I am trying to be diverse with the animals I pick for this blog, so today will be our first bird, the sociable weaver! This bird is a little brown and black passerine (or perching) bird. The weaver is remarkable for a few reasons, but most notably for its nest-building traits. Looking at it, it looks like a pretty standard bird, not much to get excited about.
But despite its looks, the sociable weaver is a fascinating little bird. Unlike many birds, where females look quite plain and drab, while the males are extravagant and colourful, male and female sociable weavers are indistinguishable from one another. They’re just brown. And black. And boring. Right? Wrong! They are, in fact, amazing little birds. And the reason why is right in their name. The sociable weaver. So what does it do? It ‘weaves’ nests. Big ones. You may think its a long way down the road to the… wait… I’ve done this joke before. Well the point is, sociable weavers are incredible architects.
They build their communal (hence the sociable part of the name) nests on strong structures such as Acacia trees or telephone poles. They use different materials for different parts of the nest; large twigs form support beams and provide the basic structure of the nest, while grasses form separate nesting chambers within the nest. Each nesting chamber is lined with soft materials, such as fur, cotton or fluff. And to keep predators out the weavers line the entrances to nest chambers with sharp sticks. When all is finished the nest looks something like an upside-down haystack, and if you were to walk under the nest you’d see hundreds of little entrances to nest chambers.
So how big can this architectural masterpiece get? Well, each nesting chamber is about 4-6 inches in diameter, and nests may contain up to 100 separate chambers. Basically, the truly large nests can get over 20 feet wide and almost 10 feet tall. Some of them even get so large they knock down the tree they are built in. With a nest that big, sociable weavers don’t just pack in and build a new nest on a whim – instead they live in this structure year round. Some weaver nests have been occupied for over 100 years.
Why do they do this? Why spend so much time and energy on a structure that requires constant maintenance? Well, the answer lies in where the birds live. Sociable weavers live in southern Africa, in a desert in Namibia called the Kalahari. In the summer months, temperatures in the Kalahari can reach up to 50 degrees Celsius. To avoid the direct sun and keep cool, weavers hide in the cooler outer chambers of the nest, where temperatures are maintained around 7-8 degrees. In winter, when temperatures are near freezing, the weavers retreat to the inner chambers where insulation keeps them cozy and warm.
Sociable weavers aren’t the only birds to take advantage of these nests. Pygmy falcons are dependent on the sociable weaver nests for its home. Other birds, including the pied barbet, familiar chat, red-headed finch, ashy tit and rosy-faced lovebird are often found in weaver nests. Bigger birds, such as owls, eagles and vultures build their nests on the broad base provided by the nests’ roof. All these visitors provide the sociable weaver with a bit of an alarm system – more eyes means more chance of detecting predators before it’s too late.
Sociable weavers have developed a remarkable nest system that allows it to survive in a harsh environment. Interestingly, weavers don’t need training to build nests – they build them instinctively. This behaviour is so programmed that the birds can’t change the way they build the nests – they can only do what their ancestors have done for generations. Sociable weavers are truly spectacular birds. Despite being quite small, they manage to build the largest tree nests in the world. Very impressive, I think.
Cover image By Thomas Schoch – own work at http://www.retas.de/thomas/travel/namibia2003/index.html, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=716060