WEAVING The sewing and the weaving is done entirely in the construction of nests. To take up the weavers first, we can point to the Baltimore oriole, which makes a sac-shaped, pendant nest, often hung from the trailing tips of elm branches. The walls of this sac are formed of fibers pushed and pulled back and forth with the birds' bills in a seeming haphazard way so that a roughly woven or stitched fabric results. But the finest weavers belong to that group of birds known as weaverbirds. One might expect that to be an expert weaver a bird would have to have a slender bill. But no, their bills are short, stout, clumsy-looking, and sparrowlike. And yet these are the birds that weave elaborate pendant nests of fibers and straws. The finest are in shape like an inverted retort, with the nest proper in an oval chamber, fastened to a branch by a special strand of fibers, and with a tube or funnel for an entrance. The walls of these fine weaverbirds' nests are amazingly strongly and neatly woven. In captivity one of the weaverbirds, the red-billed weaver, was studied at its nest building and it was found that the strong, intricate, and beautiful weaving of this species actually included knots of several sorts. TAILORING The tailoring is done by birds of quite another group. They are Old World warblers of several sorts, some in southern Asia and some in Africa. The tailoring consists of sewing the edges of leaves together to form a place for their tiny nests. The Indian tailorbird is perhaps the best known. When these tiny olive-green and gray birds set about nest building the female punctures the margins of the leaves with her bill. Then she brings cobwebs and pushes them through the punctures in the edges of the leaves, and winds them around, and draws the edges of the leaves together. Strands of cotton are used too for this. Sometimes a single leaf is used; its two edges being drawn together to form a funnel. Sometimes a number of leaves are joined. Sometimes it is claimed knots are used, but this seems not to be the case. What are mistaken for knots seem made in this way: The cotton used is soft and frays easily, so that the part of it forced through a tiny aperture issues as a fluffy knob, which looks like a knot. "The bird makes no knots; she merely forces a portion of the cotton strand through a puncture," and the edges of the puncture catch and hold it, according to Casey Wood, who studied the birds in India. The lining of the nest is of soft material and this the bird anchors by making a puncture in the leaf, grasping a strand of this material, and pulling it out; the cotton outside then expands into a minute button which helps hold the nest and contents in place as though riveted. One nest is recorded as having been so riveted in seventy-five places.