462 SCIENCE OF HOME AND COMMUNITY 



tain length of time, say an hour. A record should be kept of the 

 number of times the young birds are fed, and if the sexes can 

 be distinguished either by color or song, the number of times each 

 parent brings food should be recorded. The birds feed from 

 sunrise till sunset, and if there are not enough groups to watch 

 them all day, an estimate for the whole day may be made from 

 the results obtained for the time the birds are watched. 



Number of insects eaten. It is possible to make an esti- 

 mate of the number of insects eaten by birds east of the 

 Mississippi River. A census has been made of the number of 

 birds found here, and observations have been made of the 

 number of times young birds are fed. On this basis we get 

 an estimate of ten trillion insects as the number eaten by the 

 birds each summer east of the Mississippi River. If these 

 were placed an inch apart, they would make a procession 

 one hundred and sixty million miles long, which would reach 

 to the sun and almost back. If it traveled at the rate of one 

 mile a minute, it would take three hundred years to pass a given 

 point. If placed one inch apart each way, these would make 

 a sheet that would completely cover the state of Delaware. 



Birds as destroyers of weed seeds. A second way in 

 which birds help man is in eating weed seeds. The most 

 valuable birds for this purpose are the mourning dove, the 

 bob white, and the native sparrows. Two thirds of the 

 entire food of the dove, and about one half of the food of 

 the bob white and sparrows is composed of weed seeds. The 

 red-winged blackbird has been known to eat fourteen kinds of 

 weed seeds, the horned lark thirty-eight kinds, and the bob- 

 white one hundred and twenty-nine kinds. A single bird 

 eats an enormous number of seeds. In a single stomach of a 

 chipping sparrow have been found one hundred and fifty 

 seeds of crabgrass, and in that of a bob white, ten thousand 

 seeds of pigweed. Professor Beal has estimated that the 

 tree sparrows in the state of Iowa alone consume every year 

 eight hundred and seventy-five tons of weed seeds. 



