BLUE-HEADED VIREO 291 



Accipiters. They evidently prefer the same type of woodland as the 

 hawks; hence this apparent community of interest. I once found a 

 pair of blue-headed vireos building a nest in a similar tract of pine 

 woods where a pair of barred owls had a nest. 



In the Allegany State Park, New York, Aretas A. Saunders (1938) 

 says that "they inhabit both the Maple-Beech-Hemlock forest and 

 the areas modified for camping, and seem to be rather more common 

 on the campaign areas or about their edges, apparently liking the 

 edge of the open area and having no fear of man's presence. Where 

 much undergrowth is removed, however, they do not occur, as there 

 are then no nesting sites near the ground, and it is my experience that 

 the nest is rarely placed very high." 



Leonard Wing (1939) says that, in the Upper Peninsula of Michi- 

 gan, "the Blue-headed Vireo lives in the heavier growth of Jack 

 Pine." 



Spring. — The spring migration of the blue-headed vireo seems to 

 be quite prolonged. Alexander f\ Skutcli tells me that few are seen 

 in Central America after April 19, only one being seen after that on 

 the 28th. Yet the species arrives in Massachusetts around the middle 

 of that month, Forbush's (1929) earliest date being April 11. We 

 look for them in numbers before the end of April, in the vanguard of 

 the migrating hosts of small birds, along with the black-throated 

 green and yellow warblers, the towhee, catbird, and brown thrasher, 

 but at least a week ahead of the other vireos. 



Territory. — Mr. Saunders (1938) writes: 



One differGnce in habit between this bird and the red-eyed vireo is that of 

 wandering about when singing, apparently with no fixed singing tree. This 

 habit malies it difiicult to determine territory and to get a definite count of 

 birds. This would be more difficult if it were not for individual differences in 

 songs. This wandering habit keeps singing birds moving about over a con- 

 siderable area, and I have known them to sing now and then in the same tree 

 in which a red-eyed vireo sings regularly. In such cases there is no jealousy 

 or animosity shown on the part of either species. Such observations leave me 

 holding some doubts about the territory theory, both in vireos and some other 

 birds. It would seem that the two sjiecies should be rivals for food, nest sites 

 and nesting materials. Yet their territories, if they have such, fi'equently overlap 

 with no hostility between them, at least in late summer. If there is some sort 

 of territory in this species, it seems to be larger than that of the red-eyed vireo. 

 Singing males are not very close together, and nests not near each other. 



Courtship. — Dr. Charles W. Townsend (1920) says: "Twice I have 

 been favored with a sight of the courtship performance. The male 

 puffs out his yellow flank feathers very conspicuously and bobs and 

 bows to the female, very slim in contrast, and sings repeatedly mean- 

 while with many variations to his song." 



In a patch of swampy woods back of a pine grove, I once watched 

 a pair of blue-headed vireos for a considerable length of time and 

 followed them about, as they seemed to be making love to each other ; 



