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ISABELLE GROC FLPA/ALAMY
“When we first noticed that an ever larger Unsurprisingly, we tend to associate them It turns out that sea otters don’t
number of sea otters were living in the slough, with mountains. But historical records show need to live in the sea, nor mountain
we did not immediately grasp the fact that the that in Patagonia they once lived in open lions in the mountains
slough could provide all their habitat needs,” grasslands. As sheep farming became
says Lilian Carswell from the US Fish and established in South America, they were These birds were thought to be small-island
Wildlife Service. The remnant population of persecuted – along with their prey, a kind of specialists, so why were they abandoning
otters had persisted exclusively on California’s llama called a guanaco. As a result, mountain their homes? His insight came when he visited
coast, and conservationists had assumed this lions survived only in the remote Andes away Castro de Baroña, an Iron Age settlement on a
is where they belonged, foraging in kelp beds. from humans. But in the past 20 years, sheep rugged peninsula in Galicia. “I realised it was a
But the fact they were thriving in Elkhorn ranching has declined. “We started to see a terrible place to live, exposed to winter storms
Slough forced a rethink. “We wiped out these change,” says Mark Elbroch from conservation and difficult to cultivate. My conclusion was
species from most of their range long before that the Iron Age people built a village there
we had ecology as a science,” says Carswell. “ If ecologists want to because they were forced to do so,” he says.
“There is so much we don’t know.” understand the present, Suddenly, Martínez-Abraín saw the
The story of California’s sea otters is not connection with the Audouin’s gulls. He
a one-off. Earlier this year, Silliman and his they should look at the past” realised that human persecution had forced
colleagues revealed a wider trend in a paper the birds to leave their preferred mainland
aptly titled “Are the ghosts of nature’s past society Panthera. “The mountain lions that habitat and eke out a living on the islands.
haunting ecology today?”. As a result of had been removed from the open grassland Now, no longer threatened by humans, they
conservation efforts, a variety of predators are began to come back out of the mountains at are returning to their historical homes – just
reappearing in ecosystems they were pushed the same time as the guanaco was beginning as the people of Castro de Baroña moved to
out of by hunting and development. “It is an to move back into the grassland.” more hospitable areas once the Roman Empire
exciting time for ecologists,” says Carswell, Such recolonisation is happening in became peaceful. “We have been studying
“because these species are coming back to Europe too. Alejandro Martínez-Abraín at the things from the wrong perspective. If
these ecosystems from which they have University of A Coruña, Spain, was puzzled to ecologists want to understand the present,
been absent for many human generations and discover that ground-nesting Audouin’s gulls they should look at the past,” he says.
they are putting their house back in order.” were relocating from archipelagos in the Martínez-Abraín’s research, published
Mountain lions are another example. western Mediterranean to the mainland. in June, documents a variety of species >
27 October 2018 | NewScientist | 29
