BIRDS 



243 



many species at many points in tiie Mississippi Valley, is 

 Cooke's "Bird Migration in the Mississippi Valley." 



It must also be kept in mind in using bird-keys and de- 

 scriptions to determine species that the descriptions and 



Fig. 198. — Nest of buff-breasted flycatcher, Empidonax fiilvifrons pyginccus, 

 on cone of pine-tree. {Photograph by R. D. Liisk; permission of 

 The Condor.) 



keys refer to adult birds, and in ordinary plumage. Among 

 numerous birds the young of the year, old enough to fly 

 and as large as the adults, still differ considerably in plum- 

 age from the latter; males differ from females, and finally 



