36 BIRDS OF FIELD, FOREST AND PARK 



pass by in the spring to nesting grounds some- 

 where to the northward, returning in the fall to 

 spend the winter somewhere to the south of us. 

 This class includes a large number of varieties 

 which we can study only during the two or 

 three weeks in the spring and a similar period 

 in the fall when they are passing by. 



This is, at best, but a relative classification, 

 as it may be readily seen that birds pass from 

 one class to another according to the locations 

 where the observations are made. A bird which 

 in New Jersey is classed as a transient visitor 

 in Maine may be a summer resident; and a bird 

 in Maine which is a permanent resident may be 

 classed in Connecticut as a winter visitor. But 

 it is well to consider these divisions in order that 

 one may the better understand the subject of 

 migration. 



