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 鈥渟ome old English friends鈥: 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 . 鈥淚f [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,鈥 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 S茫o Miguel, and a minute rail from S茫o 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鈥攁nd 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鈥檛 find the need to fly anywhere else.
Flightlessness does appear to have come at a cost, however. The researchers point out that the rails鈥 extinctions may have coincided with the arrival of human colonizers. It's to other island bird species that have lost the ability to fly鈥攎ost notably the Dodo. 鈥淭hey had restricted distribution areas,鈥 says Alcover. 鈥淭hey 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鈥 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鈥攓uiet and hard to spot among the tall reeds and dark muck of their wetland habitats. Most birders 鈥渆ither love them or hate them鈥 because of the challenge they present when it comes to spotting them, says , a PhD student at the University of Arkansas and associate wildlife biologist at Arkansas Cooperative Fish and Wildlife Unit, who wasn鈥檛 involved with the study.
Given their history with humans, it makes sense that modern rails stick to themselves and to isolated habitats. That鈥檚 why it's necessary to preserve these types of places, Alcover says, so that unique species鈥攍ike rails鈥攁ren鈥檛 lost forever.
鈥淭here鈥檚 a lot we don鈥檛 know about rails,鈥 Fournier adds. 鈥淭his study sheds a little more light on these cool and charismatic, yet covert, birds.鈥
Correction: Due to an editing error, the story previously said that there are only 13 species of rails left in the world.