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This pretty species enters Louisiana from the south as early as spring appears, at the period when most insects are found closer to the ground, and more about water-courses, than shortly after, when a warmer sun has invited every leaf and blossom to hail the approach of that season when they all become as brilliant as nature intended them to be. The little fellow under your eye is then seen flitting over damp places, such as the edges of ponds, lakes, and rivers, chasing its prey with as much activity and liveliness as any other of the delicate and interesting tribe to which it belongs. It alights on every plant in its way, runs up and down it, picks here and there a small winged insect, and should one, aware of its approach, fly off, pursues it and snatches it in an instant.
I have placed a pair of these Warblers on a handsome species of Iris. This plant grows in the water, and in the neighbourhood of New Orleans, a few miles below that city, where I found it abundantly, and in bloom, in the beginning of April. Several flowers are produced upon the same stem. I have not met with it anywhere else, and the name of Louisiana Flag is the one commonly given it.
As soon as the foliage of the forests begins to expand, the Blue Yellow-backed Warbler flies to the tops of the trees, and there remains during the season, gleaning amongst the leaves and branches, in the same active manner as it employed when nearer the ground, not leaving off its quick and short pursuit of small insects on the wing. When on the branches, it frequently raises its body (which is scarcely larger when stripped of its feathers than the first joint of a man's finger) upwards to the full length of its legs and toes, and is thus enabled to seize insects otherwise beyond its reach.
Its flight is that of a true Sylvia. It ascends for a while in a very zigzag manner, and returns suddenly to nearly the same place, as if afraid to encounter the dangers of a prolonged excursion. I do not think it ever flies to the ground. It hops sidewise as well as straight forward,
