What bird is considered the largest bird in existence?
Currently? The ostrich. That was easy.
Historically, the biggest contendah is the elephant bird.
The Ostrich, followed by the Emu.
Wow…Almost a tri-post!
I am pretty sure that Big Bird is much larger than an emu, but that is just from what I have seen on TV.
Just to show off, there was a native bird that belonged to New Zealand, the Moa, which at its largest was a contender. It became extinct around 100 or so years ago, though.
Moas probally became extinct about 1500 AD and certainly by 1800 AD at the latest. The largest 3m tall species became extinct by about 1400.
Why? Well aparently they were mighty fine eating.
Yeah, once people started settling NZ, those 500-pound chickens didn’t stand a chance.
Actually, the Maori hunted them to extinction. Not the Europeans.
I thought the last one spotted was the late 1800’s, but I may be mistaken.
What about cassuaries? I thought they were at least as big as ostriches.
Cassowaries (5ft) are generally slightly smaller than emus (6ft) whilst ostriches are said to reach 9ft.
The Family of Ratite
These birds were true bad asses.
http://www.terrorvogel.de/
"The Terror Birds
About 1890 scientists in Argentina first unearthed fossil remains of several enormous birds, entirely unlike anything previously known to man. With their large skulls, their sharp and powerful beaks, long legs equipped with vicious claws and ranging in size from large to truely gigantic, they were obviously carnivorous in nature and must have presented a terrifying appearance in life. Now, after more than a century of research, their extraordinary life history comes clearer to us, but many questions still remain. Here we give you a glance into a truely Lost World,
Back into the Age of Birds.
I like the picture of the NZ eagle at the site that’s big enough to kill a moa and apparently did kill a few Maori before it was “extincted”.
“This is not a phorusrhacid, but a scary bird anyway. In New Zealand, there is a legend about the Pooakai, a flying monster striking down from the sky and killing children and even adults. The real animal behind this legend may have been the giant eagle Harpagornis, the only indigenous carnivore capable of killing an adult moa. Maybe the eagle, specialized on killing large, bipedal prey, mistook the early Maoris for some kind of funny-shaped moas.”
http://library.christchurch.org.nz/Bookmark/1997/July/bigbird.asp
"Big Bird
As long ago as 30,000 B.C. and as recently as 1500 A.D. there lived, in the forest and sub-alpine regions of the South Island, a creature called harpagornis. Harpagornis was a giant eagle, a cousin of the Harpy of South America and the Philippine eagle. However, he was heavier, weighing between 9-10 kilograms, while his spouse weighed between 10-13 kilograms. Both male and female had a three metre wingspan, strong legs and talons wider than a tiger’s claws."
"Harpagornis was no sensitive new age guy. For long hours he patiently sat in the treetops, and, when unsuspecting geese passed, attacked at speeds of up to 80 kilometres per hour and scooped them up. As well, he hunted young and enfeebled old moa and was capable of striking down an adult moa weighing up to 250 kilograms – no mean feat when it is considered that the moa was the tallest bird ever to have lived. Not only was harpagornis the top carnivore in the early New Zealand food chain; he was also the world’s largest eagle and the largest bird of prey. "
I feel so insignificant - 8.5", standing on tip-talon.
In case this was supposed to correct Mjollnir’s “…once people started settling NZ…”, let’s not forget that the Maori did settle New Zealand.
Re the OP, I’ve seen emus, cassowaries and ostriches close up and can confirm that the ostriches were by far the biggest. Rheas are also a bit bigger than cassowaries.
I think the largest bird ever to live was tyranneus rex, but that’s another debate.
Not really - I think you’ve got your sets crossed: all birds are dinosaurs, but not all dinosaurs are birds.
This link is pretty helpful.
This one is even better 
As others have stated, the Ostrich is the largest bird currently alive.
The heaviest bird ever to have existed is usually considered to have been the Elephant Bird Aepyornis maximus of Madagascar, which may have been hunted to extinction only a few hundred years ago. It may have exceeded 500 kilos (1100 lb).
However, Stirton’s Thunder Bird Dromornis stirtoni of Australia evidently could have given Aepyornis a run for the money, also weighing in at 500 kilos plus. It became extinct much earlier, 6 million years+ BP.
The tallest known bird was the Giant Moa Dinornis maximus of New Zealand. Early reconstructions showed it standing fully erect, which would give it a height of almost 3 meters (12+ ft). However, it probably would have normally stood hunched over, like an emu, and have not reached nearly that height. It was more slenderly built than the Elephant Bird, probably a mere 250 kg (550 lb).
GuanoLad, I have heard of a questionable sighting of one of the smaller moa species as late as the 1800s, but the account may have referred to some other large flightless bird such as the Takahe. There are also some moa bones that are supposedly show cuts made by metal tools, thus post-dating European contact, but this is also controversial.