PHILADELPHIA VIREO 357 



I found the Philadelphia Vireos to be rather more active in their feeding habits 

 than are the Red-eyed Vireos. The trick mentioned by Dwight of hanging back- 

 downward, like a Chickadee, from a cluster of leaves while picking insects from 

 it was observeil frequently, but the majority of the food of this species seemed 

 to be taken while the birds were on the wing. They would leap repeatedly into 

 the air to snap up passing insects with distinct "click's" of the bill. At other 

 times they were seen hovering like Kinglets before branch-tips while they 

 gathered food therefrom. The work done by this pair of Philadelphia Vireos 

 must have aided greatly in keeping the trees in their vicinity free from insect 

 pests this summer. 



Behavior. — Much of the normal behavior of this vireo is described 

 in Mr. Brewster's remarks under "Spring" and in Dr. Lewis's account 

 of its feeding habits above. But Dr. Lewis (1921) wrote on July 3, 

 describing a rather unusual performance: 



Observation began at 6.16 a. m., when one bird was on the nest, while no song 

 of the species was to be heard. No change was noticed until 6.24 a. m., w-hen 

 the male began singing among the oaks. A moment later, still singing, he 

 flew to a perch near the nest. The next instant there was a series of excited 

 squeakings, and both birds were away in a mad chase, lighting at frequent inter- 

 vals with one another, apparently without mercy. They would circle around 

 and around, passing repeatedly through the nesting-tree, then turn face to face 

 In the air and struggle furiously, with much lluttering of wings and sharp click- 

 ing of bills, until often they fell nearly to the ground. After the first few sec- 

 onds the squeakings stopped and shortly afterward the male began to sing as 

 he fought. As the birds passed through the tree they would sometimes alight 

 for a moment, two or three feet apart. After the briefest of pauses the female 

 would attempt to fly back to the nest, when the male would dash after her again 

 and the fight would be resumed. 



Voice. — Every observer seems to agree that the song of the Phila- 

 delphia vireo closely resembles that of the red-eyed vireo, yet there is 

 a subtle difference that a practiced ear can detect, especially if the 

 two are heard at the same time. Mr. Brewster's (1880) first impres- 

 sion follows: 



Contrary to what might be expected from the apparently close relationship 

 of the two birds, the song of this species does not in the least resemble that of 

 Vireo gilvus. It is, on the other hand, so nearly identical with that of V. oUv- 

 aceiis that the most critical ear will, in many cases, find great difiiculty in dis- 

 tinguishing between the two. The notes of philadelphicus are generally pitched 

 a little higher in the scale, while many of the utterances are feebler, and the whole 

 strain is a trifle more disconnected. But these differences are of a very subtile 

 character, and, like most comparative ones, they are not to be depended upon 

 unless the two species can be heard together. The Philadelphia Vireo lias, 

 however, one note which seems to be peculiarly its own, a very abrupt, double- 

 syllabled utterance, with a rising inflection, which comes in with the general 

 song at irregular but not infrequent intervals. I have also, on one or two occa- 

 sions, heard the male, when in pursuit of his mate, utter a soft pseuo, similar 

 to that sometimes used by Vireo olivaceus and both sexes when excited or angry 

 have a harsh, petulant note exactly like that of V. yilvus. 



Referring to the "double-syllabled utterance" mentioned by Mr. 

 Brewster, Dr. Dwight (1897) says: 



