Of the 1,280 endangered animals and plants listed by the United States Fish and Wildlife Service, 557 are from Hawaii, including the short-tailed albatross, the Hawaiian hoary bat and the Kauai cave wolf spider, as well as four species of turtle, six damselflies, two varieties of pond shrimp, four snails and seven kinds of yellow-faced bee. Conservationists have called the islands “the extinction capital of the world.”

This is true in part because Hawaii is a tropical paradise so fertile that seeds from a foreign plant can spread to blanket the island in the space of a few years. When the islands were new bits of volcanic rock in the middle of a vast ocean, this fertility worked in species’ favor, allowing them to diversify, Galapagos-style, into dozens of discrete niches, with few competitive pressures. In the last hundred years, though, those same factors have become a liability. Hawaii’s tropical weather and location as a Pacific trade and tourism hub have made it a kind of petri dish for invasive species, which arrive from nearly every continent and multiply extravagantly. On the Big Island, mongoose have proliferated, devastating local bird populations; so have Puerto Rican coquí frogs, which chirp abruptly and erratically at 90 decibels, like a mobile infestation of alarm clocks. Cases of rat lungworm have risen sharply over the past five years, driven first by the arrival of the lungworm parasite, from Southeast Asia, followed by the spread of a nonnative slug that carries the disease. Kauai, meanwhile, is plagued by feral pigs, rose-ringed parakeets and a new invasive seaweed that arrived either in ballast water or in the dumped contents of aquarium tanks and that has begun to smother the island’s reef ecosystem. Since 1992, when a hurricane knocked over chicken coops, the island has also been overrun by roving bands of roosters and chickens; on my first day in Lihue, I saw dozens of them, many trailing hordes of chicks.

Faced with these cosmopolitan arrivals, island species can seem like the wildlife equivalent of a naïve Midwesterner asking a guy in Times Square to hold his wallet. Native trees and plants have often lost their defenses — the islands have stingless nettles and thornless raspberries — and in many cases grow more slowly, making them easy marks for more aggressive species like miconia, a flowering plant from Central America that grows like a weed, produces thousands of seeds and shades out everything in its vicinity. Native animals and birds don’t fare much better. “We have a seabird, the Laysan albatross, that nests on the ground,” said Joshua Fisher, a biologist with the U.S. Fish and Wildlife Service. “A rat or a cat or a mongoose can literally walk right up to it and start eating its eggs. The birds just don’t know what to do.”

And once nonnative species do begin to take over, stopping them can be a Sisyphean task. One invasive fungus that kills ohia trees can spread just from the quantity of dirt trapped in the tread of a sneaker. (To combat this, Hawaii has asked hikers to scrub their boots with alcohol or a bleach solution.) A recent study at Kahului Airport on Maui found an average of one new insect species arriving every day. In the Alakai and elsewhere, these pressures have steadily squeezed out native species, at the same time as development has left them with less land to occupy. On top of that, even when an endangered animal survives in captivity, it often can’t be reintroduced to the wild without falling victim to the same factors that drove it toward extinction in the first place.

As a result, our role as stewards of the earth is becoming more and more like that of doctors in a global intensive-care unit, trapped in a cycle of heroic, end-of-life measures. Many conservationists now operate in a state of constant maintenance: endlessly working to weed out invasive plants and predators, while trying to prop up species that have fallen into decline. At worst, an endangered animal becomes a literal ward of the state: preserved only in breeding facilities or in tiny, meticulously maintained “wild” habitats. “They’re like patients that are never going to be discharged from the hospital,” the environmental writer Emma Marris told me. “It’s a permanent situation.”

The official term for such species is “conservation-reliant.” When I spoke with Michael Scott, a wildlife biologist at the University of Idaho who helped direct the California condor research effort, he estimated that roughly 84 percent of species on the United States endangered list are currently conservation-reliant. Of those, he added, a vast majority are in Hawaii. “Hawaii is the world capital of conservation-reliant species,” Scott said.