The largest bird's nest was built by a pair of bald eagles (Haliaeetus leucocephalus), and possibly their successors, near St Petersburg, Florida, USA and measured 2.9 m (9 ft 6 in) wide and 6 m (20 ft) deep. It was examined in 1963 and was estimated to weigh more than two tonnes (4,409 lb).
The incubation mounds built by the mallee fowl (Leipoa ocellata) of Australia measure up to 4.57 m (15 ft) in height and 10.6 m (35 ft) across, and it has been calculated that a nest site may involve the mounding of 249 m³ (8,793 ft³) of material weighing 300 tonnes (661,386 lb).
The golden eagle (Aquila chrysaetos) also constructs huge nests, and one 4.57 m (15 ft) deep was reported from Scotland in 1954.
Comments below may relate to previous holders of this record.