In the deserts of southern Africa, there’s a bird that doesn’t just build a nest—it builds an entire city. Meet the sociable weaver (Philetairus socius), whose constructive ingenuity overshadows their diminutive exterior. Their sprawling homes built within tree branches can host hundreds of birds: a whole community living together.
While they live up to the first part of their name, the second part of their name is a bit deceiving. They don’t “weave,” but rather, layer materials to form their nest. Chambers are made from soft grass, cotton, or fur, and twigs form the roofs [1]. However, they are still true artisans when it comes to constructing their nest. They select pointed, sharp straw to guard nest entrances against predators such as snakes [2]. Species of snake such as the Boomslang (Dispholidus typus) and Cape Cobra (Naja nivea) are most likely to attempt a raid on the weaver’s nest and have been known to eat eggs, chicks, and even adult birds, so constructing nest defense is a top priority to the birds [3]. Sociable weavers typically stick to three kinds of trees to build their elaborate homes: the camel thorn, the shepherd tree, and the quiver tree (Acacia erioloba, Boscia albitrunca, and Aloe dichotoma). All of these species are fairly large, ranging from approximately ten to thirty feet, and grow in open savannah grassland, which holds the materials the birds need for their nests [4].
Nests this big require multigenerational upkeep—some nests have been in use for over a hundred years! Generation after generation of birds add their own “apartments” to the nest structure, which resembles something like a beehive made from hay. Different areas of their nest are sized appropriately for different activities. Entrance tunnels are up to ten inches long and three inches wide, while nesting chambers are typically four to six inches [1]. Entrance tunnels are designed to be narrow and lined with sharper materials to prevent predator access, while nesting chambers are cozier for sleeping, roosting, and breeding [2].
There is a social cost depending on what task a bird chooses to take on. Those that maintain their own nesting chambers, rather than helping at the communal thatch, are most likely to get bullied by others, as it is the most selfish position. Since the birds are monogamous, if either the male or the female in a pair work only on maintaining their own nesting chamber, it only benefits them and their mate [3]. Those that work hard at patching the communal thatch tend to be the aggressors, as they are putting in the work for everyone and are most likely to be exploited. This aggression is typically seen as one bird chasing another. However, it was effective, as after the selfish ones are punished, they show an increased willingness to help out at the communal thatch [5]. It really does take a village to maintain their nest, so cooperation is enforced!
Photo by Rui Ornelas [Source].
These impressive nests don’t just benefit the weavers. All that organic matter dropping from the nest provides a steady stream of essential nutrients in an otherwise arid environment, attracting a variety of insects. One study found that the soil beneath weavers’ nests had 3.5 times the amount of nitrogen and 4.1 times the amount of phosphorus as the soil beneath trees without nests [6], earning them their nickname ‘islands of fertility’. These birds are like little ecosystem engineers (like several previously featured creatures), greatly increasing biodiversity and soil fertility wherever they choose to nest.
Plus, the sheer mass of the nest creates a great source of protection against the grueling sun, so other bird species, like the pygmy falcon and the rosy‐faced lovebird, free-ride off the weavers [7]. But why would the weavers allow their nest, that they toiled so long on, to be shared? Well, these other birds add even more eyes and protection against predators, with snake predation on the weaver’s nest dropping when they are around, and often the weavers learn from them where to find new food sources [1]. There is always a risk involved, though; the falcons have eaten sociable weavers on occasion, but it is quite rare. The weavers seem to think this is a fair price to pay for more protection from snakes, as they do make alarm calls and nest further from the falcons once they take up residence, but the nest continues to stay in use [8]. Normally, both the falcons and the weavers share a diet of insects such as grasshoppers and termites [3].
Since the weavers can take shelter within their city-like nests, they can survive for days without water, even when desert temperatures soar to 110 degrees Fahrenheit. And when temperatures drop to twenty degrees Fahrenheit in the winter, the birds can stay warm with each other and save energy that would otherwise be lost by shivering [2].
Who knew such unassuming little birds could completely change the composition of the land around them, plus alter other species behaviors? I’d say these guys could totally give bees a run for their money in architectural ingenuity as well. Just keep in mind that if you ever feel uninspired, a one-ounce bird is out there constructing an entire city with just twigs and straw.
Main featured image by Charles J. Sharp [Source].
Written by: Capri Mills is a third-year undergraduate biology student at Bucknell University, and is a part of the Field Research Lab, which studies African bat genomics and immune responses. She is particularly interested in ecology and animal behavior, and hopes to pursue a career that combines her love of writing and science. In her free time, she loves hiking, reading new books, working on poetry, and taking care of way too many plants.
References:
[1] Sociable Weaver. San Diego Zoo Wildlife Alliance Animals and Plants. (2024). https://animals.sandiegozoo.org/animals/sociable-weaver
[2] Heinrich, B. (2023, February 21). Africa’s social weaverbirds take communal living to a whole new level. Audubon. https://www.audubon.org/magazine/march-april-2014/africas-social-weaverbirds-take-communal
[3] “Sociable Weaver (Philetairus Socius) Fact Sheet: Summary.” San Diego Zoo Wildlife Alliance Library, 30 Oct. 2024, ielc.libguides.com/sdzg/factsheets/sociableweaver/summary.
[4] Coetzee, B. J., & Werger, M. J. A. (1975). A west-east vegetation transect through Africa south of the Tropic of Capricorn. Bothalia, 11(4), 539-560.
[5] Leighton, G. M., & Meiden, L. V. (2016). Sociable weavers increase cooperative nest construction after suffering aggression. PLoS One, 11(3), e0150953.
[6] Aikins, T. K., Cramer, M. D., & Thomson, R. L. (2023). Positive feedbacks between savanna tree size and the nutritional characteristics of “Islands of fertility” are amplified by sociable weaver colonies. Journal of Arid Environments, 209, 104903.
[7] Lowney, A. M., & Thomson, R. L. (2022). Ecological engineering across a spatial gradient: Sociable weaver colonies facilitate animal associations with increasing environmental harshness. Journal of Animal Ecology, 91(7), 1385-1399.
[8] Covas, R., Huyser, O., & Doutrelant, C. (2004). Pygmy Falcon predation of nestlings of their obligate host, the Sociable Weaver. Ostrich-Journal of African Ornithology, 75(4), 325-326.
[Edited by Alice Michel & Jacob Johnson]