Laura Erickson's For the Birds

I’ve never seen this bird, but it has made the Guinness Book of World Records:

Sociable Weaver: Most populous bird’s nest. Native to southwestern Africa’s dry grasslands, the sociable weaver (Philetairus socius) builds an immense communal nest that can be up to 8 m (26 ft) long and 2 m (6 ft 6 in) high. Resembling a giant haystack that hangs from a tree or telegraph pole, it contains up to 300 individual nests. Each of these nests in turn houses a pair of weavers and their brood. Not surprisingly, these enormous communal nests can get so heavy that the tree on which they are built sometimes collapses under the weight!