In the Museum of Natural History at Soleure, in Switzerland, there is said to be a bird's nest made entirely of steel. There are a number of clockmaking shops at Soleure, and in the yards of these shops there are often found lying disused or broken springs of clocks. One day a clock-maker noticed in a tree in his yard a bird's nest of peculiar appearance. Examining it he found that a pair of wag-tails had built a nest entirely of clock springs. It was more than four inches across and perfectly comfortable for the birds. After the feathered architects had reared their brood, the nest was taken to the museum, where it is preserved as a striking illustration of the skill of birds in turning their surroundings to advantage in building their nests. [Illustration: MOURNING-WARBLER. Life-size. FROM COL. CHI. ACAD. SCIENCES. 6-99 COPYRIGHT 1899. NATURE STUDY PUB. CO., CHICAGO.] THE MOURNING WARBLER. (_Geothlypis philadelphia._) Baskett, in his valuable "Story of the Birds," says that the warbler forms feed variously, but they use little vegetable matter. Some have ground-haunting, and even swamp-haunting habits; others have fringed tongues hinting of juices and nectars, while tree-trunk exploring, as in creepers, nuthatches, titmice, etc., also prevails. They have been described as at once the most fascinating and the most exasperating of birds. In the spring they come with a rush and although the woods may be full of them, only a faint lisp from the tree tops gives note of their presence, and unless you are a very good observer you will not know they are about at all. If you listen to other birds, instead of resolutely devoting yourself to warblers, you will lose the opportunity of the sight of a diminutive bird disappearing in a tree top. Some of the warblers dash about among the leaves on the ground hunting for gnats, others hunt over the branches of the trees, though some of them hop gaily on the ground, while others walk sedately, bobbing their heads or tilting their tails. The majority of the tribe fly northward to nest in pine forests. A few, however, remain and build in our parks, gardens and shrubbery. They are all insect-eaters, destroying ants, flies, caterpillars, larvæ, plant lice, canker-worms, and May flies. They are therefore of great value in the protection of vegetation.