Some of the biggest birds on Earth can stand taller than any NBA player and spread their wings wider than kings size bed. Here are 10 of the biggest birds to inhabit our planet, including the tallest, heaviest and those whose wings spread the furthest.

1. HARPY EAGLE

Named after a human-bird hybrid in ancient Greek mythology, harpy eagles are some of the biggest birds on Earth. These dark grey birds are among the largest species of eagle on Earth, particularly when comparing their weights. An adult female can weigh up to 20 pounds (9 kilograms) and males grow up to 12 pounds (5.4 kg), according to San Diego Zoo(opens in new tab). In comparison, the bald eagle can weigh up to 14 pounds (6 kg), according to the U.S Fish & Wildlife Service(opens in new tab). These birds soar across South America, kept aloft by their impressive 6.5 feet (2 meter) wingspan, hunting for prey. When their prey is in sight, such as porcupines, deer and opossums, harpy eagles descend at speeds of 50 miles per hour (80 kilometers per hour) and use their 5 inch (13 centimetre) claws to deliver a fatal blow to their prey, according to the San Diego Zoo.

2. WANDERING ALBATROSS

Meet the biggest bird in the world, at least in terms of its wingspan. These sea birds glide over the ocean with a wingspan of up to almost 11 feet (3.35 meters), according to the International Union for the Conservation of Nature(opens in new tab) (IUCN). Wings of this size mean that these albatross can spend large amounts of time in the sky — for example — one bird was recorded to have wandered around 3,700 miles (6,000 kilometres) in only 12 days. There are 23 species of albatross, however all but one are either threatened or endangered or vulnerable to extinction. This is due to the birds getting caught in fishing hooks while scavenging fish and squid bait from fishing vessels and trawlers.

3. OSTRICH

The biggest of all the birds on Earth, both in size and weight, is undoubtedly the ostrich. These behemoth birds grow up to 9 feet (2.7 meters) tall and can weigh up to 287 pounds (130 kilograms), according to San Diego Zoo Wildlife Alliance(opens in new tab). Despite having a wingspan of up to 7 feet (2 meters), ostriches are unable to fly. Instead, they use their wings in a similar way to how a ship uses its sails. During a fierce 43 mile per hour run, these birds open out their wings and use them as air-rudders for rapid braking and steering. This agility enables them to escape some of the many threats they face on the African savanna, including predatory species such as lions and jackals. In some situations, ostriches will go on the offensive and use their powerful clawed feet to deliver a blow strong enough to kill a lion, according to PBS Nature.

4. GREATER RHEA

Although these birds might look like a juvenile ostrich, rhea are in fact their South American cousins. At only around one fifth of the size of an adult ostrich, rhea can still weigh an impressive 66 pounds (30 kilograms) and grow up to 5 feet tall (1.5 meters), according to the Smithsonian’s National Zoo & Conservation Biology Institute(opens in new tab). Rhea are flightless birds, and like ostriches use their wings as balance aids while running at high speeds of up to 40 miles per hour, according to the Houston Zoo(opens in new tab). Female rhea lay up to 40 eggs per breeding season, but it is the males of the species that will indicate the eggs for around 30 days before they hatch.

5. CASSOWARY

The southern cassowary is one of the most prehistoric-looking birds to prowl through New Guinea and mainland Australia. Towering up to 6 feet (2 meters) tall, cassowary's are one of the tallest birds on Earth, according to the Australian Museum. Topping off their height is a prominent helmet called a casque which is made of a thick layer of keratin — the same material that makes up your nails and hair. Cassowaries use these helmets to push past vegetation as they run through the forest, according to the Edinburgh Zoo(opens in new tab). As well as being one of the biggest bird species, they have also gained the reputation of being one of the most dangerous. As one of the few birds recorded to have killed humans, cassowary uses their sharp 3-toed feet — which sports a middle 4 inch (10 centimeter) long toe — to deliver a fatal swipe to its target, according to Scientific American(opens in new tab).