Most of the world's largest birds are flightless and remain permanently on the ground, using their long legs to roam the landscape and their long necks to forage for food on the floor. However, there are some feathered giants that can soar.
Some of these do so with such incredible dynamism and efficiency that we use them as models of research to improve our air transport.
Others, with weightier bodies, use their power of flight only when they have to, to search further afield for food or evade danger.
Here we look closer at the world's largest avian titans, and compare their wingspans and other incredible features.
The biggest flying birds in the world (by wingspan)
Wandering albatross
Up to 3.5m
This feathered giant, the wandering albatross (Diomedea exulans), has the longest wingspan of any bird in the world. The huge stretch gives enormous flying capabilities, enabling it to migrate up to 120,000km in a year.
It's a fantastic glider and uses more energy taking off and landing than actually flying. It can travel several hundred miles without even a single flap of its wings. When it does want to power up, it can reach speeds of 140kph.
This technique is called dynamic soaring. The birds are able to use their long, narrow wings to catch skyward drafts over the ocean, lifting them up into the air with very little effort.
You'll very rarely see the wandering albatross on land. It gathers only to breed in large colonies on remote islands near the Antarctic Circle, and on some islands in the South Atlantic. During the non-breeding season it roams the oceans to feed, mainly on fish and cephalopods, such as squid, octopus and cuttlefish.
Other giants in the albatross family include the southern royal albatross (Diomedea epomophora), which has a wingspan of 3.6m and breeds on islands near New Zealand and the southern tip of South America.
Dalmatian pelican
Up to 3.2m
Pelicans are one of the largest flying bird families in the world, and according to Guinness World Records, the Dalmatian pelican (Pelecanus crispus) is the biggest of the lot. Its body can measure up to 1.8m, with a wingspan of 3.2m.
The Dalmatian pelican got its name, not because of spotty plumage, but because its distribution range originally included Dalmatia in Croatia. It has been extinct there since the 1950s. Fossil records show that it bred in Britain until medieval times.
Today you can find them in southern Europe and Turkey across the upper Middle East into Russia, as well as China.
Dalmatian Pelicans eat around 1,200g of fish every day, but will also feed on amphibians and small reptiles.
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A great white pelican, isn't far behind in size, with a wingspan of 3.6m.
Marabou stork
Up to 3m
This ginormous stork is found in sub-Saharan Africa and is a competent scavenger, often joining vultures to feed on carrion. They've been known to move with large animal herds to catch insects and smaller animals mammals disturbed by their movements. Similarly, the marabou stork (Leptoptilos crumeniferus) can march in front of the advancing wildfire to grab fleeing animals.
On average, wingspan is 2.6m, but according to authors and naturalists Fisher and Peterson, one was recorded as reaching 3.7m.
They don't tend to fly high in the sky, preferring to stay close to the ground to hunt for food.
You can distinguish it from other species of stork by its grey and white wings and long, bare throat sacs.
Andean condor
Up to 3.2m
When it comes to birds of prey, the Andean condor (Vultur gryphus), which lives in South America is the largest generally. It can grow to weigh 15kg.
It is the largest of all the vulture species, with a wingspan of well over 3m across. Weighing up to 15 kilograms, the Andean condor uses air currents and thermal air currents (depending on their location) to help keep their heavy bodies in flight.
It has a large black body, white neck ruff and featherless heads and is unusual because there is no visible difference in size and physical characteristics between the male and the female.
Kori bustard
2.75m
The kori bustard (Ardeotis kori) deserves extra kudos as, although it has a wingspan of up to 2.75m, it can weigh up to 19kg. That's quite a mass to lift up into the air.
They are known for being the heaviest flying bird on the planet. Because of the huge weight, a kori bustard uses a lot of energy to fly, so will only take off when it really has to.
It chooses to spend most of its time foraging for food on the ground and enjoys a diet of caterpillars, dung beetles and a variety of grasses and seeds.
What was the biggest flying bird of all time?
Despite the size of all the flying giants mentioned above, they pale in comparison to the largest flying bird ever. This gong goes to, according to Guinness World Records, the South American teratorn (Argentavis magnificens), a superficially vulture-like species, which lived 6–8 million years ago, and had a 7.6m wingspan.