While there are plenty of weird birds to be found in the natural world, this avian selection is particularly extraordinary. From the only bird that hibernates, to the bird that can kick a human to death, here are 10 birds that defy the norms of nature.
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Birds that break nature's rules
Livingstone’s turaco
The bird with metal in its feathers
Many birds have fabulous plumage to attract mates or send warning messages. Some of the colours in their feathers are produced by microscopic structures on the feather surface that absorb and reflect light in a certain way. These are known as structural colours. Other colours are produced by pigments, dye-like substances that occur widely in nature. Birds may make their own pigments or obtain them from their food. But the green and red pigments in turaco feathers are wholly unique. And the secret ingredient is… copper.
Turacos are a family of pigeon-sized birds from African forests that adore fruit – a diet that happens to be rich in copper. The metal is taken up by their bodies and helps to form two dazzling pigments not found in any other bird, or indeed any other animal. Turacoverdin creates vivid green feathers, while turacin turns them red. It was once estimated that an adult turaco would take around three months to eat enough fruit to produce its gorgeous coloration. The more it eats, the brighter its plumage.
Turacos have another claim to fame. They’re the world’s only truly green birds. Parrots and many other species may appear green but aren’t really. The green in their feathers is structural, so is a sort of optical illusion, unlike the chemical, turacoverdin-based pigment in turacos.
Greater honeyguide
The bird that asks us for help
Pet parrots have been known to ask their owners for things but in the wild, such interactions are extremely rare. In fact, only one wild bird actively solicits our help – the greater honeyguide.
The behaviour does not occur throughout the honeyguide’s African range. But in parts of Kenya, Tanzania and Mozambique, it forms a partnership with humans in which both parties benefit. The little brown bird feeds on wild honeybee nests – in particular, the larvae and waxy structure. The problem is, bees’ nests are sturdy and well defended. So the honeyguide asks for assistance. Having found a nest in a tree, it uses a squeaky call to attract the attention of people nearby, then repeatedly flies a short way and calls again, guiding its helpers to the nest like a feathery satnav. The human honey hunters climb the tree and soon are sharing the spoils with their guide.
Montezuma oropendola
The bird that sings upside-down
One of the most bizarre bird songs on the planet rings out through the forests and fruit plantations of Central America. It belongs to the male Montezuma oropendola, which produces a torrent of rattles and gurgles with a strangely metallic quality. But that’s not the only remarkable thing about it. The oropendola also likes to sing upside-down, while swinging energetically under his perch like an avian trapeze artist, which no doubt enhances the impact of his singing and helps him attract a mate.
There are other birds that hang upside-down to display to would-be partners, including several birds of paradise. But their songs are mostly croaks and can’t compete with the oropendola’s virtuoso vocals.
Another of the Montezuma oropendola’s curious habits is that the species often nests close to colonies of warrior wasps. You might think this unwise but the aggressive wasps do the oropendola a favour by acting as a deterrent to parasitic botflies, whose larvae would otherwise feed on its helpless chicks.
Oilbird
The bird that flies in the dark
Flying in total darkness would be potentially fatal for most birds. But there are a handful that fly with confidence in pitch-black conditions, because they can navigate their surroundings by echolocation. South America’s oilbird is the best-studied. Like bats, it produces clicks and listens for the returning echoes to build up a detailed picture of its surroundings. It ‘sees’ with sound.
The oilbird resembles a cross between a hawk and a nightjar, with a hooked beak, big eyes, oval nostrils, white-spotted plumage and walrus-style moustache. It eats fruit and its chicks are so plump that people used to harvest them for their copious oil. Thanks to this unique combination of features, ornithologists have placed the species in its own taxonomic group, the order Steatornithiformes.
A colonial breeder, the oilbird nests in rainforest caves, where large numbers of the birds flap around without ever colliding. The cacophony of ear-piercing shrieks they make has earned them the local name guácharos, meaning ‘one who cries and laments’. Mingling with these harsh calls is the constant stream of clicks with which the birds echolocate. Since the clicks are deeper in pitch than those of bats, they are easily audible to human ears.
Hummingbirds
The bird that flies backwards
Everything about hummingbird flight is a marvel. These dazzling sprites zip through the air at around 50kph, their wings beating 40-80 times a second. And that is just flying normally. During courtship displays, some species accelerate to 80kph, powered by 200 wing beats a second. Meanwhile, their tiny heart is pumping up to 20 times a second, roughly twice as fast as in many flying birds.
Hummingbirds owe their aerial prowess to the way in which they move their wings. All other birds flap their wings using an up–down motion. But hummingbirds rotate them, moving each wing through a complete circle by twisting the humerus bone near the shoulder joint. This is closer to how insects do it than typical birds. As a result, hummingbirds generate lift during the upstroke as well as the downstroke, rather than only when flapping down like in other birds. Hummingbirds can also hover beautifully and fly upside-down, sideways and even backwards. Other birds may pull off some of these manoeuvres but not as elegantly – and none can fly backwards properly.
Such phenomenal athleticism is made possible by feeding on masses of sugary flower nectar and frequent refuelling. ‘Hummers’ consume at least half their body weight in sugar every day – and often far more. They hover at flowers to feed, which is much faster than having to land first. It also means they can access flowers out of reach to less agile birds.
Hoatzin
The bird that behaves like a cow
The Amazon’s swamps are home to a bird so strange there’s nothing else like it alive today. It can barely walk, sports a mohican crest and, when young, has claws on its wings, which it uses as grappling hooks to clamber up trees. Meet the hoatzin, an ungainly oddball that bears more than a passing resemblance to bird-like dinosaurs from the late Jurassic period.
Weirdest of all, the hoatzin eats leaves. Leaf-eating is not as straightforward as it sounds, because leaves are full of difficult-to-digest cellulose and laden with toxins. What’s more, they are poor in nutrients, so you need to consume a lot of them. To succeed, the hoatzin has evolved its own version of the foregut fermentation system seen in cattle, where plant material is broken down by passing through a series of chambers packed with friendly bacteria. It has become a cow with feathers.
Much of the magic takes place in the crop. Every bird has one – it’s a food storage pouch near the throat. But the hoatzin’s crop is enormous, so it can process large quantities of leaves, with a ridged inner surface to grind them down. This is a slow process, taking up to two days. So bloated it can hardly take off, the hoatzin is prone to monster burps and produces droppings that reek of cow dung. No wonder locals call it the ‘stink bird’.
Common poorwill
The bird that hibernates
Hibernation of one form or another is widespread in the animal kingdom. When the going gets tough, many reptiles, amphibians, mammals and insects opt to zone out until things improve. By slowing their metabolism, they save large amounts of energy and are able to live off their reserves for several months. Yet the common poorwill is the only species of bird that hibernates.
A member of the nightjar family, the poorwill is a beautiful bird that swoops about after dark to catch moths and beetles, much like a nocturnal swallow. It breeds in western North America, where this food source disappears at the end of summer. So, like real swallows, it migrates south for the winter. But some of the poorwill population stays behind. These individuals hide among rocks and allow their body temperature to fall to 5°C, while their oxygen intake plunges by 90 per cent. They remain dormant, camouflaged by their plumage, until spring returns.
Swifts and hummingbirds can also chill themselves and enter a resting state called torpor. However, this is a standby mode, rather than long-term hibernation. Usually the birds do it overnight or during cold, wet weather. It’s a temporary fix that allows swift nestlings to go without food for 48 hours until their parents return from a foraging trip, and enables small hummingbirds with limited fat reserves to survive freezing nights high in the Andes mountains.
Southern cassowary
The bird that kicks humans to death
As a rule, birds are not considered a threat to human life. Yet there are cases of birds harming people and, on rare occasions, killing them. Terns dive-bomb people who get too close to their nests, sometimes drawing blood with their beaks. Eagles and owls also tackle nest intruders, attacking with outstretched talons. British photographer Eric Hosking lost an eye to a tawny owl this way in 1937.
The only birds known for sure to have killed humans are mute swans, ostriches and cassowaries, all of which will defend their eggs and young fiercely. The most recent confirmed mute swan attack was in Chicago, USA, in 2012, when a kayaker drowned after a bird knocked him into the water. Ostriches can kill with a ferocious kick from their powerful back legs, which have long claws capable of disembowelling a person.
But the most dangerous bird in the wild today? That’s probably the southern cassowary. This flightless giant has huge back legs armed with dagger-like claws that can reach 12cm long. In 1926, a cassowary kicked a boy to death in Queensland, Australia. Fortunately, there have been no recorded deaths caused by cassowaries since then.
Great frigatebird
The bird that sleeps in the sky
Over the past couple of decades there has been a lot of groundbreaking research into how animals sleep. One startling discovery is that chinstrap penguins take up to 10,000 micro-naps a day. Another stunning finding is that birds are able to sleep while flying.
Research by the Max Planck Institute for Ornithology, published in 2016, showed how great frigatebirds nap while airborne. These seabirds lack waterproof plumage and can’t afford to land on the water, yet stay at sea for weeks on end. Data recorders fitted to the frigatebirds demonstrated that when flying over the sea the birds usually rested half of their brain at a time, so could stay alert and see where they where going. But occasionally, they shut down both brain hemispheres for several seconds.
So far, mid-air sleep has only been proved in frigatebirds but it might be more widespread. Given that alpine and common swifts stay in the air for many months without landing, it seems probable that these birds can also sleep in the sky.
Bearded vulture
The bird that survives on bone
Osteophagia, or bone-eating, is not for the faint-hearted. Hyenas and other carnivores will occasionally chew on a bone. A range of herbivores, including giraffes, do too, gnawing bones to obtain valuable calcium and phosphorus lacking in their plant-based diet.
But actually surviving on bone? Among vertebrates, there’s just one specialist bone-eater – the bearded vulture. Incredibly, bone makes up as much as 90 per cent of this bird’s food. Researchers discovered that, given the choice, it invariably chooses bone over juicy flesh. So how can a huge vulture – they are frequently over 1m long, with a wingspan of nearly 3m – survive on stuff as hard and unappetising as this?
Well, bone is surprisingly nutritious. A 2017 study found that fresh bone contains 8 per cent more energy than fresh meat. Even dry, old bones – which the bearded vulture prefers, possibly because they are lighter and easier to carry – are still full of protein. The bone marrow, the soft fatty substance inside bones, is particularly sought-after.
But there is, of course, a hitch: digesting it. To get the job done, the bearded vulture has ultra-acidic stomach juices, which have a pH of about 0.7 – virtually neat acid. And its thick stomach lining offers protection against lethally sharp bony fragments. Small bones it swallows whole. Larger ones – a lamb’s femur, say – call for a different technique. The birds are able to carry bones that weigh half as much as they do, and use thermals to lift them high in the air, before dropping them on rocks to smash them to bits. In Spain, the bird is known as quebrantahuesos – bone-breaker.
Main image: a great frigatebird with an inflated pouch/Credit: Getty
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