PHILADELPHIA VIREO. 849 



plumage is often found to be stained. It is frequently imposed upon 

 by the Cowbird, whose young ones it rears as tenderly as if they 

 were its own. 



In the east it is said to travel as far north as Antieosti. Rich- 

 ardson found it at Fort Simpson, and according to Mr. Fannin, it is a 

 summer resident along the southern border of British Columbia. A 

 great many spend the winter in the Gulf States, and go even farther 

 south. 



VIREO PHILADELPHICUS (Cass.). 

 257. Philadelphia Vireo. (626) 



Aliove, dull olive-green, Vjrightening on the nunj). fading insensil)ly into 

 ashy on the crown, wliich is not bordered with blackish ; a dull white super- 

 ciliary line ; Itelow, palest possible yellowish, whitening on throat and belly, 

 slightlj' olive-shaded on sides ; sometimes a slight creamy or Imfty sha<le 

 throughout the under parts ; no obvious wing bars ; no spurious cpiill. Length, 

 45-5^ i wing, about 2§ ; tail, about 2:^ ; bill, hardly or about i ; tarsus if. 



Hab. — Eastern North America, north to Hudson's Bay, south, in winter, 

 to Costa Rica. 



The only record of the nest and eggs of this species I have ever 

 seen is published by Mr. Ernest E. Thompson in the Ank; for July, 

 1885. He says: "On the 9th of June, 1884, while camped near 

 Duck Mountain, I found a nest of this species. It hung from a 

 forked twig, about eight feet from the ground, in a willow which 

 was the reverse of dense, as it grew in the shade of a poplar grove. 

 The nest was pensile, as is usual with the genus; formed of fine grass 

 a]^d birch bark. The eggs were four in number, and presented no 

 ()l)vious difference from those of the Red-eyed Vireo, but unfortun- 

 ately they were destroj^ed by an accident before they were measured." 



The owners were not secured. 



Very many of the more recent additions to the list of our Ameri- 

 can birds have been made by the discovery that within certain 

 well-known groups were individuals differing in some respects from 

 the others. If these differences were found to be uncertain and 

 irregular they received only a passing notice, but if they were found to 

 be constant they wei'e made the basis on which to build a new species. 



Thus, although the American Vireos had passed in review before 

 many distinguished ornithologists, it was not until 1842 that John 

 Cassin found one closely resembling several of the others, but differ- 

 ing in some respects from all of them. 



In 1851, he published a description of the l)ird he had found, 



