NESTING OF THE BLUE -HEADED GREENLET 511 



Notwithstanding the regularity we may thus trace in the 

 movements of the Blue-head, the bird is by no means equably 

 distributed all over the great area it occupies; and the cause 

 of its rarity in some localities, no less than of its comparative 

 abundance in others, remains unexplained. On the whole, the 

 birds appear to pursue more especially two lines of migration 

 on opposite sides of the continent, where their numbers are 

 greater than they have ever been shown to be in the interior, 

 as the Mississippi watershed at large. This is the reverse of 

 the case which the Philadelphia Yireo offers; it may be due, 

 in a measure, to the birds' inclination to follow along mount- 

 ain ranges rather than pass across stretches of low alluvium. 

 As already observed, it is only in the further half of the 

 United States that the Solitary Yireo ordinarily stops to breed. 

 The records we possess are unanimous iu this regard, and it 

 would seem to be a very just statement of Dr. Brewer's that 

 " both at the East and the West it is undoubtedly only migra- 

 tory to about the 40th parallel, and does not, except iu mount- 

 ainous localities, breed south of that lino." 



Passing over several early accounts of its nidification, as not 

 entirely free frooi suspicion — though it should be immediately 

 conceded that we have no obvious occasion to challenge Nut- 

 tail's Columbia River account — we find it first stated by Baird, 

 in 1844, that the bird breeds near Carlisle in Pennsylvania. 

 The breeding-habits, so long in question, have been studied 

 more attentively by Mr. Gentry than by any one else, for all 

 that appears, as may be inferred from the resumi of his observa- 

 tions, which I take pleasure in laying before the reader. 



The Blue-headed Vireo (says Mr. Gentry) delights to build 

 on the borders of dense forests, and along unfrequented roads, 

 its favorite trees being the red cedar and red maple — the former 

 by the roadside, the latter on the edges of the woods. Both 

 sexes reach thir breeding grounds together, though the more 

 retiring and quieter females are not so often observed as their 

 mates. The birds appear to have lately become more abundant, 

 with the modification of the face of the country, and were 

 one season nearly as numerous as the Red-eye. They began to 

 build in a week or two after their arrival, about the time when 

 the pin-oaks shed their catkins, which are largely, sometimes 

 exclusively, used in the construction of the nest. In other 

 cases, the nests are built chiefly of grasses. They are grace- 



