The Sierra Club, Defenders of Wildlife and other environmental groups have condemned the fence under construction along the U.S.-Mexican border. They claim it will disturb the habitat and movements of sensitive wildlife like pygmy owls and jaguars. And they allege it may only drive illegal immigrants into still remoter, more ecologically fragile terrain.

The Sierra Club’s Carl Pope even contends the fence could lead to the “destruction of the borderlands region.” Funny, I thought the border was already under assault from massive narcotics trafficking and the recent outburst of barbaric, deadly drug-linked crime; hundreds of tons of litter and trash dropped by illegal immigrants; polluting maquiladora plants; the mysterious and tragic deaths of female maquiladora workers (near Ciudad Juarez); and expanding habitat loss from the explosive growth of border settlements.

The border fence is indeed likely to disrupt certain wildlife populations, particularly mammals, reptiles and amphibians. The barriers may well block the movements, migration and gene flow of ground-dwelling species. In addition, there will be a linear loss of habitat in a narrow band alongside the fence.

These impacts could potentially approach those of a restricted-access interstate highway with fencing to prevent collisions between wildlife and vehicles. Since environmentalists get riled up about building freeways across natural habitat, they are being consistent in getting riled up about the border fence.

But they are being woefully inconsistent — even hypocritical — in not getting riled up about the ecological damage caused by rampant, unsustainable U.S. population growth that illegal immigration exacerbates. The wildlife habitat eliminated to accommodate an additional 3 million people annually is on a scale far vaster and more widespread than the border fence. And it mounts year after year with no end in sight, as long as our population continues to soar.

U.S. population grew by 33 million in the 1990s, more than any single decade in our history. This decade is on track to surpass that record. About 75 percent of this growth is due directly or indirectly to immigration, and more than half of 2000-2007 immigration was illegal. At 306 million today, according to the Census Bureau, the United States is on a trajectory to reach 440 million in 2050 and between 500 million and 1 billion by 2100. This will have ruinous environmental consequences.

In overpopulated California, our numbers surged by nearly 50 percent from 1970 to 1990. They grew another 14 percent in the 1990s. Already at 38 million to 39 million, Californian’s population is projected to balloon to 60 million by 2050. Unless immigration is substantially lowered, it won’t crest even there.

Not surprisingly, California has more wildlife in jeopardy than any other state. More than 800 species are now in peril — including half of all mammals and one-third of all birds. Of these 800 species, 134 are threatened or endangered, facing imminent extinction without urgent action.

A 2007 California Department of Fish & Game report, “California Wildlife: Conservation Challenges,” concluded that the state’s biodiversity is already under tremendous pressure from today’s enormous human population. Further population growth can only worsen the pressure. “Increasing needs for housing, services, transportation and other infrastructure place ever-greater demands on the state’s land, water, and other natural resources,” the report noted.

In the United States as a whole, 371 terrestrial ecological communities are listed as globally rare. An exhaustive survey by The Nature Conservancy reported that almost one-third of all plants and animals are at risk. If our country keeps adding 30 million or more new residents a decade — equal to eight times the city of Los Angeles — pressures on these precarious living resources can only increase.

Yet these troubling statistics generate nary a peep from the environmental establishment, because they are held hostage by their fear of being demonized as low-brow nativists by their political bedfellows — Democrats, liberals and beneficiaries of mass immigration. And at least one prospective donor threatened the Sierra Club that “if they ever came out anti-immigration, they would never get a dollar.” They didn’t, and he came through with two donations totaling more than $100 million, “dwarfing all previous individual contributions to the club,” according to a 2004 Los Angeles Times exposé.

Until mainstream environmental groups prove they’d rather be environmentally correct rather than politically correct and expedient, all the wailing and gnashing of teeth over the border fence can be dismissed as mimicry. Like their fellow mimics in the animal kingdom, these imposters are mimicking those who are genuinely committed to saving wildlife and wilderness.

— Leon Kolankiewicz is a wildlife biologist and senior writing fellow for Californians for Population Stabilization.