There are almost 10,000 bird species flying the skies, roaming the lands, and diving the waters of our planet. Some of them are pretty similar to one another, perhaps because the two species diverged only relatively recently. But some of them are so unique you won't believe they're not made up.

The species listed below come from a recent paper in Current Biology, which aimed to identify the species most in need of our conservation efforts. As I wrote in Conservation Magazine last week, the researchers measured each bird's evolutionary distinctness. "It's a way to assess how evolutionarily unique a species is by comparing its genome with the genomes of its closest relatives. Those who are least related to - or more different from - their closest phylogenetic relatives would be more evolutionarily distinct." As a result of being so evolutionarily distinct, some of the birds with the highest levels are also quite unique.

Here are some of the weirder birds we found while browsing the data, which is freely available.


1. Kagu

The only place on Earth you'll find a wild Kagu is in New Caledonia, a small island east of Australia. It may look like your average bird, but it's the only surviving member of both its genus and its family. Mating pairs, which last quite a long time and possibly for life, occupy large territories, 22-62 acres in size. For most of the year, the male and female live in their own, but each breeding season they come together to co-incubate a single egg. The species is so emblamatic of New Calendonia, that the nation's TV station used to play its song each night as it went off the air.

Why is it weird? It's the only bird species that has "nasal corns," small structures over the nasal openings. It's thought that they evolved to prevent dust and other particles from entering the nose, since the Kagu spends so much time rooting around the dirt with its beak its prey.


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2. Christmas Island Frigatebird

The slightly awkward looking Christmas Island Frigatebird comes from, you guessed it, Christmas Island, a small Australian territory in the Indian Ocean. They're particularly threatened by the introduced yellow crazy ant, which you may remember from National Geographic's Great Migrations as the species that eats the Christmas Island crabs. Alive.

Why is it weird? The Christmas Island Frigatebird captures its prey in one of two ways. One is it eats flying fish while they're above the sea's surface, relying on marine predators to drive the fish out of the water. That's not that weird. The second, more interesting way, this: while in flight, the bird steals food that other seabirds and gulls have managed to nab themselves, all while airborne. Scientists call them "aerial kleptoparasites." We like to call them "sky pirates."

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3. Philippine Eagle

This impressive raptor is the world's longest, measuring some three feet from beaktip to tail, though it isn't quite the world's heaviest (Steller's Sea Eagle) or bulkiest (Harpy Eagle). As an apex predator, it was once called the "Philippine Monkey-Eating Eagle," because it was believed that it preyed only on monkeys. We now know that it hunts much more opportunistically, taking whatever meat it can find, including, yes, monkeys. The fact that it doesn't exclusively dine on primate flesh doesn't make it any less terrifying.

Why is it weird? If being the longest eagle in the world and dining on monkey meat isn't enough, it's also got a fascinating relationship with human culture. It was made the national bird of the Philippines on July 4, 1995. As a result, if you kill one, you can look forward to spending twelve years in prison.

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4. Kakapo

This magnificent bird is also one of the world's rarest. By the end of 2013, there were only an estimated 124 of them in existence. Like many island predators, it evolved on New Zealand with no natural predators of its own. That's why it was so vulnerable to predation by the predators that modern humans brought with them to the island: cats and rats (obviously), but also ferrets and stoats.

Why is it weird? This parrot has so many unique features its hard to know where to begin. It is the world's heaviest and only flightless parrot. It is nocturnal, which is unusual for parrots, and is the only parrot in the world known to mate by lekking. In a lek, males gather in an arena where they form themselves into a sort of mating buffet. The females come by, watch their displays, and pick out their favorite males. It's common in ungulates like deer, and is known to occur among some birds, like prairie chickens, but the kakapo is the world's only parrot to do it. But perhaps their weirdest trait is also ultimately the source of their eventual downfall: they only breed three times, on average, each decade. Breeding occurs only when the fruit of the rimu tree (Dacrydium cupressinum) is in relative abundance.

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5. California Condor

I've you've been reading Animals.io9 for a while, then you know we're already a little bit obsessed with California Condors. Using one of the most fascinating sorts of science-based conservation, zookeepers are raising baby chicks in captivity by putting condor puppets on their hands. It's one of the world's longest-living birds, with lifespans stretching up to six decades in the wild. That is, if they can avoid poaching or lead poisoning. They're also eaters of death, feasting primarily on carrion. All living California condors are descended from just 22 individuals, captured in 1987 for a captive breeding program. As of May 2013, there are now 237 living in the wild and 198 in captivity.

Why is it weird? The bird has the largest wingspan of any in North America, and as a result it can be mistaken for a small airplane. In fact, according to John Nielson, author of Condor: To the Brink and Back the birds are confused for aircraft more often than they're confused for other birds.

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6. Oilbird

The oilbird, known locally in northern South America as guácharo, is a curious little nocturnal cave-dwelling frugivore. It finds its food by echolocation, much as bats and dolphins do, though some of the frequencies they use are actually audible to humans. It's the world's only flying nocturnal fruit-eating bird (the kakapo, above, is flightless; together, the pair are the world's only nocturnal fruit eaters).

Why is it weird? As its name implies, the oilbird is so oily that people used to hunt them and boil them down to extract their oil for use as fuel. It's got 80 million years of evolutionary distinctness, making it one of the most evolutionarily distinct birds in existence.

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7. Hoatzin

We've saved the best for last. This beautiful, pheasant-sized bird is native to South America's Amazon and Orinoco deltas. Like many of the birds on our list, it's the only species of it's genus, which is part of why it's so evolutionarily distinct. They're herbivores, feeding mainly on leaves, fruits, and flowers, but because of the way they digest those plant parts, the birds wind up quite stinky. In fact, the Hoatzin is also known locally as the "Stinkbird" for their vaguely manure-like odor. For that reason, it isn't threatened by human poaching; it's sort of a last-resort meal. You'd have to be really, really hungry to try to capture one of these critters.

Why is it weird? There's a very good reason it's such a foul smelling bird. The Hoatzin has a digestive system unlike any other bird, and actually more like a cow. They have a foregut that they use to break down the plants they eat using bacterial fermentation. It's not a rumen, as ruminants like cattle have; instead, evolution operated on part of their digestive anatomy called the crop, a feature common to birds, to make it function much like a cow's rumen. As a result, the crop is so large that it displaces muscles that otherwise would have been used for flight. Hoatzins can still fly, just not all that well.

But wait, there's more.

The Hoatzin has another feature unique among all the world's birds, and it's one that makes it a strong contender to inspire the next SyFy horror flick: it's got two claws on each of its wings!

The wing-claws let the chicks move about tree branches without falling into the water below as soon as they hatch. It's an important feature to avoid becoming the next meal of a Great Black Hawk. When a hawk attacks, the mature Hoatzins fly about to distract the predator, while the chicks hide under thicker cover. If spotted, the chicks do an avian version of stop-drop-and-roll. They plunge into the water, swim away, and use their claws to haul themselves back onto land, up the tree, and into the nest. Because of its claws, some researchers have wondered if the Hoatzin was a direct descendent of Archaeopteryx, which had three claws on each wing. Others think the claws are a more recent adaptation, having emerged as a result of the selective pressure caused by predation. Either way, the Hoatzin may be the most badass bird around. They're a good reminder that dinosaurs still live among us.

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