Economic Reasons for Protection 109 



spent the winter in the state of Iowa. Judging 

 from the stomach contents of many tree sparrows 

 examined by him, he allowed a quarter of an 

 ounce of weed seed a day for each bird, and on 

 this basis calculated that in that one state, 

 the tree sparrows destroy 1,750,000 pounds, or 

 about 875 tons of weed seed during each winter. 

 Supposing that those seeds had been left on the 

 ground and that one in a hundred had germin- 

 ated, I wonder what it would have cost the 

 farmer to grub them out. 



Our seven species of swallows may be counted 

 among the birds which are almost wholly bene- 

 ficial. They do no harm in any way beyond 

 eating a few useful parasitic insects, and comb- 

 ing the air from morning to night they destroy 

 an almost unbelievable number of noxious flying 

 things, including house flies, mosquitoes, gnats, 

 and horse flies. As most of them are quick to 

 accept the hospitality of man, they are among the 

 most useful birds we can have around our homes 

 and barns. But they are valuable in fields as 

 well, since they gather in locusts, leaf hoppers, 

 ants, wasps, and bugs. The purple martin, the 

 largest of the family, is very fond of squash 

 beetles. The stomachs of ten purple martins, 

 shot in Nebraska, were found to contain 265 

 locusts and 161 other insects. 



