birds

Not surprisingly, the heaviest birds can't fly. The heaviest bird known from fossils is Stirton's Thunder Bird (Dromornis stirtoni),¹ sometimes called Mihirung birds, meaning “giant bird” in one of the Aboriginal languages. Adults are estimated to have stood 3 meters tall and weighed 500 kilos (1100 pounds). It lived in open woodlands in what is now the Northern Territory of Australia during the Late Miocene. Although Australian, it is more closely related to geese than emus. (The nickname “demon duck of doom,” sometimes applied to Dromornis, more properly refers to Bullockornis planei.)

Slightly less massive but perhaps taller is the elephant bird or (in Malagasy) vorompatra, Aepyornia maximus (sometimes called Aepyornia titan). which lived in Madagascar as late as the 17th century. Built somewhat along the lines of an ostrich, it was much heavier than an ostrich and not made for running (the ostrich is the fastest thing on two feet). Aepyornia stood 10 feet tall, weighed a thousand pounds, and laid 9-liter (2.4 U.S. gallons), 20-pound eggs a foot long. The yolks of these eggs are the largest known cells.

New Zealand had a remote relative called Dinornis maximus which became extinct around 1800. It was the tallest bird that ever existed, at around 11 feet 6 inches.

The bird the author would least like to meet in a dark alley is Phorusrhacus inflatus, which lived in Patagonia from the Early to Middle Miocene. Ten feet tall with a heavy, flesh-tearing beak like that of an eagle, this fellow was definitely a meat-eater. New Jersey had some big birds in the Early Eocene. Diatryma gigantea stood 7 feet tall. (Its fossils are also found in New Mexico, Wyoming, and parts of Europe.) We don't know what it ate.

The ostrich is the heaviest and tallest of living birds, with adults reaching 156 kilograms (345 pounds) and 2.7 meters (9 feet).

Among all living birds there is a strong correlation between the least diameter of a bird's leg bone (its tibiotarsus) and its weight: log Y = 2.54 × log X - 0.10996, where Y is body mass in grams and X is least leg bone diameter in millimeters.² No such relationship has been found for wing bones; there are too many different ways of flying. The leg bone/weight relationship has been used to estimate the weights of fossil birds.

1. Patricia Vickers Rich.
The Dromornithidae, an extinct family of large ground birds endemic to Australia.
Bulletin of the Bureau of Mineral Resources, Geology and Geophysics, number 184, pages 1-190.
Canberra: Australian Government Publishing, 1979.

2. Kenneth E. Campbell, Jr. and Eduardo P. Tonni.
Size and Locomotion in Teratorns (Aves: Teratornithidae).
The Auk, vol. 100, pages 390-403 (April 1983).

Page 392. The authors credit John Anderson for first calling attention to this correlation.

The biggest birds that can fly

Wandering Albatross

Among living birds, the wandering albatross (Diomedea exulans) has the greatest wingspread, about 3.63 meters (about 12 feet).

Andean Condor

The Andean condor (Vultur gryphus), a living species, has a wingspan of 3.2 meters (10.5 feet), as does the marabou stork.

The heaviest modern bird that can fly is the Great Bustard (Otis tarda) or similar-sized Kori Bustard (Ardeotis kori), which weigh up to 21 kilograms.

But a vulture-like South American bird of the Late Miocene (about 6 million years ago), Argentavis magnificens, had a 7-meter (23-foot) wingspread and weighed an estimated 70 kilograms. Computer modeling¹ suggests the bird didn't have enough muscle for flapping flight, but could soar on thermals. Taking off and landing would have been a problem; probably it required a head wind and/or a slope for running downhill. Argentavis is probably about as large as a flying bird can get.

1. Sankar Chatterjee, R. Jack Templin, and Kenneth E. Campbell, Jr.
The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina.
Proceedings of the National Academy of Sciences, vol 104: pages 12398-12403 (2007). Published online on July 3, 2007, 10.1073/pnas.0702040104

The smallest birds

The smallest bird is found in Cuba: the bee hummingbird, Mellisuga helenae (Lembeye, 1850). Two inches long, it weighs less than 2 grams and its eggs are only 0.3 inches long. More than 30,000 Mellisuga helenae eggs would fit in a single Aepyornia maximus egg.

birds

The heaviest birds

The biggest birds that can fly

The smallest birds