Oriole nests are a tightly woven sack, as deep as 8 inches, hanging 30 or more feet from the end of a branch near the top of a tree with a 3" opening at the top of the pouch. The nests are difficult to spot when the leaves are on the tree, and they seldom reuse old nests although they return to the same territory. We have found several nests on the ground over the years and the construction is amazing. When horses were more common, long horsehairs from the tail and mane were tightly woven around a twig framework. Now string, yarn and plant materials are used to finish the nest.
Francis Hobard Herrick in 1935 described the building of an oriole nest:
The first strands of bast, which are apt to be long, are wound about the chosen twig rather loosely with one or more turns but subsequent modes of treatment tend to draw these threads tighter, and as their free ends are brought together, other fibers are added. From such simple beginnings a loose pendant mass or snarl of fibrous material, which I have called the primary nest mass, is slowly formed, but it is a long time before it takes on the semblance of a nest or nest frame. . . .
Behavior at each visit, after a certain number of strands had been laid and joined, was essentially the same, the oriole usually bringing in but a single fiber and carrying it around the support and working it into the nest mass by what I have called shuttle movements of the bill. Clinging to the principal twig, hanging often with head down, and holding the thread, the bird makes a number of rapid thrust-and-draw movements with her mandibles. With the first thrust a fiber is pushed through the tangle which soon arises and forms the growing mass, and with the next either that or some other fiber is drawn loosely back. . . .
While these shuttle movements are, first and last, very similar, and almost equally rapid at all times, the number made at each visit tends to increase with the growing complexity of the product. At least one hundred shuttle movements were sometimes made at a single visit, but these were often so rapid that it was impossible to count them, and many of them must have been abortive.
In all this admirable work there was certainly no deliberate tying of knots, yet, as the sequel will show, knots were in reality being made in plenty at every visit. There certainly was no deliberate directing of the thread, The work was all fairly loose at first, yet naturally some of the threads became drawn more tightly than others. I do not wish to imply that the same thread that is first thrust through the nest mass or the nest wall is immediately drawn back, but only that some thread or other is blindly seized by the bill and withdrawn. . . . The irregularity of the weave of the finished work shows conclusively that the stitching is a purely random affair, though, for all that, none the less effective.In the late stages of construction "the bird settles down in the nest and shakes all over in an effort to bring the pressure of the breast to bear upon its inner surface; he [in this case the bird was assumed to be the male] rises, turns, settles, and shakes again. These are the typical molding movements, and they are applied all over the lower parts of the pouch, their violence at times being such that the surrounding leaves, and even the slender tree itself, are all a-tremble."