INTRODUCTION 7 



weeds, and the quantity they devour is almost un- 

 believable. 



What the Tree Sparrow Does 



The Tree Sparrows that were chattering so so- 

 cially over their breakfast were at the same time do- 

 ing their share toward the destruction of seeds that, 

 without their help, we should have had to fight the 

 following summer. Perhaps we may think their 

 share a small and unimportant one; but as we con- 

 tinue our walk we find a company of Tree Sparrows 

 in nearly every field and all are gathering and crush- 

 ing seed with their sharply pointed, stout little bills. 



If we watched them throughout the day we should 

 find that they passed most of their time in the same 

 useful occupation; and we might estimate the num- 

 ber of seeds each bird devours in one day. Then, 

 with the help of others, we might continue our 

 studies of Tree Sparrows over a much larger area 

 until we knew about how many there were in each 

 square mile. 



This was the method pursued by Professor Beal, 

 one of the greatest authorities on the food of birds. 

 His studies were made in the state of Iowa, where 

 he estimated that from October to April, or for 

 some two hundred days, the Tree Sparrow popu- 

 lation averaged about ten to each square mile. Each 



