NORTH CAROLINA, USA (AP) — In the unlikely setting of the world’s most populated military installation, amid all the regimented chaos, you’ll find the Endangered Species Act at work.

There, as a 400-pound explosive resounds in the distance, a tiny St Francis Satyr butterfly flits among the splotchy leaves, ready to lay as many as 100 eggs. At one point, this brown and frankly dull-looking butterfly could be found in only one place on Earth: Fort Bragg’s artillery range.

Now, thanks in great measure to the 46-year-old federal act, they are found in eight more places — though all of them are on other parts of the army base. And if all goes well, biologists will have just seeded habitat No 10.

One of Earth’s rarest butterfly species, there are maybe 3,000 St Francis Satyrs. There are never going to be enough of them to get off the endangered list, but they’re not about to go extinct either. They are permanent patients of the bureaucratic conservation hospital ward.

In some ways, the tiny butterfly is an ideal example of the more than 1,600 US species that have been protected by the Endangered Species Act. Alive, but not exactly doing that well.

To some experts, just having these creatures around means the 46-year-old law has done its job. More than 99.2 per cent of the species protected by the act survive, The Associated Press has found. Only 11 species were declared extinct, and experts say all but a couple of them had already pretty much died out when they were listed.

On the other hand, only 39 US species — about two per cent of the overall number — have made it off the endangered list because of recovery, including such well-known successes as bald eagles, peregrine falcons and American alligators.

Most of the species on the endangered list are getting worse. And only eight per cent are getting better, according to a 2016 study by Jake Li, director for biodiversity at the Environmental Policy Innovation Center in Washington.

“Species will remain in the Endangered Species Act hospital indefinitely. And I don’t think that’s a failure of the Endangered Species Act itself,” Li said.

The Endangered Species Act “is the safety net of last resort”, said Gary Frazer, assistant director of ecological services at the US Fish and Wildlife Service, which administers the law. “We list species after all other vehicles of protection have failed.”

The act was signed into law by Republican President Richard Nixon on December 28, 1973. It had been passed overwhelmingly — the House voted 355 to four in favour and Senate approval was unanimous, margins that seem unthinkable today.

The law was designed to prevent species from going extinct and to protect their habitat. It instructed two federal agencies — the Fish and Wildlife Service and the National Marine Fisheries Service — to draw up a list of species endangered or threatened with extinction.

Under the law, it is unlawful to “harass, harm, pursue, hunt, shoot, wound, kill, trap, capture or collect” endangered animals, and it also forbids the elimination of their habitats. At first, only animals were protected, but eventually plants were protected, too.

The law caused all sorts of environmental showdowns in the 1970s and 1980s — most notoriously, the fight over the construction of the Tellico Dam in Tennessee, which threatened the tiny snail darter fish. In the end, the Supreme Court ruled in favour of the fish, but Congress exempted the dam from the law.

Now, the Act is in contention once again. In September, President Donald Trump’s Administration changed the endangered species process in ways that some say weaken the law. Critics say one change would allow costs to industry to be taken into account when deciding how to protect species.

Even putting that aside, the Act has its costs. Another species found at Fort Bragg — the red-cockaded woodpecker — is a case in point.

In 2016, the last year with per-species spending estimates, the US Government spent $25 million on the red-cockaded woodpecker, more than 100 times what it spent on the St. Francis Satyr butterfly. From 1998 to 2016, the federal government spent $408 million on the woodpecker, making it one of the most expensive species on the endangered list.

The small woodpecker is a member of the original class of 1967. It may soon fly off the endangered list or, more likely, graduate to the less-protected threatened list.

“Something is going right,” says Fort Bragg Endangered Species Branch Chief Jackie Britcher, holding a male woodpecker in her hands as a group of biologists stood under trees with giant nets to catch, count and band the birds.

The woodpeckers live only in long leaf pines, which have been disappearing across the south-east for more than a century, due to development and suppression of fires. When naturally occurring fires were tamped down, other plants and brush would crowd them out.

Unlike other woodpeckers, these birds build their nests in live trees, sometimes taking as long as a decade to drill a cavity and make a home.

In the 1980s and 1990s, efforts to save the woodpecker and their trees set off a backlash among landowners who worried about interference on their private property.

“I’ve been run off the road. I’ve been shot at,” says former Fish and Wildlife Service woodpecker official Julie Moore.

Army officials weren’t happy either: They were being told they couldn’t train in many places because of the woodpecker.

“We couldn’t manoeuvre. We couldn’t shoot because they were afraid the bird was going to blink out and go into extinction,” said former top Fort Bragg planning official Mike Lynch.

By the 1980s, the red-cockaded woodpecker population was below 10,000 nationwide, said Virginia Tech scientist Jeff Walters, a woodpecker expert. Biologists built boxes to serve as nests, attaching them to trees. The woodpeckers weren’t interested.

Then Walters tried something different. He put the boxes inside the trees. The birds started living in them.

Instead of prohibiting work on land the woodpecker needs, Fish and Wildlife Service officials allowed landowners to make some changes as long as they generally didn’t hurt the bird.