Eighty years ago, Charles Darwin made one final stop with the HMS Beagle at the Azores, a remote mid-Atlantic archipelago. In his journal Darwin described the islands as being populated by “some old English friends”: starlings, wagtails, chaffinches, and blackbirds. But little did he know that lying below his feet were the remains of birds as unique as the Galapagos finches.
Now, a few of the species that eluded Darwin have finally been revealed. Last December, Josep Antoni Alcover, a zoologist at the Mediterranean Institute for Advanced Studies, and a group of European biologists and paleontologists identified the bones of six previously undiscovered species of rails that went extinct on the Azores and the nearby archipelago of Madeira. The most modern of the bunch died out nearly 600 years ago, the scientists estimate in their recent article published in the journal Zootaxa. “If [Darwin] had visited the islands 500 years earlier, he could have seen different endemic rails, endemic quails, endemic little-owls, endemic finches, endemic pigeons, endemic thrushes, endemic wrens, and huge quantities of seabirds,” Alcover says.
The new species, which the researchers believe evolved independently from the common (still-living) ancestor Rallus aquaticus, include a slender rail from Porto Santo, a small rail from Pico, a short-legged rail from São Miguel, and a minute rail from São Jorge. The researchers also identified a plump rail on Madeira, along with a sixth species, currently unnamed, preserved in silica on Terceira.
A Band of Flightless Birds
Five of the six new rail species are thought to have been flightless. By studying the structure of the fossils, the scientists discovered that the Pico rail was the only one with aerial abilities—and even those were limited. All of the rails were probably airborne at first; but soon after they spread out and seemingly conquered the islands, they developed short legs, weak wing bones, and other signs of flightlessness. The theory is that the islands were so filled with fish, insects, crustaceans, and grassy nesting habitat that the rails didn’t find the need to fly anywhere else.
Flightlessness does appear to have come at a cost, however. The researchers point out that the rails’ extinctions may have coincided with the arrival of human colonizers. It's a similar narrative to other island bird species that have lost the ability to fly—most notably the Dodo. “They had restricted distribution areas,” says Alcover. “They bred on the ground. They evolved without terrestrial predators. All together [this] made them very vulnerable to the ecological changes that started with the humans’ arrival."
Which Rails Have Survived?
Today, there are 100-plus rail species spread out across the world. Only a few are flightless and indigenous, isolated to obscure islands, such as Tristan da Cunha and Gough. The rest are migratory. All rails, both flightless and flighted, are elusive—quiet and hard to spot among the tall reeds and dark muck of their wetland habitats. Most birders “either love them or hate them” because of the challenge they present when it comes to spotting them, says Auriel Fournier, a PhD student at the University of Arkansas and associate wildlife biologist at Arkansas Cooperative Fish and Wildlife Unit, who wasn’t involved with the study.
Given their history with humans, it makes sense that modern rails stick to themselves and to isolated habitats. That’s why it's necessary to preserve these types of places, Alcover says, so that unique species—like rails—aren’t lost forever.
“There’s a lot we don’t know about rails,” Fournier adds. “This study sheds a little more light on these cool and charismatic, yet covert, birds.”
Correction: Due to an editing error, the story previously said that there are only 13 species of rails left in the world.