The vast barren landscapes of the southern Kalahari Desert are home to sociable weavers, small birds that create giant communal nests. They typically make their nests in trees, but those of a suitable size grow sparsely in the arid conditions. The weavers have adapted to use the next best thing; recurring telephone poles that cut across their habitat. Year after year they add to their nests, creating burgeoning structures that eventually outgrow their ability to resist gravity.