twenty-two species of beneficial birds. 



Mr. H. W. Henshaw, chief of the Bureau of Biological 

 Survey, writes in a recent article : " What would happen 

 were birds exterminated, no one can foretell with absolute 

 certainty, but it is more than likely, nay, it is almost certain 

 that within a limited time not only would successful agri- 

 culture become impossible, but the destruction of the greater 

 part of vegetation would follow. It is believed that a 

 permanent reduction in the number of our birds, even if 

 no species are exterminated, will inevitably be followed by 

 disastrous consequences." 



The food habits of a few common birds are briefly sum- 

 marized in the following table, which is based on the reports 

 oc the Bureau of Biological Survey. 



2H 



