BIRD-PROTECTION IN THE SCHOOLS 299 



saw a long-billed marsh wren carry SO locusts to her young in 

 an hour. At this rate how many locusts did the brood consume 

 in a day of 12 hours? The area of Nebraska is about 77.000 

 square miles. If we assume that there were 20 broods of wrens 

 to each square mile, how many locusts did the wrens in Ne- 

 braska destroy in one day? 



8. Many birds on the average feed their young about 200 

 times a day, and the young stay in the nest about two weeks. 

 After the leaves have fallen, count the number of nests in a cer- 

 tain area and then estimate the number of insects that have been 

 destroyed by the birds reared in these nests, assuming one insect 

 brought at each feeding. 



4. A 40-acre farm in Rantoul, Kansas, had 157 pairs of birds 

 nesting on it in 1914. Assuming that the birds averaged to feed 

 their young 200 times a day, and that the young remained in the 

 nest 14 days, how many insects per acre were destroyed by these 

 birds? How many insects were destroyed on the whole farm? 



B. Problems on amount of food eaten by adult birds. 



1. A study made of owls- during the whiter months showed 

 that they destroyed 2 mice a day. It has been estimated that 

 each mouse does damage to the extent of 2 cents each year. 

 How much is an owl worth a year? 



2. A study made by the Biological Survey of the red-shoul- 

 dered hawk showed that out of 214 birds, 3 had eaten poultry and 

 102 had eaten mice. What per cent of the birds had eaten poul- 

 try and what per cent mice? 



C. Problems on the numbers of birds. 



1. A census made of birds in the eastern United States showed 

 that there was an average of 6 pairs of robins to each farm of 

 58 acres. There are about 4,000,000 farms east of the Mississippi, 

 averaging 93 acres each. How many robins are there on the 

 farms east of the Mississippi River? 



2. This census also showed that for every 100 robins there 

 were 83 English sparrows, 49 catbirds, 37 brown thrashers, 

 28 house wrens, 27 kingbirds, and 26 bluebirds. How many in- 

 dividuals of each kind of birds are there on the farms east of the 

 Mississippi River? 



3. This census also showed that there was an average of one 

 pair of birds per acre. How many birds are there altogether on 

 the farms east of the Mississippi River? 



