Birds have wings. They fly all over the place using these wings to find food, nesting sites and each other. But whilst all birds have wings, not all birds fly, so how do those birds do all of those other things too? Why evolve to have to find another way in the first place?
The most obvious reason why some birds evolved this way is because they simply no longer needed their wings. Food is either abundantly within reach on the ground, nests are easily made on the ground, potential mates are already there, on the ground. The main driver for a species to have developed flightlessness, however, is the lack of predators. The greatest concentration of flightless birds that remain in the world live in New Zealand, a country whose evolutionary path unfolded with a distinct lack of mammals, save for a few bats here and there. The geography of New Zealand is so diverse with such rich ecosystems, millennia passed for everything and everyone, settling into their own niches. Then along came the humans about 1,000 years ago, bringing their rats and cats and diseases. Until that point, their only other predators were other, larger, flightless birds.
Ground to a halt
Around 60 species of flightless bird still exist today, but studies on fossils have shown that there used to be a lot more of these guys walking around. It’s estimated there were at least 266 species at one point in the Earth’s history, with most of them made extinct by hunting, introduced predation or habitat loss after we came along. Unfortunately, due to this forced extinction, it has become harder to work out how the evolution of flightlessness occurred, given that there are markedly less representations of that diversity after our “interventions”. Many of us can name a few – the ill-fated dodo, for instance, or the great auk or the New Zealand moa or the largest bird ever recorded, the gigantic elephant bird from Madagascar. But there were also flightless owls, woodpeckers, ibis, hoopoes and finches, all now either extinct or having undergone their own evolutionary paths to the birds we know today.
The greatest concentration of flightless birds that remain in the world live in New Zealand.
Flightless birds are mostly organised into a group known as ratites, birds who have lost the keel on their sternum: flight muscles attach to this protrusion on the breastbone, so this has now disappeared in these birds. They also share a condition known as neoteny, where adults reach the size and maturity expected, but still look like chicks, having an infantile appearance, often with short stubby wings, and soft feathers instead of stiff larger ones for flight.
Ratites fall into one of a handful of species – kiwis, cassowaries, ostriches or their relatives, the emus and the rheas. Ratites are usually huge birds, but whilst gigantism is present in most of the species, it’s not a requirement, as the kiwi can testify – kiwis are among the smallest of them all, but the smallest ratite in the world is the Inaccessible Island rail, that lives blissfully predator-free on a small, well, inaccessible, island in the South Atlantic.
There were also flightless owls, woodpeckers, ibis, hoopoes and finches.
The only known species of bird to not have wings was the moa, hunted to extinction for food within two hundred years back in the 15th century. But all other species do, to some extent. But what happens to the wings in species who don’t fly? Why do these birds still have them?
Wings of destiny
Ostriches are the fastest running birds in the world, and emus come pretty close in the race. These huge birds are packing a lot of momentum, and that needs to be stalled somehow to slow down, otherwise they’ll be crashing into everything at great tumbling speeds like your drunk uncle Gary at a wedding. The wings on these birds are still massive, and that’s because they use them as brakes, pushing them out to the sides when they want to stop, acting as a parachute. They also provide great balance. And if you’re going to have huge wings, you may as well show off about it – the courtship dances of these birds involve elaborate, strutting, flapping routines that presumably require a lot of elbow space.
The endangered native of New Guinea and parts of Australia, the cassowary, is a bird for whom the word “formidable” was created: often labelled the world’s most dangerous bird, they have been known to inflict fatal wounds on people and dogs. Usually very wary of humans, they will attack if provoked. We don’t know about you, but we can’t imagine ever being that bored you’d want to provoke a cassowary. However, they are normally very shy, and have usually vanished into the forest long before you know they are there. The large bony structure atop their heads is called a casque and it is thought that not only do they use this is a tool for shifting leaf litter aside in the search for food, a weapon for dominance fights, and part of their mating ritual (mine’s bigger than yours), it also acts as a sound amplifier, probably giving them that benefit of exceptional awareness and getting out of there pronto on insanely strong legs.
Often labelled the world’s most dangerous bird, the cassowary has been known to inflict fatal wounds.
All penguins are flightless, but they are not ratites – whereas the breastbone in ratites has all but vanished, the breastbone of the penguin is a phenomenal piece of anatomy, with an incredibly well-developed keel. This is to support the exceptional musculature that penguins have for their wings, which of course they use to swim with. Their wings have developed into structures that are more like flippers, also serving as rudders through the water. Their feathers have become fluffier for warmth, more like fur, or small and dense to provide greater streamlining and insulation when swimming.
Finally, there are those poor unfortunates who have been bred by us – many domesticated birds like chickens, turkeys and ducks are unofficially considered flightless either by having had their wings clipped to prevent them from escape, or from hybridisation to produce large quantities of breast meat for food, literally making them too heavy to take off. However, as these domestic breeds have had their lack of flying ability forced upon them via artificial means, they aren’t included in the true category.
More than 50% of flightless bird species are now classed as either threatened or vulnerable. They face more threats than flying birds, with predators invading nests more effectively, they are easier to hunt, and they are more susceptible to litter, pollution, or fishing debris. Lacking the ability to fly, they can’t leave for another place to set up home, and habitat loss is the greatest threat.
The adorable kakapo, the world’s only flightless parrot, was almost eradicated entirely through invasive predation, habitat loss and humans wanting stuffed ones for their private collections, but thankfully some sterling efforts by a group of New Zealand conservationists have successfully increased their numbers to a whopping 213 in 2019.
As noted by those scientists who strive to understand evolution, and those who seek to further conservation, we can only fully understand how the world of nature works if not only do we know what came before us, but also what it may become because of us. A new study by researchers in University College of London, UK, concluded that if human influences had not existed, there would have been at least four times as many flightless bird species on Earth today. That is a sorry cross to bear, but now that we know this, there is no excuse to ignore it. We need to do our best to save those who cannot fly away from us.