Which bird builds the largest nest?

Sociable weavers in the deserts of southern Africa construct enormous communal nests that look like giant haystacks draped over trees and poles. These structures can be several metres wide, weigh a great deal, house over a hundred pairs of birds, and last for generations. For a single pair, the bald eagle holds the record; one nest in Florida measured about 2.9 metres wide and 6 metres deep and weighed roughly two tonnes. Nest size depends on whether you count communal or individual efforts. Large nests provide shelter, warmth, and protection from predators.