In the three decades since it was signed into law, the Endangered Species Act has had some remarkable successes: Wolves have made a comeback in the Northern Rockies; bald eagles have rebounded. But the ESA is an imperfect tool.

The endangered species list is often likened to the hospital emergency room, and the comparison is an apt one. By the time a plant or animal lands on the list, it is far down the road to destruction. The chance for preventive medicine has passed.

As a result, we have stories like that of the endangered Rio Grande silvery minnow, which, barring a miracle — or a little sacrifice from the farmers and city dwellers who live along the Rio Grande in New Mexico — will soon survive only in what amounts to a giant fish tank. Attempts by environmentalists to keep water in the minnow’s native habitat — the river — have been shot down by big agriculture and growth-hungry politicians. The city of San Diego faced its own conundrum in the 1990s.

Environmentalists were using the Endangered Species Act to beat back a subdivision here, a strip mall there, while the rest of the landscape unraveled. Developers were losing money as projects were delayed, while native wildlife steadily lost ground.

So, with a little prodding from the Clinton administration, San Diego did something new. It tried to set aside large chunks of wildlife habitat that would, in theory, protect a whole suite of plants and animals. Land outside of these habitat preserves could be developed, giving builders some financial certainty.

The Multiple Species Conservation Program was a huge undertaking, and the result was groundbreaking. But the program came at least a decade late. And as veteran Arizona reporter Tony Davis writes in this issue, doubts abound over whether it is ambitious enough to save San Diego’s imperiled wildlife.

It’s too early to know whether San Diego’s conservation program will succeed; the fires now scorching Southern California cast this in some doubt. Meanwhile, the program is being imitated by habitat conservation plans all over the country.

San Diego experiment offers one lesson, it is this: Start early, and err on the side of the endangered species, because the forces of development will whittle away at habitat wherever they can.

Perhaps some day we’ll convince Congress to pass an Endangered Ecosystem Act. But for now, we’re stuck with an imperfect tool. Habitat conservation plans ensure that developers can build. We need to be sure that endangered species get assurances that are just as strong.