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974 ORNITHOLOGY AND OOLOGY. 
The Warbling Vireo seems to arrive here in pairs ; for they 
seem to be mated when we first discover them. Whether 
their attachment continues through several seasons, I am 
ignorant. 
About the first of June, the pair commence building. 
The nest is pensile, and usually built in tall trees (usually 
poplars), often fifty feet from the ground. It is constructed 
of strips of grape-vine bark, grass, leaves, or bass-wood 
bark; and sometimes bunches of caterpillars’ silk are left on 
the outside, as if for ornament. The following very inter- 
esting account of the breeding habits of this bird is given 
by Audubon, who watched a pair building in a Lombardy 
poplar : — 
“One morning, I observed both of them at work: they had 
already attached some slender blades of grass to the knots of the 
branch and the bark of the trunk, and had given them a circular 
disposition. ‘They continued working downwards and outwards 
until the structure exhibited the form of their delicate tenement. 
Before the end of the second day, bits of hornets’ nests and particles 
of corn husks had been attached to it by pushing them between the 
rows of grass, and fixing them with silky substances. On the third 
day, the birds were absent, nor could I hear them anywhere in the 
neighborhood ; and, thinking that a cat might have caught them from 
the edge of the roof, I despaired of seeing them again. On the 
fourth morning, however, their notes attracted my attention before 
I arose; and I had the pleasure of finding them at their labors. 
The materials which they now used consisted chiefly of extremely 
slender grasses, which the birds worked in a circular form within 
the frame which they had previously made. The little creatures 
were absent nearly an hour at a time, and returned together, bring- 
ing the grass, which, I concluded, they found at a considerable 
distance. Going into the street to see in what direction they went, 
I watched them for some time, and followed them as they flew from 
tree to tree towards the river. There they stopped, and looked as 
if carefully watching me, when they resumed their journey, and 
led me quite out of the village to a large meadow, where stood an 
old hay-stack. They alighted on it, and, in a few minutes, each had 
