Birds
Weaver
Ploceidae · also called weavers, weaverbirds
A weaver is a small Old World bird that builds by tying knots — one of the very few animals that does. A male strips long blades of grass and loops, twists, and knots them around a twig into a hanging chamber, then hangs beneath it and displays while a female inspects the workmanship and, if it is not good enough, makes him tear it down and start again.
Overview
Weavers are the family Ploceidae, around 120 species, overwhelmingly African with some in southern Asia and on Madagascar. They are small seed-and-insect eaters of savanna, grassland, wetland, and farmland, and the males of many species are bright yellow in the breeding season. Their signature is the woven nest, and their signature failure mode is a young male’s first clumsy attempts — because the skill is learned and refined with practice, not just instinct.
The biggest and the most numerous
Two weavers hold records. The sociable weaver of southern Africa builds the largest structure made by any bird — a communal thatch up to 6 m across with a hundred-plus chambers, draped over a tree or a utility pole and used for up to a century. And the red-billed quelea, a small weaver of sub-Saharan Africa, is the most numerous wild bird on Earth — around 1.5 billion, moving in flocks of millions that strip grain fields and earn the name “feathered locust”.
Status
Most of the ~120 species are Least Concern and stable, and the quelea is abundant enough to be controlled by the million as a pest. A minority — forest and island specialists like several Madagascar fodies and Bannerman’s weaver — are threatened by habitat clearing.
Weaver: common questions
How does a weaver bird build its nest?
A male weaver begins by anchoring a few long grass strips to a thin branch or reed to make a vertical ring, then perches in the ring and works outward, adding strips and weaving them over and under each other and around the frame, often tying actual knots to lock them in place. He shapes a roughly spherical or kidney-shaped chamber and, in many species, a downward-facing entrance tube that makes it hard for snakes and other predators to get in. The whole nest of a typical weaver is built in a day or a few days from hundreds of individual strips, using only the bill and one foot, and the male may build and rebuild several before a female accepts one.
Which bird builds the biggest nest, and is it the weaver?
Yes. The single largest nest structure built by any bird is the communal nest of the sociable weaver of the arid savannas of Namibia, Botswana, and South Africa. Unlike most weavers, which build individual hanging nests, sociable weavers cooperate to construct one massive permanent thatch of grass and twigs over a large tree, a rock outcrop, or often a telephone or power pole, with many separate nesting chambers entered from below. A big colony nest can measure several metres in every direction, weigh a tonne or more, house over a hundred pairs, and be maintained and expanded by successive generations for up to a hundred years, sometimes until its weight brings the supporting tree or pole down.
What is the difference between a weaver and a sparrow or a finch?
They are all small seed-eating songbirds and are related, but they are separate families. Weavers, family Ploceidae, are an Old World group centred on Africa, and their defining feature is the elaborate woven nest, along with, in many species, bright yellow breeding plumage in the males. True sparrows, family Passeridae, include the house sparrow and are drabber, mostly brown and grey, and build untidy rather than woven nests. Finches, family Fringillidae, have conical seed-cracking bills, are often colourful, and are found worldwide. Some weavers, especially the sparrow-weavers and the queleas, look very sparrow-like, and the boundaries were long confused, but the nest-building behaviour and DNA place the weavers as their own family.
Why is the red-billed quelea such a problem for farmers?
The red-billed quelea is a small weaver that has become the most numerous bird on the planet, with perhaps 1.5 billion individuals, because it breeds explosively when rain produces a flush of grass seed and it moves nomadically in enormous flocks tracking food across sub-Saharan Africa. When those flocks encounter fields of millet, sorghum, wheat, rice, or barley, they descend in numbers that can consume or flatten a small farm's entire crop within a day, and a single large roost can hold tens of millions of birds. Governments have responded with aerial spraying of the roosts and colonies with pesticides and with fire bombing, killing many millions of queleas a year, though the effect on the overall population is limited and the practice raises serious environmental concerns.