Birds that flock together
Sociable Weaver – Philetairus socius (Afrikaans: Versamelvoël)
The Sociable Weaver is a small bird, the size of a Cape Sparrow, that inhabits the dry parts of the Northern Cape, Namibia (excluding the Namib Desert) and along the Orange River to Northwest Province and the western part of the Free State.
The little birds’ claim to fame is the huge communal nests that they build – the largest tree nest of any bird in the world. Some of these nests are over a hundred years old, which means that more than ten generations of the same family have lived there. A very large nest may weigh as much as 1000 kilograms and house more than 100 pairs of birds. The size depends on the tree available for the building, with the biggest nests usually in Acacia thorn trees. However, these birds utilize more Aloe dichotoma (Quiver Trees) than thorn trees because in many areas the biggest trees available are these tree aloes. The aloe offers less scope for building big nests so some nests only house 10–20 pairs.
The nests are almost always constructed of Bushman’s Grass which they clip off with their beaks. They are constantly maintaining the nests, winter and summer. In certain areas like around Verneukpan near Calvinia where trees are non-existent, they utilize the next best thing, telephone poles. The nests, attached to the insulators, hang down to a metre from the ground. To prevent damage to the insulators the Post Office (now Telkom) very wisely bolted angle-iron brackets onto the poles just below the insulators. The birds also thought this was a wonderful idea – along the Putsonderwater road there used to be nests on 16 consecutive poles; there may be more by now.
On the farm Nuwerus on Verneukpan, the farmhouse was locked up for almost a year at a time, depending on any rainfall, after which the grass would grow fast on the sandy soil. The farmer then brought sheep in from his other farm. We were there with the farmer after rain had fallen and what a sight it was! On the front stoep, attached to the roof, was a huge nest, at least 1000 kilograms. It filled almost the entire stoep, hanging down to just above the floor. These birds also occasionally nest on cliffs, and windpumps are also very popular nest sites.
It is fascinating to sit in a hide near a big nest and observe the goings-on. One minute the nest will seem to be deserted, then with a whooshing sound the whole flock, about 200 birds, will come flying in at top speed and all will be quiet again, the birds having all gone inside together. Then suddenly after about 30 minutes, with a whirring sound this time, the whole flock will come out together, to fly off. After about an hour it will be the same story again. Some big nests can have 150 or more individual nest holes in the underside of the nest, with each hole accommodating a single pair of birds.
The nest holes are all lined with grass stems facing forward towards the opening, the points all carefully sharpened. No predator bigger than a social weaver will risk going in, but snakes can get in and do a lot of damage.
The Rosy-faced Lovebirds use the nest holes for breeding, but they do not do any damage except just using a nest hole. The Pygmy Falcon also utilizes the nest holes for breeding, solving the spike problem by lining the nest tunnel with their droppings which are sticky and harden like crystals, thereby smoothing the entrance hole. Only one pair of the Pygmy Falcons will use a nest. Owls and other birds of prey will sometimes nest on top of weaver nests, but they will not harm the weavers.
The nests offer excellent insulation against heat and cold. Summer temperatures may rise to anything between 45 or 50°C, with winter temperatures sometimes dropping to 10 degrees below zero, but the nests maintain an even temperature at all times. This could be the reason for the huge size of the Social Weaver nests.
Whatever the reason for living together like this, the little birds have developed a very good system and they are harmless to farmers as they feed on insects and grass seeds, doing no harm to crops at all. There was a time when sheep farmers chopped the acacia trees with huge nests down and used the nests for sheep fodder, but this no longer happens. Without these birds and their huge nests, the Northern Cape would be a barren place indeed.
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