Coming like whirling leaves, half autumn yellow, half green of spring, their colors blending like the outer petals of grass-green daffodils, no more sociable and confiding little creatures are to be found in our midst than the Yellow Warblers. They are as much at home in the trees by the house as in the fields and woods. Wherever they wander, the glints of sunshine that flash from their backs should make the most miserable complainer feel the summer’s charm. But in spite of their seeming preference for man, they are prone to build in lonely fields and by-ways. In such places it becomes one of the especial victims which the Cow Bird selects to foster its random eggs. But the Warbler puts its intelligence effectively to work, and builds a second story to its nest, thus flooring over the unwelcome eggs. This expedient is repeated as long as the Cow Bird continues her mischief, until sometimes a three-story nest is achieved. The outside of the nest, composed of glistening milkweed flax, is pressed into a felt-like case, the fibres serving at the same time to lash the nest to its support. Within, to the depth of an inch, is a soft sponge-like material, which the birds have made from the wool they have gathered from the stems of young ferns. A few horse-hairs, to give shape and stability to the nest, are to be found in the inside of the felt-like lining. [Illustration: THREE-STORY NEST OF YELLOW WARBLER. Showing the Builder’s Manner of Out-witting the Cow Bird.] Hundreds of nests, quite as novel as any that have been described, might be instanced, showing varieties from so-called normal forms, but I shall content myself with only another example. Everyone is familiar with the Ruby-throated Humming Bird, so common in the eastern half of the United States. It is the smallest of all our birds. But its nest, which is by no means scarce, is a rare sight to the average man and woman. No nest can be compared with it. It is a thing of beauty and a joy forever. A mass of cotton, with a hole in the top, and thatched all round with blue-gray lichens, and just as big as a walnut, conveys a good idea of its appearance. But all nests are not made of cotton. The yellow wool that forms the dress of the undeveloped fern-frond, or the red shoddy that is wind-swept into heaps outside some woollen factory, is often made to take the place of the down of the seed of the poplar. Not to be mentioned in the same breath with these, is the nest I am now about to describe. It was saddled upon the horizontal bough of a small white oak-tree that grew on the side of a thicket, and was peculiar from the nature of the material that composed its inner fabric. This substance resembled burnt umber in color, and was as soft as the finest wool, or the fluffiest down, and proved, upon examination, to be the mycelium of a fungus which the builders had gathered from decaying stumps or mildewing tree-branch. STRANGE FRIENDSHIP.