30 



CIVIC BIOLOGY 



with neighboring districts in which no such provisions are 

 made ? What is the practical value of such work as shown 

 by your account of insect injury ? of losses caused by birds ? 

 Other important lines of bird work relate to destruction of 

 weed seeds and the control by owls, hawks, and shrikes of nox- 

 ious mammals, mice, moles, rats, gophers, etc. Keep these 

 matters in mind throughout the year while doing the field work. 



FIG. 12. Bird house for study of home life ; windowpane is back wall of house 

 Photograph by the author 



The birds in your district will change during different sea- 

 sons. During the fall migration the " summer residents " will 

 leave for the south, and many species whose breeding range is 

 farther north will migrate through the territory. These species 

 may be designated as "transient visitants." They migrate by 

 us to the northward in the spring and southward in the fall. 

 After settled cold weather begins there will be left the " per- 

 manent residents," about thirty-six species for the latitude 



