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Islands: All Too Often, Laboratories of Extinction

By David S. Wilcove; Photograph by Tui De Roy/Minden Pictures
extinctions on islands

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A person can spend only so much time lounging around a pool, sipping a cold drink…even if there are White-cheeked Pintails swimming in the pool and Lava Gulls, the world’s rarest gull, begging for handouts by the bar. Such is life in Puerto Ayora, the largest town in the Galápagos Islands. So a few of us decided to forego further doses of sunscreen and alcohol and wander over to a nearby patch of trees that had somehow escaped the developers. Soon someone spotted an olive-gray bird hopping around the branches of a small tree. “Woodpecker Finch!” he shouted, and the rest us jostled for a better view of this most-wanted species.

The Woodpecker Finch chiseled into the bark of a mossy branch with its long, stout bill. It then hopped to another branch and snapped off a small twig. Apparently finding that particular twig unacceptable, the bird dropped it and tried a couple others before finding one more to its liking. The finch then returned to the spot where it had been drilling. Holding one end of the twig in its leg, it used its bill to break off a few millimeters from the other end. Now possessing a tool of the right size and shape, the Woodpecker Finch held the twig in its bill and used it to pry a fat grub out of the wood. The whole process took about a half hour— a half hour that seemed straight out of a David Attenborough film.

There was a time when tool use was thought to be a uniquely human skill. Then a small number of other animals, ranging from chimpanzees to Egyptian Vultures, were discovered to use tools. Anthropologists quickly moved on to other criteria for defining humanness, while the ranks of documented tool-using animals continued to grow. Nonetheless, it remains an exceptionally rare talent among birds. In the Galápagos Islands, which were never colonized by woodpeckers, the Woodpecker Finch is able to fill the woodpecker niche by using twigs as a substitute for a woodpecker’s long, barbed tongue.

Islands have long played an outsized role in biology. They give scientists the ability to see how isolated populations of plants and animals respond to different selective pressures and thereby provide fundamental insights into how species diversify, how they adapt, and how they interact with each other. Islands, in short, are invaluable natural laboratories for the study of ecology and evolution.

But islands have also played an outsized role in another, less happy context: as laboratories of extinction. More than 93 percent of the bird species that have perished since 1500 have been island species. Some, like the Dodo, are iconic; many others are all but forgotten with the passage of time. Today, virtually all of the major archipelagos of the world have suffered serious to catastrophic losses of their endemic species. In the Hawaiian Islands, for example, there were about 50 species of forest birds when Captain James Cook arrived in 1778; nearly half of them have since disappeared. Moreover, once scientists began exploring Hawaii’s sinkholes, caverns, sand dunes, and lava tubes, they uncovered a wealth of bird bones representing dozens of species that must have disappeared sometime between the arrival of the Polynesians (about 1,500 years ago) and Captain Cook.

More or less the same story can be told about the North and South Islands of New Zealand, the Marquesas, Micronesia, the Cook Islands, Melanesia, and the Caribbean. On virtually every archipelago, scientists have uncovered evidence of the extinction of native species, and those losses can be tied to the arrival of people. People cleared the native vegetation, accidentally introduced some species such as the ship rat, and intentionally brought others, such as dogs, cats, and goats. The consequence of all these changes was a tidal wave of extinction that has swept over almost every major isolated archipelago.

Yet, thus far, the Galápagos Islands have been spared that fate. True, several distinctive populations of the Galápagos tortoise have been extirpated. And at least three species of endemic rodents are now believed to be gone, too, probably due to predation by cats and competition with introduced rats. Yet bird watchers can still enjoy all of the bird species that greeted Charles Darwin when he arrived aboard the HMS Beagle, from the comical Flightless Cormorant to the 13 species of Darwin’s finches that are featured in every textbook on evolution.

But that may not be the case much longer. The total population of the Mangrove Finch, a close relative of the Woodpecker Finch, may be less than 100 individuals. The Medium Tree-Finch, restricted to the island of Fernandina, is now critically endangered. Populations of warbler-finches and Vermilion Flycatchers have crashed or disappeared from some of the islands they used to inhabit. Where the causes of these declines are understood, they point to human activities: habitat destruction, the introduction of new invasive species, and new diseases.

As tourism blossomed in the Galápagos Islands, Ecuadorians from the mainland flocked to the archipelago in search of employment. Commercial fishermen, too, were drawn to the islands’ productive waters (which they proceeded to fish in an unsustainable way). According to the non-profit Galápagos Conservancy, between 1991 and 2010, the number of people living in the Galápagos Islands almost tripled to more than 30,000. Meanwhile, the number of tourists quadrupled, rising from 40,000 in 1990 to more than 173,000 in 2010. The Ecuadorian government has worked to limit the direct impacts of tourism by restricting where tourists can go on the islands and by ensuring that they do not disturb the wildlife. But it has been far less successful in monitoring the constant flow of residents and commerce to and from the islands, which inevitably results in the arrival of new, sometimes harmful species.

For birds in particular, one of the newest and most dangerous threats is the flyPhilornis downsi. Larvae of this fly feed on the blood and body tissues of nestling birds, either by attaching themselves to the birds’ bodies or by entering through their nasal cavities. Recent studies have shown very high rates of infestation among songbirds nesting in the highlands, accompanied by high rates of nestling mortality. And, as is so often the case with invasive species, there currently is no way to control the flies.

In contrast to these grim trends, conservationists have racked up a number of success stories involving the elimination of non-native mammals and the restoration of degraded ecosystems in the Galápagos. Feral goats have been eradicated from Pinta, Santiago, and the northern part of Isabela, resulting in the return of native vegetation. Pigs have been eradicated from Santiago. And on several islands, efforts are underway to restore tortoise populations through a combination of captive propagation and release to the wild.

Yet until the Ecuadorian government is able to stabilize and even reduce the human population living in the Galápagos Islands, and until it is able to institute effective quarantine and inspection procedures to prevent the introduction of harmful species, the irreplaceable flora and fauna of these islands will be at risk. Undertaking these steps ultimately may mean fewer hotels with Lava Gulls and White-cheeked Pintails, and fewer T-shirt shops and farms, but I think that’s a fair price to pay to ensure the well-being of this unique place. The Galápagos Islands represent the last chance we have to preserve a reasonably intact community of island species. For the sake of science and for the sake of wonder, let’s hope Ecuador is up to the task.

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