What are these mysterious structures in the southern Kalahari?

They look like alien incubation pods, but these massive grass-and-mud structures are home to a species called sociable weaver birds. Like bees, these birds live in hives together, collectively building them out of mud, grass, and other materials in their environments. In the southern Kalahari, they use telephone… »2/18/13 8:00pm2/18/13 8:00pm