“The Blue-green Warbler has a peculiar cunning manner of leaning downwards to view a person, or while searching for an insect, and which is very different from that of any other bird, although I am unable to describe it.  While thus leaning, it moves its head sideways so very slowly that the motion is hardly perceptible, unless much attention is paid to it.  After this, it either starts off and flies to some distance from the observer, or darts towards the prey that had attracted its notice.  While catching an insect on the wing, it produces a slight clicking sound with its bill, and in this respect approaches the Vireos.  Like some of them also, it descends from the highest tops of the trees to low bushes, and eats small berries, particularly towards autumn, when insects begin to fail . . .

The plant on which I have figured a male is found in Louisiana, growing along the skirts of woods and by fences.  It is called the Spanish Mulberry.  It is a herbaceous perennial plant, attaining a height of from four to eight feet.  The fruits are eaten by children, but are insipid.”

–J. J. Audubon, Ornithological Biography, I (1831), 258-259 [excerpted].