They’re gigantic, they’re often defensive, and you wouldn’t want to run into them in a zoo after hours. Meet a few of the world’s biggest birds with attitude, from flightless giants to modern-day pterodactyls.

1. Ostrich

Everyone knows that the ostrich is the world’s biggest bird, weighing an average of 230 pounds and standing 7 feet tall (and some individuals can grow up to 9 feet). They can also chase you down: Ostriches are the fastest species on two legs, with a top speed of about 43 mph. They can maintain a swift 30 mph pace for 10 miles, making them the marathon champs of the avian world.

2. Southern Cassowary

Often called the most dangerous bird on Earth, in addition to being one of the planet’s biggest birds, the southern cassowary is roughly 150 pounds of mean. On each foot is a 5-inch claw that cassowaries use to defend themselves. At least two people have been kicked to death by cassowaries, the most recent being a Florida man who unwisely kept one of the birds as a pet.

3. Emu

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Like a smaller, shaggier ostrich, the 5- to 6-foot emu is the second-largest bird on Earth (as well as a goofy spokesbird for insurance). During the breeding season, female emus fight enthusiastically over unattached males. But the results of this mating ritual are impressive: clutches of forest-green, oval eggs that resemble giant avocados.

4. Greater Rhea

This flightless bird is named for the Titan goddess Rhea, who gave birth to all of the Olympian gods and goddesses in Greek mythology. At up to 5 feet tall and 66 pounds, the greater rhea may not seem like as much of a terror as the ostrich. But it gathers in massive flocks of up to 100 birds during the non-breeding season, so watch out if you happen to be in its South American habitat.

5. Dalmatian Pelican

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How scary can a pelican be, you ask? When it stands almost 6 feet tall, weighs 33 pounds, and has a wingspan of 9 feet—all traits of the Dalmatian pelican—it's pretty petrifying. These scruffy-feathered monsters, native to Europe and Asia, breed in colonies of up to 250 pairs and can gulp impressive mouthfuls of fish in one go.

6. Mute Swan

One of the heaviest flying birds, mute swans look harmless as they glide over ponds, lakes, and rivers. But mute swans are far from silent when defending their families and territory. Male swans warn interlopers that they’re getting too close with a hiss, then can launch a straight-up assault, bashing the intruder with their wings. They’ll even attack kayakers, canoeists, and people just minding their own business.

7. Andean Condor

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This freakishly big vulture isn’t satisfied with just any carrion—it prefers large carcasses like cattle and deer for dinner. Maintaining its average weight of 25 pounds requires a lot of calories, after all. Its wingspan is slightly less than its northern cousin, the California condor, but it still reaches a dramatic 9 to 10 feet.

8. Cinereous Vulture

Another big bird with a 10-foot wingspan, this Old World vulture has excellent vision to spot carrion while it flies, and a featherless head that resists the accumulation of gore when it feeds. Though it’s intimidating to look at, the cinereous vulture plays an important role in its ecosystem by cleaning up roadkill and other dead animals.

9. Marabou Stork

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As if its red-tinged wattle, black back, and dagger-esque bill weren’t alarming enough, the marabou stork is sometimes called the “undertaker bird” thanks to its Dracula-like appearance. It also eats other birds. The largest verified wingspan on a marabou stork measured 10.5 feet, though unverified reports cited a specimen with 13.3-foot span.

10. Shoebill

Shoebill storks may not be the tallest, heaviest, or widest-winged birds, but just look at that death stare. On top of having a nutcracker for a face, the 5-foot-tall shoebill leads a fearsome lifestyle. It stands absolutely still for hours to hunt prey, watching for lungfish or baby crocodiles, then spreads its wings and collapses over it while trapping the target in its bill.