Male Ostrich in the Kalahari

What is the largest bird in the world?


Ostriches (Struthio camelus) are the largest living birds in the world, with an average mass of 104 kg and average length of 210 cm. They lay the largest eggs and hold the record for the fastest land speed of any bird, reaching speeds of 70 kmph. It is also thought that ostriches have the largest eyes of any land vertebrate at 50 mm in diameter.

Ostriches are native to Africa but are farmed all over the world, particularly for their feathers, their skin, which is used in leather products, and their meat. In 2014, the Somali ostrich (Struthio molybdophanes) was recognized as a distinct species, separate from the common ostrich.


The southern cassowary (Casuarius casuarius), also known as the double-wattled cassowary, Australian cassowary, or two-wattled cassowary, has an average weight of 45 kg and is around 155 cm long. Southern cassowaries are found in north-eastern Australia, Indonesia, and New Guinea.

Northern cassowaries (Casuarius unappendiculatus), also known as the single-wattled cassowary or golden-necked cassowary, are slightly smaller, with an average weight of 44 kg and average length of 149 cm. They are endemic to northern New Guinea.


Endemic to Australia, emus (Dromaius novaehollandiae) are the second-tallest living birds in the world and can reach up to 190 cm tall. They weigh an average of 33 kg. Female emus are usually slightly larger than males and have significantly wider rumps.

Emus have evolved to run fast, and despite being flightless, they have vestigial wings, which they flap when they run to stabilize themselves. They only have three toes and a reduced number of bones and foot muscles. Emus are the only birds with gastrocnemius muscles found in the back of the lower legs.


Emperor penguins (Aptenodytes forsteri) are endemic to Antarctica and are the tallest and heaviest of all living penguins, weighing an average of 31.5 kg and measuring 114 cm in height.

During breeding season, male Emperor penguins lose up to 15 kg as they do not eat anything while they protect their eggs from extreme cold for more than 2 months.

Like all penguins, Emperor penguins are flightless, but they have adapted to the harsh conditions of their environment, which is the coldest for any breeding bird. Feathers provide up to 90% of their insulation, and they are able to thermoregulate their core body temperature without altering their metabolism.

King penguins (Aptenodytes patagonicus) weigh 13.6 kg on average and are 92 cm in length. They breed on Subantarctic islands, as well as Tierra del Fuego, the Falkland Islands, and other temperate islands in the region.


Greater rheas (Rhea americana) are flightless birds native to South America. They are also known as gray, common, or American rheas.

A small population of greater rheas has established itself in Germany. One male and five females escaped from a German farm in August 2000. They survived the winter and began breeding. It is estimated that there is now a population of about 250 birds that are considered domestic and therefore protected from hunting.

Lesser rheas (Rhea pennata), also known as Darwin’s rheas, are found in the Altiplano and Patagonia regions of South America. It weighs an average 13.5 kg and has an average length of 96 cm.


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