What is a Weaverbird?
 

weaverbird: finch-like African and Asian colonial birds noted for their elaborately woven nests

ENCYCLOPÆDIA BRITANNICA
WEAVERBIRD. Of all bird nests, those made by the weaverbirds are the most extraordinary. Weaverbirds belong to the family Ploceidae. There are about 170 species in the family. Although their nests vary in size and shape, the same elaborate interweaving of grass or leaf strips is found in the nests of all of the species.

Most true weavers are seed eaters with strong, short bills; some that live in forests eat insects and have less robust bills. The weavers are primarily found in the hot, dry countryside of Africa but are also found in Asia and Australia. Ranging from 4 to 25 inches (10 to 65 centimeters) in length, the birds have plain plumage except during the mating season, when the males show bright colors. The birds chirp and chatter continually but rarely sing. A typical nest built by the baya weaver (Ploceus philippinus), which is abundant from Pakistan to Sumatra, starts from a branch as a solidly woven rope. It then broadens into a globular chamber and ends in one or more tubes through which the birds enter. Usually it is built over water for added protection.

The social weavers (Philetairus socius) of Africa build huge community nests in trees. These "apartment house" nests are woven of grass. Each pair of parents uses the same compartment year after year. The young birds add their nests to the structure until the circular roof becomes so large that from a distance it may be mistaken for the thatched roof of a human dwelling.
 

from The Orange Weaver, An Exceptionally Aggressive and Industrious Bird by: Stuart Balfour "The Birdman" (March/April 1998)
http://www.nfss.org/Articles/Article/OWeaver1.html

Nest Building: The most remarkable attribute of the weaver cocks, from which they take their name, is their nest building prowess. In this sense, the "weavers" with which we are familiar the American sparrows - have lost their heritage, and make poor thumb-like nests of sticks and twigs. The African weavers all make densely woven and intricately knotted deep cup-like nests with a reinforced circular opening on one side. The nests are just wide enough for a single adult bird to occupy, but deep enough to hold the hen and chicks. The nest often contains more than one chamber, or a chamber and a mat-like roost. The nest may be built and reorganized several times before the cock is finished, and he may come back later and add on to it.

The best materials for nest building are fine strong fibrous grasses like raffia and fountain grass. But the weavers are marvelous with man-made materials like string, bread ties and thread, and will cannibalize just about anything that can be carried in their beaks and tied in a knot. I've seen them gather human hair they plucked off the carpet. I've never seen the weavers make a production out of lining their nests, but they do pick up feathers and fuzz from here and there and carry them to the nest. It would take a human a very long time to clip a weaver nest from its mooring, and the nest would be destroyed in the process. The nests are so durable and defensible that other birds preferentially seek out weaver nests in the wild instead of building their own. The weavers weave continuously during the offseason and well into the mating season, making as many nests as there are reasonable scattered places to make them.

Territoriality and Mating: The weaver cock's nest building prowess is an integral part of the weaver's claim on its territory, something like the scent a dog deposits on its turf, and it is also an essential part of the selection and mating process. A weaver will never accept a box or basket or any other kind of nest, and will if he is able, destroy or cannibalize it for his use.... When the weaver has several completed nests to show, he will select among his harem or court a weaver hen passing through, and escort the selected hen to several of his nests. If the hen selects a nest, she settles there, perhaps after adjusting the nest somewhat, and mating and laying take place within a few days there after. If the hen does not select a nest, the cock drives her away from his nests and selects another hen. The quality of the nest, however the birds judge quality, is an important part of the hen's selection criteria in the wild and in captivity. My most industrious nest builders build the best nests, and command the most attention from the hens. However, the common experience with the weavers is that they build and build and build but rarely mate.